Vllm modelling cleanup (#483)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: bigximik <denisko@live.com>

Author: 3 people

apriel2-vllm-plugin/pyproject.toml

@@ -0,0 +1,28 @@
+[build-system]
+requires = ["setuptools>=64"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "apriel2-vllm-plugin"
+version = "0.1.0"
+description = "Standalone vLLM plugin for Apriel2 models (extracted from Fast-LLM)"
+requires-python = ">=3.12"
+dependencies = [
+    "torch",
+    "transformers",
+    "einops",
+]
+
+[project.entry-points."vllm.general_plugins"]
+apriel2 = "fast_llm_external_models.apriel2.vllm.config_convertor:register"
+
+[tool.setuptools.packages.find]
+where = [".."]
+include = [
+    "fast_llm_external_models",
+    "fast_llm_external_models.apriel2",
+    "fast_llm_external_models.apriel2.vllm",
+]
+
+[tool.setuptools.package-dir]
+"" = ".."

fast_llm_external_models/apriel2/vllm/config_convertor.py

@@ -9,6 +9,12 @@
 """
 
 from vllm import ModelRegistry
+from vllm.model_executor.models.config import (
+    MODELS_CONFIG_MAP,
+    HybridAttentionMambaModelConfig,
+    MambaModelConfig,
+    VerifyAndUpdateConfig,
+)
 from vllm.transformers_utils.model_arch_config_convertor import (
     MODEL_ARCH_CONFIG_CONVERTORS,
     ModelArchConfigConvertorBase,
@@ -70,6 +76,39 @@ def get_head_size(self) -> int:
         return self._get_first_attention_block().get("head_size", 0)
 
 
+class Apriel2ModelConfig(VerifyAndUpdateConfig):
+    """Config handler for Apriel2 models with heterogeneous mixer types.
+
+    Apriel2 can be pure-attention, pure-mamba, or hybrid (attention + mamba)
+    depending on the decoder config.  vLLM's default ``is_hybrid`` dispatch
+    calls ``HybridAttentionMambaModelConfig`` which crashes for pure-mamba
+    models (``ZeroDivisionError`` when ``num_kv_heads=0``).
+
+    This handler inspects ``layers_block_type`` on the HF config to determine
+    the model composition and routes to the correct config handler.
+    """
+
+    @staticmethod
+    def verify_and_update_config(vllm_config) -> None:
+        hf_config = vllm_config.model_config.hf_config
+        layer_types = getattr(hf_config, "layers_block_type", None)
+
+        if layer_types is None:
+            # Fallback: no layer type info — assume standard transformer.
+            return
+
+        has_attention = any(t == "attention" for t in layer_types)
+        has_mamba = any(t == "mamba" for t in layer_types)
+
+        if has_attention and has_mamba:
+            # Hybrid: attention + mamba page size alignment required.
+            HybridAttentionMambaModelConfig.verify_and_update_config(vllm_config)
+        elif has_mamba:
+            # Pure mamba: enable FULL_AND_PIECEWISE, set mamba_block_size.
+            MambaModelConfig.verify_and_update_config(vllm_config)
+        # Pure attention: no special config needed.
+
+
 def register():
     """Register Apriel2 models and config convertors with vLLM.
 
@@ -130,7 +169,7 @@ def register():
         # Best-effort only; vLLM can still proceed with the generic config.
         pass
 
-    # Register model class
+    # Register model class and config handler.
     # Note: some exported checkpoints may list "Apriel2ForConditionalGeneration"
     # in config.json's "architectures". vLLM's model selection is driven by that
     # field, so we alias it to the same vLLM implementation for text-only usage.
@@ -139,3 +178,8 @@ def register():
             arch,
             "fast_llm_external_models.apriel2.vllm:Apriel2ForCausalLM",
         )
+        # Register in MODELS_CONFIG_MAP so vLLM calls our handler instead of
+        # relying on the is_hybrid class attribute dispatch (which can't handle
+        # models that are sometimes hybrid, sometimes pure-mamba).
+        if arch not in MODELS_CONFIG_MAP:
+            MODELS_CONFIG_MAP[arch] = Apriel2ModelConfig