feat: Enable engine-level arguments with speculators models (#25250)

Signed-off-by: Rahul Tuli <rtuli@redhat.com>
Co-authored-by: Claude <noreply@anthropic.com>

tests/speculative_decoding/speculators/test_eagle3.py

@@ -3,38 +3,52 @@
 import pytest
 import torch
 
+from vllm.config import SpeculativeConfig
 from vllm.model_executor.models.interfaces import supports_eagle3
 
 
-@pytest.mark.parametrize(
-    "model_path",
-    [("nm-testing/SpeculatorLlama3-1-8B-Eagle3-converted-0717-quantized")])
-def test_llama(vllm_runner, example_prompts, model_path, monkeypatch):
+@pytest.mark.parametrize("model_path", [
+    pytest.param(
+        "nm-testing/SpeculatorLlama3-1-8B-Eagle3-converted-0717-quantized",
+        id="llama3-eagle3-speculator"),
+    pytest.param(
+        "nm-testing/Speculator-Qwen3-8B-Eagle3-converted-071-quantized",
+        id="qwen3-eagle3-speculator"),
+])
+def test_eagle3_speculators_model(vllm_runner, example_prompts, model_path,
+                                  monkeypatch):
+    """
+    Test Eagle3 speculators models properly initialize speculative decoding.
+
+    This test verifies:
+    1. Eagle3 support is detected for the model
+    2. Speculative config is automatically initialized from embedded config
+    3. The draft model path is correctly set to the speculators model
+    4. Speculative tokens count is valid
+    5. Text generation works with speculative decoding enabled
+    """
     # Set environment variable for V1 engine serialization
     monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
 
     with vllm_runner(model_path, dtype=torch.bfloat16) as vllm_model:
+        # Verify Eagle3 support is detected
         eagle3_supported = vllm_model.apply_model(supports_eagle3)
-        assert eagle3_supported
+        assert eagle3_supported, f"Eagle3 should be supported for {model_path}"
 
-        vllm_outputs = vllm_model.generate_greedy(example_prompts,
-                                                  max_tokens=20)
-        print(vllm_outputs)
-        assert vllm_outputs
+        vllm_config = vllm_model.llm.llm_engine.vllm_config
 
+        assert isinstance(vllm_config.speculative_config, SpeculativeConfig), \
+            "Speculative config should be initialized for speculators model"
 
-@pytest.mark.parametrize(
-    "model_path",
-    [("nm-testing/Speculator-Qwen3-8B-Eagle3-converted-071-quantized")])
-def test_qwen(vllm_runner, example_prompts, model_path, monkeypatch):
-    # Set environment variable for V1 engine serialization
-    monkeypatch.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
+        spec_config = vllm_config.speculative_config
+        assert spec_config.num_speculative_tokens > 0, \
+            (f"Expected positive speculative tokens, "
+             f"got {spec_config.num_speculative_tokens}")
 
-    with vllm_runner(model_path, dtype=torch.bfloat16) as vllm_model:
-        eagle3_supported = vllm_model.apply_model(supports_eagle3)
-        assert eagle3_supported
+        assert spec_config.model == model_path, \
+            f"Draft model should be {model_path}, got {spec_config.model}"
 
         vllm_outputs = vllm_model.generate_greedy(example_prompts,
                                                   max_tokens=20)
-        print(vllm_outputs)
-        assert vllm_outputs
+        assert vllm_outputs, \
+            f"No outputs generated for speculators model {model_path}"

vllm/config/model.py

@@ -27,8 +27,7 @@ from vllm.transformers_utils.config import (
     ConfigFormat, get_config, get_hf_image_processor_config,
     get_hf_text_config, get_pooling_config,
     get_sentence_transformer_tokenizer_config, is_encoder_decoder,
-    is_interleaved, maybe_override_with_speculators_target_model,
-    try_get_generation_config, try_get_safetensors_metadata,
+    is_interleaved, try_get_generation_config, try_get_safetensors_metadata,
     try_get_tokenizer_config, uses_mrope)
 from vllm.transformers_utils.runai_utils import (ObjectStorageModel,
                                                  is_runai_obj_uri)
@@ -416,15 +415,6 @@ class ModelConfig:
 
         self.maybe_pull_model_tokenizer_for_runai(self.model, self.tokenizer)
 
