diff --git a/jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFields.java b/jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFields.java
index 66db59325e36..c810498886b2 100644
--- a/jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFields.java
+++ b/jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFields.java
@@ -927,6 +927,21 @@ default int size()
         return size;
     }
 
+    /**
+     * <p>Wraps an instance of {@link HttpFields} as a {@link Map}.</p>
+     * <p>If the provided {@link HttpFields} is an instance of {@link HttpFields.Mutable} then changes to the
+     * {@link Map} will be reflected in the underlying {@link HttpFields}.
+     * Otherwise, any modification to the {@link Map} will throw {@link UnsupportedOperationException}.</p>
+     * @param fields the {@link HttpFields} to convert to a {@link Map}.
+     * @return an {@link Map} representing the contents of the {@link HttpFields}.
+     */
+    static Map<String, List<String>> asMap(HttpFields fields)
+    {
+        return (fields instanceof HttpFields.Mutable mutable)
+            ? new HttpFieldsMap.Mutable(mutable)
+            : new HttpFieldsMap.Immutable(fields);
+    }
+
     /**
      * @return a sequential stream of the {@link HttpField}s in this instance
      */
diff --git a/jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFieldsMap.java b/jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFieldsMap.java
new file mode 100644
index 000000000000..f5d19855d9fa
--- /dev/null
+++ b/jetty-core/jetty-http/src/main/java/org/eclipse/jetty/http/HttpFieldsMap.java
@@ -0,0 +1,237 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.http;
+
+import java.util.AbstractMap;
+import java.util.AbstractSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+
+import org.eclipse.jetty.util.StringUtil;
+
+/**
+ * <p>A {@link java.util.Map} which is backed by an instance of {@link HttpFields.Mutable}.</p>
+ * @see HttpFieldsMap.Mutable
+ * @see HttpFieldsMap.Immutable
+ */
+abstract class HttpFieldsMap extends AbstractMap<String, List<String>>
+{
+    /**
+     * <p>A {@link java.util.Map} which is backed by an instance of {@link HttpFields.Mutable}.</p>
+     * <p>Any changes to the {@link java.util.Map} will be reflected in the underlying instance of {@link HttpFields.Mutable}.</p>
+     */
+    public static class Mutable extends HttpFieldsMap
+    {
+        private final HttpFields.Mutable httpFields;
+
+        public Mutable(HttpFields.Mutable httpFields)
+        {
+            this.httpFields = httpFields;
+        }
+
+        @Override
+        public List<String> get(Object key)
+        {
+            if (key instanceof String s)
+                return httpFields.getValuesList(s);
+            return null;
+        }
+
+        @Override
+        public List<String> put(String key, List<String> value)
+        {
+            List<String> oldValue = get(key);
+            httpFields.put(key, value);
+            return oldValue;
+        }
+
+        @Override
+        public List<String> remove(Object key)
+        {
+            if (key instanceof String s)
+            {
+                List<String> oldValue = get(s);
+                httpFields.remove(s);
+                return oldValue;
+            }
+            return null;
+        }
+
+        @Override
+        public Set<Entry<String, List<String>>> entrySet()
+        {
+            return new AbstractSet<>()
+            {
+                @Override
+                public Iterator<Entry<String, List<String>>> iterator()
+                {
+                    return new Iterator<>()
+                    {
+                        private final Iterator<String> iterator = httpFields.getFieldNamesCollection().iterator();
+                        private String name = null;
+
+                        @Override
+                        public boolean hasNext()
+                        {
+                            return iterator.hasNext();
+                        }
+
+                        @Override
+                        public Entry<String, List<String>> next()
+                        {
+                            name = iterator.next();
+                            return new HttpFieldsEntry(name);
+                        }
+
+                        @Override
+                        public void remove()
+                        {
+                            if (name != null)
+                            {
+                                Mutable.this.remove(name);
+                                name = null;
+                            }
+                        }
+                    };
+                }
+
+                @Override
+                public int size()
+                {
+                    return httpFields.getFieldNamesCollection().size();
+                }
+            };
+        }
+    }
+
+    /**
+     * <p>A {@link java.util.Map} which is backed by an instance of {@link HttpFields.Mutable}.</p>
+     * <p>Any attempt to modify the map will throw {@link UnsupportedOperationException}.</p>
+     */
+    public static class Immutable extends HttpFieldsMap
+    {
+        private final HttpFields httpFields;
+
+        public Immutable(HttpFields httpFields)
+        {
+            this.httpFields = httpFields;
+        }
+
+        @Override
+        public List<String> get(Object key)
+        {
+            if (key instanceof String s)
+                return httpFields.getValuesList(s);
+            return null;
+        }
+
+        @Override
+        public List<String> put(String key, List<String> value)
+        {
+            throw new UnsupportedOperationException();
+        }
+
+        @Override
+        public List<String> remove(Object key)
+        {
+            throw new UnsupportedOperationException();
+        }
+
+        @Override
+        public Set<Entry<String, List<String>>> entrySet()
+        {
+            return new AbstractSet<>()
+            {
+                @Override
+                public Iterator<Entry<String, List<String>>> iterator()
+                {
+                    return new Iterator<>()
+                    {
+                        private final Iterator<String> iterator = httpFields.getFieldNamesCollection().iterator();
+
+                        @Override
+                        public boolean hasNext()
+                        {
+                            return iterator.hasNext();
+                        }
+
+                        @Override
+                        public Entry<String, List<String>> next()
+                        {
+                            return new HttpFieldsEntry(iterator.next());
+                        }
+
+                        @Override
+                        public void remove()
+                        {
+                            throw new UnsupportedOperationException();
+                        }
+                    };
+                }
+
+                @Override
+                public int size()
+                {
+                    return httpFields.getFieldNamesCollection().size();
+                }
+            };
+        }
+    }
+
+    private class HttpFieldsEntry implements Entry<String, List<String>>
+    {
+        private final String _name;
+
+        public HttpFieldsEntry(String name)
+        {
+            _name = name;
+        }
+
+        @Override
+        public String getKey()
+        {
+            return _name;
+        }
+
+        @Override
+        public List<String> getValue()
+        {
+            return HttpFieldsMap.this.get(_name);
+        }
+
+        @Override
+        public List<String> setValue(List<String> value)
+        {
+            return HttpFieldsMap.this.put(_name, value);
+        }
+
+        @Override
+        public boolean equals(Object o)
+        {
+            if (this == o)
+                return true;
+            if (o instanceof HttpFieldsEntry other)
+                return StringUtil.asciiEqualsIgnoreCase(_name, other.getKey());
+            return false;
+        }
+
+        @Override
+        public int hashCode()
+        {
+            return Objects.hash(StringUtil.asciiToLowerCase(_name));
+        }
+    }
+}
diff --git a/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeRequest.java b/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeRequest.java
index a76104afe63c..0d5d67e62bed 100644
--- a/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeRequest.java
+++ b/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeRequest.java
@@ -22,6 +22,7 @@
 import java.util.stream.Collectors;
 
