Add support for ModelOpt MXFP8 MoE models (#35986)

Signed-off-by: Daniel Serebrenik <daserebrenik@nvidia.com>

tests/kernels/moe/test_ocp_mx_moe.py

@@ -20,6 +20,8 @@ TRTLLM_GEN_MXFP4_AVAILABLE = (
     current_platform.is_cuda() and current_platform.is_device_capability_family(100)
 )
 
+TRTLLM_GEN_MXFP8_AVAILABLE = TRTLLM_GEN_MXFP4_AVAILABLE
+
 HOPPER_MXFP4_BF16_AVAILABLE = (
     current_platform.is_cuda()
     and current_platform.is_device_capability(90)
@@ -34,9 +36,15 @@ if TRTLLM_GEN_MXFP4_AVAILABLE:
         shuffle_matrix_a,
         shuffle_matrix_sf_a,
         trtllm_fp4_block_scale_moe,
+        trtllm_fp8_block_scale_moe,
     )
     from flashinfer.fp4_quantization import nvfp4_block_scale_interleave
-    from flashinfer.fused_moe.core import get_w2_permute_indices_with_cache
+
+if TRTLLM_GEN_MXFP8_AVAILABLE:
+    from flashinfer.fused_moe.core import (
+        Fp8QuantizationType,
+        get_w2_permute_indices_with_cache,
+    )
 
 
 @dataclass
@@ -160,6 +168,7 @@ def reference_moe(
     beta,
     limit,
     act_type,
+    is_gated,
 ):
     # renormalize routing
     experts = torch.topk(roouting_logits, k=topk, dim=-1, sorted=True)
@@ -170,7 +179,12 @@ def reference_moe(
     mlp1_weight = w13[expert_indices, ...]
     mlp1_bias = bias13[expert_indices, ...]
     t = torch.einsum("beck,bk->bec", mlp1_weight, t) + mlp1_bias
-    t = swiglu(t, alpha=alpha, beta=beta, limit=limit)
+    if is_gated:
+        t = swiglu(t, alpha=alpha, beta=beta, limit=limit)
+    else:
+        # RELU2_NO_MUL: relu(x)^2
+        t = torch.relu(t)
+        t = t * t
 
     if act_type == "mxfp8":
         t_quantized, t_scale = mxfp8_quantize(
@@ -569,6 +583,7 @@ def test_trtllm_gen_mxfp4_fused_moe(
             beta,
             limit,
             act_type,
+            is_gated=True,
         )
         ref_result[start_idx:end_idx].copy_(chunk_result)
 
@@ -705,6 +720,7 @@ def test_flashinfer_cutlass_mxfp4_fused_moe(
         beta,
         limit,
         "bf16",
+        is_gated=True,
     )
 
     from vllm.utils.flashinfer import flashinfer_cutlass_fused_moe
@@ -890,6 +906,7 @@ def test_flashinfer_cutlass_mxfp4_mxfp8_fused_moe(
         beta,
         limit,
         "mxfp8",
+        is_gated=True,
     )
 
     # Prepare inputs for FlashInfer CUTLASS fused MoE
@@ -965,3 +982,169 @@ def test_flashinfer_cutlass_mxfp4_mxfp8_fused_moe(
 
