diff --git a/interop/kotlinx-metadata/specs-tests/build.gradle.kts b/interop/kotlinx-metadata/specs-tests/build.gradle.kts
index f586543b7..57d23c79a 100644
--- a/interop/kotlinx-metadata/specs-tests/build.gradle.kts
+++ b/interop/kotlinx-metadata/specs-tests/build.gradle.kts
@@ -15,9 +15,10 @@
  */
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 
-val compileTestKotlin: KotlinCompile by tasks
-compileTestKotlin.kotlinOptions {
-  freeCompilerArgs = listOf("-Xjvm-default=all")
+tasks.withType<KotlinCompile>().named("compileTestKotlin") {
+  kotlinOptions {
+    freeCompilerArgs = listOf("-Xjvm-default=all")
+  }
 }
 
 dependencies {
diff --git a/kotlinpoet/build.gradle.kts b/kotlinpoet/build.gradle.kts
index 8bb202ed5..a83350af9 100644
--- a/kotlinpoet/build.gradle.kts
+++ b/kotlinpoet/build.gradle.kts
@@ -13,6 +13,8 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
 val GROUP: String by project
 val VERSION_NAME: String by project
 
@@ -25,6 +27,12 @@ tasks.named<Jar>("jar") {
   }
 }
 
+tasks.withType<KotlinCompile>().named("compileTestKotlin") {
+  kotlinOptions {
+    freeCompilerArgs = listOf("-Xopt-in=com.squareup.kotlinpoet.DelicateKotlinPoetApi")
+  }
+}
+
 dependencies {
   implementation(deps.kotlin.reflect)
   testImplementation(deps.kotlin.junit)
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/AnnotationSpec.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/AnnotationSpec.kt
index d6c139cfd..d956425af 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/AnnotationSpec.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/AnnotationSpec.kt
@@ -23,7 +23,6 @@ import javax.lang.model.element.TypeElement
 import javax.lang.model.element.VariableElement
 import javax.lang.model.type.TypeMirror
 import javax.lang.model.util.SimpleAnnotationValueVisitor7
-import kotlin.DeprecationLevel.WARNING
 import kotlin.reflect.KClass
 
 /** A generated annotation on a declaration. */
@@ -181,7 +180,13 @@ public class AnnotationSpec private constructor(
   }
 
   public companion object {
-    @JvmStatic @JvmOverloads public fun get(
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
+    @JvmStatic
+    @JvmOverloads
+    public fun get(
       annotation: Annotation,
       includeDefaultValues: Boolean = false
     ): AnnotationSpec {
@@ -223,10 +228,9 @@ public class AnnotationSpec private constructor(
       }
     }
 
-    @Deprecated(
+    @DelicateKotlinPoetApi(
       message = "Mirror APIs don't give complete information on Kotlin types. Consider using" +
-        " the kotlinpoet-metadata APIs instead.",
-      level = WARNING
+        " the kotlinpoet-metadata APIs instead."
     )
     @JvmStatic
     public fun get(annotation: AnnotationMirror): AnnotationSpec {
@@ -248,7 +252,12 @@ public class AnnotationSpec private constructor(
 
     @JvmStatic public fun builder(type: ParameterizedTypeName): Builder = Builder(type)
 
-    @JvmStatic public fun builder(type: Class<out Annotation>): Builder =
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
+    @JvmStatic
+    public fun builder(type: Class<out Annotation>): Builder =
       builder(type.asClassName())
 
     @JvmStatic public fun builder(type: KClass<out Annotation>): Builder =
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ClassName.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ClassName.kt
index 8a5ce5105..ad3943f31 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ClassName.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ClassName.kt
@@ -23,7 +23,6 @@ import javax.lang.model.element.NestingKind.MEMBER
 import javax.lang.model.element.NestingKind.TOP_LEVEL
 import javax.lang.model.element.PackageElement
 import javax.lang.model.element.TypeElement
-import kotlin.DeprecationLevel.WARNING
 import kotlin.reflect.KClass
 
 /** A fully-qualified class name for top-level and member classes.  */
@@ -209,6 +208,10 @@ public class ClassName internal constructor(
   }
 }
 
+@DelicateKotlinPoetApi(
+  message = "Java reflection APIs don't give complete information on Kotlin types. Consider using" +
+    " the kotlinpoet-metadata APIs instead."
+)
 @JvmName("get")
 public fun Class<*>.asClassName(): ClassName {
   require(!isPrimitive) { "primitive types cannot be represented as a ClassName" }
@@ -235,10 +238,9 @@ public fun KClass<*>.asClassName(): ClassName {
 }
 