 import org.eclipse.jetty.http.HttpField;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.http.HttpScheme;
 import org.eclipse.jetty.io.EndPoint;
@@ -78,7 +79,7 @@ public List<String> getHeaders(String name)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return null;
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override
diff --git a/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeResponse.java b/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeResponse.java
index 1b93d80ba20f..0e05930cc2f7 100644
--- a/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeResponse.java
+++ b/jetty-core/jetty-websocket/jetty-websocket-jetty-client/src/main/java/org/eclipse/jetty/websocket/client/internal/DelegatedJettyClientUpgradeResponse.java
@@ -13,7 +13,6 @@
 
 package org.eclipse.jetty.websocket.client.internal;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -21,6 +20,7 @@
 import java.util.stream.Collectors;
 
 import org.eclipse.jetty.client.Response;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.websocket.api.ExtensionConfig;
 import org.eclipse.jetty.websocket.api.UpgradeResponse;
@@ -65,9 +65,7 @@ public List<String> getHeaders(String name)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = getHeaderNames().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(getHeaders(name))));
-        return Collections.unmodifiableMap(headers);
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override
diff --git a/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/ServerWebSocketContainer.java b/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/ServerWebSocketContainer.java
index cf8a1755fad3..9d50cd242f5e 100644
--- a/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/ServerWebSocketContainer.java
+++ b/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/ServerWebSocketContainer.java
@@ -359,13 +359,12 @@ private org.eclipse.jetty.websocket.core.server.WebSocketCreator newWebSocketCre
         {
             try
             {
-                Object webSocket = creator.createWebSocket(new ServerUpgradeRequestDelegate(rq), new ServerUpgradeResponseDelegate(rq, rs), cb);
-                if (webSocket == null)
-                    cb.succeeded();
-                return webSocket;
+                return creator.createWebSocket(new ServerUpgradeRequestDelegate(rq), new ServerUpgradeResponseDelegate(rq, rs), cb);
             }
             catch (Throwable x)
             {
+                if (LOG.isDebugEnabled())
+                    LOG.debug("Could not create WebSocket endpoint", x);
                 cb.failed(x);
                 return null;
             }
diff --git a/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeRequestDelegate.java b/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeRequestDelegate.java
index 2006890f8010..921aea05a477 100644
--- a/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeRequestDelegate.java
+++ b/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeRequestDelegate.java
@@ -21,7 +21,6 @@
 import java.util.Map;
 import java.util.stream.Collectors;
 
-import org.eclipse.jetty.http.HttpField;
 import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.http.HttpScheme;
@@ -73,14 +72,7 @@ public int getHeaderInt(String name)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> result = new LinkedHashMap<>();
-        HttpFields headers = request.getHeaders();
-        for (HttpField header : headers)
-        {
-            String name = header.getName();
-            result.put(name, headers.getValuesList(name));
-        }
-        return result;
+        return HttpFields.asMap(request.getHeaders());
     }
 
     @Override
diff --git a/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeResponseDelegate.java b/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeResponseDelegate.java
index c798e1e20a8f..46b704851647 100644
--- a/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeResponseDelegate.java
+++ b/jetty-core/jetty-websocket/jetty-websocket-jetty-server/src/main/java/org/eclipse/jetty/websocket/server/internal/UpgradeResponseDelegate.java
@@ -13,13 +13,11 @@
 
 package org.eclipse.jetty.websocket.server.internal;
 
-import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
 
-import org.eclipse.jetty.http.HttpField;
 import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.websocket.api.ExtensionConfig;
 import org.eclipse.jetty.websocket.api.UpgradeResponse;
@@ -64,14 +62,7 @@ public Set<String> getHeaderNames()
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> result = new LinkedHashMap<>();
-        HttpFields.Mutable headers = response.getHeaders();
-        for (HttpField header : headers)
-        {
-            String name = header.getName();
-            result.put(name, headers.getValuesList(name));
-        }
-        return result;
+        return HttpFields.asMap(response.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/client/internal/JsrUpgradeListener.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/client/internal/JsrUpgradeListener.java
index 8406e494e4f5..5c14b0bd5e98 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/client/internal/JsrUpgradeListener.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/client/internal/JsrUpgradeListener.java
@@ -13,9 +13,6 @@
 
 package org.eclipse.jetty.ee10.websocket.jakarta.client.internal;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -41,23 +38,11 @@ public void onHandshakeRequest(Request request)
         if (configurator == null)
             return;
 
-        HttpFields fields = request.getHeaders();
-        Map<String, List<String>> originalHeaders = new HashMap<>();
-        fields.forEach(field ->
-        {
-            originalHeaders.putIfAbsent(field.getName(), new ArrayList<>());
-            List<String> values = originalHeaders.get(field.getName());
-            Collections.addAll(values, field.getValues());
-        });
-
-        // Give headers to configurator
-        configurator.beforeRequest(originalHeaders);
-
-        // Reset headers on HttpRequest per configurator
         request.headers(headers ->
         {
-            headers.clear();
-            originalHeaders.forEach(headers::put);
+            // Give headers to configurator
+            Map<String, List<String>> headersMap = HttpFields.asMap(headers);
+            configurator.beforeRequest(headersMap);
         });
     }
 
@@ -67,18 +52,7 @@ public void onHandshakeResponse(Request request, Response response)
         if (configurator == null)
             return;
 
-        HandshakeResponse handshakeResponse = () ->
-        {
-            Map<String, List<String>> ret = new HashMap<>();
-            response.getHeaders().forEach(field ->
-            {
-                ret.putIfAbsent(field.getName(), new ArrayList<>());
-                List<String> values = ret.get(field.getName());
-                Collections.addAll(values, field.getValues());
-            });
-            return ret;
-        };
-
+        HandshakeResponse handshakeResponse = () -> HttpFields.asMap(response.getHeaders());
         configurator.afterResponse(handshakeResponse);
     }
 }
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/JakartaWebSocketServerContainer.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/JakartaWebSocketServerContainer.java
index 041bf6b427af..c576cb79e27d 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/JakartaWebSocketServerContainer.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/JakartaWebSocketServerContainer.java
@@ -322,9 +322,9 @@ public void upgradeHttpToWebSocket(Object httpServletRequest, Object httpServlet
             servletContextRequest.setAttribute(WebSocketConstants.WEBSOCKET_WRAPPED_RESPONSE_ATTRIBUTE, response);
 
             if (handshaker.upgradeRequest(negotiator, servletContextRequest, servletContextResponse, callback, components, defaultCustomizer))
-            {
                 callback.block();
-            }
+            else
+                throw new IllegalStateException("Invalid WebSocket Upgrade Request");
         }
         finally
         {
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JakartaWebSocketCreator.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JakartaWebSocketCreator.java
index 6382b8c77ee1..994ec93a9162 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JakartaWebSocketCreator.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JakartaWebSocketCreator.java
@@ -156,8 +156,6 @@ public Map<String, Object> getUserProperties()
 