     # Allow some mismatch due to MXFP4 quantization
     check_accuracy(ref, out, atol=0, rtol=0.3, percent=0.8)
+
+
+@pytest.mark.parametrize("topk", [1, 4])
+@pytest.mark.parametrize("num_experts", [32])
+@pytest.mark.parametrize("num_tokens", [1, 128])
+@pytest.mark.parametrize("intermediate_size,hidden_size", [(3072, 3072)])
+@pytest.mark.parametrize("is_gated", [True], ids=["gated"])
+@pytest.mark.skipif(
+    not TRTLLM_GEN_MXFP8_AVAILABLE,
+    reason="nvidia gpu and compute capability sm100 is required for this test",
+)
+def test_trtllm_gen_mxfp8_block_scale_moe(
+    topk: int,
+    num_experts: int,
+    num_tokens: int,
+    intermediate_size: int,
+    hidden_size: int,
+    is_gated: bool,
+):
+    torch.manual_seed(42)
+    device = "cuda:0"
+
+    inter_size = intermediate_size * (2 if is_gated else 1)
+
+    hidden_states = (
+        torch.randn(num_tokens, hidden_size, device=device, dtype=torch.bfloat16) / 20
+    )
+    w13 = (
+        torch.randn(
+            num_experts,
+            inter_size,
+            hidden_size,
+            device=device,
+            dtype=torch.bfloat16,
+        )
+        / 20
+    )
+    w2 = (
+        torch.randn(
+            num_experts,
+            hidden_size,
+            intermediate_size,
+            device=device,
+            dtype=torch.bfloat16,
+        )
+        / 20
+    )
+    router_logits = torch.rand(
+        num_tokens, num_experts, dtype=torch.float32, device=device
+    )
+    router_logits_kernel = router_logits.to(torch.bfloat16)
+
+    # Quantize weights to MXFP8 and normalize scales to [E, M, K//32].
+    w13_q, w13_scale = mxfp8_quantize(w13, is_sf_swizzled_layout=False)
+    w2_q, w2_scale = mxfp8_quantize(w2, is_sf_swizzled_layout=False)
+    if w13_scale.ndim == 1:
+        w13_scale = w13_scale.view(
+            num_experts,
+            inter_size,
+            hidden_size // 32,
+        )
+    if w2_scale.ndim == 1:
+        w2_scale = w2_scale.view(num_experts, hidden_size, intermediate_size // 32)
+
+    # Quantize activations to MXFP8.
+    hidden_states_q, hidden_states_scale = mxfp8_quantize(
+        hidden_states, is_sf_swizzled_layout=False
+    )
+    if hidden_states_scale.ndim == 1:
+        hidden_states_scale = hidden_states_scale.view(num_tokens, hidden_size // 32)
+
+    # Reference output using dequantized tensors + MXFP8 intermediate quantization.
+    w13_ref = mxfp8_dequantize(w13_q, w13_scale).to(torch.float32)
+    w2_ref = mxfp8_dequantize(w2_q, w2_scale).to(torch.float32)
+    hidden_states_ref = mxfp8_dequantize(hidden_states_q, hidden_states_scale).to(
+        torch.float32
+    )
+    bias13 = torch.zeros(
+        num_experts,
+        intermediate_size * (2 if is_gated else 1),
+        device=device,
+    )
+    bias2 = torch.zeros(num_experts, hidden_size, device=device)
+    ref = reference_moe(
+        router_logits_kernel.to(torch.float32),
+        topk,
+        num_experts,
+        hidden_states_ref,
+        w13_ref,
+        bias13,
+        w2_ref,
+        bias2,
+        alpha=1.0,
+        beta=0.0,
+        limit=None,
+        act_type="mxfp8",
+        is_gated=is_gated,
+    )
+
+    # Shuffle weights/scales with the same indexed layout used by TRTLLM kernels.
+    epilogue_tile_m = 128
+    gemm1_weights_shuffled = []
+    gemm1_scales_shuffled = []
+    gemm2_weights_shuffled = []
+    gemm2_scales_shuffled = []
+    for i in range(num_experts):
+        w13_rows = intermediate_size * (2 if is_gated else 1)
+        w13_interleaved = w13_q[i].clone().reshape(w13_rows, -1)
+        w13_scale_interleaved = w13_scale[i].clone().reshape(w13_rows, -1)
+        if is_gated:
+            w13_interleaved = reorder_rows_for_gated_act_gemm(w13_interleaved)
+            w13_scale_interleaved = reorder_rows_for_gated_act_gemm(
+                w13_scale_interleaved
+            )
+        gemm1_weights_shuffled.append(
+            shuffle_matrix_a(w13_interleaved.view(torch.uint8), epilogue_tile_m)
+            .contiguous()
+            .view(w13_q.dtype)
+        )
+        gemm2_weights_shuffled.append(
+            shuffle_matrix_a(w2_q[i].view(torch.uint8), epilogue_tile_m)
+            .contiguous()
+            .view(w2_q.dtype)
+        )
+
+        gemm1_scales_shuffled.append(
+            shuffle_matrix_sf_a(
+                w13_scale_interleaved.view(torch.uint8).reshape(w13_rows, -1),
+                epilogue_tile_m,
+            )
+            .contiguous()
+            .view(w13_scale.dtype)
+        )
+        gemm2_scales_shuffled.append(
+            shuffle_matrix_sf_a(
+                w2_scale[i].view(torch.uint8).reshape(hidden_size, -1), epilogue_tile_m
+            )
+            .contiguous()
+            .view(w2_scale.dtype)
+        )
+
+    out = trtllm_fp8_block_scale_moe(
+        routing_logits=router_logits_kernel,
+        routing_bias=None,
+        hidden_states=hidden_states_q,
+        hidden_states_scale=hidden_states_scale,
+        gemm1_weights=torch.stack(gemm1_weights_shuffled),
+        gemm1_weights_scale=torch.stack(gemm1_scales_shuffled),
+        gemm2_weights=torch.stack(gemm2_weights_shuffled),
+        gemm2_weights_scale=torch.stack(gemm2_scales_shuffled),
+        num_experts=num_experts,
+        top_k=topk,
+        n_group=None,
+        topk_group=None,
+        intermediate_size=intermediate_size,
+        local_expert_offset=0,
+        local_num_experts=num_experts,
+        routed_scaling_factor=None,
+        routing_method_type=1,  # renormalize routing
+        use_shuffled_weight=True,
+        weight_layout=0,  # MajorK
+        fp8_quantization_type=Fp8QuantizationType.MxFp8,
+    )
+
+    # Block-scale MXFP8 kernels are approximate; require majority close.
+    check_accuracy(ref, out, atol=0.1, rtol=0.85, percent=0.8)

