diff --git a/changelog.d/19646.bugfix b/changelog.d/19646.bugfix
new file mode 100644
index 0000000000..5c8d505e87
--- /dev/null
+++ b/changelog.d/19646.bugfix
@@ -0,0 +1 @@
+Advertise `org.matrix.msc4143` in `unstable_features` when `msc4143_enabled` is set.
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index f5e91ded1b..809e920a2b 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -191,6 +191,8 @@ class VersionsRestServlet(RestServlet):
                     ),
                     # MSC4140: Delayed events
                     "org.matrix.msc4140": bool(self.config.server.max_event_delay_ms),
+                    # MSC4143: Matrix RTC transports (LiveKit backend)
+                    "org.matrix.msc4143": self.config.experimental.msc4143_enabled,
                     # Simplified sliding sync
                     "org.matrix.simplified_msc3575": msc3575_enabled,
                     # Arbitrary key-value profile fields.
diff --git a/tests/rest/client/test_matrixrtc.py b/tests/rest/client/test_matrixrtc.py
index b5216c7adc..87969467fb 100644
--- a/tests/rest/client/test_matrixrtc.py
+++ b/tests/rest/client/test_matrixrtc.py
@@ -20,10 +20,11 @@
 from twisted.internet.testing import MemoryReactor
 
 from synapse.rest import admin
-from synapse.rest.client import login, matrixrtc, register, room
+from synapse.rest.client import login, matrixrtc, register, room, versions
 from synapse.server import HomeServer
 from synapse.util.clock import Clock
 
+from tests import unittest
 from tests.unittest import HomeserverTestCase, override_config
 
 PATH_PREFIX = "/_matrix/client/unstable/org.matrix.msc4143"
@@ -103,3 +104,20 @@ class MatrixRtcTestCase(HomeserverTestCase):
         )
         self.assertEqual(200, channel.code, channel.json_body)
         self.assert_dict({"rtc_transports": [LIVEKIT_ENDPOINT]}, channel.json_body)
+
+
+class MatrixRtcVersionsTestCase(HomeserverTestCase):
+    """Tests that org.matrix.msc4143 is correctly advertised in /versions."""
+
+    servlets = [versions.register_servlets]
+
+    def test_msc4143_false_by_default(self) -> None:
+        channel = self.make_request("GET", "/_matrix/client/versions")
+        self.assertEqual(channel.code, 200, channel.result)
+        self.assertFalse(channel.json_body["unstable_features"]["org.matrix.msc4143"])
+
+    @unittest.override_config({"experimental_features": {"msc4143_enabled": True}})
+    def test_msc4143_true_if_enabled(self) -> None:
+        channel = self.make_request("GET", "/_matrix/client/versions")
+        self.assertEqual(channel.code, 200, channel.result)
+        self.assertTrue(channel.json_body["unstable_features"]["org.matrix.msc4143"])