 /** Returns the class name for `element`. */
-@Deprecated(
+@DelicateKotlinPoetApi(
   message = "Element APIs don't give complete information on Kotlin types. Consider using" +
-    " the kotlinpoet-metadata APIs instead.",
-  level = WARNING
+    " the kotlinpoet-metadata APIs instead."
 )
 @JvmName("get")
 public fun TypeElement.asClassName(): ClassName {
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/DelicateKotlinPoetApi.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/DelicateKotlinPoetApi.kt
new file mode 100644
index 000000000..3d0608389
--- /dev/null
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/DelicateKotlinPoetApi.kt
@@ -0,0 +1,17 @@
+package com.squareup.kotlinpoet
+
+/**
+ * Marks declarations in the KotlinPoet API that are **delicate** &mdash;
+ * they have limited use-case and shall be used with care in general code.
+ * Any use of a delicate declaration has to be carefully reviewed to make sure it is
+ * properly used and does not create problems like lossy Java -> Kotlin type parsing.
+ * Carefully read documentation and [message] of any declaration marked as `DelicateKotlinPoetApi`.
+ */
+@MustBeDocumented
+@Retention(value = AnnotationRetention.BINARY)
+@RequiresOptIn(
+  level = RequiresOptIn.Level.WARNING,
+  message = "This is a delicate API and its use requires care." +
+    " Make sure you fully read and understand documentation of the declaration that is marked as a delicate API."
+)
+public annotation class DelicateKotlinPoetApi(val message: String)
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/FunSpec.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/FunSpec.kt
index 0ab3ea1b8..121146fba 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/FunSpec.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/FunSpec.kt
@@ -555,10 +555,9 @@ public class FunSpec private constructor(
 
     @JvmStatic public fun setterBuilder(): Builder = Builder(SETTER)
 
-    @Deprecated(
+    @DelicateKotlinPoetApi(
       message = "Element APIs don't give complete information on Kotlin types. Consider using" +
-        " the kotlinpoet-metadata APIs instead.",
-      level = WARNING
+        " the kotlinpoet-metadata APIs instead."
     )
     @JvmStatic
     public fun overriding(method: ExecutableElement): Builder {
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/MemberName.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/MemberName.kt
index 2f370533c..c330d66fb 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/MemberName.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/MemberName.kt
@@ -81,7 +81,14 @@ public data class MemberName internal constructor(
       MemberName(this, simpleName)
     @JvmStatic @JvmName("get") public fun KClass<*>.member(simpleName: String): MemberName =
       asClassName().member(simpleName)
-    @JvmStatic @JvmName("get") public fun Class<*>.member(simpleName: String): MemberName =
+
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
+    @JvmStatic
+    @JvmName("get")
+    public fun Class<*>.member(simpleName: String): MemberName =
       asClassName().member(simpleName)
   }
 }
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterSpec.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterSpec.kt
index a1983e907..9e8375ac8 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterSpec.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterSpec.kt
@@ -19,7 +19,6 @@ import java.lang.reflect.Type
 import javax.lang.model.element.ExecutableElement
 import javax.lang.model.element.Modifier
 import javax.lang.model.element.VariableElement
-import kotlin.DeprecationLevel.WARNING
 import kotlin.reflect.KClass
 
 /** A generated parameter declaration. */
@@ -146,10 +145,9 @@ public class ParameterSpec private constructor(
   }
 
   public companion object {
-    @Deprecated(
+    @DelicateKotlinPoetApi(
       message = "Element APIs don't give complete information on Kotlin types. Consider using" +
-        " the kotlinpoet-metadata APIs instead.",
-      level = WARNING
+        " the kotlinpoet-metadata APIs instead."
     )
     @JvmStatic
     public fun get(element: VariableElement): ParameterSpec {
@@ -160,10 +158,9 @@ public class ParameterSpec private constructor(
         .build()
     }
 
-    @Deprecated(
+    @DelicateKotlinPoetApi(
       message = "Element APIs don't give complete information on Kotlin types. Consider using" +
-        " the kotlinpoet-metadata APIs instead.",
-      level = WARNING
+        " the kotlinpoet-metadata APIs instead."
     )
     @JvmStatic
     public fun parametersOf(method: ExecutableElement): List<ParameterSpec> =
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterizedTypeName.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterizedTypeName.kt
index 757241a1b..dd722d4d9 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterizedTypeName.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/ParameterizedTypeName.kt
@@ -194,6 +194,10 @@ public class ParameterizedTypeName internal constructor(
 }
 
