[Kernel]Support W4A8 Grouped GEMM on Hopper (#29691)

Signed-off-by: czhu-cohere <conway.zhu@cohere.com>

CMakeLists.txt

@@ -874,7 +874,10 @@ if(VLLM_GPU_LANG STREQUAL "CUDA")
   cuda_archs_loose_intersection(W4A8_ARCHS "9.0a" "${CUDA_ARCHS}")
   if(${CMAKE_CUDA_COMPILER_VERSION} VERSION_GREATER_EQUAL 12.0 AND W4A8_ARCHS)
     set(SRCS
-       "csrc/quantization/cutlass_w4a8/w4a8_mm_entry.cu")
+       "csrc/quantization/cutlass_w4a8/w4a8_mm_entry.cu"
+       "csrc/quantization/cutlass_w4a8/w4a8_grouped_mm_entry.cu"
+       "csrc/quantization/cutlass_w4a8/w4a8_utils.cu"
+       )
 
     set_gencode_flags_for_srcs(
       SRCS "${SRCS}"

csrc/ops.h

@@ -262,7 +262,8 @@ void get_cutlass_moe_mm_data(
 void get_cutlass_moe_mm_problem_sizes(
     const torch::Tensor& topk_ids, torch::Tensor& problem_sizes1,
     torch::Tensor& problem_sizes2, const int64_t num_experts, const int64_t n,
-    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets);
+    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets,
+    std::optional<bool> force_swap_ab = std::nullopt);
 
 void get_cutlass_pplx_moe_mm_data(torch::Tensor& expert_offsets,
                                   torch::Tensor& problem_sizes1,

csrc/quantization/cutlass_w4a8/get_group_starts.cuh

+// see csrc/quantization/w8a8/cutlass/moe/get_group_starts.cuh
+#pragma once
+
+#include <cuda.h>
+#include <torch/all.h>
+#include <c10/cuda/CUDAStream.h>
+
+#include "core/scalar_type.hpp"
+#include "cutlass/bfloat16.h"
+#include "cutlass/float8.h"
+
+// ElementB is int32 (packed int4)
+// ElementGroupScale is cutlass::Array<cutlass::float_e4m3_t, 8> (packed fp8)
+template <typename ElementA, typename ElementB, typename ElementC,
+          typename ElementAccumulator, typename ElementGroupScale>
+__global__ void get_group_gemm_starts(
+    int64_t* expert_offsets, ElementA** a_offsets, ElementB** b_offsets,
+    ElementC** out_offsets, ElementAccumulator** a_scales_offsets,
+    ElementAccumulator** b_scales_offsets,
+    ElementGroupScale** b_group_scales_offsets, ElementA* a_base_as_int,
+    ElementB* b_base_as_int, ElementC* out_base_as_int,
+    ElementAccumulator* a_scales_base_as_int,
+    ElementAccumulator* b_scales_base_as_int,
+    ElementGroupScale* b_group_scales_base_as_int, int64_t n, int64_t k,
+    int64_t scale_k) {
+  int expert_id = threadIdx.x;
+
+  int64_t expert_offset = expert_offsets[expert_id];
+
+  // same as w8a8
+  a_offsets[expert_id] = a_base_as_int + expert_offset * k;
+  out_offsets[expert_id] = out_base_as_int + expert_offset * n;
+  a_scales_offsets[expert_id] = a_scales_base_as_int + expert_offset;
+  b_scales_offsets[expert_id] = b_scales_base_as_int + (n * expert_id);
+
+  // w4a8 specific
+  constexpr int pack_factor = 8;  // pack 8 int4 into int32
+  b_offsets[expert_id] = b_base_as_int + (expert_id * k * n / pack_factor);
+  b_group_scales_offsets[expert_id] =
+      b_group_scales_base_as_int + (expert_id * scale_k * n);
+}
+
+#define __CALL_GET_STARTS_KERNEL(TENSOR_C_TYPE, C_TYPE)                  \
+  else if (out_tensors.dtype() == TENSOR_C_TYPE) {                       \
+    get_group_gemm_starts<cutlass::float_e4m3_t, int32_t, C_TYPE, float, \
+                          cutlass::Array<cutlass::float_e4m3_t, 8>>      \
+        <<<1, num_experts, 0, stream>>>(                                 \
+            static_cast<int64_t*>(expert_offsets.data_ptr()),            \
+            static_cast<cutlass::float_e4m3_t**>(a_ptrs.data_ptr()),     \
+            static_cast<int32_t**>(b_ptrs.data_ptr()),                   \
+            static_cast<C_TYPE**>(out_ptrs.data_ptr()),                  \
+            static_cast<float**>(a_scales_ptrs.data_ptr()),              \
+            static_cast<float**>(b_scales_ptrs.data_ptr()),              \
+            static_cast<cutlass::Array<cutlass::float_e4m3_t, 8>**>(     \
+                b_group_scales_ptrs.data_ptr()),                         \
+            static_cast<cutlass::float_e4m3_t*>(a_tensors.data_ptr()),   \
+            static_cast<int32_t*>(b_tensors.data_ptr()),                 \
+            static_cast<C_TYPE*>(out_tensors.data_ptr()),                \
+            static_cast<float*>(a_scales.data_ptr()),                    \
+            static_cast<float*>(b_scales.data_ptr()),                    \
+            static_cast<cutlass::Array<cutlass::float_e4m3_t, 8>*>(      \
+                b_group_scales.data_ptr()),                              \
+            n, k, scale_k);                                              \
+  }
+
+namespace {
+
+void run_get_group_gemm_starts(
+    torch::Tensor const& expert_offsets, torch::Tensor& a_ptrs,
+    torch::Tensor& b_ptrs, torch::Tensor& out_ptrs,
+    torch::Tensor& a_scales_ptrs, torch::Tensor& b_scales_ptrs,
+    torch::Tensor& b_group_scales_ptrs, torch::Tensor const& a_tensors,
+    torch::Tensor const& b_tensors, torch::Tensor& out_tensors,
+    torch::Tensor const& a_scales, torch::Tensor const& b_scales,
+    torch::Tensor const& b_group_scales, const int64_t b_group_size) {
+  TORCH_CHECK(a_tensors.dtype() == torch::kFloat8_e4m3fn);
+  TORCH_CHECK(b_tensors.dtype() == torch::kInt32);  // int4 8x packed into int32
+  TORCH_CHECK(a_scales.dtype() == torch::kFloat32);
+  TORCH_CHECK(b_scales.dtype() == torch::kFloat32);
+  TORCH_CHECK(b_group_scales.dtype() ==
+              torch::kFloat8_e4m3fn);  // the underlying torch type is e4m3
+  TORCH_CHECK(out_tensors.dtype() ==
+              torch::kBFloat16);  // only support bf16 for now
+  // expect int64_t to avoid overflow during offset calculations
+  TORCH_CHECK(expert_offsets.dtype() == torch::kInt64);
+
+  int num_experts = static_cast<int>(expert_offsets.size(0));
+  // logical k, n
+  int64_t n = out_tensors.size(1);
+  int64_t k = a_tensors.size(1);
+  int64_t scale_k = cutlass::ceil_div(k, b_group_size);
+
+  auto stream = at::cuda::getCurrentCUDAStream(a_tensors.device().index());
+
+  if (false) {
+  }
+  __CALL_GET_STARTS_KERNEL(torch::kBFloat16, cutlass::bfloat16_t)
+  __CALL_GET_STARTS_KERNEL(torch::kFloat16, half)
+  else {
+    TORCH_CHECK(false, "Invalid output type (must be float16 or bfloat16)");
+  }
+}
+
+}  // namespace
\ No newline at end of file