         // [JSR] Step 5: Call modifyHandshake
         configurator.modifyHandshake(config, jsrHandshakeRequest, jsrHandshakeResponse);
-        // Set modified headers Map back into response properly
-        jsrHandshakeResponse.setHeaders(jsrHandshakeResponse.getHeaders());
 
         try
         {
@@ -168,7 +166,8 @@ public Map<String, Object> getUserProperties()
         }
         catch (Throwable x)
         {
-            LOG.warn("Unable to create websocket: {}", config.getEndpointClass().getName(), x);
+            if (LOG.isDebugEnabled())
+                LOG.debug("Unable to create websocket: {}", config.getEndpointClass().getName(), x);
             callback.failed(x);
             return null;
         }
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeRequest.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeRequest.java
index a9f8ac6e7147..546794d54f5e 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeRequest.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeRequest.java
@@ -15,16 +15,14 @@
 
 import java.net.URI;
 import java.security.Principal;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.stream.Collectors;
 
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.websocket.server.HandshakeRequest;
 import org.eclipse.jetty.ee10.websocket.jakarta.server.JakartaWebSocketServerContainer;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.pathmap.PathSpec;
 import org.eclipse.jetty.server.Request;
 import org.eclipse.jetty.util.Fields;
@@ -47,9 +45,7 @@ public JsrHandshakeRequest(ServerUpgradeRequest req)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = delegate.getHeaders().getFieldNamesCollection().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(delegate.getHeaders().getValuesList(name))));
-        return Collections.unmodifiableMap(headers);
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeResponse.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeResponse.java
index b4d5986dd106..c1d9b1dfff2a 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeResponse.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee10/websocket/jakarta/server/internal/JsrHandshakeResponse.java
@@ -13,24 +13,20 @@
 
 package org.eclipse.jetty.ee10.websocket.jakarta.server.internal;
 
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
-import java.util.stream.Collectors;
 
 import jakarta.websocket.HandshakeResponse;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.websocket.core.server.ServerUpgradeResponse;
 
 public class JsrHandshakeResponse implements HandshakeResponse
 {
-    private final ServerUpgradeResponse delegate;
     private final Map<String, List<String>> headers;
 
     public JsrHandshakeResponse(ServerUpgradeResponse resp)
     {
-        this.delegate = resp;
-        this.headers = delegate.getHeaders().getFieldNamesCollection().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(delegate.getHeaders().getValuesList(name))));
+        this.headers = HttpFields.asMap(resp.getHeaders());
     }
 
     @Override
@@ -38,9 +34,4 @@ public Map<String, List<String>> getHeaders()
     {
         return headers;
     }
-
-    public void setHeaders(Map<String, List<String>> headers)
-    {
-        headers.forEach((key, values) -> delegate.getHeaders().put(key, values));
-    }
 }
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee10/websocket/jakarta/tests/UpgradeHeadersTest.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee10/websocket/jakarta/tests/UpgradeHeadersTest.java
new file mode 100644
index 000000000000..d19b00d8ba66
--- /dev/null
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee10/websocket/jakarta/tests/UpgradeHeadersTest.java
@@ -0,0 +1,138 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.ee10.websocket.jakarta.tests;
+
+import java.net.URI;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+import jakarta.websocket.ClientEndpointConfig;
+import jakarta.websocket.Endpoint;
+import jakarta.websocket.EndpointConfig;
+import jakarta.websocket.HandshakeResponse;
+import jakarta.websocket.Session;
+import jakarta.websocket.server.HandshakeRequest;
+import jakarta.websocket.server.ServerEndpointConfig;
+import org.eclipse.jetty.ee10.servlet.ServletContextHandler;
+import org.eclipse.jetty.ee10.websocket.jakarta.client.JakartaWebSocketClientContainer;
+import org.eclipse.jetty.ee10.websocket.jakarta.server.config.JakartaWebSocketServletContainerInitializer;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.ServerConnector;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class UpgradeHeadersTest
+{
+    private Server _server;
+    private JakartaWebSocketClientContainer _client;
+    private ServerConnector _connector;
+
+    public static class MyEndpoint extends Endpoint
+    {
+        @Override
+        public void onOpen(Session session, EndpointConfig config)
+        {
+        }
+    }
+
+    public void start(ServerEndpointConfig.Configurator configurator) throws Exception
+    {
+        _server = new Server();
+        _connector = new ServerConnector(_server);
+        _server.addConnector(_connector);
+
+        ServletContextHandler contextHandler = new ServletContextHandler();
+        _server.setHandler(contextHandler);
+        JakartaWebSocketServletContainerInitializer.configure(contextHandler, (context, container) ->
+        {
+            container.addEndpoint(ServerEndpointConfig.Builder
+                .create(MyEndpoint.class, "/")
+                .configurator(configurator)
+                .build());
+        });
+
+        _server.start();
+        _client = new JakartaWebSocketClientContainer();
+        _client.start();
+    }
+
+    @AfterEach
+    public void after() throws Exception
+    {
+        _client.stop();
+        _server.stop();
+    }
+
+    @Test
+    public void testCaseInsensitiveUpgradeHeaders() throws Exception
+    {
+        ClientEndpointConfig.Configurator configurator = new ClientEndpointConfig.Configurator()
+        {
+            @Override
+            public void beforeRequest(Map<String, List<String>> headers)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (headers.get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on client Request");
+                headers.put("sentHeader", List.of("value123"));
+            }
+
+            @Override
+            public void afterResponse(HandshakeResponse hr)
+            {
+                if (hr.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+                if (hr.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            }
+        };
+
+        start(new ServerEndpointConfig.Configurator()
+        {
+            @Override
+            public void modifyHandshake(ServerEndpointConfig sec, HandshakeRequest request, HandshakeResponse response)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (request.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+                if (response.getHeaders().get("sErVeR") == null)
+                    throw new IllegalStateException("No Server Header on HandshakeResponse");
+
+                // Verify custom header sent from client.
+                if (request.getHeaders().get("SeNtHeadEr") == null)
+                    throw new IllegalStateException("No sent Header on HandshakeResponse");
+
+                // Add custom response header.
+                response.getHeaders().put("myHeader", List.of("foobar"));
+                if (response.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+
+                super.modifyHandshake(sec, request, response);
+            }
+        });
+
+        WSEndpointTracker clientEndpoint = new WSEndpointTracker(){};
+        ClientEndpointConfig clientConfig = ClientEndpointConfig.Builder.create().configurator(configurator).build();
+        URI uri = URI.create("ws://localhost:" + _connector.getLocalPort());
+
+        // If any of the above throw it would fail to upgrade to websocket.
+        Session session = _client.connectToServer(clientEndpoint, clientConfig, uri);
+        assertTrue(clientEndpoint.openLatch.await(5, TimeUnit.SECONDS));
+        session.close();
+        assertTrue(clientEndpoint.closeLatch.await(5, TimeUnit.SECONDS));
+    }
+}
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee10/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee10/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java
index d68ff6bed0e2..83ac45d0cbee 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee10/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee10/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java
@@ -15,14 +15,12 @@
 
