Add LMF2 MoE model architecture (sgl-project#17997)

Author: tugot17

python/sglang/srt/configs/__init__.py

@@ -14,6 +14,7 @@
 from sglang.srt.configs.kimi_vl import KimiVLConfig
 from sglang.srt.configs.kimi_vl_moonvit import MoonViTConfig
 from sglang.srt.configs.lfm2 import Lfm2Config
+from sglang.srt.configs.lfm2_moe import Lfm2MoeConfig
 from sglang.srt.configs.longcat_flash import LongcatFlashConfig
 from sglang.srt.configs.nano_nemotron_vl import NemotronH_Nano_VL_V2_Config
 from sglang.srt.configs.nemotron_h import NemotronHConfig
@@ -50,6 +51,7 @@
     "DotsOCRConfig",
     "FalconH1Config",
     "Lfm2Config",
+    "Lfm2MoeConfig",
     "NemotronHConfig",
     "NemotronH_Nano_VL_V2_Config",
     "JetNemotronConfig",

python/sglang/srt/configs/lfm2_moe.py

@@ -0,0 +1,192 @@
+# Copyright 2025 SGLang Team
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""LFM2-MoE (Liquid Foundation Model 2 - Mixture of Experts) configuration
+
+Note: HF transformers has Lfm2MoeConfig in v5.0.0rc2 (unreleased).
+Once released, we could inherit from it like Lfm2Config does with HFLfm2Config.
+For now, we define a standalone config to support the model immediately.
+"""
+
+from typing import List, Optional
+
+from transformers import CONFIG_MAPPING
+from transformers.configuration_utils import PretrainedConfig
+
+from sglang.srt.configs.mamba_utils import Mamba2CacheParams, Mamba2StateShape
+
+
+class Lfm2MoeConfig(PretrainedConfig):
+    """
+    Configuration for LFM2-MoE models (e.g., LiquidAI/LFM2-8B-A1B).
+
+    LFM2-MoE is a hybrid architecture with:
+    - Attention layers and ShortConv layers (like dense LFM2)
+    - MoE (Mixture of Experts) FFN layers with sigmoid routing
+
+    Key MoE specifics:
+    - First `num_dense_layers` use dense MLP, rest use MoE
+    - Sigmoid routing (not softmax) with expert_bias for load balancing
+    - expert_bias is fp32 for numerical stability
+    """
+
+    model_type = "lfm2_moe"
+    keys_to_ignore_at_inference = ["past_key_values"]
+
+    def __init__(
+        self,
+        vocab_size: int = 65536,
+        hidden_size: int = 2048,
+        intermediate_size: int = 7168,
+        moe_intermediate_size: int = 1792,
+        num_hidden_layers: int = 32,
+        num_attention_heads: int = 32,
+        num_key_value_heads: int = 8,
+        max_position_embeddings: int = 128000,
+        initializer_range: float = 0.02,
+        norm_eps: float = 1e-5,
+        use_cache: bool = True,
+        pad_token_id: int = 0,
+        bos_token_id: int = 1,
+        eos_token_id: int = 2,
+        tie_word_embeddings: bool = True,
+        rope_parameters: Optional[dict] = None,
+        conv_bias: bool = False,
+        conv_L_cache: int = 3,
+        # MoE-specific parameters
+        num_dense_layers: int = 2,
+        num_experts: int = 32,
+        num_experts_per_tok: int = 4,
+        use_expert_bias: bool = True,
+        routed_scaling_factor: float = 1.0,
+        norm_topk_prob: bool = True,
+        # Layer types
+        layer_types: Optional[List[str]] = None,
+        **kwargs,
+    ):
+        self.vocab_size = vocab_size
+        self.hidden_size = hidden_size
+        self.intermediate_size = intermediate_size
+        self.moe_intermediate_size = moe_intermediate_size
+        self.num_hidden_layers = num_hidden_layers
+        self.num_attention_heads = num_attention_heads
+        self.num_key_value_heads = num_key_value_heads
+        self.max_position_embeddings = max_position_embeddings
+        self.initializer_range = initializer_range
+        self.norm_eps = norm_eps
+        self.use_cache = use_cache
+
+        # Conv parameters
+        self.conv_bias = conv_bias
+        self.conv_L_cache = conv_L_cache
+
+        # MoE parameters
+        self.num_dense_layers = num_dense_layers
+        self.num_experts = num_experts
+        self.num_experts_per_tok = num_experts_per_tok
+        self.use_expert_bias = use_expert_bias
+        self.routed_scaling_factor = routed_scaling_factor
+        self.norm_topk_prob = norm_topk_prob
+
+        # Layer types (attention vs conv)
