diff --git a/changelog.d/13920.feature b/changelog.d/13920.feature
new file mode 100644
index 0000000000..aee702bcd2
--- /dev/null
+++ b/changelog.d/13920.feature
@@ -0,0 +1 @@
+Support a `dir` parameter on the `/relations` endpoint per [MSC3715](https://github.com/matrix-org/matrix-doc/pull/3715).
diff --git a/synapse/rest/client/relations.py b/synapse/rest/client/relations.py
index ce97080013..205c556f64 100644
--- a/synapse/rest/client/relations.py
+++ b/synapse/rest/client/relations.py
@@ -56,15 +56,21 @@ class RelationPaginationServlet(RestServlet):
         requester = await self.auth.get_user_by_req(request, allow_guest=True)
 
         limit = parse_integer(request, "limit", default=5)
-        if self._msc3715_enabled:
-            direction = parse_string(
-                request,
-                "org.matrix.msc3715.dir",
-                default="b",
-                allowed_values=["f", "b"],
-            )
-        else:
-            direction = "b"
+        # Fetch the direction parameter, if provided.
+        #
+        # TODO Use PaginationConfig.from_request when the unstable parameter is
+        #      no longer needed.
+        direction = parse_string(request, "dir", allowed_values=["f", "b"])
+        if direction is None:
+            if self._msc3715_enabled:
+                direction = parse_string(
+                    request,
+                    "org.matrix.msc3715.dir",
+                    default="b",
+                    allowed_values=["f", "b"],
+                )
+            else:
+                direction = "b"
         from_token_str = parse_string(request, "from")
         to_token_str = parse_string(request, "to")
 
diff --git a/tests/rest/client/test_relations.py b/tests/rest/client/test_relations.py
index d33e34d829..fef3b72d76 100644
--- a/tests/rest/client/test_relations.py
+++ b/tests/rest/client/test_relations.py
@@ -728,7 +728,6 @@ class RelationsTestCase(BaseRelationsTestCase):
 
 
 class RelationPaginationTestCase(BaseRelationsTestCase):
-    @unittest.override_config({"experimental_features": {"msc3715_enabled": True}})
     def test_basic_paginate_relations(self) -> None:
         """Tests that calling pagination API correctly the latest relations."""
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")
@@ -771,7 +770,7 @@ class RelationPaginationTestCase(BaseRelationsTestCase):
         channel = self.make_request(
             "GET",
             f"/_matrix/client/v1/rooms/{self.room}/relations"
-            f"/{self.parent_id}?limit=1&org.matrix.msc3715.dir=f",
+            f"/{self.parent_id}?limit=1&dir=f",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -788,7 +787,6 @@ class RelationPaginationTestCase(BaseRelationsTestCase):
             channel.json_body["chunk"][0],
         )
 
-    @unittest.override_config({"experimental_features": {"msc3715_enabled": True}})
     def test_repeated_paginate_relations(self) -> None:
         """Test that if we paginate using a limit and tokens then we get the
         expected events.
@@ -838,7 +836,7 @@ class RelationPaginationTestCase(BaseRelationsTestCase):
 
             channel = self.make_request(
                 "GET",
-                f"/_matrix/client/v1/rooms/{self.room}/relations/{self.parent_id}?org.matrix.msc3715.dir=f&limit=3{from_token}",
+                f"/_matrix/client/v1/rooms/{self.room}/relations/{self.parent_id}?dir=f&limit=3{from_token}",
                 access_token=self.user_token,
             )
             self.assertEqual(200, channel.code, channel.json_body)