 import java.io.IOException;
 import java.nio.ByteBuffer;
-import java.util.Collections;
 import java.util.Date;
 
 import jakarta.websocket.ClientEndpoint;
 import jakarta.websocket.ClientEndpointConfig;
 import jakarta.websocket.ContainerProvider;
 import jakarta.websocket.EndpointConfig;
-import jakarta.websocket.HandshakeResponse;
 import jakarta.websocket.OnMessage;
 import jakarta.websocket.OnOpen;
 import jakarta.websocket.Session;
@@ -75,12 +73,6 @@ public Date onBinary(ByteBuffer buf)
 
     public static class AnnotatedEndpointConfigurator extends ClientEndpointConfig.Configurator
     {
-        @Override
-        public void afterResponse(HandshakeResponse hr)
-        {
-            hr.getHeaders().put("X-Test", Collections.singletonList("Extra"));
-            super.afterResponse(hr);
-        }
     }
 
     private static CoreServer server;
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServerContainer.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServerContainer.java
index d9e329f0cdbb..9c896bebc301 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServerContainer.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServerContainer.java
@@ -158,6 +158,8 @@ public void addMapping(String pathSpec, JettyWebSocketCreator creator)
             }
             catch (Throwable t)
             {
+                if (LOG.isDebugEnabled())
+                    LOG.debug("Could not create WebSocket endpoint", t);
                 cb.failed(t);
                 return null;
             }
@@ -203,11 +205,14 @@ public boolean upgrade(JettyWebSocketCreator creator, HttpServletRequest request
             try
             {
                 Object webSocket = creator.createWebSocket(new DelegatedServerUpgradeRequest(req), new DelegatedServerUpgradeResponse(resp));
-                cb.succeeded();
+                if (webSocket == null)
+                    cb.succeeded();
                 return webSocket;
             }
             catch (Throwable t)
             {
+                if (LOG.isDebugEnabled())
+                    LOG.debug("Could not create WebSocket endpoint", t);
                 cb.failed(t);
                 return null;
             }
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServlet.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServlet.java
index 9d412559321f..b3c7bf38fb51 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServlet.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/JettyWebSocketServlet.java
@@ -303,7 +303,8 @@ public Object createWebSocket(ServerUpgradeRequest upgradeRequest, ServerUpgrade
             try
             {
                 Object webSocket = creator.createWebSocket(request, response);
-                callback.succeeded();
+                if (webSocket == null)
+                    callback.succeeded();
                 return webSocket;
             }
             catch (Throwable t)
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeRequest.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeRequest.java
index a5dc510102ad..3f8f0155fa45 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeRequest.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeRequest.java
@@ -18,7 +18,6 @@
 import java.net.URI;
 import java.security.Principal;
 import java.security.cert.X509Certificate;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Enumeration;
@@ -33,6 +32,7 @@
 import jakarta.servlet.http.HttpSession;
 import org.eclipse.jetty.ee10.websocket.server.JettyServerUpgradeRequest;
 import org.eclipse.jetty.http.BadMessageException;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.util.URIUtil;
 import org.eclipse.jetty.websocket.api.ExtensionConfig;
@@ -121,9 +121,7 @@ public int getHeaderInt(String name)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = upgradeRequest.getHeaders().getFieldNamesCollection().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(getHeaders(name))));
-        return Collections.unmodifiableMap(headers);
+        return HttpFields.asMap(upgradeRequest.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeResponse.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeResponse.java
index a1688d5749e0..51f0d8eed7f4 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeResponse.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/DelegatedServerUpgradeResponse.java
@@ -14,7 +14,6 @@
 package org.eclipse.jetty.ee10.websocket.server.internal;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -24,6 +23,7 @@
 import jakarta.servlet.http.HttpServletResponse;
 import org.eclipse.jetty.ee10.servlet.ServletContextResponse;
 import org.eclipse.jetty.ee10.websocket.server.JettyServerUpgradeResponse;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpStatus;
 import org.eclipse.jetty.server.Response;
 import org.eclipse.jetty.websocket.api.ExtensionConfig;
@@ -35,13 +35,22 @@ public class DelegatedServerUpgradeResponse implements JettyServerUpgradeRespons
 {
     private final ServerUpgradeResponse upgradeResponse;
     private final HttpServletResponse httpServletResponse;
+    private final boolean isUpgraded;
+    private final Map<String, List<String>> headers;
 
     public DelegatedServerUpgradeResponse(ServerUpgradeResponse response)
+    {
+        this(response, false);
+    }
+
+    public DelegatedServerUpgradeResponse(ServerUpgradeResponse response, boolean isUpgraded)
     {
         upgradeResponse = response;
+        this.isUpgraded = isUpgraded;
         ServletContextResponse servletContextResponse = Response.as(response, ServletContextResponse.class);
         this.httpServletResponse = (HttpServletResponse)servletContextResponse.getRequest()
             .getAttribute(WebSocketConstants.WEBSOCKET_WRAPPED_RESPONSE_ATTRIBUTE);
+        headers = HttpFields.asMap(upgradeResponse.getHeaders());
     }
 
     @Override
@@ -55,13 +64,13 @@ public void addHeader(String name, String value)
     @Override
     public void setHeader(String name, String value)
     {
-        upgradeResponse.getHeaders().put(name, value);
+        headers.put(name, List.of(value));
     }
 
     @Override
     public void setHeader(String name, List<String> values)
     {
-        upgradeResponse.getHeaders().put(name, values);
+        headers.put(name, values);
     }
 
     @Override
@@ -91,9 +100,7 @@ public Set<String> getHeaderNames()
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = getHeaderNames().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(getHeaders(name))));
-        return Collections.unmodifiableMap(headers);
+        return isUpgraded ? Collections.unmodifiableMap(headers) : headers;
     }
 