csrc/quantization/cutlass_w4a8/w4a8_mm_entry.cu

@@ -7,6 +7,7 @@
 #include <c10/cuda/CUDAGuard.h>
 #include <torch/all.h>
 #include "cutlass_extensions/torch_utils.hpp"
+#include "w4a8_utils.cuh"
 
 #include "core/registration.h"
 
@@ -395,71 +396,6 @@ torch::Tensor pack_scale_fp8(torch::Tensor const& scales) {
   return packed_scales;
 }
 
-/*
-  GPU-accelerated implementation of cutlass::unified_encode_int4b.
-  Constructs a lookup table in constant memory to map 8 bits
-  (two 4-bit values) at a time. Assumes memory is contiguous
-  and pointers are 16-byte aligned.
-*/
-__constant__ uint8_t kNibbleLUT[256];
-
-__global__ void unified_encode_int4b_device(const uint8_t* in, uint8_t* out,
-                                            size_t nbytes) {
-  constexpr size_t V = sizeof(uint4);  // 16 bytes
-  const size_t tid = blockIdx.x * blockDim.x + threadIdx.x;
-  const size_t nthreads = size_t(gridDim.x) * blockDim.x;
-  const size_t nvec = nbytes / V;
-
-  // 1-D grid-stride loop over 16-byte chunks
-  for (size_t vec = tid; vec < nvec; vec += nthreads) {
-    uint4 v = reinterpret_cast<const uint4*>(in)[vec];
-    uint8_t* b = reinterpret_cast<uint8_t*>(&v);
-#pragma unroll
-    for (int i = 0; i < int(V); ++i) b[i] = kNibbleLUT[b[i]];
-    reinterpret_cast<uint4*>(out)[vec] = v;
-  }
-}
-
-static bool upload_lut() {
-  std::array<uint8_t, 256> lut{};
-  auto map_nib = [](uint8_t v) -> uint8_t {
-    // 1..7 -> (8 - v); keep 0 and 8..15
-    return (v == 0 || (v & 0x8)) ? v : uint8_t(8 - v);
-  };
-  for (int b = 0; b < 256; ++b) {
-    uint8_t lo = b & 0xF;
-    uint8_t hi = (b >> 4) & 0xF;
-    lut[b] = uint8_t((map_nib(hi) << 4) | map_nib(lo));
-  }
-  cudaError_t e = cudaMemcpyToSymbol(kNibbleLUT, lut.data(), lut.size(),
-                                     /*offset=*/0, cudaMemcpyHostToDevice);
-
-  return (e == cudaSuccess);
-}
-
-static bool unified_encode_int4b(cutlass::int4b_t const* in,
-                                 cutlass::int4b_t* out, size_t num_int4_elems) {
-  // Build/upload LUT
-  if (!upload_lut()) return false;
-
-  static_assert(sizeof(typename cutlass::int4b_t::Storage) == 1,
-                "int4 storage must be 1 byte");
-  const size_t nbytes = num_int4_elems >> 1;
-
-  auto* in_bytes = reinterpret_cast<uint8_t const*>(in);
-  auto* out_bytes = reinterpret_cast<uint8_t*>(out);
-
-  // kernel launch params
-  constexpr int block = 256;
-  const size_t nvec = nbytes / sizeof(uint4);  // # of 16B vectors
-  int grid = int((nvec + block - 1) / block);
-  if (grid == 0) grid = 1;  // ensure we still cover the tail in the kernel
-
-  unified_encode_int4b_device<<<grid, block>>>(in_bytes, out_bytes, nbytes);
-  cudaError_t err = cudaGetLastError();
-  return (err == cudaSuccess);
-}
-
 torch::Tensor encode_and_reorder_int4b(torch::Tensor const& B) {
   TORCH_CHECK(B.dtype() == torch::kInt32);
   TORCH_CHECK(B.dim() == 2);
@@ -477,8 +413,8 @@ torch::Tensor encode_and_reorder_int4b(torch::Tensor const& B) {
   LayoutB_Reordered layout_B_reordered =
       cute::tile_to_shape(LayoutAtomQuant{}, shape_B);
 
-  bool ok =
-      vllm::cutlass_w4a8::unified_encode_int4b(B_ptr, B_packed_ptr, n * k);
+  bool ok = vllm::cutlass_w4a8_utils::unified_encode_int4b(B_ptr, B_packed_ptr,
+                                                           n * k);
   TORCH_CHECK(ok, "unified_encode_int4b failed");
   cutlass::reorder_tensor(B_packed_ptr, layout_B, layout_B_reordered);
 