vllm/model_executor/layers/fused_moe/layer.py

@@ -1204,17 +1204,26 @@ class FusedMoE(CustomOp):
             # Determine per-tensor weight scale patterns based on variant
             # Use the dedicated method instead of brittle string matching
             uses_weight_scale_2 = self.quant_method.uses_weight_scale_2_pattern()
+            quant_method = getattr(param, "quant_method", None)
 
             # Call _load_per_tensor_weight_scale() to load per-tensor (scalar)
             # weights scales.
             # Input scales are always per-tensor.
             # Weight scales: FP4 uses "weight_scale_2" and FP8 uses
             # "weight_scale" for per-tensor scales.
+            # NOTE: ModelOpt MXFP8 MoE uses block scales in weight_scale
+            # tensors (quant_method=BLOCK), so those must not be treated
+            # as per-tensor scalars here.
+            is_block_weight_scale = (
+                "weight_scale" in weight_name
+                and quant_method == FusedMoeWeightScaleSupported.BLOCK.value
+            )
             is_per_tensor = (
                 "weight_scale_2" in weight_name
                 if uses_weight_scale_2
                 else "weight_scale" in weight_name
             ) or "input_scale" in weight_name
+            is_per_tensor = is_per_tensor and not is_block_weight_scale
             if is_per_tensor:
                 self._load_per_tensor_weight_scale(
                     shard_id=shard_id,

