Fix GPT OSS tensor sharding with upstream MLX LM (#1223)

## Motivation
MLX LM has given GPT OSS a shard method, but MLX does not have an update
to match.

## Changes

<!-- Describe what you changed in detail -->

## Why It Works

<!-- Explain why your approach solves the problem -->

## Test Plan

### Manual Testing
<!-- Hardware: (e.g., MacBook Pro M1 Max 32GB, Mac Mini M2 16GB,
connected via Thunderbolt 4) -->
<!-- What you did: -->
<!-- - -->

### Automated Testing
<!-- Describe changes to automated tests, or how existing tests cover
this change -->
<!-- - -->

pyproject.toml

@@ -24,6 +24,7 @@ dependencies = [
     "hypercorn>=0.18.0",
     "openai-harmony>=0.0.8",
     "httpx>=0.28.1",
+    "tomlkit>=0.14.0",
 ]
 
 [project.scripts]

src/exo/master/api.py

@@ -19,8 +19,11 @@ from exo.master.placement import place_instance as get_instance_placements
 from exo.shared.apply import apply
 from exo.shared.election import ElectionMessage
 from exo.shared.logging import InterceptLogger
-from exo.shared.models.model_cards import MODEL_CARDS, ModelCard, ModelId
+from exo.shared.models.model_cards import (
-from exo.shared.models.model_meta import get_model_card
+    MODEL_CARDS,
+    ModelCard,
+    ModelId,
+)
 from exo.shared.types.api import (
     BenchChatCompletionResponse,
     BenchChatCompletionTaskParams,
@@ -86,12 +89,12 @@ def chunk_to_response(
     )
 
 
-async def resolve_model_card(model_id: str) -> ModelCard:
+async def resolve_model_card(model_id: ModelId) -> ModelCard:
     if model_id in MODEL_CARDS:
         model_card = MODEL_CARDS[model_id]
         return model_card
     else:
-        return await get_model_card(model_id)
+        return await ModelCard.from_hf(model_id)
 
 
 class API:
@@ -236,7 +239,7 @@ class API:
 
     async def get_placement(
         self,
-        model_id: str,
+        model_id: ModelId,
         sharding: Sharding = Sharding.Pipeline,
         instance_meta: InstanceMeta = InstanceMeta.MlxRing,
         min_nodes: int = 1,
@@ -551,7 +554,7 @@ class API:
         self, payload: ChatCompletionTaskParams
     ) -> ChatCompletionResponse | StreamingResponse:
         """Handle chat completions, supporting both streaming and non-streaming responses."""
-        model_card = await resolve_model_card(payload.model)
+        model_card = await resolve_model_card(ModelId(payload.model))
         payload.model = model_card.model_id
 
         if not any(
@@ -578,7 +581,7 @@ class API:
     async def bench_chat_completions(
         self, payload: BenchChatCompletionTaskParams
     ) -> BenchChatCompletionResponse:
-        model_card = await resolve_model_card(payload.model)
+        model_card = await resolve_model_card(ModelId(payload.model))
         payload.model = model_card.model_id
 
         if not any(

src/exo/shared/models/model_cards.py

@@ -1,16 +1,18 @@
-from pydantic import PositiveInt
+from typing import Annotated
 
-from exo.shared.types.common import Id
+import aiofiles
+import aiofiles.os as aios
+import tomlkit
+from anyio import Path, open_file
+from huggingface_hub import model_info
+from loguru import logger
+from pydantic import BaseModel, Field, PositiveInt
+
+from exo.shared.types.common import ModelId
 from exo.shared.types.memory import Memory
 from exo.utils.pydantic_ext import CamelCaseModel
 
-
+_card_cache: dict[str, "ModelCard"] = {}
-class ModelId(Id):
-    def normalize(self) -> str:
-        return self.replace("/", "--")
-
-    def short(self) -> str:
-        return self.split("/")[-1]
 
 
 class ModelCard(CamelCaseModel):
@@ -20,6 +22,43 @@ class ModelCard(CamelCaseModel):
     hidden_size: PositiveInt
     supports_tensor: bool
 
+    async def save(self, path: Path) -> None:
+        async with await open_file(path, "w") as f:
+            py = self.model_dump()
+            data = tomlkit.dumps(py)  # pyright: ignore[reportUnknownMemberType]
+            await f.write(data)
+
+    @staticmethod
+    async def load_from_path(path: Path) -> "ModelCard":
+        async with await open_file(path, "r") as f:
+            py = tomlkit.loads(await f.read())
+            return ModelCard.model_validate(py)
+
+    @staticmethod
+    async def load(model_id: ModelId) -> "ModelCard":
+        if model_id in MODEL_CARDS:
+            return MODEL_CARDS[model_id]
+        return await ModelCard.from_hf(model_id)
+
+    @staticmethod
+    async def from_hf(model_id: ModelId) -> "ModelCard":
+        """Fetches storage size and number of layers for a Hugging Face model, returns Pydantic ModelMeta."""
+        if (mc := _card_cache.get(model_id)) is not None:
+            return mc
+        config_data = await get_config_data(model_id)
+        num_layers = config_data.layer_count
+        mem_size_bytes = await get_safetensors_size(model_id)
+
+        mc = ModelCard(
+            model_id=ModelId(model_id),
+            storage_size=mem_size_bytes,
+            n_layers=num_layers,
+            hidden_size=config_data.hidden_size or 0,
+            supports_tensor=config_data.supports_tensor,
+        )
+        _card_cache[model_id] = mc
+        return mc
+
 