     @Override
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/JettyServerFrameHandlerFactory.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/JettyServerFrameHandlerFactory.java
index 17f50e82a461..5fd68de68f75 100644
--- a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/JettyServerFrameHandlerFactory.java
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee10/websocket/server/internal/JettyServerFrameHandlerFactory.java
@@ -41,7 +41,7 @@ public FrameHandler newFrameHandler(Object websocketPojo, ServerUpgradeRequest u
     {
         JettyWebSocketFrameHandler frameHandler = super.newJettyFrameHandler(websocketPojo);
         frameHandler.setUpgradeRequest(new DelegatedServerUpgradeRequest(upgradeRequest));
-        frameHandler.setUpgradeResponse(new DelegatedServerUpgradeResponse(upgradeResponse));
+        frameHandler.setUpgradeResponse(new DelegatedServerUpgradeResponse(upgradeResponse, true));
         return frameHandler;
     }
 }
diff --git a/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee10/websocket/tests/UpgradeHeadersTest.java b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee10/websocket/tests/UpgradeHeadersTest.java
new file mode 100644
index 000000000000..6d228db7475c
--- /dev/null
+++ b/jetty-ee10/jetty-ee10-websocket/jetty-ee10-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee10/websocket/tests/UpgradeHeadersTest.java
@@ -0,0 +1,124 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.ee10.websocket.tests;
+
+import java.net.URI;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import org.eclipse.jetty.client.Request;
+import org.eclipse.jetty.client.Response;
+import org.eclipse.jetty.ee10.servlet.ServletContextHandler;
+import org.eclipse.jetty.ee10.websocket.server.JettyWebSocketCreator;
+import org.eclipse.jetty.ee10.websocket.server.config.JettyWebSocketServletContainerInitializer;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.ServerConnector;
+import org.eclipse.jetty.websocket.client.ClientUpgradeRequest;
+import org.eclipse.jetty.websocket.client.JettyUpgradeListener;
+import org.eclipse.jetty.websocket.client.WebSocketClient;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class UpgradeHeadersTest
+{
+    private Server _server;
+    private WebSocketClient _client;
+    private ServerConnector _connector;
+
+    public void start(JettyWebSocketCreator creator) throws Exception
+    {
+        _server = new Server();
+        _connector = new ServerConnector(_server);
+        _server.addConnector(_connector);
+
+        ServletContextHandler contextHandler = new ServletContextHandler();
+        JettyWebSocketServletContainerInitializer.configure(contextHandler, (servletContext, container) ->
+            container.addMapping("/", creator));
+        _server.setHandler(contextHandler);
+
+        _server.start();
+        _client = new WebSocketClient();
+        _client.start();
+    }
+
+    @AfterEach
+    public void after() throws Exception
+    {
+        _client.stop();
+        _server.stop();
+    }
+
+    @Test
+    public void testCaseInsensitiveUpgradeHeaders() throws Exception
+    {
+        start((request, response) ->
+        {
+            // Verify that existing headers can be accessed in a case-insensitive way.
+            if (request.getHeaders().get("cOnnEcTiOn") == null)
+                throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            if (response.getHeaders().get("sErVeR") == null)
+                throw new IllegalStateException("No Server Header on HandshakeResponse");
+
+            // Verify custom header sent from client.
+            if (request.getHeaders().get("SeNtHeadEr") == null)
+                throw new IllegalStateException("No sent Header on HandshakeResponse");
+
+            // Add custom response header.
+            response.getHeaders().put("myHeader", List.of("foobar"));
+            if (response.getHeaders().get("MyHeAdEr") == null)
+                throw new IllegalStateException("No custom Header on HandshakeResponse");
+
+            return new EchoSocket();
+        });
+
+        EventSocket clientEndpoint = new EventSocket();
+        URI uri = URI.create("ws://localhost:" + _connector.getLocalPort());
+
+        ClientUpgradeRequest clientUpgradeRequest = new ClientUpgradeRequest();
+        clientUpgradeRequest.getHeaders().put("sentHeader", List.of("value123"));
+        if (clientUpgradeRequest.getHeaders().get("SenTHeaDer") == null)
+            throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+
+        JettyUpgradeListener upgradeListener = new JettyUpgradeListener()
+        {
+            @Override
+            public void onHandshakeRequest(Request request)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (request.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on client Request");
+                if (request.getHeaders().get("SenTHeaDer") == null)
+                    throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+            }
+
+            @Override
+            public void onHandshakeResponse(Request request, Response response)
+            {
+                if (response.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+                if (response.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            }
+        };
+
+        // If any of the above throw it would fail to upgrade to websocket.
+        assertNotNull(_client.connect(clientEndpoint, uri, clientUpgradeRequest, upgradeListener).get(5, TimeUnit.SECONDS));
+        assertTrue(clientEndpoint.openLatch.await(5, TimeUnit.SECONDS));
+        clientEndpoint.session.close();
+        assertTrue(clientEndpoint.closeLatch.await(5, TimeUnit.SECONDS));
+    }
+}
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/client/internal/JsrUpgradeListener.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/client/internal/JsrUpgradeListener.java
index f2185174426b..35660cb92556 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/client/internal/JsrUpgradeListener.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-client/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/client/internal/JsrUpgradeListener.java
@@ -13,9 +13,6 @@
 
 package org.eclipse.jetty.ee9.websocket.jakarta.client.internal;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -41,23 +38,11 @@ public void onHandshakeRequest(Request request)
         if (configurator == null)
             return;
 
-        HttpFields fields = request.getHeaders();
-        Map<String, List<String>> originalHeaders = new HashMap<>();
-        fields.forEach(field ->
-        {
-            originalHeaders.putIfAbsent(field.getName(), new ArrayList<>());
-            List<String> values = originalHeaders.get(field.getName());
-            Collections.addAll(values, field.getValues());
-        });
-
-        // Give headers to configurator
-        configurator.beforeRequest(originalHeaders);
-
-        // Reset headers on HttpRequest per configurator
         request.headers(headers ->
         {
-            headers.clear();
-            originalHeaders.forEach(headers::put);
+            // Give headers to configurator
+            Map<String, List<String>> headersMap = HttpFields.asMap(headers);
+            configurator.beforeRequest(headersMap);
         });
     }
 
@@ -67,18 +52,7 @@ public void onHandshakeResponse(Request request, Response response)
         if (configurator == null)
             return;
 