csrc/quantization/cutlass_w4a8/w4a8_utils.cu

+#include "w4a8_utils.cuh"
+
+#include <array>
+#include <cuda_runtime.h>
+#include <cstdio>
+
+namespace vllm::cutlass_w4a8_utils {
+
+/*
+  GPU-accelerated implementation of cutlass::unified_encode_int4b.
+  Constructs a lookup table in constant memory to map 8 bits
+  (two 4-bit values) at a time. Assumes memory is contiguous
+  and pointers are 16-byte aligned.
+*/
+__constant__ uint8_t kNibbleLUT[256];
+
+__global__ void unified_encode_int4b_device(const uint8_t* in, uint8_t* out,
+                                            size_t nbytes) {
+  constexpr size_t V = sizeof(uint4);  // 16 bytes
+  const size_t tid = blockIdx.x * blockDim.x + threadIdx.x;
+  const size_t nthreads = size_t(gridDim.x) * blockDim.x;
+  const size_t nvec = nbytes / V;
+
+  // 1-D grid-stride loop over 16-byte chunks
+  for (size_t vec = tid; vec < nvec; vec += nthreads) {
+    uint4 v = reinterpret_cast<const uint4*>(in)[vec];
+    uint8_t* b = reinterpret_cast<uint8_t*>(&v);
+#pragma unroll
+    for (int i = 0; i < int(V); ++i) b[i] = kNibbleLUT[b[i]];
+    reinterpret_cast<uint4*>(out)[vec] = v;
+  }
+}
+
+static bool upload_lut() {
+  std::array<uint8_t, 256> lut{};
+  auto map_nib = [](uint8_t v) -> uint8_t {
+    // 1..7 -> (8 - v); keep 0 and 8..15
+    return (v == 0 || (v & 0x8)) ? v : uint8_t(8 - v);
+  };
+  for (int b = 0; b < 256; ++b) {
+    uint8_t lo = b & 0xF;
+    uint8_t hi = (b >> 4) & 0xF;
+    lut[b] = uint8_t((map_nib(hi) << 4) | map_nib(lo));
+  }
+  cudaError_t e = cudaMemcpyToSymbol(kNibbleLUT, lut.data(), lut.size(),
+                                     /*offset=*/0, cudaMemcpyHostToDevice);
+
+  return (e == cudaSuccess);
+}
+
+bool unified_encode_int4b(cutlass::int4b_t const* in, cutlass::int4b_t* out,
+                          size_t num_int4_elems) {
+  // Build/upload LUT
+  if (!upload_lut()) return false;
+
+  static_assert(sizeof(typename cutlass::int4b_t::Storage) == 1,
+                "int4 storage must be 1 byte");
+  const size_t nbytes = num_int4_elems >> 1;
+
+  auto* in_bytes = reinterpret_cast<uint8_t const*>(in);
+  auto* out_bytes = reinterpret_cast<uint8_t*>(out);
+
+  // kernel launch params
+  constexpr int block = 256;
+  const size_t nvec = nbytes / sizeof(uint4);  // # of 16B vectors
+  int grid = int((nvec + block - 1) / block);
+  if (grid == 0) grid = 1;  // ensure we still cover the tail in the kernel
+
+  unified_encode_int4b_device<<<grid, block>>>(in_bytes, out_bytes, nbytes);
+
+  // launch errors
+  cudaError_t err = cudaGetLastError();
+  if (err != cudaSuccess) {
+    printf("unified_encode_int4b_device launch error: %s (%d)\n",
+           cudaGetErrorString(err), err);
+    return false;
+  }
+
+  // runtime errors
+  err = cudaDeviceSynchronize();
+  if (err != cudaSuccess) {
+    printf("unified_encode_int4b_device runtime error: %s (%d)\n",
+           cudaGetErrorString(err), err);
+    return false;
+  }
+
+  return true;
+}
+
+}  // namespace vllm::cutlass_w4a8_utils
\ No newline at end of file

csrc/quantization/cutlass_w4a8/w4a8_utils.cuh

+#pragma once
+
+#include <cstddef>
+#include "cutlass/numeric_types.h"
+
+namespace vllm::cutlass_w4a8_utils {
+
+bool unified_encode_int4b(cutlass::int4b_t const* in, cutlass::int4b_t* out,
+                          size_t num_int4_elems);
+
+}  // namespace vllm::cutlass_w4a8_utils
\ No newline at end of file

csrc/quantization/w8a8/cutlass/moe/moe_data.cu

@@ -136,15 +136,17 @@ inline void launch_compute_problem_sizes(const torch::Tensor& topk_ids,
 void get_cutlass_moe_mm_problem_sizes_caller(
     const torch::Tensor& topk_ids, torch::Tensor& problem_sizes1,
     torch::Tensor& problem_sizes2, const int64_t num_experts, const int64_t n,
-    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets) {
+    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets,
+    std::optional<bool> force_swap_ab = std::nullopt) {
   auto stream = at::cuda::getCurrentCUDAStream(topk_ids.device().index());
   auto options_int32 =
       torch::TensorOptions().dtype(torch::kInt32).device(topk_ids.device());
   torch::Tensor atomic_buffer = torch::zeros(num_experts, options_int32);
 
   // Swap-AB should be disabled for FP4 path
-  bool may_swap_ab = (!blockscale_offsets.has_value()) &&
-                     (topk_ids.numel() <= SWAP_AB_THRESHOLD);
+  bool may_swap_ab =
+      force_swap_ab.value_or((!blockscale_offsets.has_value()) &&
+                             (topk_ids.numel() <= SWAP_AB_THRESHOLD));
 
   launch_compute_problem_sizes(topk_ids, problem_sizes1, problem_sizes2,
                                atomic_buffer, num_experts, n, k, stream,

csrc/quantization/w8a8/cutlass/scaled_mm_entry.cu

@@ -80,7 +80,8 @@ void get_cutlass_moe_mm_data_caller(
 void get_cutlass_moe_mm_problem_sizes_caller(
     const torch::Tensor& topk_ids, torch::Tensor& problem_sizes1,
     torch::Tensor& problem_sizes2, const int64_t num_experts, const int64_t n,
-    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets);
+    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets,
+    std::optional<bool> force_swap_ab = std::nullopt);
 
 void get_cutlass_pplx_moe_mm_data_caller(torch::Tensor& expert_offsets,
                                          torch::Tensor& problem_sizes1,
@@ -303,14 +304,15 @@ void get_cutlass_moe_mm_data(
 void get_cutlass_moe_mm_problem_sizes(
     const torch::Tensor& topk_ids, torch::Tensor& problem_sizes1,
     torch::Tensor& problem_sizes2, const int64_t num_experts, const int64_t n,
-    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets) {
+    const int64_t k, const std::optional<torch::Tensor>& blockscale_offsets,
+    std::optional<bool> force_swap_ab = std::nullopt) {
   int32_t version_num = get_sm_version_num();
 #if (defined ENABLE_CUTLASS_MOE_SM90 && ENABLE_CUTLASS_MOE_SM90) ||   \
     (defined ENABLE_CUTLASS_MOE_SM100 && ENABLE_CUTLASS_MOE_SM100) || \
     (defined ENABLE_CUTLASS_MOE_SM120 && ENABLE_CUTLASS_MOE_SM120)
   get_cutlass_moe_mm_problem_sizes_caller(topk_ids, problem_sizes1,
                                           problem_sizes2, num_experts, n, k,
-                                          blockscale_offsets);
+                                          blockscale_offsets, force_swap_ab);
   return;
 #endif
   TORCH_CHECK_NOT_IMPLEMENTED(

csrc/torch_bindings.cpp

@@ -350,6 +350,29 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
   ops.def("cutlass_encode_and_reorder_int4b(Tensor B) -> Tensor");
   // conditionally compiled so impl registration is in source file
 
+  // CUTLASS w4a8 grouped GEMM
+  ops.def(
+      "cutlass_w4a8_moe_mm("
+      "   Tensor! out_tensors,"
+      "   Tensor a_tensors,"
+      "   Tensor b_tensors,"
+      "   Tensor a_scales,"
+      "   Tensor b_scales,"
+      "   Tensor b_group_scales,"
+      "   int b_group_size,"
+      "   Tensor expert_offsets,"
+      "   Tensor problem_sizes,"
+      "   Tensor a_strides,"
+      "   Tensor b_strides,"
+      "   Tensor c_strides,"
+      "   Tensor group_scale_strides,"
+      "   str? maybe_schedule"
+      ") -> ()");
+  ops.def(
+      "cutlass_encode_and_reorder_int4b_grouped(Tensor b_tensors) -> (Tensor, "
+      "Tensor)");
+  // conditionally compiled so impl registration is in source file
+
 #endif
 