 MODEL_CARDS: dict[str, ModelCard] = {
     # deepseek v3
@@ -308,3 +347,99 @@ MODEL_CARDS: dict[str, ModelCard] = {
         supports_tensor=True,
     ),
 }
+
+from exo.worker.download.download_utils import (  # noqa: E402
+    ModelSafetensorsIndex,
+    download_file_with_retry,
+    ensure_models_dir,
+)
+
+
+class ConfigData(BaseModel):
+    model_config = {"extra": "ignore"}  # Allow unknown fields
+
+    # Common field names for number of layers across different architectures
+    num_hidden_layers: Annotated[int, Field(ge=0)] | None = None
+    num_layers: Annotated[int, Field(ge=0)] | None = None
+    n_layer: Annotated[int, Field(ge=0)] | None = None
+    n_layers: Annotated[int, Field(ge=0)] | None = None  # Sometimes used
+    num_decoder_layers: Annotated[int, Field(ge=0)] | None = None  # Transformer models
+    decoder_layers: Annotated[int, Field(ge=0)] | None = None  # Some architectures
+    hidden_size: Annotated[int, Field(ge=0)] | None = None
+    architectures: list[str] | None = None
+
+    @property
+    def supports_tensor(self) -> bool:
+        return self.architectures in [
+            ["Glm4MoeLiteForCausalLM"],
+            ["DeepseekV32ForCausalLM"],
+            ["DeepseekV3ForCausalLM"],
+            ["Qwen3NextForCausalLM"],
+            ["Qwen3MoeForCausalLM"],
+            ["MiniMaxM2ForCausalLM"],
+            ["LlamaForCausalLM"],
+            ["GptOssForCausalLM"],
+        ]
+
+    @property
+    def layer_count(self) -> int:
+        # Check common field names for layer count
+        layer_fields = [
+            self.num_hidden_layers,
+            self.num_layers,
+            self.n_layer,
+            self.n_layers,
+            self.num_decoder_layers,
+            self.decoder_layers,
+        ]
+
+        for layer_count in layer_fields:
+            if layer_count is not None:
+                return layer_count
+
+        raise ValueError(
+            f"No layer count found in config.json: {self.model_dump_json()}"
+        )
+
+
+async def get_config_data(model_id: ModelId) -> ConfigData:
+    """Downloads and parses config.json for a model."""
+    target_dir = (await ensure_models_dir()) / model_id.normalize()
+    await aios.makedirs(target_dir, exist_ok=True)
+    config_path = await download_file_with_retry(
+        model_id,
+        "main",
+        "config.json",
+        target_dir,
+        lambda curr_bytes, total_bytes, is_renamed: logger.info(
+            f"Downloading config.json for {model_id}: {curr_bytes}/{total_bytes} ({is_renamed=})"
+        ),
+    )
+    async with aiofiles.open(config_path, "r") as f:
+        return ConfigData.model_validate_json(await f.read())
+
+
+async def get_safetensors_size(model_id: ModelId) -> Memory:
+    """Gets model size from safetensors index or falls back to HF API."""
+    target_dir = (await ensure_models_dir()) / model_id.normalize()
+    await aios.makedirs(target_dir, exist_ok=True)
+    index_path = await download_file_with_retry(
+        model_id,
+        "main",
+        "model.safetensors.index.json",
+        target_dir,
+        lambda curr_bytes, total_bytes, is_renamed: logger.info(
+            f"Downloading model.safetensors.index.json for {model_id}: {curr_bytes}/{total_bytes} ({is_renamed=})"
+        ),
+    )
+    async with aiofiles.open(index_path, "r") as f:
+        index_data = ModelSafetensorsIndex.model_validate_json(await f.read())
+
+    metadata = index_data.metadata
+    if metadata is not None:
+        return Memory.from_bytes(metadata.total_size)
+
+    info = model_info(model_id)
+    if info.safetensors is None:
+        raise ValueError(f"No safetensors info found for {model_id}")
+    return Memory.from_bytes(info.safetensors.total)

