[MLX] Add native MLX execution backend for Apple Silicon Mac (#20342)

Signed-off-by: Xiaodong Ye <yeahdongcn@gmail.com>

python/pyproject_other.toml

@@ -142,6 +142,9 @@ diffusion_mps = [
   "cache-dit==1.2.3",
   "addict==2.4.0",
   "av==16.1.0",
+  "scikit-image==0.25.2",
+  "trimesh>=4.0.0",
+  "xatlas",
 ]
 
 test = [

python/sglang/bench_one_batch.py

@@ -88,6 +88,7 @@ from sglang.srt.utils import (
     suppress_other_loggers,
 )
 from sglang.srt.utils.hf_transformers_utils import get_tokenizer
+from sglang.srt.utils.tensor_bridge import use_mlx
 
 
 def start_profile(profile_activities, profile_record_shapes=False, rank_print=print):
@@ -262,7 +263,7 @@ def load_model(server_args, port_args, gpu_id, tp_rank):
     moe_ep_rank = tp_rank // (server_args.tp_size // server_args.ep_size)
 
     model_config = ModelConfig.from_server_args(server_args)
-    model_runner = ModelRunner(
+    runner_kwargs = dict(
         model_config=model_config,
         mem_fraction_static=server_args.mem_fraction_static,
         gpu_id=gpu_id,
@@ -275,6 +276,16 @@ def load_model(server_args, port_args, gpu_id, tp_rank):
         nccl_port=port_args.nccl_port,
         server_args=server_args,
     )
+
+    _use_mlx = use_mlx()
+    if _use_mlx:
+        from sglang.srt.hardware_backend.mlx.model_runner_stub import (
+            MlxModelRunnerStub,
+        )
+
+        model_runner = MlxModelRunnerStub(**runner_kwargs)
+    else:
+        model_runner = ModelRunner(**runner_kwargs)
     rank_print(f"max_total_num_tokens={model_runner.max_total_num_tokens}")
     tokenizer = get_tokenizer(
         server_args.tokenizer_path,
@@ -283,6 +294,12 @@ def load_model(server_args, port_args, gpu_id, tp_rank):
     )
     if server_args.tp_size > 1:
         dist.barrier()
+
+    if _use_mlx:
+        model_runner = _MlxBenchRunner(model_runner, server_args)
+    else:
+        model_runner = _TorchBenchRunner(model_runner)
+
     return model_runner, tokenizer
 
 
@@ -337,6 +354,7 @@ def prepare_extend_inputs_for_correctness_test(
     for i in range(len(reqs)):
         req: Req = reqs[i]
         req.fill_ids += input_ids[i][bench_args.cut_len :]
+        if model_runner is not None:
             req.prefix_indices = model_runner.req_to_token_pool.req_to_token[
                 i, : bench_args.cut_len
             ].to(req.prefix_indices.dtype)
@@ -445,6 +463,69 @@ def _maybe_prepare_mlp_sync_batch(batch: ScheduleBatch, model_runner):
         )
 
 
+class _TorchBenchRunner:
+    """Wraps ModelRunner for the standard PyTorch benchmark path."""
+
+    def __init__(self, model_runner):
+        self.torch_runner = model_runner
+
+    def clear(self):
+        self.torch_runner.req_to_token_pool.clear()
+        self.torch_runner.token_to_kv_pool_allocator.clear()
+
+    def extend(self, reqs):
+        return extend(reqs, self.torch_runner)
+
+    def decode(self, next_token_ids, batch):
+        return decode(next_token_ids, batch, self.torch_runner)
+
+    def cleanup(self, batch):
+        pass
+
+    def synchronize(self):
+        synchronize(self.torch_runner.device)
+
+    def max_batch_size(self, input_len, output_len):
+        return self.torch_runner.max_total_num_tokens // (input_len + output_len)
+
+
+class _MlxBenchRunner:
+    """Wraps MlxModelRunner for the MLX benchmark path."""
+
+    def __init__(self, model_runner, server_args):
+        from sglang.srt.hardware_backend.mlx.model_runner import MlxModelRunner
+
+        self.mlx_runner = MlxModelRunner(
+            model_path=server_args.model_path,
+            trust_remote_code=server_args.trust_remote_code,
+        )
+        self.fake_torch_runner = model_runner
+
+    def clear(self):
+        self.mlx_runner.clear()
+
+    def extend(self, reqs):
+        req_ids = [str(req.rid) for req in reqs]
+        token_ids_list = [[int(t) for t in req.fill_ids] for req in reqs]
+        next_token_ids = self.mlx_runner.prefill_batch(req_ids, token_ids_list)
+        return torch.tensor(next_token_ids), None, req_ids
+
+    def decode(self, next_token_ids, req_ids):
+        next_token_ids = self.mlx_runner.decode_batch(req_ids)
+        return torch.tensor(next_token_ids), None
+
+    def cleanup(self, batch):
+        if isinstance(batch, list):
+            for req_id in batch:
+                self.mlx_runner.remove_request(req_id)
+
+    def synchronize(self):
+        pass
+
+    def max_batch_size(self, input_len, output_len):
+        return self.fake_torch_runner.max_total_num_tokens // (input_len + output_len)
+
+
 def _read_prompts_from_file(prompt_file, rank_print):
     """Read custom prompts from the file specified by `--prompt-filename`."""
     if not prompt_file:
@@ -504,26 +585,30 @@ def correctness_test(
 
     if bench_args.cut_len > 0:
         # Prefill
-        next_token_ids, next_token_logits, batch = extend(reqs, model_runner)
+        next_token_ids, next_token_logits, batch = model_runner.extend(reqs)
         rank_print(f"prefill logits (first half): {next_token_logits} \n")
 
         # Prepare extend inputs
+        torch_runner = getattr(model_runner, "torch_runner", None)
         reqs = prepare_extend_inputs_for_correctness_test(
-        bench_args, input_ids, reqs, model_runner
+            bench_args, input_ids, reqs, torch_runner
         )
 
     # Extend (prefill w/ KV cache)
-    next_token_ids, next_token_logits, batch = extend(reqs, model_runner)
+    next_token_ids, next_token_logits, batch = model_runner.extend(reqs)
     rank_print(f"prefill logits (final): {next_token_logits} \n")
 
