Add GPT-OSS model code and config [1/N] (#22327)

Signed-off-by: Woosuk Kwon <woosuk.kwon@berkeley.edu>

tests/models/registry.py

@@ -197,6 +197,7 @@ _TEXT_GENERATION_EXAMPLE_MODELS = {
                                        {"6b": "EleutherAI/gpt-j-6b"}),
     "GPTNeoXForCausalLM": _HfExamplesInfo("EleutherAI/pythia-70m",
                                           {"1b": "EleutherAI/pythia-1.4b"}),
+    "GptOssForCausalLM": _HfExamplesInfo("openai/gpt-oss-20b"),
     "GraniteForCausalLM": _HfExamplesInfo("ibm/PowerLM-3b"),
     "GraniteMoeForCausalLM": _HfExamplesInfo("ibm/PowerMoE-3b"),
     "GraniteMoeHybridForCausalLM": _HfExamplesInfo("ibm-granite/granite-4.0-tiny-preview"),  # noqa: E501

vllm/model_executor/models/config.py

@@ -247,6 +247,34 @@ class GraniteMoeHybridModelConfig(VerifyAndUpdateConfig):
             config.max_model_len)
 
 
+class GptOssConfig(VerifyAndUpdateConfig):
+
+    @staticmethod
+    def verify_and_update_config(vllm_config: "VllmConfig") -> None:
+        decoding_config = vllm_config.decoding_config
+        if decoding_config.reasoning_backend == "":
+            decoding_config.reasoning_backend = "openai"
+
+        # Increase the max capture size from 512 to 1024 for performance.
+        # NOTE(woosuk): This will increase the number of CUDA graphs
+        # from 67 to 83.
+        scheduler_config = vllm_config.scheduler_config
+        if len(scheduler_config.cuda_graph_sizes) == 1:
+            max_capture_size = scheduler_config.cuda_graph_sizes[0]
+            # FIXME(woosuk): When using full cuda graph with FA3, the max
+            # supported size is 992.
+            if max_capture_size < 1024:
+                cuda_graph_sizes = [1, 2, 4]
+                # Step size 8 for small batch sizes
+                cuda_graph_sizes += [i for i in range(8, 256, 8)]
+                # Step size 16 for larger batch sizes
+                cuda_graph_sizes += [i for i in range(256, 1025, 16)]
+                scheduler_config.cuda_graph_sizes = cuda_graph_sizes
+                logger.info(
+                    "Overriding max cuda graph capture size to "
+                    "%d for performance.", 1024)
+
+
 class HybridAttentionMambaModelConfig(VerifyAndUpdateConfig):
 
     @classmethod
@@ -345,4 +373,5 @@ MODELS_CONFIG_MAP: dict[str, type[VerifyAndUpdateConfig]] = {
     "JinaVLForRanking": JinaVLForSequenceClassificationConfig,
     "JambaForSequenceClassification": JambaForSequenceClassificationConfig,
     "GraniteMoeHybridForCausalLM": GraniteMoeHybridModelConfig,
+    "GptOssForCausalLM": GptOssConfig,
 }