src/exo/shared/models/model_meta.py

@@ -1,122 +0,0 @@
-from typing import Annotated
-
-import aiofiles
-import aiofiles.os as aios
-from huggingface_hub import model_info
-from loguru import logger
-from pydantic import BaseModel, Field
-
-from exo.shared.models.model_cards import MODEL_CARDS, ModelCard, ModelId
-from exo.shared.types.memory import Memory
-from exo.worker.download.download_utils import (
-    ModelSafetensorsIndex,
-    download_file_with_retry,
-    ensure_models_dir,
-)
-
-
-class ConfigData(BaseModel):
-    model_config = {"extra": "ignore"}  # Allow unknown fields
-
-    # Common field names for number of layers across different architectures
-    num_hidden_layers: Annotated[int, Field(ge=0)] | None = None
-    num_layers: Annotated[int, Field(ge=0)] | None = None
-    n_layer: Annotated[int, Field(ge=0)] | None = None
-    n_layers: Annotated[int, Field(ge=0)] | None = None  # Sometimes used
-    num_decoder_layers: Annotated[int, Field(ge=0)] | None = None  # Transformer models
-    decoder_layers: Annotated[int, Field(ge=0)] | None = None  # Some architectures
-    hidden_size: Annotated[int, Field(ge=0)] | None = None
-
-    @property
-    def layer_count(self) -> int:
-        # Check common field names for layer count
-        layer_fields = [
-            self.num_hidden_layers,
-            self.num_layers,
-            self.n_layer,
-            self.n_layers,
-            self.num_decoder_layers,
-            self.decoder_layers,
-        ]
-
-        for layer_count in layer_fields:
-            if layer_count is not None:
-                return layer_count
-
-        raise ValueError(
-            f"No layer count found in config.json: {self.model_dump_json()}"
-        )
-
-
-async def get_config_data(model_id: str) -> ConfigData:
-    """Downloads and parses config.json for a model."""
-    target_dir = (await ensure_models_dir()) / str(model_id).replace("/", "--")
-    await aios.makedirs(target_dir, exist_ok=True)
-    config_path = await download_file_with_retry(
-        model_id,
-        "main",
-        "config.json",
-        target_dir,
-        lambda curr_bytes, total_bytes, is_renamed: logger.info(
-            f"Downloading config.json for {model_id}: {curr_bytes}/{total_bytes} ({is_renamed=})"
-        ),
-    )
-    async with aiofiles.open(config_path, "r") as f:
-        return ConfigData.model_validate_json(await f.read())
-
-
-async def get_safetensors_size(model_id: str) -> Memory:
-    """Gets model size from safetensors index or falls back to HF API."""
-    target_dir = (await ensure_models_dir()) / str(model_id).replace("/", "--")
-    await aios.makedirs(target_dir, exist_ok=True)
-    index_path = await download_file_with_retry(
-        model_id,
-        "main",
-        "model.safetensors.index.json",
-        target_dir,
-        lambda curr_bytes, total_bytes, is_renamed: logger.info(
-            f"Downloading model.safetensors.index.json for {model_id}: {curr_bytes}/{total_bytes} ({is_renamed=})"
-        ),
-    )
-    async with aiofiles.open(index_path, "r") as f:
-        index_data = ModelSafetensorsIndex.model_validate_json(await f.read())
-
-    metadata = index_data.metadata
-    if metadata is not None:
-        return Memory.from_bytes(metadata.total_size)
-
-    info = model_info(model_id)
-    if info.safetensors is None:
-        raise ValueError(f"No safetensors info found for {model_id}")
-    return Memory.from_bytes(info.safetensors.total)
-
-
-_model_card_cache: dict[str, ModelCard] = {}
-
-
-async def get_model_card(model_id: str) -> ModelCard:
-    if model_id in _model_card_cache:
-        return _model_card_cache[model_id]
-    model_card = await _get_model_card(model_id)
-    _model_card_cache[model_id] = model_card
-    return model_card
-
-
-async def _get_model_card(model_id: str) -> ModelCard:
-    """Fetches storage size and number of layers for a Hugging Face model, returns Pydantic ModelMeta."""
-    config_data = await get_config_data(model_id)
-    num_layers = config_data.layer_count
-    mem_size_bytes = await get_safetensors_size(model_id)
-    model_card = next(
-        (card for card in MODEL_CARDS.values() if card.model_id == ModelId(model_id)),
-        None,
-    )
-
-    return ModelCard(
-        model_id=ModelId(model_id),
-        storage_size=mem_size_bytes,
-        n_layers=num_layers,
-        hidden_size=config_data.hidden_size or 0,
-        # TODO: all custom models currently do not support tensor. We could add a dynamic test for this?
-        supports_tensor=model_card.supports_tensor if model_card is not None else False,
-    )

src/exo/shared/types/api.py

@@ -168,7 +168,7 @@ class BenchChatCompletionTaskParams(ChatCompletionTaskParams):
 
 
 class PlaceInstanceParams(BaseModel):
-    model_id: str
+    model_id: ModelId
     sharding: Sharding = Sharding.Pipeline
     instance_meta: InstanceMeta = InstanceMeta.MlxRing
     min_nodes: int = 1

src/exo/shared/types/common.py

@@ -25,6 +25,14 @@ class NodeId(Id):
     pass
 
 
+class ModelId(Id):
+    def normalize(self) -> str:
+        return self.replace("/", "--")
+
+    def short(self) -> str:
+        return self.split("/")[-1]
+
+
 class SessionId(CamelCaseModel):
     master_node_id: NodeId
     election_clock: int

src/exo/shared/types/worker/downloads.py

@@ -1,3 +1,8 @@
+from datetime import timedelta
+from typing import Literal
+
+from pydantic import BaseModel, ConfigDict, Field, PositiveInt
+
 from exo.shared.types.common import NodeId
 from exo.shared.types.memory import Memory
 from exo.shared.types.worker.shards import ShardMetadata
@@ -42,3 +47,50 @@ class DownloadOngoing(BaseDownloadProgress):
 DownloadProgress = (
     DownloadPending | DownloadCompleted | DownloadFailed | DownloadOngoing
 )
+
+
+class ModelSafetensorsIndexMetadata(BaseModel):
+    total_size: PositiveInt
+
+
+class ModelSafetensorsIndex(BaseModel):
+    metadata: ModelSafetensorsIndexMetadata | None
+    weight_map: dict[str, str]
+
+
+class FileListEntry(BaseModel):
+    type: Literal["file", "directory"]
+    path: str
+    size: int | None = None
+
+
+class RepoFileDownloadProgress(BaseModel):
+    repo_id: str
+    repo_revision: str
+    file_path: str
+    downloaded: Memory
+    downloaded_this_session: Memory
+    total: Memory
+    speed: float
+    eta: timedelta
+    status: Literal["not_started", "in_progress", "complete"]
+    start_time: float
+
+    model_config = ConfigDict(frozen=True)
+
+
+class RepoDownloadProgress(BaseModel):
+    repo_id: str
+    repo_revision: str
+    shard: ShardMetadata
+    completed_files: int
+    total_files: int
+    downloaded_bytes: Memory
+    downloaded_bytes_this_session: Memory
+    total_bytes: Memory
+    overall_speed: float
+    overall_eta: timedelta
+    status: Literal["not_started", "in_progress", "complete"]
+    file_progress: dict[str, RepoFileDownloadProgress] = Field(default_factory=dict)
+
+    model_config = ConfigDict(frozen=True)

