diff --git a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
index a3690b108c9..4e8e04245c2 100644
--- a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
+++ b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
@@ -57,7 +57,6 @@ from litellm.proxy._experimental.mcp_server.sampling_handler import (
 )
 from litellm.proxy._experimental.mcp_server.oauth2_token_cache import resolve_mcp_auth
 from litellm.proxy._experimental.mcp_server.outbound_credentials import (
-    ApiKeyConfig,
     Error,
     Ok,
     UpstreamCredentialProvider,
@@ -1956,23 +1955,11 @@ class MCPServerManager:
         """
         transport = server.transport or MCPTransport.sse
         spec = None if transport == MCPTransport.stdio else to_server_spec(server)
-        # Credential-isolation invariant (mirrors the v2 egress path): the resolved credential
-        # rides the httpx auth flow, which writes its header after extra_headers, so it would
-        # overwrite an inbound credential. Defer to v1 when a per-request override is present, or
-        # when the credential's header is already supplied via extra_headers (guardrail hook,
-        # static_headers, or a forwarded caller header) — v1 lets those win. ``none`` writes no
-        # header, so it never conflicts.
-        if spec is not None and (
-            mcp_auth_header
-            or (
-                isinstance(spec.config, ApiKeyConfig)
-                and extra_headers
-                and any(
-                    key.lower() == spec.config.header_name.lower()
-                    for key in extra_headers
-                )
-            )
-        ):
+        # A per-request override is the caller-supplied credential v1 turns into the upstream
+        # auth, so it must win; defer those to v1 (this defer falls away once the per-user modes
+        # stop writing mcp_auth_header). An inbound header already in extra_headers is handled on
+        # the v2 path below, not here.
+        if spec is not None and mcp_auth_header:
             spec = None
         auth_value = (
             await resolve_mcp_auth(server, mcp_auth_header, subject_token=subject_token)
@@ -2055,6 +2042,20 @@ class MCPServerManager:
                 ):
                     case Ok(auth):
                         resolved_auth = auth
+                        # Do not override an Authorization already supplied via extra_headers
+                        # (a guardrail hook such as the JWT signer, static_headers, or a
+                        # forwarded caller header): v1 applies those last, so they win. NoOpAuth
+                        # has no header_name and so never skips.
+                        header_name = getattr(resolved_auth, "header_name", None)
+                        if (
+                            header_name
+                            and extra_headers
+                            and any(
+                                key.lower() == header_name.lower()
+                                for key in extra_headers
+                            )
+                        ):
+                            resolved_auth = None
                     case Error(err):
                         raise_public(err)
                 return MCPClient(
diff --git a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
index 77bc0057dda..35a67391315 100644
--- a/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
+++ b/tests/test_litellm/proxy/_experimental/mcp_server/test_mcp_server_manager.py
@@ -4705,10 +4705,10 @@ class TestCreateMcpClientV2Graft:
         assert client._resolved_auth is None
         assert client._mcp_auth_value == "caller-override"
 
-    async def test_conflicting_extra_header_defers_to_v1(self):
+    async def test_conflicting_extra_header_skips_resolved_auth_on_v2(self):
         # An Authorization already supplied via extra_headers (guardrail hook like the JWT
-        # signer, static_headers, or a forwarded caller header) must not be clobbered by the
-        # resolved static credential, so the static server defers to v1.
+        # signer, static_headers, or a forwarded caller header) must win. The server stays on
+        # the v2 path but skips resolved_auth, so nothing overwrites the inbound header.
         client = await MCPServerManager()._create_mcp_client(
             self._http_server(
                 auth_type=MCPAuth.bearer_token, authentication_token="shared-tok"
@@ -4717,8 +4717,7 @@ class TestCreateMcpClientV2Graft:
         )
 
         assert client._resolved_auth is None
-        assert client._mcp_auth_value == "shared-tok"
-        # v1 applies extra_headers last, so the inbound header wins on the wire.
+        assert client._mcp_auth_value is None
         assert client._get_auth_headers()["Authorization"] == "Bearer hook-jwt"
 
     async def test_none_with_extra_header_stays_v2_without_clobbering(self):