Remove `from_dict` from `SpeculativeConfig` (#22451)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

tests/v1/spec_decode/test_ngram.py

@@ -47,13 +47,12 @@ def test_ngram_proposer():
         model_config = ModelConfig(model="facebook/opt-125m")
         return NgramProposer(
             vllm_config=VllmConfig(model_config=model_config,
-                                   speculative_config=SpeculativeConfig.
-                                   from_dict({
-                                       "prompt_lookup_min": min_n,
-                                       "prompt_lookup_max": max_n,
-                                       "num_speculative_tokens": k,
-                                       "method": "ngram",
-                                   })))
+                                   speculative_config=SpeculativeConfig(
+                                       prompt_lookup_min=min_n,
+                                       prompt_lookup_max=max_n,
+                                       num_speculative_tokens=k,
+                                       method="ngram",
+                                   )))
 
     # No match.
     result = ngram_proposer(

vllm/config.py

@@ -2895,11 +2895,6 @@ class SpeculativeConfig:
                                usedforsecurity=False).hexdigest()
         return hash_str
 
-    @classmethod
-    def from_dict(cls, dict_value: dict) -> "SpeculativeConfig":
-        """Parse the CLI value for the speculative config."""
-        return cls(**dict_value)
-
     @staticmethod
     def hf_config_override(hf_config: PretrainedConfig) -> PretrainedConfig:
         if hf_config.model_type == "deepseek_v3":

vllm/engine/arg_utils.py

@@ -757,18 +757,6 @@ class EngineArgs:
         lora_group.add_argument("--default-mm-loras",
                                 **lora_kwargs["default_mm_loras"])
 
-        # Speculative arguments
-        speculative_group = parser.add_argument_group(
-            title="SpeculativeConfig",
-            description=SpeculativeConfig.__doc__,
-        )
-        speculative_group.add_argument(
-            "--speculative-config",
-            type=json.loads,
-            default=None,
-            help="The configurations for speculative decoding. Should be a "
-            "JSON string.")
-
         # Observability arguments
         observability_kwargs = get_kwargs(ObservabilityConfig)
         observability_group = parser.add_argument_group(
@@ -848,6 +836,8 @@ class EngineArgs:
             title="VllmConfig",
             description=VllmConfig.__doc__,
         )
+        vllm_group.add_argument("--speculative-config",
+                                **vllm_kwargs["speculative_config"])
         vllm_group.add_argument("--kv-transfer-config",
                                 **vllm_kwargs["kv_transfer_config"])
         vllm_group.add_argument('--kv-events-config',
@@ -1033,10 +1023,7 @@ class EngineArgs:
             "enable_chunked_prefill": enable_chunked_prefill,
             "disable_log_stats": disable_log_stats,
         })
-        speculative_config = SpeculativeConfig.from_dict(
-            self.speculative_config)
-
-        return speculative_config
+        return SpeculativeConfig(**self.speculative_config)
 
     def create_engine_config(
         self,