modelcontextprotocol
diff --git a/docs/client/oauth-clients.md b/docs/client/oauth-clients.md
@@ -112,7 +112,7 @@ A nightly job, a CI step, another service. There is no browser and nobody to cli
 What changed:
 
 * No `OAuthClientMetadata`, no handlers. You pass `client_id` and `client_secret`; the provider builds a minimal `client_credentials` registration around them and skips dynamic registration entirely.
-* `scopes` is a space-separated string, the OAuth wire format.
+* `scope` is a space-separated string, the OAuth wire format.
 * Everything downstream is identical: the same `TokenStorage`, the same `httpx2.AsyncClient(auth=...)`, the same `streamable_http_client`.
 
 By default the secret travels as HTTP Basic auth on the token request (`client_secret_basic`). Pass `token_endpoint_auth_method="client_secret_post"` to put it in the form body instead. Some authorization servers only accept one of the two.

diff --git a/docs/migration.md b/docs/migration.md
@@ -1954,6 +1954,22 @@ async def callback_handler() -> AuthorizationCodeResult:
 
 Forward the `iss` query parameter from the redirect so the validation can run: omitting it makes the flow fail with `OAuthFlowError` against servers that advertise `authorization_response_iss_parameter_supported`, and silently skips the check for servers that send `iss` without advertising it.
 
+### `scopes=` renamed to `scope=` on the client-credentials providers
+
+`ClientCredentialsOAuthProvider` and `PrivateKeyJWTOAuthProvider` took the requested scope as a keyword named `scopes`, even though the value is a single space-separated string, not a list. The parameter is now `scope`, matching the RFC 6749 wire parameter, `OAuthClientMetadata.scope`, and the newer `IdentityAssertionOAuthProvider`.
+
+**Before (v1):**
+
+```python
+ClientCredentialsOAuthProvider(..., scopes="read write")
+```
+
+**After (v2):**
+
+```python
+ClientCredentialsOAuthProvider(..., scope="read write")
+```
+
 ### Client rejects authorization server metadata with a mismatched `issuer`
 
 During OAuth discovery, `OAuthClientProvider` now validates that the authorization server

diff --git a/docs_src/oauth_clients/tutorial002.py b/docs_src/oauth_clients/tutorial002.py
@@ -29,7 +29,7 @@ async def set_client_info(self, client_info: OAuthClientInformationFull) -> None
     storage=InMemoryTokenStorage(),
     client_id="reporting-agent",
     client_secret="...",
-    scopes="user",
+    scope="user",
 )
 
 

diff --git a/examples/stories/oauth_client_credentials/client.py b/examples/stories/oauth_client_credentials/client.py
@@ -26,7 +26,7 @@ def build_auth(_http: httpx2.AsyncClient) -> httpx2.Auth:
         storage=InMemoryTokenStorage(),
         client_id=DEMO_CLIENT_ID,
         client_secret=DEMO_CLIENT_SECRET,
-        scopes=DEMO_SCOPE,
+        scope=DEMO_SCOPE,
     )
 
 

diff --git a/src/mcp/client/auth/extensions/client_credentials.py b/src/mcp/client/auth/extensions/client_credentials.py
@@ -46,7 +46,7 @@ def __init__(
         client_id: str,
         client_secret: str,
         token_endpoint_auth_method: Literal["client_secret_basic", "client_secret_post"] = "client_secret_basic",
-        scopes: str | None = None,
+        scope: str | None = None,
     ) -> None:
         """Initialize client_credentials OAuth provider.
 
@@ -57,14 +57,14 @@ def __init__(
             client_secret: The OAuth client secret.
             token_endpoint_auth_method: Authentication method for token endpoint.
                 Either "client_secret_basic" (default) or "client_secret_post".
-            scopes: Optional space-separated list of scopes to request.
+            scope: Optional space-separated list of scopes to request.
         """
         # Build minimal client_metadata for the base class
         client_metadata = OAuthClientMetadata(
             redirect_uris=None,
             grant_types=["client_credentials"],
             token_endpoint_auth_method=token_endpoint_auth_method,
-            scope=scopes,
+            scope=scope,
         )
         super().__init__(server_url, client_metadata, storage, None, None, 300.0)
         # Store client_info to be set during _initialize - no dynamic registration needed
@@ -74,7 +74,7 @@ def __init__(
             client_secret=client_secret,
             grant_types=["client_credentials"],
             token_endpoint_auth_method=token_endpoint_auth_method,
-            scope=scopes,
+            scope=scope,
         )
 
     async def _initialize(self) -> None:
@@ -258,7 +258,7 @@ def __init__(
         storage: TokenStorage,
         client_id: str,
         assertion_provider: Callable[[str], Awaitable[str]],
-        scopes: str | None = None,
+        scope: str | None = None,
     ) -> None:
         """Initialize private_key_jwt OAuth provider.
 
