diff --git a/headroom/proxy/handlers/anthropic.py b/headroom/proxy/handlers/anthropic.py
index ad237137c..d78f762fb 100644
--- a/headroom/proxy/handlers/anthropic.py
+++ b/headroom/proxy/handlers/anthropic.py
@@ -399,6 +399,10 @@ class AnthropicHandlerMixin:
         # Rate limiting
         if self.rate_limiter:
             api_key = headers.get("x-api-key", "")
+            if not api_key:
+                auth = headers.get("authorization", "")
+                if auth.startswith("Bearer "):
+                    api_key = auth[7:]
             client_ip = request.client.host if request.client else "unknown"
             rate_key = f"{api_key[:16]}:{client_ip}" if api_key else client_ip
             allowed, wait_seconds = await self.rate_limiter.check_request(rate_key)
diff --git a/headroom/proxy/helpers.py b/headroom/proxy/helpers.py
index f3e8b93b8..ea97851b5 100644
--- a/headroom/proxy/helpers.py
+++ b/headroom/proxy/helpers.py
@@ -144,6 +144,16 @@ def _get_rtk_stats() -> dict[str, Any] | None:
     }
 
 
+def is_anthropic_auth(headers: dict[str, str]) -> bool:
+    """Detect Anthropic auth signals in request headers."""
+    if headers.get("x-api-key") or headers.get("anthropic-version"):
+        return True
+    auth = headers.get("authorization", "")
+    if auth.startswith("Bearer sk-ant-"):
+        return True
+    return False
+
+
 async def _read_request_json(request: Request) -> dict[str, Any]:
     """Read and parse JSON from a request, handling compressed bodies.
 
diff --git a/headroom/proxy/server.py b/headroom/proxy/server.py
index 7ee1f19a4..2d6fa60ea 100644
--- a/headroom/proxy/server.py
+++ b/headroom/proxy/server.py
@@ -112,6 +112,7 @@ from headroom.proxy.helpers import (
     _get_rtk_stats,  # noqa: F401
     _read_request_json,  # noqa: F401
     _setup_file_logging,  # noqa: F401
+    is_anthropic_auth,  # noqa: F401
 )
 from headroom.proxy.memory_handler import MemoryConfig, MemoryHandler
 
@@ -2173,10 +2174,10 @@ def create_app(config: ProxyConfig | None = None) -> FastAPI:
     async def list_models(request: Request):
         """List models - route based on auth header.
 
-        - x-api-key header present -> Anthropic
-        - Authorization: Bearer header -> OpenAI
+        - x-api-key / anthropic-version / Bearer sk-ant-* -> Anthropic
+        - Otherwise -> OpenAI
         """
-        if request.headers.get("x-api-key"):
+        if is_anthropic_auth(dict(request.headers)):
             return await proxy.handle_passthrough(
                 request, proxy.ANTHROPIC_API_URL, "models", "anthropic"
             )
@@ -2186,10 +2187,10 @@ def create_app(config: ProxyConfig | None = None) -> FastAPI:
     async def get_model(request: Request, model_id: str):
         """Get model details - route based on auth header.
 
-        - x-api-key header present -> Anthropic
-        - Authorization: Bearer header -> OpenAI
+        - x-api-key / anthropic-version / Bearer sk-ant-* -> Anthropic
+        - Otherwise -> OpenAI
         """
-        if request.headers.get("x-api-key"):
+        if is_anthropic_auth(dict(request.headers)):
             return await proxy.handle_passthrough(
                 request, proxy.ANTHROPIC_API_URL, "models", "anthropic"
             )
@@ -2319,8 +2320,8 @@ def create_app(config: ProxyConfig | None = None) -> FastAPI:
         if custom_base:
             return await proxy.handle_passthrough(request, custom_base.rstrip("/"))
 
