fix(proxy): accept slashes in the model id on GET /v1/models/{model_id}

A model group named provider/model is listed by GET /v1/models under that
exact id, but retrieving it came back 404 from the routing layer because the
default path convertor matches a single segment and the ASGI path is decoded
before routing, so a percent encoded slash cannot escape the separator either.

Use the path convertor, as /v1/fine_tuning/jobs/{fine_tuning_job_id:path}
already does, so retrieve accepts every id the listing hands out.

litellm/proxy/proxy_server.py

@@ -9694,12 +9694,12 @@ async def model_list(
 
 
 @router.get(
-    "/v1/models/{model_id}",
+    "/v1/models/{model_id:path}",
     dependencies=[Depends(user_api_key_auth)],
     tags=["model management"],
 )
 @router.get(
-    "/models/{model_id}",
+    "/models/{model_id:path}",
     dependencies=[Depends(user_api_key_auth)],
     tags=["model management"],
 )

tests/test_litellm/proxy/proxy_server/test_routes_models.py

@@ -265,3 +265,32 @@ def test_anthropic_format_returns_public_team_model_name(
     assert response.status_code == 200
     assert [m["id"] for m in response.json()["data"]] == ["gpt-4-team"]
     assert internal_name not in response.text
+
+
+@pytest.mark.parametrize("prefix", ["/v1/models", "/models"])
+def test_get_model_by_id_accepts_slash_in_model_name(
+    client, auth_as, patched_models, monkeypatch, prefix
+):
+    """Regression: a model group named ``provider/model`` is listed under that id,
+    so retrieve has to match the whole id rather than its first path segment."""
+    from litellm.proxy import utils as proxy_utils
+
+    model_id = "mistralai/mistral-7b-instruct"
+
+    async def _fake_get_available_models_for_user(**kwargs):
+        return [model_id]
+
+    monkeypatch.setattr(
+        proxy_utils,
+        "get_available_models_for_user",
+        _fake_get_available_models_for_user,
+    )
+    patched_models.get_model_names = MagicMock(return_value=[model_id])
+
+    with auth_as():
+        listed = client.get(prefix)
+        retrieved = client.get(f"{prefix}/{model_id}")
+
+    assert [entry["id"] for entry in listed.json()["data"]] == [model_id]
+    assert retrieved.status_code == 200
+    assert retrieved.json()["id"] == model_id