diff --git a/changelog.d/15293.misc b/changelog.d/15293.misc
new file mode 100644
index 000000000000..57447956204a
--- /dev/null
+++ b/changelog.d/15293.misc
@@ -0,0 +1 @@
+Add a `/versions` flag for [MSC3952](https://github.com/matrix-org/matrix-spec-proposals/pull/3952).
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index dba0f0891ac6..ec171582b3d6 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -122,6 +122,8 @@ def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
                     is not None,
                     # Adds support for relation-based redactions as per MSC3912.
                     "org.matrix.msc3912": self.config.experimental.msc3912_enabled,
+                    # Adds support for unstable "intentional mentions" behaviour.
+                    "org.matrix.msc3952_intentional_mentions": self.config.experimental.msc3952_intentional_mentions,
                 },
             },
         )