   // Dequantization for GGML.
@@ -466,7 +489,8 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
       "                                 Tensor! problem_sizes1, "
       "                                 Tensor! problem_sizes2, "
       "                                 int num_experts, int n, int k, "
-      "                                 Tensor? blockscale_offsets) -> ()");
+      "                                 Tensor? blockscale_offsets, "
+      "                                 bool? force_swap_ab) -> ()");
   ops.impl("get_cutlass_moe_mm_problem_sizes", torch::kCUDA,
            &get_cutlass_moe_mm_problem_sizes);
 

tests/kernels/quantization/test_cutlass_w4a8.py

@@ -12,8 +12,11 @@ import torch
 
 from vllm import _custom_ops as ops
 from vllm.model_executor.layers.quantization.utils.quant_utils import (
+    convert_packed_uint4b8_to_signed_int4_inplace,
+    pack_cols,
     pack_rows,
     quantize_weights,
+    unpack_quantized_values_into_int32,
 )
 from vllm.platforms import current_platform
 from vllm.scalar_type import ScalarType, scalar_types
@@ -167,8 +170,7 @@ def create_test_tensors(
 
     # for the practical use case we need per-tok scales for fp8 activations
     w_tok_s = torch.randn((m,), device="cuda", dtype=types.token_scale_type)
-    # weights are already per-group quantized, use placeholder here
-    w_ch_s = torch.ones((n,), device="cuda", dtype=types.channel_scale_type)
+    w_ch_s = torch.randn((n,), device="cuda", dtype=types.channel_scale_type)
 
     return Tensors(
         w_ref=w_ref,
@@ -211,7 +213,7 @@ def mm_test_helper(
     print(output_ref)
 
     torch.testing.assert_close(
-        output, output_ref.to(output.dtype), rtol=1e-3, atol=1e-3
+        output, output_ref.to(output.dtype), rtol=1e-2, atol=1e-2
     )
 
 
@@ -257,7 +259,7 @@ def test_w4a8_cuda_graph():
     )
 
     w_tok_s = torch.randn((m,), device="cuda", dtype=torch.float32)
-    w_ch_s = torch.ones((n,), device="cuda", dtype=torch.float32)
+    w_ch_s = torch.randn((n,), device="cuda", dtype=torch.float32)
 
     # Construct a trivial model with a single layer that calls the kernel
     model = W4A8Layer(
@@ -287,4 +289,38 @@ def test_w4a8_cuda_graph():
     output.zero_()
     g.replay()
 
-    torch.testing.assert_close(output, output_ref, rtol=1e-3, atol=1e-3)
+    torch.testing.assert_close(output, output_ref, rtol=1e-2, atol=1e-2)
+
+
+@pytest.mark.skipif(
+    not IS_SUPPORTED_BY_GPU, reason="CUTLASS W4A8 is not supported on this GPU type."
+)
+@pytest.mark.parametrize("shape", MNK_SHAPES)
+def test_convert_packed_uint4b8_to_signed_int4_inplace(shape):
+    """
+    The W4A16 checkpoints encode the weights as int4b8 packed to int32.
+    The CUTLASS kernels expect signed int4 packed to int32.
+    This tests checks that the runtime int4b8 -> signed int4 conversion
+    matches the offline conversion step exactly.
+    """
+    _, N, K = shape
+    # random weights packed to int32
+    t = torch.randint(
+        low=torch.iinfo(torch.int32).min,
+        high=torch.iinfo(torch.int32).max + 1,
+        size=(N, K // 8),
+        dtype=torch.int32,
+        device="cuda",
+    )
+
+    # compute reference
+    unpacked = unpack_quantized_values_into_int32(
+        t.clone(), scalar_types.uint4b8, packed_dim=1
+    )
+    unpacked = unpacked - 8  # int4b8 -> signed int4
+    ref = pack_cols(unpacked & 0x0F, 4, *unpacked.shape)
+
+    out = convert_packed_uint4b8_to_signed_int4_inplace(t.clone())
+
+    assert torch.equal(ref, out)
+    assert not torch.equal(ref, t)