-        HandshakeResponse handshakeResponse = () ->
-        {
-            Map<String, List<String>> ret = new HashMap<>();
-            response.getHeaders().forEach(field ->
-            {
-                ret.putIfAbsent(field.getName(), new ArrayList<>());
-                List<String> values = ret.get(field.getName());
-                Collections.addAll(values, field.getValues());
-            });
-            return ret;
-        };
-
+        HandshakeResponse handshakeResponse = () -> HttpFields.asMap(response.getHeaders());
         configurator.afterResponse(handshakeResponse);
     }
 }
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/JakartaWebSocketServerContainer.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/JakartaWebSocketServerContainer.java
index e646f5eb141b..a0e2540450a0 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/JakartaWebSocketServerContainer.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/JakartaWebSocketServerContainer.java
@@ -323,9 +323,9 @@ public void upgradeHttpToWebSocket(Object httpServletRequest, Object httpServlet
             baseRequest.setAttribute(WebSocketConstants.WEBSOCKET_WRAPPED_RESPONSE_ATTRIBUTE, response);
 
             if (handshaker.upgradeRequest(negotiator, baseRequest, baseResponse, callback, components, defaultCustomizer))
-            {
                 callback.block();
-            }
+            else
+                throw new IllegalStateException("Invalid WebSocket Upgrade Request");
         }
         finally
         {
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JakartaWebSocketCreator.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JakartaWebSocketCreator.java
index b2587594f6a0..1bde01dcbc95 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JakartaWebSocketCreator.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JakartaWebSocketCreator.java
@@ -156,8 +156,6 @@ public Map<String, Object> getUserProperties()
 
         // [JSR] Step 5: Call modifyHandshake
         configurator.modifyHandshake(config, jsrHandshakeRequest, jsrHandshakeResponse);
-        // Set modified headers Map back into response properly
-        jsrHandshakeResponse.setHeaders(jsrHandshakeResponse.getHeaders());
 
         try
         {
@@ -168,7 +166,8 @@ public Map<String, Object> getUserProperties()
         }
         catch (Throwable x)
         {
-            LOG.warn("Unable to create websocket: {}", config.getEndpointClass().getName(), x);
+            if (LOG.isDebugEnabled())
+                LOG.debug("Unable to create WebSocket: {}", config.getEndpointClass().getName(), x);
             callback.failed(x);
             return null;
         }
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeRequest.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeRequest.java
index a0ff17b5c7f8..840d718512dc 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeRequest.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeRequest.java
@@ -15,16 +15,14 @@
 
 import java.net.URI;
 import java.security.Principal;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.stream.Collectors;
 
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.websocket.server.HandshakeRequest;
 import org.eclipse.jetty.ee9.websocket.jakarta.server.JakartaWebSocketServerContainer;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.pathmap.PathSpec;
 import org.eclipse.jetty.server.Request;
 import org.eclipse.jetty.util.Fields;
@@ -47,9 +45,7 @@ public JsrHandshakeRequest(ServerUpgradeRequest req)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = delegate.getHeaders().getFieldNamesCollection().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(delegate.getHeaders().getValuesList(name))));
-        return Collections.unmodifiableMap(headers);
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeResponse.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeResponse.java
index 7be47d85817a..8de0a2d94bb7 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeResponse.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-server/src/main/java/org/eclipse/jetty/ee9/websocket/jakarta/server/internal/JsrHandshakeResponse.java
@@ -13,24 +13,20 @@
 
 package org.eclipse.jetty.ee9.websocket.jakarta.server.internal;
 
-import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
-import java.util.stream.Collectors;
 
 import jakarta.websocket.HandshakeResponse;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.websocket.core.server.ServerUpgradeResponse;
 
 public class JsrHandshakeResponse implements HandshakeResponse
 {
-    private final ServerUpgradeResponse delegate;
     private final Map<String, List<String>> headers;
 
     public JsrHandshakeResponse(ServerUpgradeResponse resp)
     {
-        this.delegate = resp;
-        this.headers = delegate.getHeaders().getFieldNamesCollection().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(delegate.getHeaders().getValuesList(name))));
+        this.headers = HttpFields.asMap(resp.getHeaders());
     }
 
     @Override
@@ -38,9 +34,4 @@ public Map<String, List<String>> getHeaders()
     {
         return headers;
     }
-
-    public void setHeaders(Map<String, List<String>> headers)
-    {
-        headers.forEach((key, values) -> delegate.getHeaders().put(key, values));
-    }
 }
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee9/websocket/jakarta/tests/UpgradeHeadersTest.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee9/websocket/jakarta/tests/UpgradeHeadersTest.java
new file mode 100644
index 000000000000..4f9b80c65bdb
--- /dev/null
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee9/websocket/jakarta/tests/UpgradeHeadersTest.java
@@ -0,0 +1,138 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.ee9.websocket.jakarta.tests;
+
+import java.net.URI;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.TimeUnit;
+
+import jakarta.websocket.ClientEndpointConfig;
+import jakarta.websocket.Endpoint;
+import jakarta.websocket.EndpointConfig;
+import jakarta.websocket.HandshakeResponse;
+import jakarta.websocket.Session;
+import jakarta.websocket.server.HandshakeRequest;
+import jakarta.websocket.server.ServerEndpointConfig;
+import org.eclipse.jetty.ee9.servlet.ServletContextHandler;
+import org.eclipse.jetty.ee9.websocket.jakarta.client.JakartaWebSocketClientContainer;
+import org.eclipse.jetty.ee9.websocket.jakarta.server.config.JakartaWebSocketServletContainerInitializer;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.ServerConnector;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class UpgradeHeadersTest
+{
+    private Server _server;
+    private JakartaWebSocketClientContainer _client;
+    private ServerConnector _connector;
+
+    public static class MyEndpoint extends Endpoint
+    {
+        @Override
+        public void onOpen(Session session, EndpointConfig config)
+        {
+        }
+    }
+
+    public void start(ServerEndpointConfig.Configurator configurator) throws Exception
+    {
+        _server = new Server();
+        _connector = new ServerConnector(_server);
+        _server.addConnector(_connector);
+
+        ServletContextHandler contextHandler = new ServletContextHandler();
+        _server.setHandler(contextHandler);
+        JakartaWebSocketServletContainerInitializer.configure(contextHandler, (context, container) ->
+        {
+            container.addEndpoint(ServerEndpointConfig.Builder
+                .create(MyEndpoint.class, "/")
+                .configurator(configurator)
+                .build());
+        });
+
+        _server.start();
+        _client = new JakartaWebSocketClientContainer();
+        _client.start();
+    }
+
+    @AfterEach
+    public void after() throws Exception
+    {
+        _client.stop();
+        _server.stop();
+    }
+
+    @Test
+    public void testCaseInsensitiveUpgradeHeaders() throws Exception
+    {
+        ClientEndpointConfig.Configurator configurator = new ClientEndpointConfig.Configurator()
+        {
+            @Override
+            public void beforeRequest(Map<String, List<String>> headers)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (headers.get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on client Request");
+                headers.put("sentHeader", List.of("value123"));
+            }
+
+            @Override
+            public void afterResponse(HandshakeResponse hr)
+            {
+                if (hr.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+                if (hr.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            }
+        };
+
+        start(new ServerEndpointConfig.Configurator()
+        {
+            @Override
+            public void modifyHandshake(ServerEndpointConfig sec, HandshakeRequest request, HandshakeResponse response)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (request.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+                if (response.getHeaders().get("sErVeR") == null)
+                    throw new IllegalStateException("No Server Header on HandshakeResponse");
+
+                // Verify custom header sent from client.
+                if (request.getHeaders().get("SeNtHeadEr") == null)
+                    throw new IllegalStateException("No sent Header on HandshakeResponse");
+
+                // Add custom response header.
+                response.getHeaders().put("myHeader", List.of("foobar"));
+                if (response.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+
+                super.modifyHandshake(sec, request, response);
+            }
+        });
+
+        WSEndpointTracker clientEndpoint = new WSEndpointTracker(){};
+        ClientEndpointConfig clientConfig = ClientEndpointConfig.Builder.create().configurator(configurator).build();
+        URI uri = URI.create("ws://localhost:" + _connector.getLocalPort());
+
+        // If any of the above throw it would fail to upgrade to websocket.
+        Session session = _client.connectToServer(clientEndpoint, clientConfig, uri);
+        assertTrue(clientEndpoint.openLatch.await(5, TimeUnit.SECONDS));
+        session.close();
+        assertTrue(clientEndpoint.closeLatch.await(5, TimeUnit.SECONDS));
+    }
+}
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee9/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee9/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java
index 2fec835746dc..9e5b2d29853f 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee9/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jakarta-tests/src/test/java/org/eclipse/jetty/ee9/websocket/jakarta/tests/client/AnnotatedClientEndpointTest.java
@@ -15,14 +15,12 @@
 