-        # Anthropic: sends anthropic-version header and x-api-key
-        if request.headers.get("anthropic-version") or request.headers.get("x-api-key"):
+        # Anthropic: x-api-key, anthropic-version, or Bearer sk-ant-* token
+        if is_anthropic_auth(dict(request.headers)):
             base_url = proxy.ANTHROPIC_API_URL
         # Gemini: sends x-goog-api-key
         elif request.headers.get("x-goog-api-key"):
diff --git a/tests/test_oauth_bearer_routing.py b/tests/test_oauth_bearer_routing.py
new file mode 100644
index 000000000..b93404f51
--- /dev/null
+++ b/tests/test_oauth_bearer_routing.py
@@ -0,0 +1,206 @@
+"""Tests for OAuth Bearer token routing and auth detection."""
+
+import httpx
+import pytest
+from fastapi.testclient import TestClient
+
+from headroom.proxy.helpers import is_anthropic_auth
+from headroom.proxy.server import HeadroomProxy, ProxyConfig, create_app
+
+
+# ---------------------------------------------------------------------------
+# Unit tests: is_anthropic_auth
+# ---------------------------------------------------------------------------
+
+
+class TestIsAnthropicAuth:
+    def test_x_api_key(self):
+        assert is_anthropic_auth({"x-api-key": "sk-ant-api03-xxx"}) is True
+
+    def test_anthropic_version(self):
+        assert is_anthropic_auth({"anthropic-version": "2023-06-01"}) is True
+
+    def test_bearer_sk_ant_oat(self):
+        assert is_anthropic_auth({"authorization": "Bearer sk-ant-oat01-xxx"}) is True
+
+    def test_bearer_sk_ant_api(self):
+        """API key prefix in Bearer header still detected as Anthropic."""
+        assert is_anthropic_auth({"authorization": "Bearer sk-ant-api03-xxx"}) is True
+
+    def test_bearer_openai(self):
+        assert is_anthropic_auth({"authorization": "Bearer sk-proj-xxx"}) is False
+
+    def test_bearer_arbitrary_uuid(self):
+        """Non-Anthropic Bearer tokens don't auto-detect as Anthropic."""
+        assert is_anthropic_auth({"authorization": "Bearer 1a18a113-ab50-43c8"}) is False
+
+    def test_no_auth_headers(self):
+        assert is_anthropic_auth({}) is False
+
+    def test_anthropic_version_plus_bearer(self):
+        """Claude Code sends both anthropic-version and Bearer token."""
+        assert is_anthropic_auth({
+            "anthropic-version": "2023-06-01",
+            "authorization": "Bearer 1a18a113-ab50-43c8",
+        }) is True
+
+    def test_empty_authorization(self):
+        assert is_anthropic_auth({"authorization": ""}) is False
+
+
+# ---------------------------------------------------------------------------
+# Integration tests: /v1/models routing
+# ---------------------------------------------------------------------------
+
+
+class FakeAsyncClient:
+    """Captures outbound requests instead of making real HTTP calls."""
+
+    def __init__(self) -> None:
+        self.calls: list[tuple[str, str]] = []
+
+    async def request(self, method, url, **_kwargs):
+        self.calls.append((method, url))
+        return httpx.Response(200, json={"data": []})
+
+    async def aclose(self) -> None:
+        return None
+
+
+class TestModelsRouting:
+    def _make_client(self):
+        app = create_app(ProxyConfig())
+        client = TestClient(app)
+        fake = FakeAsyncClient()
+        client.app.state.proxy.http_client = fake
+        client.app.state.proxy.ANTHROPIC_API_URL = "https://api.anthropic.test"
+        client.app.state.proxy.OPENAI_API_URL = "https://api.openai.test"
+        return client, fake
+
+    def test_models_with_x_api_key_routes_anthropic(self):
+        with self._make_client() as (client, fake):
+            client.get("/v1/models", headers={"x-api-key": "sk-ant-api03-test"})
+        assert any("anthropic.test" in url for _, url in fake.calls)
+
+    def test_models_with_anthropic_version_routes_anthropic(self):
+        with self._make_client() as (client, fake):
+            client.get("/v1/models", headers={"anthropic-version": "2023-06-01"})
+        assert any("anthropic.test" in url for _, url in fake.calls)
+
+    def test_models_with_bearer_sk_ant_routes_anthropic(self):
+        with self._make_client() as (client, fake):
+            client.get(
+                "/v1/models",
+                headers={"authorization": "Bearer sk-ant-oat01-testtoken"},
+            )
+        assert any("anthropic.test" in url for _, url in fake.calls)
+