vllm/model_executor/models/gpt_oss.py

@@ -0,0 +1,472 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from collections.abc import Iterable
+from typing import Optional
+
+import torch
+import torch.distributed as dist
+from torch import nn
+from transformers import GptOssConfig
+
+from vllm import envs
+from vllm.attention import Attention, AttentionType
+from vllm.compilation.decorators import support_torch_compile
+from vllm.config import CacheConfig, VllmConfig
+from vllm.distributed import (get_ep_group, get_tensor_model_parallel_rank,
+                              get_tensor_model_parallel_world_size)
+from vllm.model_executor.layers.fused_moe import FusedMoE
+from vllm.model_executor.layers.layernorm import RMSNorm
+from vllm.model_executor.layers.linear import (QKVParallelLinear,
+                                               RowParallelLinear)
+from vllm.model_executor.layers.logits_processor import LogitsProcessor
+from vllm.model_executor.layers.quantization import QuantizationConfig
+from vllm.model_executor.layers.rotary_embedding import get_rope
+from vllm.model_executor.layers.vocab_parallel_embedding import (
+    ParallelLMHead, VocabParallelEmbedding)
+from vllm.model_executor.model_loader.weight_utils import default_weight_loader
+from vllm.model_executor.sampling_metadata import SamplingMetadata
+from vllm.sequence import IntermediateTensors
+from vllm.utils import cdiv
+
+from .utils import extract_layer_index, maybe_prefix
+
+
+class OAIAttention(nn.Module):
+
+    def __init__(
+        self,
+        config: GptOssConfig,
+        quant_config: Optional[QuantizationConfig] = None,
+        cache_config: Optional[CacheConfig] = None,
+        prefix: str = "",
+    ):
+        super().__init__()
+        self.layer_idx = extract_layer_index(prefix)
+        self.head_dim = config.head_dim
+        self.num_attention_heads = config.num_attention_heads
+        self.num_key_value_heads = config.num_key_value_heads
+        self.hidden_size = config.hidden_size
+
+        self.rotary_emb = get_rope(
+            self.head_dim,
+            rotary_dim=self.head_dim,
+            max_position=config.max_position_embeddings,
+            base=config.rope_theta,
+            dtype=torch.float32,
+            rope_scaling={
+                "rope_type":
+                "yarn",
+                "factor":
+                config.rope_scaling["factor"],
+                "original_max_position_embeddings":
+                config.rope_scaling["original_max_position_embeddings"],
+                "beta_fast":
+                config.rope_ntk_beta,
+                "beta_slow":
+                config.rope_ntk_alpha,
+            },
+            is_neox_style=True,
+        )
+
+        tp_size = get_tensor_model_parallel_world_size()
+
+        attention_sink_dtype = (
+            torch.float32 if envs.VLLM_USE_TRTLLM_CONTEXT_ATTENTION
+            or envs.VLLM_USE_TRTLLM_DECODE_ATTENTION else torch.bfloat16)
+        self.sinks = torch.nn.Parameter(
+            torch.empty(config.num_attention_heads // tp_size,
+                        dtype=attention_sink_dtype,
+                        requires_grad=False))
+
+        self.norm = RMSNorm(config.hidden_size, eps=1e-5)
+
+        self.q_size = self.num_attention_heads * self.head_dim // tp_size
+        self.kv_size = self.num_key_value_heads * self.head_dim // tp_size
+        self.scaling = self.head_dim**-0.5
+        self.rope_theta = config.rope_theta
+
+        self.qkv = QKVParallelLinear(
+            hidden_size=self.hidden_size,
+            head_size=self.head_dim,
+            total_num_heads=self.num_attention_heads,
+            total_num_kv_heads=self.num_key_value_heads,
+            quant_config=quant_config,
+            prefix=f"{prefix}.qkv_proj",
+        )
+
+        self.o_proj = RowParallelLinear(
+            input_size=self.num_attention_heads * self.head_dim,
+            output_size=self.hidden_size,
+            quant_config=quant_config,
+            prefix=f"{prefix}.o_proj",
+        )
+
+        self.num_local_attention_heads = config.num_attention_heads // tp_size
+        self.num_local_key_value_heads = config.num_key_value_heads // tp_size
+
+        # Only apply sliding window to every other layer
+        sliding_window = (config.sliding_window if self.layer_idx %
+                          2 == 0 else None)
+        self.attn = Attention(
+            self.num_local_attention_heads,
+            self.head_dim,
+            self.scaling,
+            num_kv_heads=self.num_local_key_value_heads,
+            cache_config=cache_config,
+            quant_config=quant_config,
+            per_layer_sliding_window=sliding_window,
+            attn_type=AttentionType.DECODER,
+            prefix=f"{prefix}.attn",
+            sinks=self.sinks,
+        )
+
+    def forward(self, hidden_states: torch.Tensor,
+                positions: torch.Tensor) -> torch.Tensor:
+        t = self.norm(hidden_states)
+
+        qkv, _ = self.qkv(t)
+        q, k, v = qkv.split([self.q_size, self.kv_size, self.kv_size], dim=-1)