@@ -271,14 +271,14 @@ def __init__(
                 `SignedJWTParameters.create_assertion_provider()` for SDK-signed JWTs,
                 `static_assertion_provider()` for pre-built JWTs, or provide your own
                 callback for workload identity federation.
-            scopes: Optional space-separated list of scopes to request.
+            scope: Optional space-separated list of scopes to request.
         """
         # Build minimal client_metadata for the base class
         client_metadata = OAuthClientMetadata(
             redirect_uris=None,
             grant_types=["client_credentials"],
             token_endpoint_auth_method="private_key_jwt",
-            scope=scopes,
+            scope=scope,
         )
         super().__init__(server_url, client_metadata, storage, None, None, 300.0)
         self._assertion_provider = assertion_provider
@@ -288,7 +288,7 @@ def __init__(
             client_id=client_id,
             grant_types=["client_credentials"],
             token_endpoint_auth_method="private_key_jwt",
-            scope=scopes,
+            scope=scope,
         )
 
     async def _initialize(self) -> None:

diff --git a/tests/client/auth/extensions/test_client_credentials.py b/tests/client/auth/extensions/test_client_credentials.py
@@ -210,7 +210,7 @@ async def test_init_with_scopes(self, mock_storage: MockTokenStorage):
             storage=mock_storage,
             client_id="test-client-id",
             client_secret="test-client-secret",
-            scopes="read write",
+            scope="read write",
         )
 
         await provider._initialize()
@@ -240,7 +240,7 @@ async def test_exchange_token_client_credentials(self, mock_storage: MockTokenSt
             storage=mock_storage,
             client_id="test-client-id",
             client_secret="test-client-secret",
-            scopes="read write",
+            scope="read write",
         )
         provider.context.oauth_metadata = OAuthMetadata(
             issuer=AnyHttpUrl("https://api.example.com"),
@@ -268,7 +268,7 @@ async def test_exchange_token_client_secret_post_includes_client_id(self, mock_s
             client_id="test-client-id",
             client_secret="test-client-secret",
             token_endpoint_auth_method="client_secret_post",
-            scopes="read write",
+            scope="read write",
         )
         await provider._initialize()
         provider.context.oauth_metadata = OAuthMetadata(
@@ -296,7 +296,7 @@ async def test_exchange_token_client_secret_post_without_client_id(self, mock_st
             client_id="placeholder",
             client_secret="test-client-secret",
             token_endpoint_auth_method="client_secret_post",
-            scopes="read write",
+            scope="read write",
         )
         await provider._initialize()
         provider.context.oauth_metadata = OAuthMetadata(
@@ -386,7 +386,7 @@ async def mock_assertion_provider(audience: str) -> str:
             storage=mock_storage,
             client_id="test-client-id",
             assertion_provider=mock_assertion_provider,
-            scopes="read write",
+            scope="read write",
         )
         provider.context.oauth_metadata = OAuthMetadata(
             issuer=AnyHttpUrl("https://auth.example.com"),

diff --git a/tests/interaction/auth/test_lifecycle.py b/tests/interaction/auth/test_lifecycle.py
@@ -372,7 +372,7 @@ async def test_client_credentials_provider_obtains_a_token_without_an_authorize_
         storage=InMemoryTokenStorage(),
         client_id="m2m-client",
         client_secret="m2m-secret",
-        scopes="mcp",
+        scope="mcp",
     )
 
     with anyio.fail_after(5):
@@ -423,7 +423,7 @@ async def assertion_provider(audience: str) -> str:
         storage=InMemoryTokenStorage(),
         client_id="m2m-jwt-client",
         assertion_provider=assertion_provider,
-        scopes="mcp",
+        scope="mcp",
     )
 
     with anyio.fail_after(5):