diff --git a/news/10128.removal.rst b/news/10128.removal.rst
new file mode 100644
index 00000000000..850b645642f
--- /dev/null
+++ b/news/10128.removal.rst
@@ -0,0 +1 @@
+Improve deprecation warning regarding the copying of source trees when installing from a local directory.
diff --git a/src/pip/_internal/operations/prepare.py b/src/pip/_internal/operations/prepare.py
index 247e63fc86c..8bb5a6843f5 100644
--- a/src/pip/_internal/operations/prepare.py
+++ b/src/pip/_internal/operations/prepare.py
@@ -216,14 +216,16 @@ def unpack_url(
     # be removed.
     if link.is_existing_dir():
         deprecated(
-            "A future pip version will change local packages to be built "
-            "in-place without first copying to a temporary directory. "
-            "We recommend you use --use-feature=in-tree-build to test "
-            "your packages with this new behavior before it becomes the "
-            "default.\n",
+            reason=(
+                "pip copied the source tree into a temporary directory "
+                "before building it. This is changing so that packages "
+                "are built in-place "
+                'within the original source tree ("in-tree build").'
+            ),
             replacement=None,
             gone_in="21.3",
-            issue=7555
+            feature_flag="in-tree-build",
+            issue=7555,
         )
         if os.path.isdir(location):
             rmtree(location)