 /** Returns a parameterized type equivalent to `type`.  */
+@DelicateKotlinPoetApi(
+  message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+    "using the kotlinpoet-metadata APIs instead."
+)
 @JvmName("get")
 public fun ParameterizedType.asParameterizedTypeName(): ParameterizedTypeName =
   ParameterizedTypeName.get(this, mutableMapOf())
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/PropertySpec.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/PropertySpec.kt
index c19f5f063..2748c0ed0 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/PropertySpec.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/PropertySpec.kt
@@ -206,6 +206,10 @@ public class PropertySpec private constructor(
       annotations += AnnotationSpec.builder(annotation).build()
     }
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun addAnnotation(annotation: Class<*>): Builder =
       addAnnotation(annotation.asClassName())
 
@@ -258,6 +262,10 @@ public class PropertySpec private constructor(
       this.receiverType = receiverType
     }
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun receiver(receiverType: Type): Builder = receiver(receiverType.asTypeName())
 
     public fun receiver(receiverType: KClass<*>): Builder = receiver(receiverType.asTypeName())
@@ -302,7 +310,12 @@ public class PropertySpec private constructor(
       return Builder(name, type).addModifiers(modifiers)
     }
 
-    @JvmStatic public fun builder(
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
+    @JvmStatic
+    public fun builder(
       name: String,
       type: Type,
       modifiers: Iterable<KModifier>
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeAliasSpec.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeAliasSpec.kt
index 2bbf01e1a..1fdd81e78 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeAliasSpec.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeAliasSpec.kt
@@ -117,6 +117,10 @@ public class TypeAliasSpec private constructor(
       annotations += AnnotationSpec.builder(annotation).build()
     }
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun addAnnotation(annotation: Class<*>): Builder =
       addAnnotation(annotation.asClassName())
 
@@ -140,7 +144,12 @@ public class TypeAliasSpec private constructor(
   public companion object {
     @JvmStatic public fun builder(name: String, type: TypeName): Builder = Builder(name, type)
 
-    @JvmStatic public fun builder(name: String, type: Type): Builder =
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
+    @JvmStatic
+    public fun builder(name: String, type: Type): Builder =
       builder(name, type.asTypeName())
 
     @JvmStatic public fun builder(name: String, type: KClass<*>): Builder =
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeName.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeName.kt
index 260000309..7f8dd45d2 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeName.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeName.kt
@@ -34,7 +34,6 @@ import javax.lang.model.type.PrimitiveType
 import javax.lang.model.type.TypeKind
 import javax.lang.model.type.TypeMirror
 import javax.lang.model.util.SimpleTypeVisitor7
-import kotlin.DeprecationLevel.WARNING
 import kotlin.reflect.KClass
 import kotlin.reflect.typeOf
 
@@ -276,10 +275,9 @@ public sealed class TypeName constructor(
 @JvmField public val DYNAMIC: Dynamic = Dynamic
 
 /** Returns a [TypeName] equivalent to this [TypeMirror]. */
-@Deprecated(
+@DelicateKotlinPoetApi(
   message = "Mirror APIs don't give complete information on Kotlin types. Consider using" +
-    " the kotlinpoet-metadata APIs instead.",
-  level = WARNING
+    " the kotlinpoet-metadata APIs instead."
 )
 @JvmName("get")
 public fun TypeMirror.asTypeName(): TypeName = TypeName.get(this, mutableMapOf())
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeSpec.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeSpec.kt
index 4e89df5d8..2a060f6a7 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeSpec.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeSpec.kt
@@ -500,6 +500,10 @@ public class TypeSpec private constructor(
     public fun addAnnotation(annotation: ClassName): Builder =
       addAnnotation(AnnotationSpec.builder(annotation).build())
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun addAnnotation(annotation: Class<*>): Builder =
       addAnnotation(annotation.asClassName())
 
@@ -566,6 +570,10 @@ public class TypeSpec private constructor(
       }
     }
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun superclass(superclass: Type): Builder = superclass(superclass.asTypeName())
 
     public fun superclass(superclass: KClass<*>): Builder = superclass(superclass.asTypeName())
@@ -607,6 +615,10 @@ public class TypeSpec private constructor(
       }
     }
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun addSuperinterface(
       superinterface: Type,
       delegate: CodeBlock = CodeBlock.EMPTY
@@ -662,6 +674,10 @@ public class TypeSpec private constructor(
     public fun addProperty(name: String, type: TypeName, vararg modifiers: KModifier): Builder =
       addProperty(PropertySpec.builder(name, type, *modifiers).build())
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun addProperty(name: String, type: Type, vararg modifiers: KModifier): Builder =
       addProperty(name, type.asTypeName(), *modifiers)
 