 import java.io.IOException;
 import java.nio.ByteBuffer;
-import java.util.Collections;
 import java.util.Date;
 
 import jakarta.websocket.ClientEndpoint;
 import jakarta.websocket.ClientEndpointConfig;
 import jakarta.websocket.ContainerProvider;
 import jakarta.websocket.EndpointConfig;
-import jakarta.websocket.HandshakeResponse;
 import jakarta.websocket.OnMessage;
 import jakarta.websocket.OnOpen;
 import jakarta.websocket.Session;
@@ -75,12 +73,6 @@ public Date onBinary(ByteBuffer buf)
 
     public static class AnnotatedEndpointConfigurator extends ClientEndpointConfig.Configurator
     {
-        @Override
-        public void afterResponse(HandshakeResponse hr)
-        {
-            hr.getHeaders().put("X-Test", Collections.singletonList("Extra"));
-            super.afterResponse(hr);
-        }
     }
 
     private static CoreServer server;
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeRequest.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeRequest.java
index 27deb9bb3684..d0388a1d0e8b 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeRequest.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeRequest.java
@@ -24,6 +24,7 @@
 import org.eclipse.jetty.ee9.websocket.api.ExtensionConfig;
 import org.eclipse.jetty.ee9.websocket.api.UpgradeRequest;
 import org.eclipse.jetty.http.HttpField;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.http.HttpScheme;
 import org.eclipse.jetty.io.EndPoint;
@@ -78,7 +79,7 @@ public List<String> getHeaders(String name)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        return null;
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeResponse.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeResponse.java
index 0c6c57b77dc3..2f14bce6288a 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeResponse.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-client/src/main/java/org/eclipse/jetty/ee9/websocket/client/impl/DelegatedJettyClientUpgradeResponse.java
@@ -13,7 +13,6 @@
 
 package org.eclipse.jetty.ee9.websocket.client.impl;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@@ -23,6 +22,7 @@
 import org.eclipse.jetty.client.Response;
 import org.eclipse.jetty.ee9.websocket.api.ExtensionConfig;
 import org.eclipse.jetty.ee9.websocket.api.UpgradeResponse;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpHeader;
 
 /**
@@ -65,9 +65,7 @@ public List<String> getHeaders(String name)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = getHeaderNames().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(getHeaders(name))));
-        return Collections.unmodifiableMap(headers);
+        return HttpFields.asMap(delegate.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServerContainer.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServerContainer.java
index f57c41314736..245fc7855641 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServerContainer.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServerContainer.java
@@ -155,11 +155,14 @@ public void addMapping(String pathSpec, JettyWebSocketCreator creator)
             try
             {
                 Object webSocket = creator.createWebSocket(new DelegatedServerUpgradeRequest(req), new DelegatedServerUpgradeResponse(resp));
-                cb.succeeded();
+                if (webSocket == null)
+                    cb.succeeded();
                 return webSocket;
             }
             catch (Throwable t)
             {
+                if (LOG.isDebugEnabled())
+                    LOG.debug("Could not create WebSocket endpoint", t);
                 cb.failed(t);
                 return null;
             }
@@ -205,11 +208,14 @@ public boolean upgrade(JettyWebSocketCreator creator, HttpServletRequest request
             try
             {
                 Object webSocket = creator.createWebSocket(new DelegatedServerUpgradeRequest(req), new DelegatedServerUpgradeResponse(resp));
-                cb.succeeded();
+                if (webSocket == null)
+                    cb.succeeded();
                 return webSocket;
             }
             catch (Throwable t)
             {
+                if (LOG.isDebugEnabled())
+                    LOG.debug("Could not create WebSocket endpoint", t);
                 cb.failed(t);
                 return null;
             }
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServlet.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServlet.java
index 1d8a8263f9ad..87d7c47a409f 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServlet.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/JettyWebSocketServlet.java
@@ -299,18 +299,22 @@ public boolean removeMapping(String pathSpec)
 
     private record WrappedJettyCreator(JettyWebSocketCreator creator) implements WebSocketCreator
     {
+
         private JettyWebSocketCreator getJettyWebSocketCreator()
         {
             return creator;
         }
 
         @Override
-        public Object createWebSocket(ServerUpgradeRequest request, ServerUpgradeResponse response, Callback callback)
+        public Object createWebSocket(ServerUpgradeRequest upgradeRequest, ServerUpgradeResponse upgradeResponse, Callback callback)
         {
+            DelegatedServerUpgradeRequest request = new DelegatedServerUpgradeRequest(upgradeRequest);
+            DelegatedServerUpgradeResponse response = new DelegatedServerUpgradeResponse(upgradeResponse);
             try
             {
-                Object webSocket = creator.createWebSocket(new DelegatedServerUpgradeRequest(request), new DelegatedServerUpgradeResponse(response));
-                callback.succeeded();
+                Object webSocket = creator.createWebSocket(request, response);
+                if (webSocket == null)
+                    callback.succeeded();
                 return webSocket;
             }
             catch (Throwable t)
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeRequest.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeRequest.java
index 6f99d2229cb1..256a3451d9ec 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeRequest.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeRequest.java
@@ -18,7 +18,6 @@
 import java.net.URI;
 import java.security.Principal;
 import java.security.cert.X509Certificate;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.Enumeration;
@@ -35,6 +34,7 @@
 import org.eclipse.jetty.ee9.websocket.common.JettyExtensionConfig;
 import org.eclipse.jetty.ee9.websocket.server.JettyServerUpgradeRequest;
 import org.eclipse.jetty.http.BadMessageException;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpHeader;
 import org.eclipse.jetty.util.URIUtil;
 import org.eclipse.jetty.websocket.core.WebSocketConstants;
@@ -114,9 +114,7 @@ public int getHeaderInt(String name)
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = upgradeRequest.getHeaders().getFieldNamesCollection().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(getHeaders(name))));
-        return Collections.unmodifiableMap(headers);
+        return HttpFields.asMap(upgradeRequest.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeResponse.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeResponse.java
index 23af9f519bf7..f1a1ff95b377 100644
--- a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeResponse.java
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-server/src/main/java/org/eclipse/jetty/ee9/websocket/server/internal/DelegatedServerUpgradeResponse.java
@@ -14,8 +14,6 @@
 package org.eclipse.jetty.ee9.websocket.server.internal;
 