     # Decode
     output_ids = [input_ids[i] + [next_token_ids[i]] for i in range(len(input_ids))]
     for _ in range(bench_args.output_len[0] - 1):
-        next_token_ids, _ = decode(next_token_ids, batch, model_runner)
+        next_token_ids, _ = model_runner.decode(next_token_ids, batch)
         next_token_ids_list = next_token_ids.tolist()
         for i in range(len(reqs)):
             output_ids[i].append(next_token_ids_list[i])
 
+    # Clean up
+    model_runner.cleanup(batch)
+
     # Print output texts
     for i in range(len(reqs)):
         rank_print(f"========== Prompt {i} ==========")
@@ -542,7 +627,6 @@ def latency_test_run_once(
     batch_size,
     input_len,
     output_len,
-    device,
     log_decode_step,
     profile,
     profile_record_shapes,
@@ -553,15 +637,14 @@ def latency_test_run_once(
     profile_start_step=None,
     profile_steps=None,
 ):
-    max_batch_size = model_runner.max_total_num_tokens // (input_len + output_len)
+    max_batch_size = model_runner.max_batch_size(input_len, output_len)
     if batch_size > max_batch_size:
         rank_print(
             f"skipping ({batch_size}, {input_len}, {output_len}) due to max batch size limit"
         )
         return
 
-    model_runner.req_to_token_pool.clear()
+    model_runner.clear()
-    model_runner.token_to_kv_pool_allocator.clear()
 
     measurement_results = {
         "run_name": run_name,
@@ -581,10 +664,10 @@ def latency_test_run_once(
             rank_print=rank_print,
         )
 
-    synchronize(device)
+    model_runner.synchronize()
     tic = time.perf_counter()
-    next_token_ids, _, batch = extend(reqs, model_runner)
+    next_token_ids, _, batch = model_runner.extend(reqs)
-    synchronize(device)
+    model_runner.synchronize()
     prefill_latency = time.perf_counter() - tic
 
     if enable_profile_prefill:
@@ -617,7 +700,7 @@ def latency_test_run_once(
     enable_profile_decode = profile and profile_stage in ["all", "decode"]
     profiler = None
     for i in range(output_len - 1):
-        synchronize(device)
+        model_runner.synchronize()
         # Start profiler at the specified step
         if enable_profile_decode and i == profile_start:
             profiler = start_profile(
@@ -627,8 +710,8 @@ def latency_test_run_once(
             )
 
         tic = time.perf_counter()
-        next_token_ids, _ = decode(next_token_ids, batch, model_runner)
+        next_token_ids, _ = model_runner.decode(next_token_ids, batch)
-        synchronize(device)
+        model_runner.synchronize()
         latency = time.perf_counter() - tic
 
         # Stop profiler after the specified number of steps
@@ -670,6 +753,8 @@ def latency_test_run_once(
     )
     measurement_results["total_latency"] = tot_latency
     measurement_results["overall_throughput"] = throughput
+
+    model_runner.cleanup(batch)
     return measurement_results
 
 
@@ -712,7 +797,6 @@ def latency_test(
         bench_args.batch_size[0],
         bench_args.input_len[0],
         min(32, bench_args.output_len[0]),  # shorter decoding to speed up the warmup
-        server_args.device,
         log_decode_step=0,
         profile=False,
         profile_record_shapes=False,
@@ -764,7 +848,6 @@ def latency_test(
             bs,
             il,
             ol,
-            server_args.device,
             bench_args.log_decode_step,
             bench_args.profile if tp_rank == 0 else None,
             bench_args.profile_record_shapes if tp_rank == 0 else None,

python/sglang/jit_kernel/diffusion/triton/mps_fallback.py

@@ -15,51 +15,13 @@ from typing import Optional
 import torch
 from torch import Tensor
 
-from sglang.srt.environ import envs
+from sglang.srt.utils.tensor_bridge import mlx_to_torch, torch_to_mlx, use_mlx
 
-# MLX acceleration – opt-in via SGLANG_USE_MLX=1
+_use_mlx = use_mlx()
-_MLX_AVAILABLE = False
+
-try:
+if _use_mlx:
     import mlx.core as mx
 
-    _MLX_AVAILABLE = True
-except ImportError:
-    pass
-
-_USE_MLX = envs.SGLANG_USE_MLX.get() and _MLX_AVAILABLE
-
-# Dtype mapping for torch <-> MLX tensor bridge
-_TORCH_TO_MLX_DTYPE = (
-    {
-        torch.float32: mx.float32,
-        torch.float16: mx.float16,
-        torch.bfloat16: mx.bfloat16,
-    }
-    if _MLX_AVAILABLE
-    else {}
-)
-
-_MLX_TO_TORCH_DTYPE = {v: k for k, v in _TORCH_TO_MLX_DTYPE.items()}
-
-
-def _torch_to_mlx(tensor: torch.Tensor) -> "mx.array":
-    """Convert a PyTorch tensor to an MLX array (via numpy on CPU)."""
-    t = tensor.cpu().detach()
-    if t.dtype == torch.bfloat16:
-        return mx.array(t.float().numpy(), dtype=mx.bfloat16)
-    return mx.array(t.numpy())
-
-
-def _mlx_to_torch(array: "mx.array", device: torch.device) -> torch.Tensor:
-    """Convert an MLX array to a PyTorch tensor (zero-copy via memoryview)."""
-    torch_dtype = _MLX_TO_TORCH_DTYPE.get(array.dtype, torch.float32)
-    array = mx.contiguous(array)
-    mx.eval(array)
-    tensor = torch.frombuffer(memoryview(array), dtype=torch_dtype).reshape(array.shape)
-    if device.type == "mps":
-        tensor = tensor.to(device)
-    return tensor
-
 
 def fuse_scale_shift_kernel_native(
     x: torch.Tensor,
@@ -197,7 +159,7 @@ def rms_norm_fn_native(
 # Uses mx.fast.rms_norm / mx.fast.layer_norm — single fused Metal kernels
 # instead of 7+ separate PyTorch MPS kernel launches.
 