tests/kernels/quantization/test_cutlass_w4a8_moe.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Tests for the CUTLASS-based W4A8 grouped GEMM kernel and the full MoE layer.
+"""
+
+import random
+from dataclasses import dataclass
+
+import pytest
+import torch
+
+from vllm import _custom_ops as ops
+from vllm.model_executor.layers.quantization.utils.quant_utils import (
+    pack_rows,
+    quantize_weights,
+)
+from vllm.platforms import current_platform
+from vllm.scalar_type import ScalarType, scalar_types
+
+IS_SUPPORTED_BY_GPU = current_platform.get_device_capability()[0] >= 9
+
+
+def to_fp8(tensor: torch.Tensor) -> torch.Tensor:
+    finfo = torch.finfo(torch.float8_e4m3fn)
+    return tensor.clamp(min=finfo.min, max=finfo.max).to(dtype=torch.float8_e4m3fn)
+
+
+def cutlass_quantize(
+    atype: torch.dtype,
+    w: torch.Tensor,
+    wtype: ScalarType,
+    stype: torch.dtype | None,
+    group_size: int | None,
+    zero_points: bool = False,
+):
+    """
+    Quantize weights into W4 and compute reference dequantized weights.
+
+    Encoding/reordering of weights and packing of scales is deferred
+    until after all experts are combined.
+    """
+    assert wtype.is_integer(), "TODO: support floating point weights"
+
+    w_ref, w_q, w_s, w_zp = quantize_weights(
+        w, wtype, group_size=group_size, zero_points=zero_points
+    )
+
+    # Since scales are later cast to fp8, recompute w_ref in atype here.
+    w_ref = (
+        w_q.to(torch.float32)
+        * w_s.to(atype).to(torch.float32).repeat_interleave(group_size, dim=0)
+    ).to(atype)
+
+    # Bit mask prevents sign extension of int4 when packing.
+    w_q = pack_rows(w_q & 0x0F, wtype.size_bits, *w_q.shape)
+    # Make weights row-major (N, K).
+    w_q = w_q.t().contiguous()
+
+    return w_ref, w_q, w_s.to(atype), w_zp
+
+
+def cutlass_preprocess(
+    w_q_experts: list[torch.Tensor], w_s_experts: list[torch.Tensor]
+):
+    """
+    Reorder/encode expert weights and pack scales.
+
+    Returns:
+        w_q_packed: Packed/encoded int4 weights for all experts.
+        w_s_packed: Packed fp8 scales for all experts.
+        packed_layout: Layout/stride metadata for grouped GEMM.
+    """
+    w_s_packed = ops.cutlass_pack_scale_fp8(torch.stack(w_s_experts))
+    w_q_packed, packed_layout = ops.cutlass_encode_and_reorder_int4b_grouped(
+        torch.stack(w_q_experts)
+    )  # expects dim 3
+    return w_q_packed, w_s_packed, packed_layout
+
+
+GROUP_SIZE = 128
+# (num_experts, N, K)
+TEST_SHAPES = [
+    (8, 512, 2048),
+    (8, 2048, 2048),
+    (64, 512, 1024),
+    (64, 2048, 2048),
+    (4, 2048, 768),
+    (8, 768, 2048),
+    (64, 1536, 2048),
+    (128, 8192, 4096),  # test overflow int32
+]
+ALIGNMENT = 16  # torch._scaled_mm alignment for M, needed for reference check
+
+
+@dataclass
+class MoETestSetup:
+    num_experts: int
+    K: int
+    N: int
+    Ms: list[int]
+    M_full: int
+    a: torch.Tensor
+    a_ref: torch.Tensor
+    a_strides: torch.Tensor
+    out: torch.Tensor
+    c_strides: torch.Tensor
+    per_tok_scales: torch.Tensor
+    per_chan_scales: torch.Tensor
+    w_refs: list[torch.Tensor]
+    w_q_packed: torch.Tensor
+    w_s_packed: torch.Tensor
+    problem_sizes: torch.Tensor
+    expert_offsets: torch.Tensor
+    b_strides: torch.Tensor
+    group_scale_strides: torch.Tensor
+
+
+def make_moe_test_setup(
+    num_experts: int,
+    K: int,
+    N: int,
+    *,
+    alignment: int = ALIGNMENT,
+    max_blocks: int = 64,
+    device: str = "cuda",
+    random_zero: bool = False,
+) -> MoETestSetup:
+    """Create a full set of tensors for testing cutlass_w4a8_moe_mm."""
+
+    assert K % GROUP_SIZE == 0
+    # Token counts per expert (multiples of `alignment`).
+    Ms = [alignment * random.randint(1, max_blocks) for _ in range(num_experts)]
+
+    # set random experts to 0 tokens
+    if random_zero and num_experts > 1:
+        num_zero = max(1, num_experts // 8)
+        zero_indices = random.sample(range(num_experts), k=num_zero)
+        for idx in zero_indices:
+            Ms[idx] = 0
+
+    M_full = sum(Ms)
+    assert M_full > 0
+
+    # Activations.
+    a = to_fp8(torch.randn((M_full, K), device=device))
+    a_ref = a.to(torch.float32)
+    a_strides = torch.full((num_experts,), K, dtype=torch.int64, device=device)
+
+    # Output buffer.
+    out = torch.empty((M_full, N), dtype=torch.bfloat16, device=device)
+    c_strides = torch.full((num_experts,), N, dtype=torch.int64, device=device)
+
+    # Channel/token scales.
+    per_tok_scales = torch.randn((M_full, 1), dtype=torch.float32, device=device)
+    per_chan_scales = torch.randn(
+        (num_experts, N, 1), dtype=torch.float32, device=device
+    )
+
+    # Expert weights and scales.
+    wtype = scalar_types.int4
+    atype = stype = torch.float8_e4m3fn
+    w_refs, w_qs, w_ss = [], [], []
+    for _ in range(num_experts):
+        b = to_fp8(torch.randn((K, N), device=device))
+        w_ref, w_q, w_s, _ = cutlass_quantize(
+            atype, b.to(torch.float16), wtype, stype, GROUP_SIZE, zero_points=False
+        )
+        w_refs.append(w_ref)
+        w_qs.append(w_q)
+        w_ss.append(w_s)
+
+    w_q_packed, w_s_packed, packed_layout = cutlass_preprocess(w_qs, w_ss)
+
+    problem_sizes = torch.tensor(
+        [[N, M, K] for M in Ms], dtype=torch.int32, device=device
+    )
+
+    expert_offsets = torch.cat(
+        [
+            torch.tensor([0], dtype=torch.int64),
+            torch.cumsum(torch.tensor(Ms, dtype=torch.int64), dim=0)[:-1],
+        ]
+    ).to(device=device)
+
+    # B strides and group scale strides.
+    b_strides = packed_layout
+    group_scale_strides = torch.zeros(
+        (num_experts, 2), dtype=torch.int64, device=device
+    )
+    group_scale_strides[:, 0] = N
+
+    return MoETestSetup(
+        num_experts=num_experts,
+        K=K,
+        N=N,
+        Ms=Ms,
+        M_full=M_full,
+        a=a,
+        a_ref=a_ref,
+        a_strides=a_strides,
+        out=out,
+        c_strides=c_strides,
+        per_tok_scales=per_tok_scales,
+        per_chan_scales=per_chan_scales,
+        w_refs=w_refs,
+        w_q_packed=w_q_packed,
+        w_s_packed=w_s_packed,
+        problem_sizes=problem_sizes,
+        expert_offsets=expert_offsets,
+        b_strides=b_strides,
+        group_scale_strides=group_scale_strides,
+    )
+
+
+def compute_moe_reference_output(setup: MoETestSetup) -> torch.Tensor:
+    """Compute reference output using torch._scaled_mm per expert."""
+    out_ref = torch.empty_like(setup.out)
+
+    ends = torch.cumsum(torch.tensor(setup.Ms), 0).tolist()
+    starts = setup.expert_offsets.cpu().tolist()
+
+    for i in range(setup.num_experts):
+        start, end = starts[i], ends[i]
+        if start == end:
+            continue
+
+        out_ref_i = torch._scaled_mm(
+            setup.a_ref[start:end].to(torch.float8_e4m3fn),
+            setup.w_refs[i].to(torch.float8_e4m3fn).t().contiguous().t(),
+            setup.per_tok_scales[start:end],  # (M, 1)
+            setup.per_chan_scales[i].reshape(1, -1),  # (1, N)
+            out_dtype=torch.bfloat16,
+            use_fast_accum=True,
+        )
+        out_ref[start:end] = out_ref_i
+
+    return out_ref
+
+
+@pytest.mark.skipif(
+    not IS_SUPPORTED_BY_GPU,
+    reason="W4A8 Grouped GEMM is not supported on this GPU type.",
+)
+@pytest.mark.parametrize("shape", TEST_SHAPES)
+@pytest.mark.parametrize("random_zero", [True, False])
+def test_cutlass_w4a8_moe_mm_end_to_end(shape, random_zero):
+    num_experts, N, K = shape
+    current_platform.seed_everything(42)
+    setup = make_moe_test_setup(
+        num_experts=num_experts, K=K, N=N, max_blocks=64, random_zero=random_zero
+    )
+
+    ops.cutlass_w4a8_moe_mm(
+        setup.out,
+        setup.a,
+        setup.w_q_packed,
+        setup.per_tok_scales,
+        setup.per_chan_scales,
+        setup.w_s_packed,
+        GROUP_SIZE,
+        setup.expert_offsets,
+        setup.problem_sizes,
+        setup.a_strides,
+        setup.b_strides,
+        setup.c_strides,
+        setup.group_scale_strides,
+    )
+    torch.cuda.synchronize()
+
+    out_ref = compute_moe_reference_output(setup)
+    torch.testing.assert_close(setup.out, out_ref, rtol=1e-2, atol=1e-2)
+
+
+class W4A8MoELayer(torch.nn.Module):
+    """
+    Minimal wrapper module to test cuda graphs
+    """
+
+    def __init__(self, setup: MoETestSetup):
+        super().__init__()
+        self.setup = setup
+
+    def forward(self, a: torch.Tensor) -> torch.Tensor:
+        s = self.setup
+        ops.cutlass_w4a8_moe_mm(
+            s.out,
+            a,
+            s.w_q_packed,
+            s.per_tok_scales,
+            s.per_chan_scales,
+            s.w_s_packed,
+            GROUP_SIZE,
+            s.expert_offsets,
+            s.problem_sizes,
+            s.a_strides,
+            s.b_strides,
+            s.c_strides,
+            s.group_scale_strides,
+        )
+        return s.out
+
+
+@pytest.mark.skipif(
+    not IS_SUPPORTED_BY_GPU,
+    reason="W4A8 Grouped GEMM is not supported on this GPU type.",
+)
+def test_cutlass_w4a8_moe_mm_cuda_graph():
+    current_platform.seed_everything(42)
+    # Fixed config for CUDA graph test (single parameter point).
+    num_experts = 8
+    K = 512
+    N = 2048
+
+    setup = make_moe_test_setup(
+        num_experts=num_experts,
+        K=K,
+        N=N,
+        max_blocks=32,
+    )
+
+    # Construct model that calls the grouped GEMM kernel.
+    model = W4A8MoELayer(setup)
+
+    # Build reference output once.
+    out_ref = compute_moe_reference_output(setup)
+
+    # Capture and run the model in a CUDA graph.
+    a_static = setup.a.clone()  # static input tensor for graph replay
+
+    stream = torch.cuda.Stream()
+    with torch.cuda.stream(stream):
+        g = torch.cuda.CUDAGraph()
+        with torch.cuda.graph(g):
+            out_static = model(a_static)
+
+    out_static.zero_()
+    g.replay()
+
+    torch.testing.assert_close(out_static, out_ref, rtol=1e-2, atol=1e-2)