@@ -671,6 +687,10 @@ public class TypeSpec private constructor(
     public fun addProperty(name: String, type: TypeName, modifiers: Iterable<KModifier>): Builder =
       addProperty(PropertySpec.builder(name, type, modifiers).build())
 
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
     public fun addProperty(name: String, type: Type, modifiers: Iterable<KModifier>): Builder =
       addProperty(name, type.asTypeName(), modifiers)
 
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeVariableName.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeVariableName.kt
index b3caeff65..6bb013aa5 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeVariableName.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/TypeVariableName.kt
@@ -222,11 +222,19 @@ public class TypeVariableName private constructor(
 }
 
 /** Returns type variable equivalent to `mirror`. */
+@DelicateKotlinPoetApi(
+  message = "Java reflection APIs don't give complete information on Kotlin types. Consider using" +
+    " the kotlinpoet-metadata APIs instead."
+)
 @JvmName("get")
 public fun TypeVariable.asTypeVariableName(): TypeVariableName =
   (asElement() as TypeParameterElement).asTypeVariableName()
 
 /** Returns type variable equivalent to `element`. */
+@DelicateKotlinPoetApi(
+  message = "Element APIs don't give complete information on Kotlin types. Consider using" +
+    " the kotlinpoet-metadata APIs instead."
+)
 @JvmName("get")
 public fun TypeParameterElement.asTypeVariableName(): TypeVariableName {
   val name = simpleName.toString()
diff --git a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/WildcardTypeName.kt b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/WildcardTypeName.kt
index 08c86532c..40745151a 100644
--- a/kotlinpoet/src/main/java/com/squareup/kotlinpoet/WildcardTypeName.kt
+++ b/kotlinpoet/src/main/java/com/squareup/kotlinpoet/WildcardTypeName.kt
@@ -20,7 +20,6 @@ package com.squareup.kotlinpoet
 import java.lang.reflect.Type
 import java.lang.reflect.WildcardType
 import javax.lang.model.element.TypeParameterElement
-import kotlin.DeprecationLevel.WARNING
 import kotlin.reflect.KClass
 
 public class WildcardTypeName private constructor(
@@ -62,7 +61,12 @@ public class WildcardTypeName private constructor(
     @JvmStatic public fun producerOf(outType: TypeName): WildcardTypeName =
       WildcardTypeName(listOf(outType), emptyList())
 
-    @JvmStatic public fun producerOf(outType: Type): WildcardTypeName =
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
+    @JvmStatic
+    public fun producerOf(outType: Type): WildcardTypeName =
       producerOf(outType.asTypeName())
 
     @JvmStatic public fun producerOf(outType: KClass<*>): WildcardTypeName =
@@ -75,7 +79,12 @@ public class WildcardTypeName private constructor(
     @JvmStatic public fun consumerOf(inType: TypeName): WildcardTypeName =
       WildcardTypeName(listOf(ANY), listOf(inType))
 
-    @JvmStatic public fun consumerOf(inType: Type): WildcardTypeName =
+    @DelicateKotlinPoetApi(
+      message = "Java reflection APIs don't give complete information on Kotlin types. Consider " +
+        "using the kotlinpoet-metadata APIs instead."
+    )
+    @JvmStatic
+    public fun consumerOf(inType: Type): WildcardTypeName =
       consumerOf(inType.asTypeName())
 
     @JvmStatic public fun consumerOf(inType: KClass<*>): WildcardTypeName =
@@ -110,15 +119,18 @@ public class WildcardTypeName private constructor(
   }
 }
 
-@Deprecated(
+@DelicateKotlinPoetApi(
   message = "Mirror APIs don't give complete information on Kotlin types. Consider using" +
-    " the kotlinpoet-metadata APIs instead.",
-  level = WARNING
+    " the kotlinpoet-metadata APIs instead."
 )
 @JvmName("get")
 public fun javax.lang.model.type.WildcardType.asWildcardTypeName(): TypeName =
   WildcardTypeName.get(this, mutableMapOf())
 
+@DelicateKotlinPoetApi(
+  message = "Java reflection APIs don't give complete information on Kotlin types. Consider using" +
+    " the kotlinpoet-metadata APIs instead."
+)
 @JvmName("get")
 public fun WildcardType.asWildcardTypeName(): TypeName =
   WildcardTypeName.get(this, mutableMapOf())