-if _USE_MLX:
+if _use_mlx:
 
     def norm_infer_native(  # noqa: F811
         x: Tensor,
@@ -210,17 +172,17 @@ if _USE_MLX:
         """MLX-accelerated norm_infer (layer norm / rms norm inference)."""
         device = x.device
         orig_dtype = x.dtype
-        x_mx = _torch_to_mlx(x)
+        x_mx = torch_to_mlx(x)
         if is_rms_norm:
             w_mx = (
-                _torch_to_mlx(weight) if weight is not None else mx.ones(x_mx.shape[-1])
+                torch_to_mlx(weight) if weight is not None else mx.ones(x_mx.shape[-1])
             )
             result_mx = mx.fast.rms_norm(x_mx, w_mx, eps)
         else:
-            w_mx = _torch_to_mlx(weight) if weight is not None else None
+            w_mx = torch_to_mlx(weight) if weight is not None else None
-            b_mx = _torch_to_mlx(bias) if bias is not None else None
+            b_mx = torch_to_mlx(bias) if bias is not None else None
             result_mx = mx.fast.layer_norm(x_mx, w_mx, b_mx, eps)
-        result = _mlx_to_torch(result_mx, device).to(orig_dtype)
+        result = mlx_to_torch(result_mx, device).to(orig_dtype)
         if out is not None:
             out.copy_(result)
             return out
@@ -230,13 +192,12 @@ if _USE_MLX:
         x: torch.Tensor, w: torch.Tensor, eps: float = 1e-6
     ) -> torch.Tensor:
         """MLX-accelerated triton_one_pass_rms_norm."""
-        shape = x.shape
         device = x.device
         orig_dtype = x.dtype
-        x_mx = _torch_to_mlx(x.reshape(-1, x.shape[-1]))
+        x_mx = torch_to_mlx(x)
-        w_mx = _torch_to_mlx(w)
+        w_mx = torch_to_mlx(w)
         result_mx = mx.fast.rms_norm(x_mx, w_mx, eps)
-        return _mlx_to_torch(result_mx, device).to(orig_dtype).view(shape)
+        return mlx_to_torch(result_mx, device).to(orig_dtype)
 
     def rms_norm_fn_native(  # noqa: F811
         x,
@@ -258,30 +219,25 @@ if _USE_MLX:
         residual_out=None,
     ):
         """MLX-accelerated rms_norm_fn (inference only, no dropout/x1 support)."""
-        x_shape_og = x.shape
         device = x.device
         orig_dtype = x.dtype
-        x_flat = x.reshape(-1, x.shape[-1])
         if residual is not None:
-            residual = residual.reshape(-1, residual.shape[-1]).float()
+            x = x.float() + residual.float()
-            x_flat = x_flat.float() + residual
+            residual_out_val = x.to(torch.float32 if residual_in_fp32 else orig_dtype)
-            residual_out_val = x_flat.to(
-                torch.float32 if residual_in_fp32 else orig_dtype
-            )
         else:
             residual_out_val = None
         if weight is not None and zero_centered_weight:
             w = weight.float() + 1.0
         else:
             w = weight
-        x_mx = _torch_to_mlx(x_flat)
+        x_mx = torch_to_mlx(x)
-        w_mx = _torch_to_mlx(w) if w is not None else mx.ones(x_mx.shape[-1])
+        w_mx = torch_to_mlx(w) if w is not None else mx.ones(x_mx.shape[-1])
         result_mx = mx.fast.rms_norm(x_mx, w_mx, eps)
-        x_hat = _mlx_to_torch(result_mx, device)
+        x_hat = mlx_to_torch(result_mx, device)
         if bias is not None:
             x_hat = x_hat + bias.to(x_hat.device, x_hat.dtype)
         final_dtype = out_dtype if out_dtype is not None else orig_dtype
-        y = x_hat.to(final_dtype).reshape(x_shape_og)
+        y = x_hat.to(final_dtype)
         if residual is not None and residual_out_val is not None:
-            return y, residual_out_val.reshape(x_shape_og)
+            return y, residual_out_val
         return y