src/exo/worker/download/download_utils.py

@@ -17,17 +17,20 @@ import aiohttp
 import certifi
 from loguru import logger
 from pydantic import (
-    BaseModel,
-    ConfigDict,
     DirectoryPath,
-    Field,
-    PositiveInt,
     TypeAdapter,
 )
 
 from exo.shared.constants import EXO_MODELS_DIR
+from exo.shared.types.common import ModelId
 from exo.shared.types.memory import Memory
-from exo.shared.types.worker.downloads import DownloadProgressData
+from exo.shared.types.worker.downloads import (
+    DownloadProgressData,
+    FileListEntry,
+    ModelSafetensorsIndex,
+    RepoDownloadProgress,
+    RepoFileDownloadProgress,
+)
 from exo.shared.types.worker.shards import ShardMetadata
 from exo.worker.download.huggingface_utils import (
     filter_repo_objects,
@@ -37,53 +40,6 @@ from exo.worker.download.huggingface_utils import (
 )
 
 
-class ModelSafetensorsIndexMetadata(BaseModel):
-    total_size: PositiveInt
-
-
-class ModelSafetensorsIndex(BaseModel):
-    metadata: ModelSafetensorsIndexMetadata | None
-    weight_map: dict[str, str]
-
-
-class FileListEntry(BaseModel):
-    type: Literal["file", "directory"]
-    path: str
-    size: int | None = None
-
-
-class RepoFileDownloadProgress(BaseModel):
-    repo_id: str
-    repo_revision: str
-    file_path: str
-    downloaded: Memory
-    downloaded_this_session: Memory
-    total: Memory
-    speed: float
-    eta: timedelta
-    status: Literal["not_started", "in_progress", "complete"]
-    start_time: float
-
-    model_config = ConfigDict(frozen=True)
-
-
-class RepoDownloadProgress(BaseModel):
-    repo_id: str
-    repo_revision: str
-    shard: ShardMetadata
-    completed_files: int
-    total_files: int
-    downloaded_bytes: Memory
-    downloaded_bytes_this_session: Memory
-    total_bytes: Memory
-    overall_speed: float
-    overall_eta: timedelta
-    status: Literal["not_started", "in_progress", "complete"]
-    file_progress: dict[str, RepoFileDownloadProgress] = Field(default_factory=dict)
-
-    model_config = ConfigDict(frozen=True)
-
-
 def trim_etag(etag: str) -> str:
     if (etag[0] == '"' and etag[-1] == '"') or (etag[0] == "'" and etag[-1] == "'"):
         return etag[1:-1]
@@ -125,12 +81,12 @@ def map_repo_download_progress_to_download_progress_data(
     )
 
 
-def build_model_path(model_id: str) -> DirectoryPath:
+def build_model_path(model_id: ModelId) -> DirectoryPath:
-    return EXO_MODELS_DIR / model_id.replace("/", "--")
+    return EXO_MODELS_DIR / model_id.normalize()
 
 
-async def resolve_model_path_for_repo(repo_id: str) -> Path:
+async def resolve_model_path_for_repo(model_id: ModelId) -> Path:
-    return (await ensure_models_dir()) / repo_id.replace("/", "--")
+    return (await ensure_models_dir()) / model_id.normalize()
 
 
 async def ensure_models_dir() -> Path:
@@ -138,8 +94,8 @@ async def ensure_models_dir() -> Path:
     return EXO_MODELS_DIR
 
 
-async def delete_model(repo_id: str) -> bool:
+async def delete_model(model_id: ModelId) -> bool:
-    model_dir = await ensure_models_dir() / repo_id.replace("/", "--")
+    model_dir = await ensure_models_dir() / model_id.normalize()
     if not await aios.path.exists(model_dir):
         return False
     await asyncio.to_thread(shutil.rmtree, model_dir, ignore_errors=False)
@@ -164,19 +120,17 @@ async def seed_models(seed_dir: str | Path):
 
 
 async def fetch_file_list_with_cache(
-    repo_id: str, revision: str = "main", recursive: bool = False
+    model_id: ModelId, revision: str = "main", recursive: bool = False
 ) -> list[FileListEntry]:
-    target_dir = (
+    target_dir = (await ensure_models_dir()) / "caches" / model_id.normalize()
-        (await ensure_models_dir()) / "caches" / str(repo_id).replace("/", "--")
-    )
     await aios.makedirs(target_dir, exist_ok=True)
-    cache_file = (
+    cache_file = target_dir / f"{model_id.normalize()}--{revision}--file_list.json"
-        target_dir / f"{repo_id.replace('/', '--')}--{revision}--file_list.json"
-    )
     if await aios.path.exists(cache_file):
         async with aiofiles.open(cache_file, "r") as f:
             return TypeAdapter(list[FileListEntry]).validate_json(await f.read())
-    file_list = await fetch_file_list_with_retry(repo_id, revision, recursive=recursive)
+    file_list = await fetch_file_list_with_retry(
+        model_id, revision, recursive=recursive
+    )
     await aios.makedirs(cache_file.parent, exist_ok=True)
     async with aiofiles.open(cache_file, "w") as f:
         await f.write(TypeAdapter(list[FileListEntry]).dump_json(file_list).decode())
@@ -184,25 +138,25 @@ async def fetch_file_list_with_cache(
 