vllm/model_executor/layers/fused_moe/oracle/mxfp8.py

@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+from enum import Enum
+
+from vllm.logger import init_logger
+from vllm.model_executor.layers.fused_moe.config import FusedMoEConfig
+
+logger = init_logger(__name__)
+
+
+class MxFp8MoeBackend(Enum):
+    FLASHINFER_TRTLLM = "FLASHINFER_TRTLLM"
+
+
+def select_mxfp8_moe_backend(
+    config: FusedMoEConfig,
+) -> MxFp8MoeBackend:
+    if config.is_lora_enabled:
+        raise NotImplementedError("LoRA is not supported for MXFP8 MoE.")
+
+    AVAILABLE_BACKENDS = [
+        MxFp8MoeBackend.FLASHINFER_TRTLLM,
+    ]
+
+    runner_backend = config.moe_backend
+    if runner_backend != "auto":
+        mapping = {
+            "flashinfer_trtllm": MxFp8MoeBackend.FLASHINFER_TRTLLM,
+        }
+        if backend := mapping.get(runner_backend):
+            logger.info_once(
+                "Using '%s' MxFp8 MoE backend (user-requested).",
+                backend.value,
+            )
+            return backend
+        raise ValueError(
+            f"moe_backend='{runner_backend}' is not supported for MXFP8 MoE. "
+            f"Expected one of {list(mapping.keys())}."
+        )
+
+    # Auto-select: only one backend available for now.
+    backend = AVAILABLE_BACKENDS[0]
+    logger.info_once("Using '%s' MxFp8 MoE backend.", backend.value)
+    return backend

vllm/model_executor/layers/quantization/modelopt.py

@@ -9,17 +9,19 @@ from torch.nn.parameter import Parameter
 
 import vllm.model_executor.layers.fused_moe.modular_kernel as mk
 from vllm.logger import init_logger
-from vllm.model_executor.kernels.linear import (
+from vllm.model_executor.kernels.linear import init_fp8_linear_kernel
-    init_fp8_linear_kernel,
-)
 from vllm.model_executor.layers.attention import Attention, MLAAttention
+from vllm.model_executor.layers.fused_moe.activation import MoEActivation
 from vllm.model_executor.layers.fused_moe.config import (
     FusedMoEConfig,
     FusedMoEQuantConfig,
+    RoutingMethodType,
+)
+from vllm.model_executor.layers.fused_moe.fused_moe_method_base import (
+    FusedMoEMethodBase,
 )
 from vllm.model_executor.layers.fused_moe.layer import (
     FusedMoE,
-    FusedMoEMethodBase,
     FusedMoeWeightScaleSupported,
 )
 from vllm.model_executor.layers.fused_moe.oracle.fp8 import (
@@ -28,6 +30,10 @@ from vllm.model_executor.layers.fused_moe.oracle.fp8 import (
     make_fp8_moe_quant_config,
     select_fp8_moe_backend,
 )
+from vllm.model_executor.layers.fused_moe.oracle.mxfp8 import (
+    MxFp8MoeBackend,
+    select_mxfp8_moe_backend,
+)
 from vllm.model_executor.layers.fused_moe.oracle.nvfp4 import (
     convert_to_nvfp4_moe_kernel_format,
     is_global_sf_supported_for_nvfp4_backend,
@@ -46,6 +52,9 @@ from vllm.model_executor.layers.quantization.base_config import (
     QuantizeMethodBase,
 )
 from vllm.model_executor.layers.quantization.kv_cache import BaseKVCacheMethod
+from vllm.model_executor.layers.quantization.utils.flashinfer_utils import (
+    swap_w13_to_w31,
+)
 from vllm.model_executor.layers.quantization.utils.fp8_utils import (
     W8A8BlockFp8LinearOp,
     process_fp8_input_tensor_strategy_moe,
@@ -60,6 +69,7 @@ from vllm.model_executor.layers.quantization.utils.mxfp8_utils import (
     MXFP8_VALUE_DTYPE,
     Mxfp8LinearBackend,
     Mxfp8LinearOp,
+    mxfp8_e4m3_quantize,
     swizzle_mxfp8_scale,
 )
 from vllm.model_executor.layers.quantization.utils.nvfp4_utils import (
@@ -86,7 +96,8 @@ from vllm.model_executor.parameter import (
     ModelWeightParameter,
     PerTensorScaleParameter,
 )
-from vllm.model_executor.utils import replace_parameter
+from vllm.model_executor.utils import replace_parameter, set_weight_attrs
+from vllm.utils.flashinfer import flashinfer_trtllm_fp8_block_scale_moe
 