+        self.layer_types = layer_types
+
+        # RoPE parameters
+        self.rope_parameters = rope_parameters
+
+        # Validate layer_types length matches num_hidden_layers
+        if layer_types is not None and len(layer_types) != num_hidden_layers:
+            raise ValueError(
+                f"layer_types length ({len(layer_types)}) must match "
+                f"num_hidden_layers ({num_hidden_layers})"
+            )
+
+        # Handle tie_embedding alias from original config
+        tie_word_embeddings = kwargs.pop("tie_embedding", tie_word_embeddings)
+
+        super().__init__(
+            pad_token_id=pad_token_id,
+            bos_token_id=bos_token_id,
+            eos_token_id=eos_token_id,
+            tie_word_embeddings=tie_word_embeddings,
+            **kwargs,
+        )
+
+    @property
+    def full_attention_layer_ids(self) -> List[int]:
+        """Return indices of attention layers for KV cache."""
+        if self.layer_types is None:
+            return []
+        return [i for i, lt in enumerate(self.layer_types) if lt == "full_attention"]
+
+    @property
+    def linear_layer_ids(self) -> List[int]:
+        """Return indices of conv layers for conv state cache."""
+        if self.layer_types is None:
+            return []
+        return [
+            i for i, lt in enumerate(self.layer_types) if lt in ("conv", "short_conv")
+        ]
+
+    @property
+    def mamba_chunk_size(self) -> int:
+        """Return chunk size for Mamba2 backend. LFM2 doesn't use chunking."""
+        return 1
+
+    @property
+    def mamba2_cache_params(self) -> Optional[Mamba2CacheParams]:
+        """
+        Get cache params for HybridReqToTokenPool initialization.
+
+        LFM2-MoE uses ShortConv layers with a small fixed-size cache.
+        """
+        from sglang.srt.layers.dp_attention import get_attention_tp_size
+
+        conv_layer_ids = self.linear_layer_ids
+        if not conv_layer_ids:
+            return None
+
+        hidden_size = self.hidden_size
+        # conv_L_cache in config is kernel_size (e.g., 3)
+        conv_kernel = int(self.conv_L_cache)
+        # actual cache size is kernel_size - 1 (e.g., 2 for kernel=3)
+
+        try:
+            tp_size = get_attention_tp_size()
+        except (AssertionError, RuntimeError):
+            tp_size = 1
+
+        shape = Mamba2StateShape.create(
+            tp_world_size=tp_size,
+            intermediate_size=hidden_size,
+            n_groups=1,
+            num_heads=tp_size,  # Ensures divide works; temporal state is empty anyway
+            head_dim=hidden_size,
+            state_size=0,
+            conv_kernel=conv_kernel,
+        )
+
+        # Uses default mamba2_state_dtype() which reads SGLANG_MAMBA_CONV_DTYPE env var
+        # (defaults to bfloat16). Set SGLANG_MAMBA_CONV_DTYPE=float16 for fp16 inference.
+        return Mamba2CacheParams(
+            shape=shape,
+            layers=conv_layer_ids,
+        )
+
+
+# Register with transformers CONFIG_MAPPING so AutoConfig.from_pretrained()
+# can instantiate our config class when loading models with model_type="lfm2_moe"
+try:
+    CONFIG_MAPPING.register("lfm2_moe", Lfm2MoeConfig)
+except Exception:
+    # Already registered or registration failed - use direct assignment
+    CONFIG_MAPPING._extra_content["lfm2_moe"] = Lfm2MoeConfig

python/sglang/srt/model_executor/model_runner.py

@@ -36,6 +36,7 @@
     JetVLMConfig,
     KimiLinearConfig,
     Lfm2Config,
+    Lfm2MoeConfig,
     NemotronH_Nano_VL_V2_Config,
     NemotronHConfig,
     Qwen3_5Config,
@@ -1571,7 +1572,9 @@ def mamba2_config(self):
             pattern = getattr(config, "mtp_hybrid_override_pattern", None)
             if pattern is not None and "M" not in pattern:
                 return None
-        if isinstance(config, FalconH1Config | NemotronHConfig | Lfm2Config):
+        if isinstance(
+            config, FalconH1Config | NemotronHConfig | Lfm2Config | Lfm2MoeConfig
+        ):
             return config
         if isinstance(config, NemotronH_Nano_VL_V2_Config):
             return config.llm_config