vllm/_custom_ops.py

@@ -695,6 +695,10 @@ if hasattr(torch.ops._C, "gptq_marlin_24_gemm"):
     def cutlass_encode_and_reorder_int4b_fake(b: torch.Tensor) -> torch.Tensor:
         return torch.empty_like(b, memory_format=torch.contiguous_format)
 
+    @register_fake("_C::cutlass_encode_and_reorder_int4b_grouped")
+    def cutlass_encode_and_reorder_int4b_grouped_fake(b: torch.Tensor) -> torch.Tensor:
+        return torch.empty_like(b, memory_format=torch.contiguous_format)
+
 
 if hasattr(torch.ops._C, "allspark_w8a16_gemm"):
 
@@ -1058,6 +1062,7 @@ def get_cutlass_moe_mm_problem_sizes(
     n: int,
     k: int,
     blockscale_offsets: torch.Tensor | None = None,
+    force_swap_ab: bool | None = None,
 ):
     """
     Compute only the per-expert problem sizes needed by the two grouped matrix
@@ -1067,9 +1072,20 @@ def get_cutlass_moe_mm_problem_sizes(
     - problem_sizes1, problem_sizes2: M×N×K sizes of each expert's
                                     multiplication for the two grouped MMs
                                     used in the fused MoE operation.
+    Optional:
+    - force_swap_ab: If set to True or False, explicitly enable or disable the
+                     A/B input swap optimization. If None (default), the swap
+                     is selected automatically based on tensor sizes.
     """
     return torch.ops._C.get_cutlass_moe_mm_problem_sizes(
-        topk_ids, problem_sizes1, problem_sizes2, num_experts, n, k, blockscale_offsets
+        topk_ids,
+        problem_sizes1,
+        problem_sizes2,
+        num_experts,
+        n,
+        k,
+        blockscale_offsets,
+        force_swap_ab,
     )
 
 
@@ -1457,6 +1473,78 @@ def cutlass_encode_and_reorder_int4b(b: torch.Tensor) -> torch.Tensor:
     return torch.ops._C.cutlass_encode_and_reorder_int4b(b)
 
 
+def cutlass_w4a8_moe_mm(
+    out_tensors: torch.Tensor,
+    a_tensors: torch.Tensor,
+    b_tensors: torch.Tensor,
+    a_scales: torch.Tensor,
+    b_scales: torch.Tensor,
+    b_group_scales: torch.Tensor,
+    b_group_size: int,
+    expert_offsets: torch.Tensor,
+    problem_sizes: torch.Tensor,
+    a_strides: torch.Tensor,
+    b_strides: torch.Tensor,
+    c_strides: torch.Tensor,
+    group_scale_strides: torch.Tensor,
+    maybe_schedule: str | None = None,
+):
+    """
+    Executes the CUTLASS-based fused-MoE grouped matrix multiplication for the
+    W4A8 quantization scheme. Uses group-wise quantization (INT4 -> FP8)
+    and both per-channel + per-token scaling in the epilogue.
+
+    Args:
+        out_tensors:
+            Output buffer for all experts (updated in-place).
+        a_tensors:
+            FP8 (E4M3FN) activations for all experts.
+        b_tensors:
+            INT4-packed weight matrix for all experts, packed to INT32
+        a_scales:
+            Per-token FP8 activation scales, applied in the epilogue.
+        b_scales:
+            Per-channel FP8 weight scales for each expert, applied in the epilogue.
+        b_group_scales:
+            FP8 scale values for group-wise INT4 weight blocks.
+        b_group_size:
+            Number of elements grouped under each entry of b_group_scales.
+        expert_offsets:
+            Cumulative token offsets
+        problem_sizes:
+            Per-expert (M, N, K) GEMM sizes used by the grouped GEMM launcher.
+        a/b/c/group_scale_strides:
+            Strides describing the memory layout of the input tensors.
+        maybe_schedule:
+            Optional override to choose a specific kernel or epilogue schedule.
+
+    Returns:
+        out_tensors updated in-place with the dequantized INT4xFP8 grouped GEMM result.
+    """
+    return torch.ops._C.cutlass_w4a8_moe_mm(
+        out_tensors,
+        a_tensors,
+        b_tensors,
+        a_scales,
+        b_scales,
+        b_group_scales,
+        b_group_size,
+        expert_offsets,
+        problem_sizes,
+        a_strides,
+        b_strides,
+        c_strides,
+        group_scale_strides,
+        maybe_schedule,
+    )
+
+
+def cutlass_encode_and_reorder_int4b_grouped(
+    b_tensors: torch.Tensor,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    return torch.ops._C.cutlass_encode_and_reorder_int4b_grouped(b_tensors)
+
+
 if hasattr(torch.ops._C, "permute_cols"):
 