 if TYPE_CHECKING:
     from vllm.model_executor.models.utils import WeightsMapper
@@ -1487,17 +1498,6 @@ class ModelOptMxFp8Config(ModelOptQuantConfigBase):
         # MXFP8 hardware acceleration requires Blackwell (SM100) or newer
         return 100
 
-    def get_quant_method(
-        self, layer: torch.nn.Module, prefix: str
-    ) -> "QuantizeMethodBase | None":
-        # MXFP8 does not yet support MoE models
-        if isinstance(layer, FusedMoE):
-            raise NotImplementedError(
-                "MXFP8 quantization does not yet support MoE models. "
-                "Please use FP8 or NVFP4 quantization for MoE models."
-            )
-        return super().get_quant_method(layer, prefix)
-
     @classmethod
     def override_quantization_method(
         cls, hf_quant_cfg, user_quant
@@ -1699,8 +1699,351 @@ class ModelOptMxFp8LinearMethod(LinearMethodBase):
         )
 
 
+class ModelOptMxFp8FusedMoE(FusedMoEMethodBase):
+    """FlashInfer TRTLLM MXFP8 block-scale MoE for ModelOpt checkpoints."""
+
+    def __init__(
+        self,
+        quant_config: ModelOptMxFp8Config,
+        moe_config: FusedMoEConfig,
+    ) -> None:
+        super().__init__(moe_config)
+        self.quant_config = quant_config
+        assert self.quant_config.is_checkpoint_mxfp8_serialized
+
+        # Select MXFP8 MoE backend
+        self.mxfp8_backend = select_mxfp8_moe_backend(self.moe)
+
+    def create_weights(
+        self,
+        layer: torch.nn.Module,
+        num_experts: int,
+        hidden_size: int,
+        intermediate_size_per_partition: int,
+        params_dtype: torch.dtype,
+        **extra_weight_attrs,
+    ):
+        layer.intermediate_size_per_partition = intermediate_size_per_partition
+        layer.hidden_size = hidden_size
+        layer.orig_dtype = params_dtype
+
+        if hidden_size % MXFP8_BLOCK_SIZE != 0:
+            raise ValueError(
+                f"MXFP8 MoE requires hidden_size divisible by {MXFP8_BLOCK_SIZE}, "
+                f"got {hidden_size}."
+            )
+        if intermediate_size_per_partition % MXFP8_BLOCK_SIZE != 0:
+            raise ValueError(
+                "MXFP8 MoE requires intermediate_size_per_partition divisible by "
+                f"{MXFP8_BLOCK_SIZE}, got {intermediate_size_per_partition}."
+            )
+
+        layer.num_experts = num_experts
+        weight_loader = extra_weight_attrs.get("weight_loader")
+        w13_num_shards = 2 if self.moe.is_act_and_mul else 1
+
+        # GEMM 1 weights: [E, (2I or I), H]
+        w13_weight = ModelWeightParameter(
+            data=torch.empty(
+                num_experts,
+                w13_num_shards * intermediate_size_per_partition,
+                hidden_size,
+                dtype=MXFP8_VALUE_DTYPE,
+            ),
+            input_dim=2,
+            output_dim=1,
+            weight_loader=weight_loader,
+        )
+        layer.register_parameter("w13_weight", w13_weight)
+
+        # GEMM 2 weights: [E, H, I]
+        w2_weight = ModelWeightParameter(
+            data=torch.empty(
+                num_experts,
+                hidden_size,
+                intermediate_size_per_partition,
+                dtype=MXFP8_VALUE_DTYPE,
+            ),
+            input_dim=2,
+            output_dim=1,
+            weight_loader=weight_loader,
+        )
+        layer.register_parameter("w2_weight", w2_weight)
+
+        # Per-block (K=32) E8M0 scales.
+        w13_weight_scale = ModelWeightParameter(
+            data=torch.empty(