 
 async def fetch_file_list_with_retry(
-    repo_id: str, revision: str = "main", path: str = "", recursive: bool = False
+    model_id: ModelId, revision: str = "main", path: str = "", recursive: bool = False
 ) -> list[FileListEntry]:
     n_attempts = 30
     for attempt in range(n_attempts):
         try:
-            return await _fetch_file_list(repo_id, revision, path, recursive)
+            return await _fetch_file_list(model_id, revision, path, recursive)
         except Exception as e:
             if attempt == n_attempts - 1:
                 raise e
             await asyncio.sleep(min(8, 0.1 * float(2.0 ** int(attempt))))
     raise Exception(
-        f"Failed to fetch file list for {repo_id=} {revision=} {path=} {recursive=}"
+        f"Failed to fetch file list for {model_id=} {revision=} {path=} {recursive=}"
     )
 
 
 async def _fetch_file_list(
-    repo_id: str, revision: str = "main", path: str = "", recursive: bool = False
+    model_id: ModelId, revision: str = "main", path: str = "", recursive: bool = False
 ) -> list[FileListEntry]:
-    api_url = f"{get_hf_endpoint()}/api/models/{repo_id}/tree/{revision}"
+    api_url = f"{get_hf_endpoint()}/api/models/{model_id}/tree/{revision}"
     url = f"{api_url}/{path}" if path else api_url
 
     headers = await get_download_headers()
@@ -219,7 +173,7 @@ async def _fetch_file_list(
                     files.append(FileListEntry.model_validate(item))
                 elif item.type == "directory" and recursive:
                     subfiles = await _fetch_file_list(
-                        repo_id, revision, item.path, recursive
+                        model_id, revision, item.path, recursive
                     )
                     files.extend(subfiles)
             return files
@@ -276,10 +230,10 @@ async def calc_hash(path: Path, hash_type: Literal["sha1", "sha256"] = "sha1") -
 
 
 async def file_meta(
-    repo_id: str, revision: str, path: str, redirected_location: str | None = None
+    model_id: ModelId, revision: str, path: str, redirected_location: str | None = None
 ) -> tuple[int, str]:
     url = (
-        urljoin(f"{get_hf_endpoint()}/{repo_id}/resolve/{revision}/", path)
+        urljoin(f"{get_hf_endpoint()}/{model_id}/resolve/{revision}/", path)
         if redirected_location is None
         else f"{get_hf_endpoint()}{redirected_location}"
     )
@@ -298,7 +252,7 @@ async def file_meta(
                 return content_length, etag
             # Otherwise, follow the redirect to get authoritative size/hash
             redirected_location = r.headers.get("location")
-            return await file_meta(repo_id, revision, path, redirected_location)
+            return await file_meta(model_id, revision, path, redirected_location)
         content_length = int(
             r.headers.get("x-linked-size") or r.headers.get("content-length") or 0
         )
@@ -310,7 +264,7 @@ async def file_meta(
 
 
 async def download_file_with_retry(
-    repo_id: str,
+    model_id: ModelId,
     revision: str,
     path: str,
     target_dir: Path,
@@ -320,23 +274,23 @@ async def download_file_with_retry(
     for attempt in range(n_attempts):
         try:
             return await _download_file(
-                repo_id, revision, path, target_dir, on_progress
+                model_id, revision, path, target_dir, on_progress
             )
         except Exception as e:
             if isinstance(e, FileNotFoundError) or attempt == n_attempts - 1:
                 raise e
             logger.error(
-                f"Download error on attempt {attempt}/{n_attempts} for {repo_id=} {revision=} {path=} {target_dir=}"
+                f"Download error on attempt {attempt}/{n_attempts} for {model_id=} {revision=} {path=} {target_dir=}"
             )
             logger.error(traceback.format_exc())
             await asyncio.sleep(min(8, 0.1 * (2.0**attempt)))
     raise Exception(
-        f"Failed to download file {repo_id=} {revision=} {path=} {target_dir=}"
+        f"Failed to download file {model_id=} {revision=} {path=} {target_dir=}"
     )
 
 
 async def _download_file(
-    repo_id: str,
+    model_id: ModelId,
     revision: str,
     path: str,
     target_dir: Path,
@@ -345,7 +299,7 @@ async def _download_file(
     if await aios.path.exists(target_dir / path):
         return target_dir / path
     await aios.makedirs((target_dir / path).parent, exist_ok=True)
-    length, etag = await file_meta(repo_id, revision, path)
+    length, etag = await file_meta(model_id, revision, path)
     remote_hash = etag[:-5] if etag.endswith("-gzip") else etag
     partial_path = target_dir / f"{path}.partial"
     resume_byte_pos = (
@@ -354,7 +308,7 @@ async def _download_file(
         else None
     )
     if resume_byte_pos != length:
-        url = urljoin(f"{get_hf_endpoint()}/{repo_id}/resolve/{revision}/", path)
+        url = urljoin(f"{get_hf_endpoint()}/{model_id}/resolve/{revision}/", path)
         headers = await get_download_headers()
         if resume_byte_pos:
             headers["Range"] = f"bytes={resume_byte_pos}-"
@@ -394,7 +348,7 @@ async def _download_file(
 
 def calculate_repo_progress(
     shard: ShardMetadata,
-    repo_id: str,
+    model_id: ModelId,
     revision: str,
     file_progress: dict[str, RepoFileDownloadProgress],
     all_start_time: float,
@@ -423,7 +377,7 @@ def calculate_repo_progress(
         else "not_started"
     )
     return RepoDownloadProgress(
-        repo_id=repo_id,
+        repo_id=model_id,
         repo_revision=revision,
         shard=shard,
         completed_files=len(
@@ -442,11 +396,11 @@ def calculate_repo_progress(
     )
 
