diff --git a/.all-contributorsrc b/.all-contributorsrc
index 21c67e2ee..2a34d1fe8 100644
--- a/.all-contributorsrc
+++ b/.all-contributorsrc
@@ -622,6 +622,16 @@
         "code",
         "test"
       ]
+    },
+    {
+      "login": "KakatkarAkshay",
+      "name": "Akshay Kakatkar",
+      "avatar_url": "https://avatars.githubusercontent.com/u/49910222?v=4",
+      "profile": "https://github.com/KakatkarAkshay",
+      "contributions": [
+        "code",
+        "test"
+      ]
     }
   ],
   "contributorsPerLine": 7,
diff --git a/app/modules/proxy/api.py b/app/modules/proxy/api.py
index c6cef928e..da1de56af 100644
--- a/app/modules/proxy/api.py
+++ b/app/modules/proxy/api.py
@@ -1716,7 +1716,7 @@ async def _build_models_response(api_key: ApiKeyData | None) -> Response:
 
     if not models:
         await _release_reservation(reservation)
-        return JSONResponse(content=ModelListResponse(data=[]).model_dump(mode="json"))
+        return JSONResponse(content=_dump_v1_models_response(ModelListResponse(data=[])))
 
     items: list[ModelListItem] = []
     for slug, model in models.items():
@@ -1745,7 +1745,19 @@ async def _build_models_response(api_key: ApiKeyData | None) -> Response:
             )
         )
     await _release_reservation(reservation)
-    return JSONResponse(content=ModelListResponse(data=items).model_dump(mode="json"))
+    return JSONResponse(content=_dump_v1_models_response(ModelListResponse(data=items)))
+
+
+def _dump_v1_models_response(response: ModelListResponse) -> dict[str, JsonValue]:
+    payload = response.model_dump(mode="json")
+    for item in payload["data"]:
+        metadata = item.get("metadata")
+        if not isinstance(metadata, dict):
+            continue
+        for key in ("additional_speed_tiers", "service_tiers", "default_service_tier"):
+            if metadata.get(key) is None:
+                metadata.pop(key, None)
+    return payload
 
 
 def _allowed_models_for_api_key(api_key: ApiKeyData | None) -> set[str] | None:
@@ -1896,9 +1908,31 @@ def _to_model_metadata(model: UpstreamModel) -> ModelMetadata:
         supported_in_api=model.supported_in_api,
         minimal_client_version=model.minimal_client_version,
         priority=model.priority,
+        additional_speed_tiers=_raw_string_list(model.raw, "additional_speed_tiers"),
+        service_tiers=_raw_object_list(model.raw, "service_tiers"),
+        default_service_tier=_raw_optional_string(model.raw, "default_service_tier"),
     )
 
 
+def _raw_string_list(raw: Mapping[str, JsonValue], key: str) -> list[str] | None:
+    value = raw.get(key)
+    if not isinstance(value, list):
+        return None
+    return [item for item in value if isinstance(item, str)]
+
+
+def _raw_object_list(raw: Mapping[str, JsonValue], key: str) -> list[dict[str, JsonValue]] | None:
+    value = raw.get(key)
+    if not isinstance(value, list):
+        return None
+    return [dict(cast(Mapping[str, JsonValue], item)) for item in value if isinstance(item, Mapping)]
+
+
+def _raw_optional_string(raw: Mapping[str, JsonValue], key: str) -> str | None:
+    value = raw.get(key)
+    return value if isinstance(value, str) else None
+
+
 @v1_router.post(
     "/chat/completions",
     response_model=ChatCompletionResult,
diff --git a/app/modules/proxy/schemas.py b/app/modules/proxy/schemas.py
index 0877b78ad..6c9444a37 100644
--- a/app/modules/proxy/schemas.py
+++ b/app/modules/proxy/schemas.py
@@ -178,6 +178,9 @@ class ModelMetadata(BaseModel):
     supported_in_api: bool = True
     minimal_client_version: str | None = None
     priority: int = 0
+    additional_speed_tiers: list[str] | None = None
+    service_tiers: list[dict[str, JsonValue]] | None = None
+    default_service_tier: str | None = None
 