     @register_fake("_C::permute_cols")

vllm/model_executor/layers/fused_moe/__init__.py

@@ -63,8 +63,10 @@ if HAS_TRITON:
     from vllm.model_executor.layers.fused_moe.cutlass_moe import (
         CutlassBatchedExpertsFp8,
         CutlassExpertsFp8,
+        CutlassExpertsW4A8Fp8,
         cutlass_moe_fp4,
         cutlass_moe_fp8,
+        cutlass_moe_w4a8_fp8,
     )
     from vllm.model_executor.layers.fused_moe.deep_gemm_moe import DeepGemmExperts
     from vllm.model_executor.layers.fused_moe.fused_batched_moe import (
@@ -88,8 +90,10 @@ if HAS_TRITON:
         "grouped_topk",
         "cutlass_moe_fp8",
         "cutlass_moe_fp4",
+        "cutlass_moe_w4a8_fp8",
         "CutlassExpertsFp8",
         "CutlassBatchedExpertsFp8",
+        "CutlassExpertsW4A8Fp8",
         "TritonExperts",
         "BatchedTritonExperts",
         "DeepGemmExperts",

vllm/model_executor/layers/fused_moe/config.py

@@ -143,6 +143,7 @@ class FusedMoEQuantDesc:
     scale: Union[torch.Tensor, "PrecisionConfig", None] = None
 
     # Quantization alphas or gscales, used for nvfp4 types.
+    # W4A8 FP8: used for per-channel scales
     # TODO(bnell): put some of these in subclasses
     alpha_or_gscale: torch.Tensor | None = None
 
@@ -442,7 +443,9 @@ class FusedMoEQuantConfig:
         - a1_scale: Optional scale to be used for a1.
         - a2_scale: Optional scale to be used for a2.
         - g1_alphas: Optional global quantization scales for w1 (for nvfp4).
+            per-channel scales for w1 (for W4A8 FP8).
         - g2_alphas: Optional global quantization scales for w2 (for nvfp4).
+            per-channel scales for w2 (for W4A8 FP8).
         - a1_gscale: Optional global quantization scales for a1 (for nvfp4).
         - a2_gscale: Optional global quantization scales for a2 (for nvfp4).
         - w1_bias: Optional biases for w1 (GPT OSS Triton).
@@ -461,6 +464,7 @@ class FusedMoEQuantConfig:
             "mxfp4",
             "mxfp6_e3m2",
             "mxfp6_e2m3",
+            "int4",
         }
 
         if weight_dtype is None:
@@ -671,6 +675,31 @@ def int8_w8a16_moe_quant_config(
     )
 
 
+def int4_w4afp8_moe_quant_config(
+    w1_scale: torch.Tensor,
+    w2_scale: torch.Tensor,
+    g1_alphas: torch.Tensor,
+    g2_alphas: torch.Tensor,
+    per_act_token_quant: bool = False,
+    per_out_ch_quant: bool = False,
+    block_shape: list[int] | None = None,
+) -> FusedMoEQuantConfig:
+    """
+    Construct a quant config for fp8 activations and int4 weights.
+    """
+    return FusedMoEQuantConfig.make(
+        torch.float8_e4m3fn,  # quant dtype for activations
+        w1_scale=w1_scale,
+        w2_scale=w2_scale,
+        g1_alphas=g1_alphas,
+        g2_alphas=g2_alphas,
+        per_act_token_quant=per_act_token_quant,
+        per_out_ch_quant=per_out_ch_quant,
+        block_shape=block_shape,
+        weight_dtype="int4",  # weight dtype for weights
+    )
+
+
 def biased_moe_quant_config(
     w1_bias: torch.Tensor | None,
     w2_bias: torch.Tensor | None,