python/sglang/srt/hardware_backend/mlx/model_runner.py

@@ -0,0 +1,306 @@
+"""End-to-end MLX model runner for Apple Silicon.
+
+Runs the entire model within MLX, bypassing PyTorch MPS entirely.
+"""
+
+import logging
+import time
+from dataclasses import dataclass
+
+import mlx.core as mx
+from mlx_lm import load as mlx_lm_load
+from mlx_lm.models.cache import (
+    BatchKVCache,
+    BatchRotatingKVCache,
+    KVCache,
+    RotatingKVCache,
+    make_prompt_cache,
+)
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class MlxRequestState:
+    """Per-request state for MLX inference."""
+
+    token_ids: list[int]
+    cache: list  # List of KVCache per layer
+    generated_tokens: int = 0
+
+
+def _merge_kv_caches(
+    caches_list: list[list],
+) -> list:
+    """Merge multiple per-request caches into batched caches."""
+    if not caches_list:
+        return []
+
+    num_layers = len(caches_list[0])
+    merged = []
+
+    for layer_idx in range(num_layers):
+        layer_caches = [caches[layer_idx] for caches in caches_list]
+        if isinstance(layer_caches[0], KVCache):
+            batch_cache = BatchKVCache.merge(layer_caches)
+        elif isinstance(layer_caches[0], RotatingKVCache):
+            batch_cache = BatchRotatingKVCache.merge(layer_caches)
+        else:
+            raise TypeError(f"Unsupported cache type: {type(layer_caches[0]).__name__}")
+        merged.append(batch_cache)
+
+    return merged
+
+
+def _extract_kv_cache(batch_caches: list, idx: int) -> list:
+    """Extract a single request's cache from batched caches.
+
+    Works with both BatchKVCache (has .extract) and plain KVCache
+    populated with batched data of shape (B, H, L, D).
+    """
+    extracted = []
+    for cache in batch_caches:
+        if hasattr(cache, "extract"):
+            extracted.append(cache.extract(idx))
+        else:
+            # Plain KVCache with batched data — slice along batch dim
+            new_cache = KVCache()
+            new_cache.keys = mx.contiguous(cache.keys[idx : idx + 1])
+            new_cache.values = mx.contiguous(cache.values[idx : idx + 1])
+            new_cache.offset = cache.offset
+            extracted.append(new_cache)
+    return extracted
+
+
+class MlxModelRunner:
+    """Model runner that executes the entire model in MLX.
+
+    This avoids the MPS<->MLX tensor bridge overhead by keeping all
+    computation within MLX.
+    """
+
+    def __init__(
+        self,
+        model_path: str,
+        trust_remote_code: bool = False,
+    ):
+        self.model_path = model_path
+        self.trust_remote_code = trust_remote_code
+        self.model = None
+        self._request_states: dict[str, MlxRequestState] = {}
+
+        self._load_model()
+
+    @staticmethod
+    def _extract_logits(model_output):
+        """Extract logits from model output, handling both tuple and direct returns."""
+        if isinstance(model_output, tuple):
+            return model_output[0]
+        return model_output
+
+    def _load_model(self):
+        """Load model using mlx_lm."""
+        logger.info(f"Loading MLX model: {self.model_path}")
+        start_time = time.time()
+
+        self.model, _ = mlx_lm_load(
+            self.model_path,
+            tokenizer_config={"trust_remote_code": self.trust_remote_code},
+        )
+
+        load_time = time.time() - start_time
+        logger.info(f"MLX model loaded in {load_time:.2f}s")
+
+    def prefill(
+        self,
+        req_id: str,
+        token_ids: list[int],
+    ) -> int:
+        """Run prefill for a single request.
+
+        If a request with the same req_id already has state (e.g. from a
+        previous partial prefill), the existing KV cache is reused and only
+        the new tokens are fed through the model.
+
+        Args:
+            req_id: Request identifier
+            token_ids: Input token IDs (full sequence, including any
+                previously prefilled tokens)
+
+        Returns:
+            Next token ID (greedy sampled)
+        """
+        existing_state = self._request_states.get(req_id)
+        if existing_state is not None:
+            # Continuation: reuse existing cache, feed only new tokens
+            cached_input_len = (
+                len(existing_state.token_ids) - existing_state.generated_tokens
+            )
+            new_tokens = token_ids[cached_input_len:]
+            cache = existing_state.cache
+        else:
+            new_tokens = token_ids
+            cache = make_prompt_cache(self.model)
+
+        input_ids = mx.array([new_tokens], dtype=mx.int32)
+        model_output = self.model(input_ids, cache=cache)
+
+        logits = self._extract_logits(model_output)
+
+        last_logits = logits[:, -1, :]
+        next_token_mlx = mx.argmax(last_logits, axis=-1)
+
+        # Evaluate everything together
+        mx.eval(next_token_mlx, *[c.state for c in cache])
+        next_token = int(next_token_mlx.item())
+
+        # Store state for future decoding
+        self._request_states[req_id] = MlxRequestState(
+            token_ids=list(token_ids) + [next_token],
+            cache=cache,
+            generated_tokens=1,
+        )
+
+        return next_token
+
+    def prefill_batch(
+        self,
+        req_ids: list[str],
+        token_ids_list: list[list[int]],
+    ) -> list[int]:
+        """Run batched prefill for multiple requests in a single forward pass.
+
+        When all sequences have the same length, they are stacked into a single
+        batch tensor for one forward pass.  For variable-length sequences the
+        method falls back to serial prefill.
+
+        Args:
+            req_ids: List of request identifiers
+            token_ids_list: List of token ID sequences, one per request
+
+        Returns:
+            List of next token IDs (greedy sampled)
+        """
+        if len(req_ids) == 1:
+            return [self.prefill(req_ids[0], token_ids_list[0])]
+
+        # Check if all sequences have the same length (enables true batching)
+        lengths = [len(tids) for tids in token_ids_list]
+        if len(set(lengths)) != 1:
+            # Variable lengths – fall back to serial prefill
+            return [
+                self.prefill(rid, tids) for rid, tids in zip(req_ids, token_ids_list)
+            ]
+
+        # All same length – use a single set of fresh caches;
+        # they'll be populated with shape (batch_size, ...) on the first forward pass
+        batch_cache = make_prompt_cache(self.model)
+
+        # Stack into (batch_size, seq_len)
+        batched_input = mx.array(
+            [list(tids) for tids in token_ids_list], dtype=mx.int32
+        )
+
+        # Single forward pass
+        model_output = self.model(batched_input, cache=batch_cache)
+        logits = self._extract_logits(model_output)
+
+        last_logits = logits[:, -1, :]
+        next_tokens_mlx = mx.argmax(last_logits, axis=-1)
+
+        # Evaluate everything together
+        mx.eval(next_tokens_mlx, *[c.state for c in batch_cache])
+        next_tokens = next_tokens_mlx.tolist()
+
+        # Extract individual caches and store per-request state
+        for i, req_id in enumerate(req_ids):
+            individual_cache = _extract_kv_cache(batch_cache, i)
+            self._request_states[req_id] = MlxRequestState(
+                token_ids=list(token_ids_list[i]) + [next_tokens[i]],
+                cache=individual_cache,
+                generated_tokens=1,
+            )
+
+        return next_tokens
+
+    def decode_batch(
+        self,
+        req_ids: list[str],
+    ) -> list[int]:
+        """Run batched decode for multiple requests.
+
+        Args:
+            req_ids: List of request IDs to decode
+
+        Returns:
+            List of next token IDs
+        """
+        if len(req_ids) == 1:
+            return [self._decode_single(req_ids[0])]
+
+        decode_reqs = []
+        for req_id in req_ids:
+            state = self._request_states[req_id]
+            decode_reqs.append((req_id, state))
+
+        return self._batched_decode(decode_reqs)
+
+    def _decode_single(self, req_id: str) -> int:
+        """Decode a single token for one request."""
+        state = self._request_states[req_id]
+        last_token = state.token_ids[-1]
+
+        input_ids = mx.array([[last_token]], dtype=mx.int32)
+        model_output = self.model(input_ids, cache=state.cache)
+
+        logits = self._extract_logits(model_output)
+
+        last_logits = logits[:, -1, :]
+        next_token_mlx = mx.argmax(last_logits, axis=-1)
+
+        mx.eval(next_token_mlx, *[c.state for c in state.cache])
+        next_token = int(next_token_mlx.item())
+
+        state.token_ids.append(next_token)
+        state.generated_tokens += 1
+
+        return next_token
+
+    def _batched_decode(
+        self, decode_reqs: list[tuple[str, MlxRequestState]]
+    ) -> list[int]:
+        """Run a single batched forward pass for multiple decode requests."""
+        last_tokens = [state.token_ids[-1] for _, state in decode_reqs]
+
+        # Merge individual KV caches into batched cache
+        caches_list = [state.cache for _, state in decode_reqs]
+        batch_cache = _merge_kv_caches(caches_list)
+
+        # Create batched input: shape (batch_size, 1)
+        batched_input = mx.array(last_tokens, dtype=mx.int32)[:, None]
+
+        # Single forward pass
+        model_output = self.model(batched_input, cache=batch_cache)
+        logits = self._extract_logits(model_output)
+
+        next_token_logits = logits[:, -1, :]
+        next_tokens_mlx = mx.argmax(next_token_logits, axis=-1)
+
+        mx.eval(next_tokens_mlx, *[c.state for c in batch_cache])
+        next_tokens = next_tokens_mlx.tolist()
+
+        # Extract updated caches back to individual requests
+        for i, (_, state) in enumerate(decode_reqs):
+            state.cache = _extract_kv_cache(batch_cache, i)
+            state.token_ids.append(next_tokens[i])
+            state.generated_tokens += 1
+
+        return next_tokens
+
+    def remove_request(self, req_id: str):
+        """Clean up state for a completed request."""
+        self._request_states.pop(req_id, None)
+
+    def clear(self):
+        """Clear all request states."""
+        self._request_states.clear()

