diff --git a/changelog.d/12021.feature b/changelog.d/12021.feature
new file mode 100644
index 000000000000..01378df8ca62
--- /dev/null
+++ b/changelog.d/12021.feature
@@ -0,0 +1 @@
+Support only the stable identifier for [MSC3069](https://github.com/matrix-org/matrix-doc/pull/3069)'s `is_guest` on `/_matrix/client/v3/account/whoami`.
\ No newline at end of file
diff --git a/synapse/rest/client/account.py b/synapse/rest/client/account.py
index cfa2aee76d49..efe299e69828 100644
--- a/synapse/rest/client/account.py
+++ b/synapse/rest/client/account.py
@@ -883,7 +883,9 @@ async def on_GET(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         response = {
             "user_id": requester.user.to_string(),
             # MSC: https://github.com/matrix-org/matrix-doc/pull/3069
+            # Entered spec in Matrix 1.2
             "org.matrix.msc3069.is_guest": bool(requester.is_guest),
+            "is_guest": bool(requester.is_guest),
         }
 
         # Appservices and similar accounts do not have device IDs
diff --git a/tests/rest/client/test_account.py b/tests/rest/client/test_account.py
index 89d85b0a1701..51146c471d94 100644
--- a/tests/rest/client/test_account.py
+++ b/tests/rest/client/test_account.py
@@ -486,8 +486,9 @@ def test_GET_whoami(self):
             {
                 "user_id": user_id,
                 "device_id": device_id,
-                # Unstable until MSC3069 enters spec
+                # MSC3069 entered spec in Matrix 1.2 but maintained compatibility
                 "org.matrix.msc3069.is_guest": False,
+                "is_guest": False,
             },
         )
 
@@ -505,8 +506,9 @@ def test_GET_whoami_guests(self):
             {
                 "user_id": user_id,
                 "device_id": device_id,
-                # Unstable until MSC3069 enters spec
+                # MSC3069 entered spec in Matrix 1.2 but maintained compatibility
                 "org.matrix.msc3069.is_guest": True,
+                "is_guest": True,
             },
         )
 
@@ -528,8 +530,9 @@ def test_GET_whoami_appservices(self):
             whoami,
             {
                 "user_id": user_id,
-                # Unstable until MSC3069 enters spec
+                # MSC3069 entered spec in Matrix 1.2 but maintained compatibility
                 "org.matrix.msc3069.is_guest": False,
+                "is_guest": False,
             },
         )
         self.assertFalse(hasattr(whoami, "device_id"))