 
 class ModelListItem(BaseModel):
diff --git a/openspec/changes/expose-v1-model-speed-tiers/proposal.md b/openspec/changes/expose-v1-model-speed-tiers/proposal.md
new file mode 100644
index 000000000..20fb978f9
--- /dev/null
+++ b/openspec/changes/expose-v1-model-speed-tiers/proposal.md
@@ -0,0 +1,14 @@
+## Why
+
+OpenAI-compatible model discovery clients need to know when Codex models expose upstream speed tiers, such as GPT-5.5 Fast. The Codex-native `/backend-api/codex/models` endpoint already preserves these upstream fields, but `/v1/models` drops them from `metadata`.
+
+## What Changes
+
+- Preserve upstream speed-tier metadata on `/v1/models` metadata entries.
+- Include `additional_speed_tiers`, `service_tiers`, and `default_service_tier` when upstream provides them.
+- Keep existing model IDs and pricing/request behavior unchanged.
+
+## Impact
+
+- OpenAI-compatible clients can synthesize fast-mode model aliases from `/v1/models` metadata.
+- No database migration or dashboard UI change.
diff --git a/openspec/changes/expose-v1-model-speed-tiers/specs/model-catalog-compat/spec.md b/openspec/changes/expose-v1-model-speed-tiers/specs/model-catalog-compat/spec.md
new file mode 100644
index 000000000..888bfaee9
--- /dev/null
+++ b/openspec/changes/expose-v1-model-speed-tiers/specs/model-catalog-compat/spec.md
@@ -0,0 +1,14 @@
+## ADDED Requirements
+
+### Requirement: OpenAI-compatible model metadata preserves speed tiers
+
+When serving `GET /v1/models`, the system SHALL preserve upstream speed-tier metadata in each model's `metadata` object when upstream provides it. This includes `additional_speed_tiers`, `service_tiers`, and `default_service_tier`. The system MUST NOT invent speed tiers for models whose upstream catalog entry does not advertise them.
+
+#### Scenario: /v1/models exposes upstream fast tier metadata
+
+- **WHEN** the upstream model catalog contains `gpt-5.5` with `additional_speed_tiers=["fast"]`
+- **AND** the upstream model catalog includes a `service_tiers` entry with `id="priority"` and `name="Fast"`
+- **WHEN** a client calls `GET /v1/models`
+- **THEN** the `gpt-5.5` entry's metadata includes `additional_speed_tiers=["fast"]`
+- **AND** the metadata includes the upstream `service_tiers` entry
+- **AND** the metadata includes the upstream `default_service_tier` when present
diff --git a/openspec/changes/expose-v1-model-speed-tiers/tasks.md b/openspec/changes/expose-v1-model-speed-tiers/tasks.md
new file mode 100644
index 000000000..0d1d55e46
--- /dev/null
+++ b/openspec/changes/expose-v1-model-speed-tiers/tasks.md
@@ -0,0 +1,5 @@
+## Tasks
+
+- [x] Add `/v1/models` metadata fields for upstream speed tiers.
+- [x] Map fields from the refreshed model registry raw upstream payload.
+- [x] Add integration coverage for speed-tier metadata on `/v1/models`.
diff --git a/tests/integration/test_v1_models.py b/tests/integration/test_v1_models.py
index 868bbeb34..10c158fd7 100644
--- a/tests/integration/test_v1_models.py
+++ b/tests/integration/test_v1_models.py
@@ -672,6 +672,59 @@ async def test_v1_models_reports_backend_context_window(async_client):
     assert codex_by_slug["gpt-5.5"]["max_context_window"] == 272_000
 
 
+@pytest.mark.asyncio
+async def test_v1_models_exposes_speed_tier_metadata(async_client):
+    registry = get_model_registry()
+    models = [
+        _make_upstream_model(
+            "gpt-5.5",
+            raw={
+                "additional_speed_tiers": ["fast"],
+                "default_service_tier": "priority",
+                "service_tiers": [
+                    {
+                        "id": "priority",
+                        "name": "Fast",
+                        "description": "1.5x speed, increased usage",
+                    }
+                ],
+            },
+        )
+    ]
+    await registry.update({"pro": models})
+
+    resp = await async_client.get("/v1/models")
+    assert resp.status_code == 200
+    entry = next(item for item in resp.json()["data"] if item["id"] == "gpt-5.5")
+    metadata = entry["metadata"]
+
+    assert metadata["additional_speed_tiers"] == ["fast"]
+    assert metadata["default_service_tier"] == "priority"
+    assert metadata["service_tiers"] == [
+        {
+            "id": "priority",
+            "name": "Fast",
+            "description": "1.5x speed, increased usage",
+        }
+    ]
+
+
+@pytest.mark.asyncio
+async def test_v1_models_omits_speed_tier_metadata_when_upstream_omits_it(async_client):
+    registry = get_model_registry()
+    models = [_make_upstream_model("gpt-5.5")]
+    await registry.update({"pro": models})
+
+    resp = await async_client.get("/v1/models")
+    assert resp.status_code == 200
+    entry = next(item for item in resp.json()["data"] if item["id"] == "gpt-5.5")
+    metadata = entry["metadata"]
+
+    assert "additional_speed_tiers" not in metadata
+    assert "default_service_tier" not in metadata
+    assert "service_tiers" not in metadata
+
+
 @pytest.mark.asyncio
 async def test_v1_models_does_not_promote_raw_max_context_window(async_client):
     registry = get_model_registry()