python/sglang/srt/hardware_backend/mlx/model_runner_stub.py

@@ -0,0 +1,172 @@
+"""Lightweight ModelRunner stub for MLX on Apple Silicon.
+
+Subclasses ModelRunner but overrides both load_model() and initialize()
+to skip PyTorch weight loading entirely.  No GPU memory is consumed:
+the KV cache pool uses a zero-allocation _DummyKVCache, and only
+CPU-side bookkeeping structures (req_to_token_pool,
+token_to_kv_pool_allocator) are created so the SGLang scheduler can
+function.  The actual KV cache is managed by the MLX model runner.
+"""
+
+import logging
+from typing import Tuple
+
+import torch
+
+from sglang.srt.mem_cache.allocator import TokenToKVPoolAllocator
+from sglang.srt.mem_cache.memory_pool import KVCache, ReqToTokenPool
+from sglang.srt.model_executor.model_runner import ModelRunner
+
+logger = logging.getLogger(__name__)
+
+
+class _DummyKVCache(KVCache):
+    """A KV cache that allocates no GPU memory.
+
+    Satisfies the KVCache interface so that TokenToKVPoolAllocator can be
+    constructed, but every buffer access raises — the MLX backend manages
+    its own KV cache internally.
+    """
+
+    def __init__(self, size: int, dtype: torch.dtype, device: str):
+        # Bypass KVCache.__init__ to avoid custom_mem_pool / memory_saver
+        # initialization that may touch CUDA APIs.
+        self.size = size
+        self.page_size = 1
+        self.dtype = dtype
+        self.store_dtype = dtype
+        self.device = device
+        self.layer_num = 0
+        self.start_layer = 0
+        self.end_layer = 0
+        self.mem_usage = 0
+        self.cpu_offloading_chunk_size = 8192
+        self.layer_transfer_counter = None
+        self.enable_custom_mem_pool = False
+        self.custom_mem_pool = None
+
+    def get_key_buffer(self, layer_id: int) -> torch.Tensor:
+        raise RuntimeError("_DummyKVCache has no key buffer (MLX manages KV cache)")
+
+    def get_value_buffer(self, layer_id: int) -> torch.Tensor:
+        raise RuntimeError("_DummyKVCache has no value buffer (MLX manages KV cache)")
+
+    def get_kv_buffer(self, layer_id: int) -> Tuple[torch.Tensor, torch.Tensor]:
+        raise RuntimeError("_DummyKVCache has no kv buffer (MLX manages KV cache)")
+
+    def set_kv_buffer(self, layer, loc, cache_k, cache_v) -> None:
+        raise RuntimeError("_DummyKVCache cannot set kv buffer (MLX manages KV cache)")
+
+    def get_kv_size_bytes(self):
+        return 0, 0
+
+
+class _DummyModel:
+    """Minimal stand-in so that `inspect.signature(model.forward)` and
+    `getattr(model, ...)` calls in ModelRunner.__init__ don't crash."""
+
+    @staticmethod
+    def forward():
+        pass
+
+
+class MlxModelRunnerStub(ModelRunner):
+    """ModelRunner that skips PyTorch weight loading and KV cache allocation.
+
+    Overrides both load_model() and initialize() so that no PyTorch model
+    weights are loaded and no large KV cache tensors are allocated.  Only
+    the minimal bookkeeping pools needed by the scheduler are created.
+    """
+
+    def load_model(self):
+        """Set only the metadata that downstream code needs, without
+        loading any PyTorch model weights."""
+        logger.info(
+            "MLX stub: skipping PyTorch model weight loading "
+            "(inference runs through MLX)"
+        )
+
+        self.model = _DummyModel()
+
+        self.sliding_window_size = None
+        if (
+            self.model_config.is_hybrid_swa
+            and self.model_config.sliding_window_size is not None
+        ):
+            self.sliding_window_size = self.model_config.sliding_window_size
+        elif self.model_config.attention_chunk_size is not None:
+            self.sliding_window_size = self.model_config.attention_chunk_size
+
+        self.dtype = self.model_config.dtype
+        self.weight_load_mem_usage = 0
+
+    def initialize(self, pre_model_load_memory: float):
+        """Lightweight initialize that skips heavy PyTorch setup.
+
+        Creates minimal req_to_token_pool and token_to_kv_pool_allocator
+        with a dummy KV cache (zero GPU memory) so the scheduler works.
+        """
+        from sglang.srt.utils.torch_memory_saver_adapter import TorchMemorySaverAdapter
+
+        self.memory_saver_adapter = TorchMemorySaverAdapter.create(
+            enable=self.server_args.enable_memory_saver
+        )
+
+        # Load model (sets metadata only)
+        self.sampler = None
+        self.load_model()
+
+        # Layer metadata
+        model_num_layers = max(
+            self.model_config.num_hidden_layers,
+            self.model_config.num_attention_layers,
+        )
+        self.start_layer = 0
+        self.end_layer = model_num_layers
+        self.num_effective_layers = model_num_layers
+
+        # KV cache dtype
+        self.kv_cache_dtype = self.dtype
+
+        # Pool sizing — use context_len as the capacity.
+        # No actual GPU memory is consumed because _DummyKVCache is empty.
+        self.max_total_num_tokens = self.model_config.context_len
+        self.max_running_requests = min(
+            self.max_total_num_tokens // 2,
+            4096,
+        )
+        self.is_hybrid_swa = False
+
+        # Create minimal pools
+        self.req_to_token_pool = ReqToTokenPool(
+            size=self.max_running_requests,
+            max_context_len=self.model_config.context_len,
+            device="cpu",
+            enable_memory_saver=False,
+        )
+
+        dummy_kv = _DummyKVCache(
+            size=self.max_total_num_tokens,
+            dtype=self.kv_cache_dtype,
+            device="cpu",
+        )
+        self.token_to_kv_pool = dummy_kv
+        self.token_to_kv_pool_allocator = TokenToKVPoolAllocator(
+            size=self.max_total_num_tokens,
+            dtype=self.kv_cache_dtype,
+            device="cpu",
+            kvcache=dummy_kv,
+            need_sort=False,
+        )
+
+        # No CUDA graphs, no attention backend
+        self.graph_runner = None
+        self.graph_mem_usage = 0
+        self.attn_backend = None
+
+        logger.info(
+            f"MLX stub: initialized minimal pools "
+            f"(max_total_num_tokens={self.max_total_num_tokens}, "
+            f"max_running_requests={self.max_running_requests}, "
+            f"zero GPU KV cache allocation)"
+        )