 
-async def get_weight_map(repo_id: str, revision: str = "main") -> dict[str, str]:
+async def get_weight_map(model_id: ModelId, revision: str = "main") -> dict[str, str]:
-    target_dir = (await ensure_models_dir()) / str(repo_id).replace("/", "--")
+    target_dir = (await ensure_models_dir()) / model_id.normalize()
     await aios.makedirs(target_dir, exist_ok=True)
     index_file = await download_file_with_retry(
-        repo_id, revision, "model.safetensors.index.json", target_dir
+        model_id, revision, "model.safetensors.index.json", target_dir
     )
     async with aiofiles.open(index_file, "r") as f:
         index_data = ModelSafetensorsIndex.model_validate_json(await f.read())
@@ -504,7 +458,7 @@ async def download_shard(
     # TODO: currently not recursive. Some models might require subdirectories - thus this will need to be changed.
     #  Update: <- This does not seem to be the case. Yay?
     file_list = await fetch_file_list_with_cache(
-        str(shard.model_card.model_id), revision, recursive=True
+        shard.model_card.model_id, revision, recursive=True
     )
     filtered_file_list = list(
         filter_repo_objects(
@@ -538,7 +492,7 @@ async def download_shard(
             else timedelta(seconds=0)
         )
         file_progress[file.path] = RepoFileDownloadProgress(
-            repo_id=str(shard.model_card.model_id),
+            repo_id=shard.model_card.model_id,
             repo_revision=revision,
             file_path=file.path,
             downloaded=Memory.from_bytes(curr_bytes),
@@ -555,7 +509,7 @@ async def download_shard(
             shard,
             calculate_repo_progress(
                 shard,
-                str(shard.model_card.model_id),
+                shard.model_card.model_id,
                 revision,
                 file_progress,
                 all_start_time,
@@ -565,7 +519,7 @@ async def download_shard(
     for file in filtered_file_list:
         downloaded_bytes = await get_downloaded_size(target_dir / file.path)
         file_progress[file.path] = RepoFileDownloadProgress(
-            repo_id=str(shard.model_card.model_id),
+            repo_id=shard.model_card.model_id,
             repo_revision=revision,
             file_path=file.path,
             downloaded=Memory.from_bytes(downloaded_bytes),
@@ -589,7 +543,7 @@ async def download_shard(
     async def download_with_semaphore(file: FileListEntry) -> None:
         async with semaphore:
             await download_file_with_retry(
-                str(shard.model_card.model_id),
+                shard.model_card.model_id,
                 revision,
                 file.path,
                 target_dir,
@@ -603,7 +557,7 @@ async def download_shard(
             *[download_with_semaphore(file) for file in filtered_file_list]
         )
     final_repo_progress = calculate_repo_progress(
-        shard, str(shard.model_card.model_id), revision, file_progress, all_start_time
+        shard, shard.model_card.model_id, revision, file_progress, all_start_time
     )
     await on_progress(shard, final_repo_progress)
     if gguf := next((f for f in filtered_file_list if f.path.endswith(".gguf")), None):

src/exo/worker/download/impl_shard_downloader.py

@@ -3,8 +3,7 @@ from collections.abc import Awaitable
 from pathlib import Path
 from typing import AsyncIterator, Callable
 
-from exo.shared.models.model_cards import MODEL_CARDS
+from exo.shared.models.model_cards import MODEL_CARDS, ModelCard, ModelId
-from exo.shared.models.model_meta import get_model_card
 from exo.shared.types.worker.shards import (
     PipelineShardMetadata,
     ShardMetadata,
@@ -19,8 +18,8 @@ def exo_shard_downloader(max_parallel_downloads: int = 8) -> ShardDownloader:
     )
 
 
-async def build_base_shard(model_id: str) -> ShardMetadata:
+async def build_base_shard(model_id: ModelId) -> ShardMetadata:
-    model_card = await get_model_card(model_id)
+    model_card = await ModelCard.from_hf(model_id)
     return PipelineShardMetadata(
         model_card=model_card,
         device_rank=0,
@@ -31,7 +30,7 @@ async def build_base_shard(model_id: str) -> ShardMetadata:
     )
 
 
-async def build_full_shard(model_id: str) -> PipelineShardMetadata:
+async def build_full_shard(model_id: ModelId) -> PipelineShardMetadata:
     base_shard = await build_base_shard(model_id)
     return PipelineShardMetadata(
         model_card=base_shard.model_card,
@@ -148,7 +147,7 @@ class ResumableShardDownloader(ShardDownloader):
         self,
     ) -> AsyncIterator[tuple[Path, RepoDownloadProgress]]:
         async def _status_for_model(
-            model_id: str,
+            model_id: ModelId,
         ) -> tuple[Path, RepoDownloadProgress]:
             """Helper coroutine that builds the shard for a model and gets its download status."""
             shard = await build_full_shard(model_id)

src/exo/worker/engines/mlx/auto_parallel.py

@@ -83,11 +83,11 @@ class CustomMlxLayer(nn.Module):
 
     def __init__(self, original_layer: _LayerCallable):
         super().__init__()
-        object.__setattr__(self, "_original_layer", original_layer)
+        dict.__setitem__(self, "_original_layer", original_layer)  # pyright: ignore[reportUnknownMemberType]
 
     @property
     def original_layer(self) -> _LayerCallable:
-        return cast(_LayerCallable, object.__getattribute__(self, "_original_layer"))
+        return cast(_LayerCallable, self["_original_layer"])
 