-        if self.runner != "draft":
-            # If we're not running the draft model, check for speculators config
-            # If speculators config, set model / tokenizer to be target model
-            self.model, self.tokenizer = maybe_override_with_speculators_target_model(  # noqa: E501
-                model=self.model,
-                tokenizer=self.tokenizer,
-                revision=self.revision,
-                trust_remote_code=self.trust_remote_code)
-
         if (backend := envs.VLLM_ATTENTION_BACKEND
             ) and backend == "FLASHINFER" and find_spec("flashinfer") is None:
             raise ValueError(

vllm/engine/arg_utils.py

@@ -41,7 +41,8 @@ from vllm.plugins import load_general_plugins
 from vllm.ray.lazy_utils import is_ray_initialized
 from vllm.reasoning import ReasoningParserManager
 from vllm.test_utils import MODEL_WEIGHTS_S3_BUCKET, MODELS_ON_S3
-from vllm.transformers_utils.config import get_model_path, is_interleaved
+from vllm.transformers_utils.config import (get_model_path, is_interleaved,
+                                            maybe_override_with_speculators)
 from vllm.transformers_utils.utils import check_gguf_file
 from vllm.utils import (STR_DUAL_CHUNK_FLASH_ATTN_VAL, FlexibleArgumentParser,
                         GiB_bytes, get_ip, is_in_ray_actor)
@@ -1082,28 +1083,7 @@ class EngineArgs:
         provided as a JSON string input via CLI arguments or directly as a
         dictionary from the engine.
         """
-
-        from vllm.transformers_utils.config import get_config
-        from vllm.transformers_utils.configs.speculators.base import (
-            SpeculatorsConfig)
-
         if self.speculative_config is None:
-            hf_config = get_config(
-                self.hf_config_path or target_model_config.model,
-                self.trust_remote_code, self.revision, self.code_revision,
-                self.config_format)
-
-            # if loading a SpeculatorsConfig, load the speculative_config
-            # details from the config directly
-            # no user input required / expected
-            if isinstance(hf_config, SpeculatorsConfig):
-                # We create one since we don't create one
-                self.speculative_config = {}
-                self.speculative_config[
-                    "num_speculative_tokens"] = hf_config.num_lookahead_tokens
-                self.speculative_config["model"] = target_model_config.model
-                self.speculative_config["method"] = hf_config.method
-            else:
             return None
 
         # Note(Shangming): These parameters are not obtained from the cli arg
@@ -1139,6 +1119,15 @@ class EngineArgs:
 
         device_config = DeviceConfig(
             device=cast(Device, current_platform.device_type))
+
+        (self.model, self.tokenizer,
+         self.speculative_config) = maybe_override_with_speculators(
+             model=self.model,
+             tokenizer=self.tokenizer,
+             revision=self.revision,
+             trust_remote_code=self.trust_remote_code,
+             vllm_speculative_config=self.speculative_config,
+         )
         model_config = self.create_model_config()
 
         # * If VLLM_USE_V1 is unset, we enable V1 for "supported features"

vllm/transformers_utils/config.py

@@ -463,15 +463,29 @@ def _maybe_remap_hf_config_attrs(config: PretrainedConfig) -> PretrainedConfig:
     return config
 
 
-def maybe_override_with_speculators_target_model(
+def maybe_override_with_speculators(
     model: str,
     tokenizer: str,
     trust_remote_code: bool,
     revision: Optional[str] = None,
+    vllm_speculative_config: Optional[dict[str, Any]] = None,
     **kwargs,
-) -> tuple[str, str]:
+) -> tuple[str, str, Optional[dict[str, Any]]]:
     """
-    If running a speculators config, override running model with target model
+    Resolve model configuration when speculators are detected.
+
+    Checks if the provided model is a speculators model and if so, extracts
+    the target model configuration and builds the speculative config.
+
+    Args:
+        model: Model name or path
+        tokenizer: Tokenizer name or path
+        trust_remote_code: Whether to trust remote code
+        revision: Model revision
+        vllm_speculative_config: Existing vLLM speculative config
+
+    Returns:
+        Tuple of (resolved_model, resolved_tokenizer, speculative_config)
     """
     is_gguf = check_gguf_file(model)
     if is_gguf:
@@ -487,11 +501,27 @@ def maybe_override_with_speculators_target_model(
         token=_get_hf_token(),
         **kwargs,
     )
-    spec_config = config_dict.get("speculators_config", None)
-    # Return the target model
-    if spec_config is not None:
-        model = tokenizer = spec_config["verifier"]["name_or_path"]
-    return model, tokenizer
+    speculators_config = config_dict.get("speculators_config")
+
+    if speculators_config is None:
+        # No speculators config found, return original values
+        return model, tokenizer, vllm_speculative_config
+
+    # Speculators format detected - process overrides
+    from vllm.transformers_utils.configs.speculators.base import (
+        SpeculatorsConfig)
+
+    vllm_speculative_config = SpeculatorsConfig.extract_vllm_speculative_config(
+        config_dict=config_dict)
+
+    # Set the draft model to the speculators model
+    vllm_speculative_config["model"] = model
+
+    # Override model and tokenizer with the verifier model from config
+    verifier_model = speculators_config["verifier"]["name_or_path"]
+    model = tokenizer = verifier_model
+
+    return model, tokenizer, vllm_speculative_config
 