+                num_experts,
+                w13_num_shards * intermediate_size_per_partition,
+                hidden_size // MXFP8_BLOCK_SIZE,
+                dtype=MXFP8_SCALE_DTYPE,
+            ),
+            input_dim=2,
+            output_dim=1,
+            weight_loader=weight_loader,
+        )
+        layer.register_parameter("w13_weight_scale", w13_weight_scale)
+
+        w2_weight_scale = ModelWeightParameter(
+            data=torch.empty(
+                num_experts,
+                hidden_size,
+                intermediate_size_per_partition // MXFP8_BLOCK_SIZE,
+                dtype=MXFP8_SCALE_DTYPE,
+            ),
+            input_dim=2,
+            output_dim=1,
+            weight_loader=weight_loader,
+        )
+        layer.register_parameter("w2_weight_scale", w2_weight_scale)
+
+        # Ensure the generic MoE weight-loader treats these as block scales.
+        set_weight_attrs(
+            layer.w13_weight_scale,
+            {"quant_method": FusedMoeWeightScaleSupported.BLOCK.value},
+        )
+        set_weight_attrs(
+            layer.w2_weight_scale,
+            {"quant_method": FusedMoeWeightScaleSupported.BLOCK.value},
+        )
+
+    @staticmethod
+    def _check_weight_dtypes(layer: torch.nn.Module) -> None:
+        """Validate weight and scale dtypes before processing."""
+        expected = {
+            "w13_weight": MXFP8_VALUE_DTYPE,
+            "w2_weight": MXFP8_VALUE_DTYPE,
+            "w13_weight_scale": MXFP8_SCALE_DTYPE,
+            "w2_weight_scale": MXFP8_SCALE_DTYPE,
+        }
+        for name, expected_dtype in expected.items():
+            actual = getattr(layer, name).dtype
+            if actual != expected_dtype:
+                raise ValueError(
+                    f"Expected {name} dtype {expected_dtype}, got {actual}."
+                )
+
+    def _shuffle_weights_for_trtllm(self, layer: torch.nn.Module) -> None:
+        """Shuffle weights and scales into FlashInfer TRTLLM MXFP8 layout."""
+        from flashinfer import (
+            reorder_rows_for_gated_act_gemm,
+            shuffle_matrix_a,
+            shuffle_matrix_sf_a,
+        )
+
+        epilogue_tile_m = 128
+        num_experts = layer.w13_weight.shape[0]
+        is_gated = self.moe.is_act_and_mul
+        intermediate_size_factor = 2 if is_gated else 1
+
+        w13_weight = layer.w13_weight.data
+        w13_scale = layer.w13_weight_scale.data
+        if is_gated:
+            # FI TRTLLM gated kernels use W31 ordering. Model checkpoints store
+            # gated projection as W13, so convert once before shuffling.
+            w13_weight = swap_w13_to_w31(w13_weight)
+            w13_scale = swap_w13_to_w31(w13_scale)
+
+        w13_weight_shuffled = []
+        w2_weight_shuffled = []
+        w13_scale_shuffled = []
+        w2_scale_shuffled = []
+        for i in range(num_experts):
+            w13_i = w13_weight[i].reshape(
+                intermediate_size_factor * layer.intermediate_size_per_partition, -1
+            )
+            w13_sf_i = w13_scale[i].reshape(
+                intermediate_size_factor * layer.intermediate_size_per_partition, -1
+            )
+            if is_gated:
+                # Reorder rows for gated activation layout expected by TRTLLM.
+                w13_i = reorder_rows_for_gated_act_gemm(w13_i.clone())
+                w13_sf_i = reorder_rows_for_gated_act_gemm(w13_sf_i.clone())
+
+            w13_shuffled_i = shuffle_matrix_a(w13_i.view(torch.uint8), epilogue_tile_m)