python/sglang/srt/hardware_backend/mlx/tp_worker.py

@@ -0,0 +1,176 @@
+"""MLX-specific TpModelWorker subclass for Apple Silicon.
+
+Overrides the standard TpModelWorker to route forward passes through
+the native MLX model runner, avoiding PyTorch MPS entirely for inference.
+
+PyTorch model weights are never loaded.  A lightweight ModelRunner stub
+(MlxModelRunnerStub) provides only the minimal bookkeeping structures
+(req_to_token_pool, token_to_kv_pool_allocator with a zero-memory
+dummy KV cache) that the SGLang scheduler expects.  The actual KV cache
+is managed internally by the MLX model runner.
+"""
+
+import logging
+from typing import Optional
+
+import torch
+
+from sglang.srt.managers.schedule_batch import ModelWorkerBatch
+from sglang.srt.managers.tp_worker import TpModelWorker
+from sglang.srt.managers.utils import GenerationBatchResult
+from sglang.srt.model_executor.forward_batch_info import ForwardBatch, PPProxyTensors
+
+logger = logging.getLogger(__name__)
+
+
+class MlxTpModelWorker(TpModelWorker):
+    """A tensor parallel model worker that routes inference through MLX.
+
+    Inherits from TpModelWorker for scheduler integration, but replaces
+    the standard ModelRunner with MlxModelRunnerStub (no PyTorch weights,
+    zero-memory KV cache) and delegates all forward passes to a native
+    MlxModelRunner.
+    """
+
+    def _init_model_runner(self):
+        """Override to use a lightweight ModelRunner that skips weight loading."""
+        from sglang.srt.hardware_backend.mlx.model_runner import MlxModelRunner
+        from sglang.srt.hardware_backend.mlx.model_runner_stub import (
+            MlxModelRunnerStub,
+        )
+
+        self._model_runner = MlxModelRunnerStub(
+            model_config=self.model_config,
+            mem_fraction_static=self.server_args.mem_fraction_static,
+            gpu_id=self.gpu_id,
+            tp_rank=self.tp_rank,
+            tp_size=self.tp_size,
+            moe_ep_rank=self.moe_ep_rank,
+            moe_ep_size=self.ep_size,
+            pp_rank=self.pp_rank,
+            pp_size=self.pp_size,
+            nccl_port=self.nccl_port,
+            dp_rank=self.dp_rank,
+            server_args=self.server_args,
+            is_draft_worker=self.is_draft_worker,
+            req_to_token_pool=self.req_to_token_pool,
+            token_to_kv_pool_allocator=self.token_to_kv_pool_allocator,
+            memory_pool_config=self.memory_pool_config,
+        )
+
+        # Initialize the MLX model runner (loads weights via MLX, not PyTorch)
+        logger.info("Initializing MlxModelRunner for end-to-end MLX inference")
+        self._mlx_runner = MlxModelRunner(
+            model_path=self.server_args.model_path,
+            trust_remote_code=self.server_args.trust_remote_code,
+        )
+        self._mlx_active_rids: set[str] = set()
+
+    def get_pad_input_ids_func(self):
+        """Override since the stub ModelRunner has no real model."""
+        return None
+
+    def forward_batch_generation(
+        self,
+        model_worker_batch: ModelWorkerBatch,
+        forward_batch: Optional[ForwardBatch] = None,
+        pp_proxy_tensors: Optional[PPProxyTensors] = None,
+        is_verify: bool = False,
+        skip_attn_backend_init=False,
+    ) -> GenerationBatchResult:
+        """Override to route through MLX model runner."""
+        if model_worker_batch is not None:
+            return self._forward_batch_generation_mlx(model_worker_batch)
+
+        # Fallback to standard path for None batches
+        return super().forward_batch_generation(
+            model_worker_batch,
+            forward_batch,
+            pp_proxy_tensors,
+            is_verify,
+            skip_attn_backend_init,
+        )
+
+    def _forward_batch_generation_mlx(
+        self,
+        model_worker_batch: ModelWorkerBatch,
+    ) -> GenerationBatchResult:
+        """Run forward pass through the MLX model runner.
+
+        Bypasses the standard ModelRunner forward+sample and uses native MLX
+        inference for the entire model. Only supports greedy sampling.
+        """
+        from sglang.srt.layers.logits_processor import LogitsProcessorOutput
+
+        forward_mode = model_worker_batch.forward_mode
+        reqs = model_worker_batch.reqs
+
+        if forward_mode.is_idle():
+            return GenerationBatchResult(
+                logits_output=LogitsProcessorOutput(next_token_logits=None),
+                can_run_cuda_graph=False,
+            )
+
+        # Auto-cleanup: remove MLX state for requests no longer in the batch
+        current_rids = {req.rid for req in reqs}
+        stale_rids = self._mlx_active_rids - current_rids
+        for rid in stale_rids:
+            self._mlx_runner.remove_request(rid)
+        self._mlx_active_rids = current_rids
+
+        next_token_ids_list = []
+
+        if forward_mode.is_extend():
+            # Prefill (or MIXED): extract per-request tokens from concatenated input_ids
+            input_ids_cpu = model_worker_batch.input_ids.cpu().tolist()
+            extend_seq_lens = model_worker_batch.extend_seq_lens
+            offset = 0
+            prefill_rids = []
+            decode_rids = []
+            for i, req in enumerate(reqs):
+                seq_len = extend_seq_lens[i]
+                req_token_ids = input_ids_cpu[offset : offset + seq_len]
+                offset += seq_len
+                if req.rid in self._mlx_runner._request_states:
+                    # MIXED mode: this request already has MLX state, decode it
+                    decode_rids.append(req.rid)
+                else:
+                    # Prefill: new request
+                    next_token = self._mlx_runner.prefill(req.rid, req_token_ids)
+                    prefill_rids.append((req.rid, next_token))
+
+            # Batch decode all existing requests at once
+            if decode_rids:
+                decode_results = self._mlx_runner.decode_batch(decode_rids)
+                decode_map = dict(zip(decode_rids, decode_results))
+            else:
+                decode_map = {}
+
+            prefill_map = dict(prefill_rids)
+
+            # Reassemble in original request order
+            for req in reqs:
+                if req.rid in decode_map:
+                    next_token_ids_list.append(decode_map[req.rid])
+                else:
+                    next_token_ids_list.append(prefill_map[req.rid])
+
+        elif forward_mode.is_decode():
+            # Decode: batch decode all requests
+            req_ids = [req.rid for req in reqs]
+            next_token_ids_list = self._mlx_runner.decode_batch(req_ids)
+
+        else:
+            raise ValueError(
+                f"MLX runner does not support forward mode: {forward_mode}"
+            )
+
+        next_token_ids = torch.tensor(
+            next_token_ids_list, dtype=torch.long, device="cpu"
+        )
+
+        return GenerationBatchResult(
+            logits_output=LogitsProcessorOutput(next_token_logits=None),
+            next_token_ids=next_token_ids,
+            can_run_cuda_graph=False,
+        )