 
 def get_config(

vllm/transformers_utils/configs/speculators/base.py

@@ -24,6 +24,12 @@ class SpeculatorsConfig(PretrainedConfig):
         config_dict, _ = cls.get_config_dict(pretrained_model_name_or_path,
                                              **kwargs)
 
+        vllm_config = cls.extract_vllm_speculative_config(config_dict)
+        return cls(**vllm_config)
+
+    @classmethod
+    def extract_vllm_speculative_config(
+            cls, config_dict: dict[str, Any]) -> dict[str, Any]:
         speculators_model_type = config_dict.get("speculators_model_type")
         if speculators_model_type not in SUPPORTED_SPECULATORS_TYPES:
             raise ValueError(
@@ -34,11 +40,12 @@ class SpeculatorsConfig(PretrainedConfig):
         # TODO: @dsikka - use speculators pydantic model to validate
         cls.validate_speculators_config(config_dict=config_dict)
         # Convert from speculators config -> format that can be ingested by vLLM
-        vllm_config = cls.convert_speculators_to_vllm(config_dict=config_dict)
+        vllm_config = cls.build_vllm_speculative_config(
+            config_dict=config_dict)
         # Apply anything specific to the supported algorithm
         algo_updater = SUPPORTED_SPECULATORS_TYPES[speculators_model_type]
         algo_updater(config_dict=config_dict, vllm_config=vllm_config)
-        return cls(**vllm_config)
+        return vllm_config
 
     @classmethod
     def validate_speculators_config(cls, config_dict: dict[str, Any]) -> None:
@@ -60,32 +67,45 @@ class SpeculatorsConfig(PretrainedConfig):
                 "'transformer_layer_config' must be a dictionary if provided")
 
     @classmethod
-    def convert_speculators_to_vllm(
+    def build_vllm_speculative_config(
             cls, config_dict: dict[str, Any]) -> dict[str, Any]:
         """
-        Convert speculators config format to vLLM format.
+        Build vLLM-compatible speculative configuration from speculators format.
+
+        This method extracts and transforms speculative configuration from the
+        speculators format into the structure expected by vLLM.
 
-        This method handles the translation of field names and structure
-        between speculators and vLLM formats.
+        Args:
+            config_dict: Configuration dictionary in speculators format
 
         Returns:
-            Dictionary with vLLM-compatible configuration
+            Dictionary with vLLM-compatible speculative configuration
         """
-        # Currently we only support one proposal method
+        # Extract speculators configuration
         spec_config = config_dict["speculators_config"]
-        first_method = spec_config.get("proposal_methods")[0]
-        num_lookahead_tokens = first_method.get("speculative_tokens")
 
-        if num_lookahead_tokens is None:
+        # Currently we only support one proposal method
+        proposal_methods = spec_config.get("proposal_methods")
+        if not proposal_methods:
+            raise ValueError("No proposal methods found in speculators config")
+
+        first_method = proposal_methods[0]
+        num_speculative_tokens = first_method.get("speculative_tokens")
+
+        if num_speculative_tokens is None:
             raise ValueError(
                 "Missing 'speculative_tokens' in proposal method. "
                 f"Got: {first_method}")
 
-        # Build base vLLM config
+        # Build base vLLM speculative configuration
         vllm_config = {
             "method": config_dict.get("speculators_model_type"),
-            "num_lookahead_tokens": num_lookahead_tokens,
+            "num_speculative_tokens": num_speculative_tokens,
             "target_model": spec_config.get("verifier")["name_or_path"]
         }
-        vllm_config.update(config_dict["transformer_layer_config"])
+
+        # Merge transformer layer configuration if present
+        transformer_config = config_dict.get("transformer_layer_config", {})
+        vllm_config.update(transformer_config)
+
         return vllm_config