+        q, k = self.rotary_emb(positions, q, k)
+        v = v.contiguous()
+        attn_output = self.attn(q, k, v)
+        output, _ = self.o_proj(attn_output)
+
+        return output + hidden_states
+
+
+class MLPBlock(torch.nn.Module):
+
+    def __init__(
+        self,
+        config: GptOssConfig,
+        layer_idx: int,
+        quant_config: QuantizationConfig,
+        prefix: str = "",
+    ):
+        super().__init__()
+        self.layer_idx = layer_idx
+        self.num_experts = config.num_local_experts
+        self.experts_per_token = config.num_experts_per_tok
+        self.world_size = dist.get_world_size() if dist.is_initialized() else 1
+        self.norm = RMSNorm(config.hidden_size, eps=1e-5)
+        self.router = torch.nn.Linear(config.hidden_size,
+                                      config.num_local_experts,
+                                      dtype=torch.bfloat16)
+        assert config.intermediate_size % self.world_size == 0
+        self.experts = FusedMoE(num_experts=config.num_local_experts,
+                                top_k=config.num_experts_per_token,
+                                hidden_size=config.hidden_size,
+                                intermediate_size=config.intermediate_size,
+                                reduce_results=True,
+                                renormalize=True,
+                                quant_config=quant_config,
+                                prefix=f"{prefix}.experts",
+                                apply_router_weight_on_input=False)
+
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        t = self.norm(x)
+        g = self.router(t)
+        t = self.experts(hidden_states=t, router_logits=g)
+        return x + t
+
+
+class TransformerBlock(torch.nn.Module):
+
+    def __init__(
+        self,
+        config: GptOssConfig,
+        quant_config: QuantizationConfig,
+        prefix: str = "",
+    ):
+        super().__init__()
+        self.layer_idx = extract_layer_index(prefix)
+        self.attn = OAIAttention(config, prefix=f"{prefix}.attn")
+        self.mlp = MLPBlock(config,
+                            self.layer_idx,
+                            quant_config=quant_config,
+                            prefix=f"{prefix}.mlp")
+
+    def forward(self, hidden_states: torch.Tensor,
+                positions: torch.Tensor) -> torch.Tensor:
+        attn_output = self.attn(hidden_states, positions)
+        output = self.mlp(attn_output)
+        return output
+
+
+@support_torch_compile
+class GptOssModel(nn.Module):
+
+    def __init__(
+        self,
+        *,
+        vllm_config: VllmConfig,
+        prefix: str = "",
+    ):
+        super().__init__()
+        self.config = vllm_config.model_config.hf_config
+        self.quant_config = vllm_config.quant_config
+        self.config.hidden_size = self.config.hidden_size
+        self.embedding = VocabParallelEmbedding(
+            self.config.vocab_size,
+            self.config.hidden_size,
+        )
+        self.layers = torch.nn.ModuleList([
+            TransformerBlock(
+                self.config,
+                quant_config=self.quant_config,
+                prefix=maybe_prefix(prefix, f"block.{layer_idx}"),
+            ) for layer_idx in range(self.config.num_hidden_layers)
+        ])
+        self.norm = RMSNorm(self.config.hidden_size, eps=1e-5)
+
+    def forward(self, input_ids: torch.Tensor,
+                positions: torch.Tensor) -> torch.Tensor:
+        x = self.embedding(input_ids)
+        for layer in self.layers:
+            x = layer(x, positions)
+        x = self.norm(x)
+        return x
+
+
+class GptOssForCausalLM(nn.Module):
+
+    def __init__(
+        self,
+        vllm_config: VllmConfig,
+        prefix: str = "",
+    ):
+        super().__init__()
+        self.vllm_config = vllm_config
+        self.model_config = vllm_config.model_config.hf_config
+        self.model = GptOssModel(
+            vllm_config=vllm_config,
+            prefix=maybe_prefix(prefix, "model"),
+        )
+        self.lm_head = ParallelLMHead(
+            self.model_config.vocab_size,
+            self.model_config.hidden_size,
+        )
+        self.logits_processor = LogitsProcessor(self.model_config.vocab_size)
+
+    def forward(self,
+                input_ids: torch.Tensor,
+                positions: torch.Tensor,
+                intermediate_tensors: Optional[IntermediateTensors] = None,
+                inputs_embeds: Optional[torch.Tensor] = None) -> torch.Tensor:
+        assert intermediate_tensors is None
+        assert inputs_embeds is None
+        return self.model(input_ids, positions)
+
+    def compute_logits(self, hidden_states: torch.Tensor,
+                       sampling_metadata: SamplingMetadata) -> torch.Tensor:
+        logits = self.logits_processor(self.lm_head, hidden_states,
+                                       sampling_metadata)
+        return logits
+
+    def load_weights(self, weights: Iterable[tuple[str,
+                                                   torch.Tensor]]) -> set[str]:
+        rename_mapping = {
+            "self_attn": "attn",
+            "input_layernorm.weight": "attn.norm.weight",
+            "post_attention_layernorm.weight": "mlp.norm.weight",
+            "embed_tokens": "embedding",
+        }
+
+        def maybe_rename(name: str) -> str:
+            for remap_name, new_name in rename_mapping.items():
+                if remap_name in name:
+                    return name.replace(remap_name, new_name)
+            return name
+
+        params_dict = dict(self.named_parameters())
+        loaded_params: set[str] = set()
+        mxfp4_block = 32
+
+        tp_rank = get_tensor_model_parallel_rank()
+        tp_size = get_tensor_model_parallel_world_size()
+        intermediate_size = self.model_config.intermediate_size
+        intermediate_size_block = intermediate_size // mxfp4_block
+        per_rank_intermediate_size_block = cdiv(intermediate_size_block,
+                                                tp_size)
+        per_rank_intermediate_size = (per_rank_intermediate_size_block *
+                                      mxfp4_block)
+
+        # Calculate common slicing bounds for current rank
+        tp_rank_start = tp_rank * per_rank_intermediate_size
+        tp_rank_end = min((tp_rank + 1) * per_rank_intermediate_size,
+                          intermediate_size)
+
+        # Attention heads per rank
+        heads_per_rank = self.model_config.num_attention_heads // tp_size
+        head_start = tp_rank * heads_per_rank
+
+        use_ep = self.vllm_config.parallel_config.enable_expert_parallel
+        ep_size = get_ep_group().world_size
+        ep_rank = get_ep_group().rank
+        num_experts = self.model_config.num_local_experts
+        experts_per_rank = num_experts // ep_size
+        ep_rank_start = ep_rank * experts_per_rank
+        ep_rank_end = (ep_rank + 1) * experts_per_rank
+
+        for name, weight in weights:
+            # FIXME(woosuk): Remove this after testing.
+            weight = weight.cuda()
+
+            if "gate_up_proj_blocks" in name:
+                # Handle MLP gate and up projection weights
+                new_name = name.replace("gate_up_proj_blocks", "w13_weight")
+
+                # flat weight from (E, 2 * N, block_size, entry_per_block)
+                # to (E, 2 * N, -1), shouldn't trigger copy for contiguous
+                weight = weight.view(num_experts, 2 * intermediate_size,
+                                     -1).contiguous()
+
+                # Extract gate and up projection parts
+                # since the weight is shuffled, we can slice directly
+                if use_ep:
+                    narrow_weight = weight[ep_rank_start:ep_rank_end, ...]
+                else:
+                    narrow_weight = weight[:,
+                                           2 * tp_rank_start:2 * tp_rank_end,
+                                           ...]
+
+                param = params_dict[new_name]
+                weight_loader = getattr(param, "weight_loader",
+                                        default_weight_loader)
+                weight_loader(param,
+                              narrow_weight,
+                              weight_name=new_name,
+                              shard_id=None,
+                              expert_id=None)
+                loaded_params.add(new_name)
+
+            elif "down_proj_blocks" in name:
+                # Handle MLP down projection weights
+                new_name = name.replace("down_proj_blocks", "w2_weight")
+                # same flatten here, but since 2 mx4 value are packed in 1
+                # uint8, divide by 2
+                weight = weight.view(num_experts, -1,
+                                     intermediate_size // 2).contiguous()
+                if use_ep:
+                    narrow_weight = weight[ep_rank_start:ep_rank_end, ...]
+                else:
+                    narrow_weight = weight[...,
+                                           tp_rank_start // 2:tp_rank_end // 2]
+
+                param = params_dict[new_name]
+                weight_loader = getattr(param, "weight_loader",
+                                        default_weight_loader)
+                weight_loader(param,
+                              narrow_weight,
+                              weight_name=new_name,
+                              shard_id=None,
+                              expert_id=None)
+                loaded_params.add(new_name)
+
+            elif "gate_up_proj_scales" in name:
+                # Handle MLP gate and up projection weights scale
+                new_name = name.replace("gate_up_proj_scales",
+                                        "w13_weight_scale")
+                if use_ep:
+                    narrow_weight = weight[ep_rank_start:ep_rank_end, ...]
+                else:
+                    narrow_weight = weight[:,
+                                           2 * tp_rank_start:2 * tp_rank_end,
+                                           ...]
+
+                param = params_dict[new_name]