 import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -25,6 +23,7 @@
 import org.eclipse.jetty.ee9.websocket.api.ExtensionConfig;
 import org.eclipse.jetty.ee9.websocket.common.JettyExtensionConfig;
 import org.eclipse.jetty.ee9.websocket.server.JettyServerUpgradeResponse;
+import org.eclipse.jetty.http.HttpFields;
 import org.eclipse.jetty.http.HttpStatus;
 import org.eclipse.jetty.websocket.core.WebSocketConstants;
 import org.eclipse.jetty.websocket.core.server.ServerUpgradeResponse;
@@ -88,9 +87,7 @@ public Set<String> getHeaderNames()
     @Override
     public Map<String, List<String>> getHeaders()
     {
-        Map<String, List<String>> headers = getHeaderNames().stream()
-            .collect(Collectors.toMap((name) -> name, (name) -> new ArrayList<>(getHeaders(name))));
-        return Collections.unmodifiableMap(headers);
+        return HttpFields.asMap(upgradeResponse.getHeaders());
     }
 
     @Override
diff --git a/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee9/websocket/tests/UpgradeHeadersTest.java b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee9/websocket/tests/UpgradeHeadersTest.java
new file mode 100644
index 000000000000..efea1435f2a4
--- /dev/null
+++ b/jetty-ee9/jetty-ee9-websocket/jetty-ee9-websocket-jetty-tests/src/test/java/org/eclipse/jetty/ee9/websocket/tests/UpgradeHeadersTest.java
@@ -0,0 +1,124 @@
+//
+// ========================================================================
+// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.ee9.websocket.tests;
+
+import java.net.URI;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import org.eclipse.jetty.client.Request;
+import org.eclipse.jetty.client.Response;
+import org.eclipse.jetty.ee9.servlet.ServletContextHandler;
+import org.eclipse.jetty.ee9.websocket.client.ClientUpgradeRequest;
+import org.eclipse.jetty.ee9.websocket.client.JettyUpgradeListener;
+import org.eclipse.jetty.ee9.websocket.client.WebSocketClient;
+import org.eclipse.jetty.ee9.websocket.server.JettyWebSocketCreator;
+import org.eclipse.jetty.ee9.websocket.server.config.JettyWebSocketServletContainerInitializer;
+import org.eclipse.jetty.server.Server;
+import org.eclipse.jetty.server.ServerConnector;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class UpgradeHeadersTest
+{
+    private Server _server;
+    private WebSocketClient _client;
+    private ServerConnector _connector;
+
+    public void start(JettyWebSocketCreator creator) throws Exception
+    {
+        _server = new Server();
+        _connector = new ServerConnector(_server);
+        _server.addConnector(_connector);
+
+        ServletContextHandler contextHandler = new ServletContextHandler();
+        JettyWebSocketServletContainerInitializer.configure(contextHandler, (servletContext, container) ->
+            container.addMapping("/", creator));
+        _server.setHandler(contextHandler);
+
+        _server.start();
+        _client = new WebSocketClient();
+        _client.start();
+    }
+
+    @AfterEach
+    public void after() throws Exception
+    {
+        _client.stop();
+        _server.stop();
+    }
+
+    @Test
+    public void testCaseInsensitiveUpgradeHeaders() throws Exception
+    {
+        start((request, response) ->
+        {
+            // Verify that existing headers can be accessed in a case-insensitive way.
+            if (request.getHeaders().get("cOnnEcTiOn") == null)
+                throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            if (response.getHeaders().get("sErVeR") == null)
+                throw new IllegalStateException("No Server Header on HandshakeResponse");
+
+            // Verify custom header sent from client.
+            if (request.getHeaders().get("SeNtHeadEr") == null)
+                throw new IllegalStateException("No sent Header on HandshakeResponse");
+
+            // Add custom response header.
+            response.getHeaders().put("myHeader", List.of("foobar"));
+            if (response.getHeaders().get("MyHeAdEr") == null)
+                throw new IllegalStateException("No custom Header on HandshakeResponse");
+
+            return new EchoSocket();
+        });
+
+        EventSocket clientEndpoint = new EventSocket();
+        URI uri = URI.create("ws://localhost:" + _connector.getLocalPort());
+
+        ClientUpgradeRequest clientUpgradeRequest = new ClientUpgradeRequest();
+        clientUpgradeRequest.getHeaders().put("sentHeader", List.of("value123"));
+        if (clientUpgradeRequest.getHeaders().get("SenTHeaDer") == null)
+            throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+
+        JettyUpgradeListener upgradeListener = new JettyUpgradeListener()
+        {
+            @Override
+            public void onHandshakeRequest(Request request)
+            {
+                // Verify that existing headers can be accessed in a case-insensitive way.
+                if (request.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on client Request");
+                if (request.getHeaders().get("SenTHeaDer") == null)
+                    throw new IllegalStateException("No custom Header on ClientUpgradeRequest");
+            }
+
+            @Override
+            public void onHandshakeResponse(Request request, Response response)
+            {
+                if (response.getHeaders().get("MyHeAdEr") == null)
+                    throw new IllegalStateException("No custom Header on HandshakeResponse");
+                if (response.getHeaders().get("cOnnEcTiOn") == null)
+                    throw new IllegalStateException("No Connection Header on HandshakeRequest");
+            }
+        };
+
+        // If any of the above throw it would fail to upgrade to websocket.
+        assertNotNull(_client.connect(clientEndpoint, uri, clientUpgradeRequest, upgradeListener).get(5, TimeUnit.SECONDS));
+        assertTrue(clientEndpoint.openLatch.await(5, TimeUnit.SECONDS));
+        clientEndpoint.session.close();
+        assertTrue(clientEndpoint.closeLatch.await(5, TimeUnit.SECONDS));
+    }
+}