     # Calls __getattr__ for any attributes not found on nn.Module (e.g. use_sliding)
     if not TYPE_CHECKING:
@@ -96,7 +96,7 @@ class CustomMlxLayer(nn.Module):
             try:
                 return super().__getattr__(name)
             except AttributeError:
-                original_layer = object.__getattribute__(self, "_original_layer")
+                original_layer = cast(_LayerCallable, self["_original_layer"])
                 return getattr(original_layer, name)
 
 
@@ -334,7 +334,7 @@ def tensor_auto_parallel(
         group=group,
     )
 
-    if hasattr(model, "shard"):
+    if hasattr(model, "shard") and not isinstance(model, GptOssModel):
         try:
             model.shard(group)  # type: ignore
             return patch_tensor_model(model)
@@ -383,7 +383,6 @@ def tensor_auto_parallel(
             all_to_sharded_linear_in_place,
             sharded_to_all_linear_in_place,
         )
-
     else:
         raise ValueError(f"Unsupported model type: {type(model)}")
 

src/exo/worker/engines/mlx/utils_mlx.py

@@ -23,6 +23,7 @@ from mlx_lm.models.deepseek_v3 import DeepseekV3Model
 from mlx_lm.models.gpt_oss import Model as GptOssModel
 from mlx_lm.tokenizer_utils import TokenizerWrapper
 
+from exo.shared.models.model_cards import ModelId
 from exo.worker.engines.mlx.constants import (
     CACHE_GROUP_SIZE,
     KV_CACHE_BITS,
@@ -296,7 +297,7 @@ def get_tokenizer(model_path: Path, shard_metadata: ShardMetadata) -> TokenizerW
     return load_tokenizer_for_model_id(shard_metadata.model_card.model_id, model_path)
 
 
-def get_eos_token_ids_for_model(model_id: str) -> list[int] | None:
+def get_eos_token_ids_for_model(model_id: ModelId) -> list[int] | None:
     """
     Get the EOS token IDs for a model based on its ID.
 
@@ -320,7 +321,9 @@ def get_eos_token_ids_for_model(model_id: str) -> list[int] | None:
     return None
 
 
-def load_tokenizer_for_model_id(model_id: str, model_path: Path) -> TokenizerWrapper:
+def load_tokenizer_for_model_id(
+    model_id: ModelId, model_path: Path
+) -> TokenizerWrapper:
     """
     Load tokenizer for a model given its ID and local path.
 

src/exo/worker/tests/unittests/test_mlx/conftest.py

@@ -11,8 +11,9 @@ import mlx.core as mx
 import mlx.nn as nn
 
 from exo.shared.constants import EXO_MODELS_DIR
-from exo.shared.models.model_cards import ModelCard, ModelId
+from exo.shared.models.model_cards import ModelCard
 from exo.shared.types.api import ChatCompletionMessage
+from exo.shared.types.common import ModelId
 from exo.shared.types.memory import Memory
 from exo.shared.types.tasks import ChatCompletionTaskParams
 from exo.shared.types.worker.shards import PipelineShardMetadata, TensorShardMetadata

src/exo/worker/tests/unittests/test_mlx/test_tokenizers.py

@@ -11,7 +11,7 @@ from pathlib import Path
 
 import pytest
 
-from exo.shared.models.model_cards import MODEL_CARDS, ModelCard
+from exo.shared.models.model_cards import MODEL_CARDS, ModelCard, ModelId
 from exo.worker.download.download_utils import (
     download_file_with_retry,
     ensure_models_dir,
@@ -50,9 +50,9 @@ def is_tokenizer_file(filename: str) -> bool:
     return False
 
 
-async def download_tokenizer_files(model_id: str) -> Path:
+async def download_tokenizer_files(model_id: ModelId) -> Path:
     """Download only the tokenizer-related files for a model."""
-    target_dir = await ensure_models_dir() / model_id.replace("/", "--")
+    target_dir = await ensure_models_dir() / model_id.normalize()
     target_dir.mkdir(parents=True, exist_ok=True)
 
     file_list = await fetch_file_list_with_cache(model_id, "main", recursive=True)
@@ -72,22 +72,22 @@ async def download_tokenizer_files(model_id: str) -> Path:
 
 
 # Get a sample of models to test (one per family to keep tests fast)
-def get_test_models() -> list[tuple[str, ModelCard]]:
+def get_test_models() -> list[ModelCard]:
     """Get a representative sample of models to test."""
     # Pick one model from each family to test
-    families: dict[str, tuple[str, ModelCard]] = {}
+    families: dict[str, ModelCard] = {}
-    for _, card in MODEL_CARDS.items():
+    for card in MODEL_CARDS.values():
         # Extract family name (e.g., "llama-3.1" from "llama-3.1-8b")
         parts = card.model_id.short().split("-")
         family = "-".join(parts[:2]) if len(parts) >= 2 else parts[0]
 
         if family not in families:
-            families[family] = (card.model_id.short(), card)
+            families[family] = card
 
     return list(families.values())
 
 
-TEST_MODELS: list[tuple[str, ModelCard]] = get_test_models()
+TEST_MODELS: list[ModelCard] = get_test_models()
 
 pytestmark = pytest.mark.slow
 
@@ -101,14 +101,13 @@ def event_loop():
 