+    def test_models_with_openai_bearer_routes_openai(self):
+        with self._make_client() as (client, fake):
+            client.get(
+                "/v1/models",
+                headers={"authorization": "Bearer sk-proj-testtoken"},
+            )
+        assert any("openai.test" in url for _, url in fake.calls)
+
+    def _make_client(self):
+        """Return (client, fake) as a context manager."""
+        import contextlib
+
+        @contextlib.contextmanager
+        def _ctx():
+            app = create_app(ProxyConfig())
+            with TestClient(app) as client:
+                fake = FakeAsyncClient()
+                client.app.state.proxy.http_client = fake
+                client.app.state.proxy.ANTHROPIC_API_URL = "https://api.anthropic.test"
+                client.app.state.proxy.OPENAI_API_URL = "https://api.openai.test"
+                yield client, fake
+
+        return _ctx()
+
+
+# ---------------------------------------------------------------------------
+# Integration tests: catch-all passthrough routing
+# ---------------------------------------------------------------------------
+
+
+class TestCatchAllRouting:
+    def _make_client(self):
+        import contextlib
+
+        @contextlib.contextmanager
+        def _ctx():
+            app = create_app(ProxyConfig())
+            with TestClient(app) as client:
+                fake = FakeAsyncClient()
+                client.app.state.proxy.http_client = fake
+                client.app.state.proxy.ANTHROPIC_API_URL = "https://api.anthropic.test"
+                client.app.state.proxy.OPENAI_API_URL = "https://api.openai.test"
+                yield client, fake
+
+        return _ctx()
+
+    def test_catchall_anthropic_version_routes_anthropic(self):
+        with self._make_client() as (client, fake):
+            client.get(
+                "/v1/some/unknown/path",
+                headers={"anthropic-version": "2023-06-01"},
+            )
+        assert any("anthropic.test" in url for _, url in fake.calls)
+
+    def test_catchall_bearer_sk_ant_routes_anthropic(self):
+        with self._make_client() as (client, fake):
+            client.get(
+                "/v1/some/unknown/path",
+                headers={"authorization": "Bearer sk-ant-oat01-xxx"},
+            )
+        assert any("anthropic.test" in url for _, url in fake.calls)
+
+    def test_catchall_no_auth_routes_openai(self):
+        with self._make_client() as (client, fake):
+            client.get("/v1/some/unknown/path")
+        assert any("openai.test" in url for _, url in fake.calls)
+
+
+# ---------------------------------------------------------------------------
+# Unit test: rate-limit key uses Bearer token when no x-api-key
+# ---------------------------------------------------------------------------
+
+
+class TestRateLimitKey:
+    def test_rate_key_with_x_api_key(self):
+        """x-api-key takes precedence for rate key."""
+        headers = {"x-api-key": "sk-ant-api03-abcdef1234567890"}
+        api_key = headers.get("x-api-key", "")
+        if not api_key:
+            auth = headers.get("authorization", "")
+            if auth.startswith("Bearer "):
+                api_key = auth[7:]
+        client_ip = "127.0.0.1"
+        rate_key = f"{api_key[:16]}:{client_ip}" if api_key else client_ip
+        assert rate_key == "sk-ant-api03-abc:127.0.0.1"
+
+    def test_rate_key_with_bearer_only(self):
+        """Bearer token used for rate key when no x-api-key."""
+        headers = {"authorization": "Bearer sk-ant-oat01-mytoken123456"}
+        api_key = headers.get("x-api-key", "")
+        if not api_key:
+            auth = headers.get("authorization", "")
+            if auth.startswith("Bearer "):
+                api_key = auth[7:]
+        client_ip = "127.0.0.1"
+        rate_key = f"{api_key[:16]}:{client_ip}" if api_key else client_ip
+        assert rate_key == "sk-ant-oat01-myt:127.0.0.1"
+
+    def test_rate_key_no_auth(self):
+        """No auth headers → IP-only rate key."""
+        headers = {}
+        api_key = headers.get("x-api-key", "")
+        if not api_key:
+            auth = headers.get("authorization", "")
+            if auth.startswith("Bearer "):
+                api_key = auth[7:]
+        client_ip = "127.0.0.1"
+        rate_key = f"{api_key[:16]}:{client_ip}" if api_key else client_ip
+        assert rate_key == "127.0.0.1"