python/sglang/srt/managers/scheduler.py

@@ -224,6 +224,7 @@ from sglang.srt.utils.hf_transformers_utils import (
     get_tokenizer_from_processor,
 )
 from sglang.srt.utils.network import get_zmq_socket
+from sglang.srt.utils.tensor_bridge import use_mlx
 from sglang.srt.utils.torch_memory_saver_adapter import TorchMemorySaverAdapter
 from sglang.utils import TypeBasedDispatcher, get_exception_traceback
 
@@ -569,9 +570,8 @@ class Scheduler(
         self.require_mlp_sync = require_mlp_sync(self.server_args)
 
     def init_tp_model_worker(self):
-        from sglang.srt.managers.tp_worker import TpModelWorker
 
-        self.tp_worker = TpModelWorker(
+        worker_kwargs = dict(
             server_args=self.server_args,
             gpu_id=self.gpu_id,
             tp_rank=self.tp_rank,
@@ -583,6 +583,16 @@ class Scheduler(
             nccl_port=self.nccl_port,
         )
 
+        # FIXME: move tp worker's init logic outside of the scheduler.
+        if use_mlx():
+            from sglang.srt.hardware_backend.mlx.tp_worker import MlxTpModelWorker
+
+            self.tp_worker = MlxTpModelWorker(**worker_kwargs)
+        else:
+            from sglang.srt.managers.tp_worker import TpModelWorker
+
+            self.tp_worker = TpModelWorker(**worker_kwargs)
+
     def maybe_init_draft_worker(self):
         if self.spec_algorithm.is_none():
             self.draft_worker = None

python/sglang/srt/server_args.py

@@ -764,6 +764,7 @@ class ServerArgs:
         self._handle_hpu_backends()
         self._handle_cpu_backends()
         self._handle_npu_backends()
+        self._handle_mps_backends()
         self._handle_xpu_backends()
 
         # Handle piecewise CUDA graph.
@@ -1043,6 +1044,10 @@ class ServerArgs:
                 )
                 self.piecewise_cuda_graph_compiler = "eager"
 
+    def _handle_mps_backends(self):
+        if self.device == "mps":
+            self.disable_overlap_schedule = True
+
     def _handle_xpu_backends(self):
         if self.device == "xpu":
             if not self.disable_piecewise_cuda_graph:

python/sglang/srt/utils/tensor_bridge.py

@@ -0,0 +1,228 @@
+# Copied and adapted from: https://github.com/vllm-project/vllm-metal
+# SPDX-License-Identifier: Apache-2.0
+"""Tensor bridge between MLX and PyTorch.
+
+Provides zero-copy conversion when possible using Apple Silicon's unified memory.
+"""
+
+from __future__ import annotations
+
+import logging
+from functools import lru_cache
+from typing import TYPE_CHECKING, Literal
+
+import torch
+
+from sglang.srt.environ import envs
+
+if TYPE_CHECKING:
+    import mlx.core as mx
+
+logger = logging.getLogger(__name__)
+
+_MLX_AVAILABLE: bool = False
+try:
+    import mlx.core as mx  # noqa: F811
+
+    _MLX_AVAILABLE = True
+except ImportError:
+    pass
+
+
+def is_mlx_available() -> bool:
+    """Return True when the ``mlx`` package can be imported."""
+    return _MLX_AVAILABLE
+
+
+@lru_cache(maxsize=1)
+def use_mlx() -> bool:
+    """Return True when the user opted-in via ``SGLANG_USE_MLX=1`` **and** MLX is importable."""
+    return bool(envs.SGLANG_USE_MLX.get()) and _MLX_AVAILABLE
+
+
+# MPS has a 4GB (2^32 bytes) limit for MPSTemporaryNDArray allocations.
+# Metal may allocate multiple temporary buffers internally, so we use a
+# conservative threshold of 1GB to avoid hitting the limit.
+# See: https://github.com/anthropics/vllm-metal/issues/43
+_MPS_SAFE_SIZE_BYTES = 1 << 30  # 1GB
+
+# MLX to PyTorch dtype mapping
+# TODO(perf): float64 is CPU-only in MLX (see ml-explore/mlx#1843).
+# When the target device is GPU/MPS we should auto-downcast float64 → float32
+# to avoid a runtime error; when the target is CPU we can keep float64.
+# For now float64 is omitted from the mapping so it hits the ValueError
+# fallback in mlx_to_torch().
+MLX_TO_TORCH_DTYPE = (
+    {
+        mx.float32: torch.float32,
+        mx.float16: torch.float16,
+        mx.bfloat16: torch.bfloat16,
+        mx.int32: torch.int32,
+        mx.int64: torch.int64,
+        mx.int16: torch.int16,
+        mx.int8: torch.int8,
+        mx.uint8: torch.uint8,
+        mx.bool_: torch.bool,
+    }
+    if _MLX_AVAILABLE
+    else {}
+)
+
+# PyTorch to MLX dtype mapping
+TORCH_TO_MLX_DTYPE = {v: k for k, v in MLX_TO_TORCH_DTYPE.items()}
+
+
+def get_torch_device() -> torch.device:
+    """Get the PyTorch device for Metal/MPS.
+
+    Returns:
+        torch.device for MPS if available, else CPU
+    """
+    if torch.backends.mps.is_available():
+        return torch.device("mps")
+    return torch.device("cpu")
+
+
+def _get_tensor_size_bytes(array: mx.array) -> int:
+    """Calculate the size of an MLX array in bytes.
+
+    Args:
+        array: MLX array
+
+    Returns:
+        Size in bytes
+    """
+    return array.size * array.dtype.size
+
+
+def _is_safe_for_mps(array: mx.array) -> bool:
+    """Check if an array is safe to transfer to MPS without hitting size limits.
+
+    MPS has a 4GB limit for MPSTemporaryNDArray, but Metal may allocate
+    multiple temporary buffers internally. We use a conservative threshold.
+
+    Args:
+        array: MLX array to check
+
+    Returns:
+        True if safe to transfer to MPS, False if should stay on CPU
+    """
+    return _get_tensor_size_bytes(array) < _MPS_SAFE_SIZE_BYTES
+
+
+def torch_to_mlx(tensor: torch.Tensor) -> mx.array:
+    """Convert PyTorch tensor to MLX array.
+
+    Uses numpy as an intermediate to enable zero-copy on unified memory.
+
+    Args:
+        tensor: PyTorch tensor (can be on any device)
+
+    Returns:
+        MLX array with the same data
+    """
+    # Move to CPU if on MPS for numpy conversion
+    if tensor.device.type != "cpu":
+        tensor = tensor.cpu()
+
+    tensor = tensor.detach()
+
+    # Note: numpy does not support bfloat16.
+    if tensor.dtype == torch.bfloat16:
+        return mx.array(tensor)
+
+    return mx.array(tensor.numpy())
+
+
+# TODO(perf): accept a list/batch of arrays and convert them in one pass
+# to reduce the Python ↔ MLX round-trip overhead.
+def mlx_to_torch(
+    array: mx.array,
+    device: torch.device | Literal["mps", "cpu"] | None = None,
+    already_contiguous: bool = False,
+) -> torch.Tensor:
+    """Convert MLX array to PyTorch tensor.
+
+    Uses numpy as an intermediate to enable zero-copy on unified memory.
+
+    Args:
+        array: MLX array
+        device: Target PyTorch device (default: MPS if available)
+        already_contiguous: Skip contiguity check if array is known contiguous
+
+    Returns:
+        PyTorch tensor with the same data
+    """
+    if device is None:
+        device = get_torch_device()
+    elif isinstance(device, str):
+        device = torch.device(device)
+
+    # Use memoryview for zero-copy conversion (bypasses numpy for bfloat16)
+    # reference: https://github.com/ml-explore/mlx/issues/403
+    torch_dtype = MLX_TO_TORCH_DTYPE.get(array.dtype)
+    if torch_dtype is not None:
+        if already_contiguous:
+            # Fast path: skip contiguity check, single eval
+            mx.eval(array)
+            buffer = memoryview(array)
+        else:
+            # MLX views / non-contiguous arrays expose a non-contiguous buffer (or
+            # sometimes no usable buffer), which `torch.frombuffer` can't consume.
+            # Make contiguous first, then eval once
+            array = mx.contiguous(array)
+            mx.eval(array)
+            buffer = memoryview(array)
+
+        tensor = torch.frombuffer(buffer, dtype=torch_dtype).reshape(array.shape)
+    else:
+        # Fallback to numpy path for unsupported dtypes
+        raise ValueError(f"Unsupported MLX dtype: {array.dtype}")
+
+    # Move to target device, but check for MPS size limits first
+    if device.type == "mps":
+        if _is_safe_for_mps(array):
+            tensor = tensor.to(device)
+        else:
+            # Large tensor - keep on CPU to avoid MPS 4GB limit crash
+            # See: https://github.com/anthropics/vllm-metal/issues/43
+            logger.debug(
+                "Tensor too large for MPS (%d bytes > %d limit), keeping on CPU",
+                _get_tensor_size_bytes(array),
+                _MPS_SAFE_SIZE_BYTES,
+            )
+    elif device.type != "cpu":
+        tensor = tensor.to(device)
+
+    return tensor
+
+
+def sync_mlx() -> None:
+    """Synchronize MLX operations.
+
+    Call this before converting MLX arrays to ensure all operations complete.
+    """
+    # Prefer an explicit MLX barrier when available; otherwise force evaluation.
+    # `mx.eval([])` is a no-op, so we evaluate a tiny scalar as a safe fallback.
+    try:
+        mx.synchronize()
+    except (AttributeError, TypeError):
+        mx.eval(mx.array(0, dtype=mx.int32))
+
+
+def sync_torch() -> None:
+    """Synchronize PyTorch MPS operations.
+
+    Call this before converting PyTorch tensors to ensure all operations complete.
+    """
+    if torch.backends.mps.is_available():
+        torch.mps.synchronize()
+
+
+__all__ = [
+    "is_mlx_available",
+    "use_mlx",
+    "mlx_to_torch",
+    "torch_to_mlx",
+    "get_torch_device",
+]