 
 @pytest.mark.parametrize(
-    "short_id,model_card",
+    "model_card",
     TEST_MODELS,
-    ids=[m[0] for m in TEST_MODELS],
 )
 @pytest.mark.asyncio
 async def test_tokenizer_encode_decode(short_id: str, model_card: ModelCard) -> None:
     """Test that tokenizer can encode and decode text correctly."""
-    model_id = str(model_card.model_id)
+    model_id = model_card.model_id
 
     # Download tokenizer files
     model_path = await download_tokenizer_files(model_id)
@@ -167,16 +166,15 @@ async def test_tokenizer_encode_decode(short_id: str, model_card: ModelCard) ->
 
 
 @pytest.mark.parametrize(
-    "short_id,model_card",
+    "model_card",
     TEST_MODELS,
-    ids=[m[0] for m in TEST_MODELS],
 )
 @pytest.mark.asyncio
 async def test_tokenizer_has_required_attributes(
     short_id: str, model_card: ModelCard
 ) -> None:
     """Test that tokenizer has required attributes for inference."""
-    model_id = str(model_card.model_id)
+    model_id = model_card.model_id
 
     model_path = await download_tokenizer_files(model_id)
 
@@ -209,19 +207,18 @@ async def test_tokenizer_has_required_attributes(
 
 
 @pytest.mark.parametrize(
-    "short_id,model_card",
+    "model_card",
     TEST_MODELS,
-    ids=[m[0] for m in TEST_MODELS],
 )
 @pytest.mark.asyncio
-async def test_tokenizer_special_tokens(short_id: str, model_card: ModelCard) -> None:
+async def test_tokenizer_special_tokens(model_card: ModelCard) -> None:
     """Test that tokenizer can encode text containing special tokens.
 
     This is critical because the actual inference path uses prompts with
     special tokens from chat templates. If special tokens aren't handled
     correctly, encoding will fail.
     """
-    model_id = str(model_card.model_id)
+    model_id = model_card.model_id
 
     model_path = await download_tokenizer_files(model_id)
 
@@ -301,16 +298,14 @@ async def test_tokenizer_special_tokens(short_id: str, model_card: ModelCard) ->
 async def test_kimi_tokenizer_specifically():
     """Test Kimi tokenizer with its specific patches and quirks."""
     kimi_models = [
-        (short_id, card)
+        card for card in MODEL_CARDS.values() if "kimi" in card.model_id.lower()
-        for short_id, card in MODEL_CARDS.items()
-        if "kimi" in short_id.lower()
     ]
 
     if not kimi_models:
         pytest.skip("No Kimi models found in MODEL_CARDS")
 
-    _, model_card = kimi_models[0]
+    model_card = kimi_models[0]
-    model_id = str(model_card.model_id)
+    model_id = model_card.model_id
 
     model_path = await download_tokenizer_files(model_id)
 
@@ -349,17 +344,15 @@ async def test_kimi_tokenizer_specifically():
 @pytest.mark.asyncio
 async def test_glm_tokenizer_specifically():
     """Test GLM tokenizer with its specific EOS tokens."""
-    glm_models = [
+    glm_model_cards = [
-        (short_id, card)
+        card for card in MODEL_CARDS.values() if "glm" in card.model_id.lower()
-        for short_id, card in MODEL_CARDS.items()
-        if "glm" in short_id.lower()
     ]
 
-    if not glm_models:
+    if not glm_model_cards:
         pytest.skip("No GLM models found in MODEL_CARDS")
 
-    _, model_card = glm_models[0]
+    model_card = glm_model_cards[0]
-    model_id = str(model_card.model_id)
+    model_id = model_card.model_id
 
     model_path = await download_tokenizer_files(model_id)
 

src/exo/worker/tests/unittests/test_plan/test_download_and_loading.py

@@ -1,6 +1,5 @@
 import exo.worker.plan as plan_mod
-from exo.shared.models.model_cards import ModelId
+from exo.shared.types.common import ModelId, NodeId
-from exo.shared.types.common import NodeId
 from exo.shared.types.memory import Memory
 from exo.shared.types.tasks import LoadModel
 from exo.shared.types.worker.downloads import DownloadCompleted, DownloadProgress

uv.lock

@@ -248,6 +248,7 @@ dependencies = [
     { name = "pydantic", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "rustworkx", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "tiktoken", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
+    { name = "tomlkit", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
     { name = "types-aiofiles", marker = "sys_platform == 'darwin' or sys_platform == 'linux'" },
 ]
 
@@ -281,6 +282,7 @@ requires-dist = [
     { name = "pydantic", specifier = ">=2.11.7" },
     { name = "rustworkx", specifier = ">=0.17.1" },
     { name = "tiktoken", specifier = ">=0.12.0" },
+    { name = "tomlkit", specifier = ">=0.14.0" },
     { name = "types-aiofiles", specifier = ">=24.1.0.20250708" },
 ]
 
@@ -315,6 +317,16 @@ dev = [
     { name = "pytest-asyncio", specifier = ">=1.0.0" },
 ]
 
+[[package]]
+name = "tomlkit"
+version = "0.14.0"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/c3/af/14b24e41977adb296d6bd1fb59402cf7d60ce364f90c890bd2ec65c43b5a/tomlkit-0.14.0.tar.gz", hash = "sha256:cf00efca415dbd57575befb1f6634c4f42d2d87dbba376128adb42c121b87064", size = 187167 }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/b5/11/87d6d29fb5d237229d67973a6c9e06e048f01cf4994dee194ab0ea841814/tomlkit-0.14.0-py3-none-any.whl", hash = "sha256:592064ed85b40fa213469f81ac584f67a4f2992509a7c3ea2d632208623a3680", size = 39310 },
+]
+
+
 [[package]]
 name = "fastapi"
 version = "0.128.0"