diff --git a/changelog.d/12099.misc b/changelog.d/12099.misc
new file mode 100644
index 000000000000..0553825dbce4
--- /dev/null
+++ b/changelog.d/12099.misc
@@ -0,0 +1 @@
+Move experimental support for [MSC3440](https://github.com/matrix-org/matrix-doc/pull/3440) to /versions.
diff --git a/synapse/rest/client/capabilities.py b/synapse/rest/client/capabilities.py
index b80fdd3712fa..4237071c61bd 100644
--- a/synapse/rest/client/capabilities.py
+++ b/synapse/rest/client/capabilities.py
@@ -72,9 +72,6 @@ async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
                 "org.matrix.msc3244.room_capabilities"
             ] = MSC3244_CAPABILITIES
 
-        if self.config.experimental.msc3440_enabled:
-            response["capabilities"]["io.element.thread"] = {"enabled": True}
-
         if self.config.experimental.msc3720_enabled:
             response["capabilities"]["org.matrix.msc3720.account_status"] = {
                 "enabled": True,
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 00f29344a8a2..2e5d0e4e2258 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -99,6 +99,8 @@ def on_GET(self, request: Request) -> Tuple[int, JsonDict]:
                     "org.matrix.msc2716": self.config.experimental.msc2716_enabled,
                     # Adds support for jump to date endpoints (/timestamp_to_event) as per MSC3030
                     "org.matrix.msc3030": self.config.experimental.msc3030_enabled,
+                    # Adds support for thread relations, per MSC3440.
+                    "org.matrix.msc3440": self.config.experimental.msc3440_enabled,
                 },
             },
         )