+            w2_shuffled_i = shuffle_matrix_a(
+                layer.w2_weight.data[i].view(torch.uint8), epilogue_tile_m
+            )
+            w13_weight_shuffled.append(
+                w13_shuffled_i.contiguous().view(MXFP8_VALUE_DTYPE)
+            )
+            w2_weight_shuffled.append(
+                w2_shuffled_i.contiguous().view(MXFP8_VALUE_DTYPE)
+            )
+            w13_sf_shuffled_i = shuffle_matrix_sf_a(
+                w13_sf_i.view(torch.uint8).reshape(
+                    intermediate_size_factor * layer.intermediate_size_per_partition,
+                    -1,
+                ),
+                epilogue_tile_m,
+            )
+            w2_sf_shuffled_i = shuffle_matrix_sf_a(
+                layer.w2_weight_scale.data[i]
+                .view(torch.uint8)
+                .reshape(layer.hidden_size, -1),
+                epilogue_tile_m,
+            )
+            w13_scale_shuffled.append(
+                w13_sf_shuffled_i.contiguous().view(MXFP8_SCALE_DTYPE)
+            )
+            w2_scale_shuffled.append(
+                w2_sf_shuffled_i.contiguous().view(MXFP8_SCALE_DTYPE)
+            )
+
+        replace_parameter(
+            layer, "w13_weight", torch.stack(w13_weight_shuffled).contiguous()
+        )
+        replace_parameter(
+            layer, "w2_weight", torch.stack(w2_weight_shuffled).contiguous()
+        )
+        replace_parameter(
+            layer,
+            "w13_weight_scale",
+            torch.stack(w13_scale_shuffled).contiguous(),
+        )
+        replace_parameter(
+            layer,
+            "w2_weight_scale",
+            torch.stack(w2_scale_shuffled).contiguous(),
+        )
+
+    def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
+        if getattr(layer, "_already_called_process_weights_after_loading", False):
+            return
+
+        self._check_weight_dtypes(layer)
+        self._shuffle_weights_for_trtllm(layer)
+        layer._already_called_process_weights_after_loading = True
+
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> mk.FusedMoEPrepareAndFinalizeModular | None:
+        raise ValueError(
+            f"{self.__class__.__name__} uses the new modular kernel initialization "
+            "logic. This function should not be called."
+        )
+
+    def select_gemm_impl(
+        self,
+        prepare_finalize: mk.FusedMoEPrepareAndFinalizeModular,
+        layer: torch.nn.Module,
+    ) -> mk.FusedMoEExpertsModular:
+        raise ValueError(
+            f"{self.__class__.__name__} uses the new modular kernel initialization "
+            "logic. This function should not be called."
+        )
+
+    def get_fused_moe_quant_config(
+        self, layer: torch.nn.Module
+    ) -> FusedMoEQuantConfig | None:
+        # TRTLLM MXFP8 path is monolithic and does not use modular kernel config.
+        return None
+
+    @property
+    def is_monolithic(self) -> bool:
+        return self.mxfp8_backend == MxFp8MoeBackend.FLASHINFER_TRTLLM
+
+    def apply_monolithic(
+        self,
+        layer: FusedMoE,
+        x: torch.Tensor,
+        router_logits: torch.Tensor,
+    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
+        from flashinfer.fused_moe.core import (
+            ActivationType,
+            Fp8QuantizationType,
+        )
+
+        assert self.mxfp8_backend == MxFp8MoeBackend.FLASHINFER_TRTLLM
+
+        if layer.enable_eplb:
+            raise NotImplementedError(
+                "EPLB is not supported for FlashInfer TRTLLM MXFP8 MoE backend."