+                weight_loader = getattr(param, "weight_loader",
+                                        default_weight_loader)
+                weight_loader(param,
+                              narrow_weight,
+                              weight_name=new_name,
+                              shard_id=None,
+                              expert_id=None)
+                loaded_params.add(new_name)
+
+            elif "down_proj_scales" in name:
+                # Handle MLP down projection weights
+                new_name = name.replace("down_proj_scales", "w2_weight_scale")
+                if use_ep:
+                    narrow_weight = weight[ep_rank_start:ep_rank_end, ...]
+                else:
+                    narrow_weight = weight[..., tp_rank_start //
+                                           mxfp4_block:tp_rank_end //
+                                           mxfp4_block]
+
+                param = params_dict[new_name]
+                weight_loader = getattr(param, "weight_loader",
+                                        default_weight_loader)
+                weight_loader(param,
+                              narrow_weight,
+                              weight_name=new_name,
+                              shard_id=None,
+                              expert_id=None)
+                loaded_params.add(new_name)
+            elif "gate_up_proj_bias" in name:
+                # Handle MLP gate and up projection biases
+                new_name = name.replace("gate_up_proj_bias", "w13_bias")
+
+                # Extract gate and up projection bias parts
+                if use_ep:
+                    narrow_weight = weight[ep_rank_start:ep_rank_end, ...]
+                else:
+                    narrow_weight = weight[:,
+                                           2 * tp_rank_start:2 * tp_rank_end]
+
+                param = params_dict[new_name]
+                weight_loader = getattr(param, "weight_loader",
+                                        default_weight_loader)
+                weight_loader(param,
+                              narrow_weight,
+                              weight_name=new_name,
+                              shard_id=None,
+                              expert_id=None)
+                loaded_params.add(new_name)
+
+            elif "down_proj_bias" in name:
+                # Handle MLP down projection bias
+                new_name = name.replace("down_proj_bias", "w2_bias")
+                param = params_dict[new_name]
+                weight_loader = getattr(param, "weight_loader",
+                                        default_weight_loader)
+                if use_ep:
+                    weight = weight[ep_rank_start:ep_rank_end, ...]
+                else:
+                    # (only load on rank 0 to avoid duplication)
+                    if tp_rank != 0:
+                        weight.zero_()
+                weight_loader(param,
+                              weight,
+                              weight_name=new_name,
+                              shard_id=None,
+                              expert_id=None)
+                loaded_params.add(new_name)
+            elif "sinks" in name:
+                # Handle attention sinks (distributed across ranks)
+                name = name.replace("self_attn", "attn")
+                param = params_dict[name]
+                narrow_weight = weight.narrow(0, head_start, heads_per_rank)
+                param.data.copy_(narrow_weight)
+                loaded_params.add(name)
+            elif "q_proj" in name or "k_proj" in name or "v_proj" in name:
+                shard_id = ("q" if "q_proj" in name else
+                            "k" if "k_proj" in name else "v")
+                name = name.replace("self_attn", "attn")
+                param_name = name.replace(f"{shard_id}_proj", "qkv")
+                param = params_dict[param_name]
+                weight_loader = param.weight_loader
+                weight_loader(param, weight, loaded_shard_id=shard_id)
+                loaded_params.add(param_name)
+            else:
+                # Handle all other weights with potential renaming
+                renamed_name = maybe_rename(name)
+                if renamed_name not in params_dict:
+                    continue
+                param = params_dict[renamed_name]
+                weight_loader = getattr(param, "weight_loader",
+                                        default_weight_loader)
+                weight_loader(param, weight)
+                loaded_params.add(renamed_name)
+
+        return loaded_params

vllm/model_executor/models/registry.py

@@ -74,6 +74,7 @@ _TEXT_GENERATION_MODELS = {
     "GlmForCausalLM": ("glm", "GlmForCausalLM"),
     "Glm4ForCausalLM": ("glm4", "Glm4ForCausalLM"),
     "Glm4MoeForCausalLM": ("glm4_moe", "Glm4MoeForCausalLM"),
+    "GptOssForCausalLM": ("gpt_oss", "GptOssForCausalLM"),
     "GPT2LMHeadModel": ("gpt2", "GPT2LMHeadModel"),
     "GPTBigCodeForCausalLM": ("gpt_bigcode", "GPTBigCodeForCausalLM"),
     "GPTJForCausalLM": ("gpt_j", "GPTJForCausalLM"),