+            )
+
+        supported_activations = [MoEActivation.SILU]
+        if layer.activation not in supported_activations:
+            raise NotImplementedError(
+                "FlashInfer TRTLLM MXFP8 MoE supports only "
+                f"{supported_activations}, got {layer.activation}."
+            )
+
+        # Map vLLM MoEActivation to FlashInfer ActivationType.
+        activation_map = {
+            MoEActivation.SILU: ActivationType.Swiglu,
+            MoEActivation.RELU2_NO_MUL: ActivationType.Relu2,
+        }
+        fi_activation_type: ActivationType = activation_map[layer.activation]
+
+        # DeepSeekV3 routing requires float32 logits; others expect bfloat16.
+        if layer.routing_method_type == RoutingMethodType.DeepSeekV3:
+            assert router_logits.dtype == torch.float32, (
+                "DeepSeekV3 routing requires float32 router_logits, "
+                f"got {router_logits.dtype}."
+            )
+        else:
+            router_logits = router_logits.to(torch.bfloat16)
+
+        # Treat 0 as "unset" for compatibility with ungrouped routing configs.
+        n_group = layer.num_expert_group or None
+        topk_group = layer.topk_group or None
+
+        hidden_states_mxfp8, hidden_states_scale = mxfp8_e4m3_quantize(
+            x,
+            is_sf_swizzled_layout=False,
+        )
+
+        kwargs: dict = dict(
+            routing_logits=router_logits,
+            routing_bias=layer.e_score_correction_bias,
+            hidden_states=hidden_states_mxfp8,
+            hidden_states_scale=hidden_states_scale,
+            gemm1_weights=layer.w13_weight,
+            gemm1_weights_scale=layer.w13_weight_scale,
+            gemm2_weights=layer.w2_weight,
+            gemm2_weights_scale=layer.w2_weight_scale,
+            num_experts=layer.global_num_experts,
+            top_k=layer.top_k,
+            # Keep Optional semantics: FlashInfer expects None for non-grouped
+            # routing (e.g. Qwen3 Renormalize), not 0.
+            n_group=n_group,
+            topk_group=topk_group,
+            intermediate_size=layer.intermediate_size_per_partition,
+            local_expert_offset=layer.ep_rank * layer.local_num_experts,
+            local_num_experts=layer.local_num_experts,
+            routed_scaling_factor=layer.routed_scaling_factor,
+            routing_method_type=layer.routing_method_type,
+            use_shuffled_weight=True,
+            weight_layout=0,
+            fp8_quantization_type=Fp8QuantizationType.MxFp8,
+        )
+
+        if fi_activation_type != ActivationType.Swiglu:
+            raise NotImplementedError(
+                "FlashInfer TRTLLM MXFP8 MoE supports only Swiglu activation, "
+                f"got {fi_activation_type}."
+            )
+
+        return flashinfer_trtllm_fp8_block_scale_moe(**kwargs)
+
+    def apply(
+        self,
+        layer: FusedMoE,
+        x: torch.Tensor,
+        topk_weights: torch.Tensor,
+        topk_ids: torch.Tensor,
+        shared_experts_input: torch.Tensor | None,
+    ) -> torch.Tensor | tuple[torch.Tensor, torch.Tensor]:
+        assert not self.is_monolithic
+        raise NotImplementedError(
+            "Non-monolithic MXFP8 MoE path is not yet implemented."
+        )
+
+
 # Register the method classes for ModelOptMxFp8Config
 ModelOptMxFp8Config.LinearMethodCls = ModelOptMxFp8LinearMethod
+ModelOptMxFp8Config.FusedMoEMethodCls = ModelOptMxFp8FusedMoE
 ModelOptMxFp8Config.KVCacheMethodCls = ModelOptFp8KVCacheMethod