vllm/model_executor/layers/fused_moe/cutlass_moe.py

@@ -1052,3 +1052,404 @@ def run_cutlass_block_scaled_fused_experts(
     return (
         c2[c_map].view(m, topk, k) * topk_weights.view(m, topk, 1).to(out_dtype)
     ).sum(dim=1)
+
+
+# W4A8
+def run_cutlass_moe_w4a8_fp8(
+    output: torch.Tensor,
+    hidden_states: torch.Tensor,
+    w1: torch.Tensor,
+    w2: torch.Tensor,
+    topk_ids: torch.Tensor,
+    activation_callable: Callable,
+    global_num_experts: int,
+    expert_map: torch.Tensor | None,
+    w1_scale: torch.Tensor | None,
+    w2_scale: torch.Tensor | None,
+    a1q_scale: torch.Tensor | None,
+    a2_scale: torch.Tensor | None,
+    w1_chan_scale: torch.Tensor,
+    w2_chan_scale: torch.Tensor,
+    a_strides1: torch.Tensor,
+    a_strides2: torch.Tensor,
+    b_strides1: torch.Tensor,
+    b_strides2: torch.Tensor,
+    c_strides1: torch.Tensor,
+    c_strides2: torch.Tensor,
+    s_strides1: torch.Tensor,
+    s_strides2: torch.Tensor,
+    workspace13: torch.Tensor,
+    workspace2: torch.Tensor,
+    expert_num_tokens: torch.Tensor | None,
+    out_dtype: torch.dtype,
+    per_act_token: bool,
+    per_out_ch: bool,
+    use_batched_format: bool,
+    topk_weights: torch.Tensor | None,
+    group_size: int,
+):
+    a1q = hidden_states
+    M = a1q.size(0)
+    local_E = w1.size(0)
+    device = a1q.device
+    _, K, N_packed = w2.shape
+    N = N_packed * 8  # logical N, pack 8 int4 into 1 int32
+
+    assert per_act_token, "W4A8 must use per-token scales"
+    assert per_out_ch, "W4A8 must use per-channel scales"
+    assert w1_scale is not None
+    assert w2_scale is not None
+    assert w1_scale.dtype == torch.float8_e4m3fn
+    assert w2_scale.dtype == torch.float8_e4m3fn
+    assert w1.dtype == torch.int32
+    assert w2.dtype == torch.int32
+    assert w1_chan_scale.dtype == torch.float32
+    assert w2_chan_scale.dtype == torch.float32
+    assert w1.size(0) == w2.size(0), "Weights expert number mismatch"
+    assert a1q_scale is not None
+    assert a2_scale is None
+    assert out_dtype in [torch.bfloat16], f"Invalid output dtype: {out_dtype}"
+    if expert_map is not None:
+        assert expert_num_tokens is None
+    assert not use_batched_format, "batched format not supported yet"
+    assert group_size == 128, f"Only group size 128 supported but got {group_size=}"
+
+    assert global_num_experts != -1
+    assert w1.size(2) * 8 == K, (
+        f"w1 hidden size mismatch: got {w1.size(2) * 8}, expected {K=}"
+    )
+
+    # Translate info from expert_map to topk_ids
+    if expert_map is not None:
+        local_topk_ids = torch.where(
+            expert_map[topk_ids] != -1, expert_map[topk_ids], -1
+        )
+    else:
+        local_topk_ids = topk_ids
+
+    topk = local_topk_ids.size(1)
+    a1q_perm = _resize_cache(workspace2.view(dtype=torch.float8_e4m3fn), (M * topk, K))
+    mm1_out = _resize_cache(workspace13, (M * topk, N * 2))
+    act_out = _resize_cache(workspace2, (M * topk, N))
+    # original workspace are based on input hidden_states dtype (bf16)
+    quant_out = _resize_cache(
+        workspace13.view(dtype=torch.float8_e4m3fn), (M * topk, N)
+    )
+    mm2_out = _resize_cache(workspace2, (M * topk, K))
+
+    problem_sizes1 = torch.empty(
+        (global_num_experts, 3), dtype=torch.int32, device=device
+    )
+    problem_sizes2 = torch.empty(
+        (global_num_experts, 3), dtype=torch.int32, device=device
+    )
+
+    num_expert = global_num_experts if expert_map is None else expert_map.size(0)
+    # permuted a1q reuses workspace2
+    a1q, a1q_scale, expert_offsets, inv_perm, _ = moe_permute(
+        a1q,
+        a1q_scale,
+        topk_ids,
+        num_expert,
+        local_E,
+        expert_map,
+        permuted_hidden_states=a1q_perm,
+    )
+    expert_offsets = expert_offsets[:-1]
+
+    # For RS gemm SwapAB is always enabled (swap logical M, N in the problem shape)
+    ops.get_cutlass_moe_mm_problem_sizes(
+        local_topk_ids,
+        problem_sizes1,
+        problem_sizes2,
+        global_num_experts,
+        N,
+        K,
+        force_swap_ab=True,
+    )
+
+    ops.cutlass_w4a8_moe_mm(
+        mm1_out,
+        a1q,
+        w1,
+        a1q_scale,
+        w1_chan_scale,
+        w1_scale,
+        group_size,
+        expert_offsets,
+        problem_sizes1,
+        a_strides1,
+        b_strides1,
+        c_strides1,
+        s_strides1,
+    )
+
+    activation_callable(act_out, mm1_out)
+
+    a2q, a2q_scale = ops.scaled_fp8_quant(
+        act_out, a2_scale, use_per_token_if_dynamic=per_act_token, output=quant_out
+    )
+
+    if expert_map is not None:
+        mm2_out.fill_(0)
+
+    ops.cutlass_w4a8_moe_mm(
+        mm2_out,
+        a2q,
+        w2,
+        a2q_scale,
+        w2_chan_scale,
+        w2_scale,
+        group_size,
+        expert_offsets,
+        problem_sizes2,
+        a_strides2,
+        b_strides2,
+        c_strides2,
+        s_strides2,
+    )
+
+    # for non-chunking mode the output is resized from workspace13
+    # so we need to make sure mm2_out uses workspace2.
+    moe_unpermute(
+        out=output,
+        permuted_hidden_states=mm2_out,
+        topk_weights=topk_weights,
+        inv_permuted_idx=inv_perm,
+    )
+
+
+class CutlassExpertsW4A8Fp8(mk.FusedMoEPermuteExpertsUnpermute):
+    def __init__(
+        self,
+        out_dtype: torch.dtype | None,
+        a_strides1: torch.Tensor,
+        a_strides2: torch.Tensor,
+        b_strides1: torch.Tensor,
+        b_strides2: torch.Tensor,
+        c_strides1: torch.Tensor,
+        c_strides2: torch.Tensor,
+        s_strides1: torch.Tensor,
+        s_strides2: torch.Tensor,
+        quant_config: FusedMoEQuantConfig,
+        group_size: int,
+    ):
+        super().__init__(quant_config)
+        self.out_dtype = out_dtype
+        self.a_strides1 = a_strides1
+        self.a_strides2 = a_strides2
+        self.b_strides1 = b_strides1
+        self.b_strides2 = b_strides2
+        self.c_strides1 = c_strides1
+        self.c_strides2 = c_strides2
+        self.s_strides1 = s_strides1
+        self.s_strides2 = s_strides2
+        self.group_size = group_size
+
+    @property
+    def activation_formats(
+        self,
+    ) -> tuple[mk.FusedMoEActivationFormat, mk.FusedMoEActivationFormat]:
+        return (
+            mk.FusedMoEActivationFormat.Standard,
+            mk.FusedMoEActivationFormat.Standard,
+        )
+
+    def supports_chunking(self) -> bool:
+        return True
+
+    def supports_expert_map(self) -> bool:
+        return True
+
+    def finalize_weight_and_reduce_impl(self) -> mk.TopKWeightAndReduce:
+        # topk weights and reduction are fused in moe_unpermute cuda kernel
+        return TopKWeightAndReduceNoOP()
+
+    def workspace_dtype(self, act_dtype: torch.dtype) -> torch.dtype:
+        return self.out_dtype if self.out_dtype is not None else act_dtype
+
+    def workspace_shapes(
+        self,
+        M: int,
+        N: int,
+        K: int,
+        topk: int,
+        global_num_experts: int,
+        local_num_experts: int,
+        expert_tokens_meta: mk.ExpertTokensMetadata | None,
+    ) -> tuple[tuple[int, ...], tuple[int, ...], tuple[int, ...]]:
+        workspace1 = (M * topk, max(N, K))
+        workspace2 = (M * topk, max(N // 2, K))
+        output = (M, K)
+        return (workspace1, workspace2, output)
+
+    def apply(
+        self,
+        output: torch.Tensor,
+        hidden_states: torch.Tensor,
+        w1: torch.Tensor,
+        w2: torch.Tensor,
+        topk_weights: torch.Tensor,
+        topk_ids: torch.Tensor,
+        activation: str,
+        global_num_experts: int,
+        expert_map: torch.Tensor | None,
+        a1q_scale: torch.Tensor | None,
+        a2_scale: torch.Tensor | None,
+        workspace13: torch.Tensor | None,
+        workspace2: torch.Tensor | None,
+        expert_tokens_meta: mk.ExpertTokensMetadata | None,
+        apply_router_weight_on_input: bool,
+    ):
+        assert self.w1_zp is None, "w1_zp is not supported in CUTLASS MoE"
+        assert self.w2_zp is None, "w2_zp is not supported in CUTLASS MoE"
+
+        expert_num_tokens = None
+        activation_callable = lambda o, i: self.activation(activation, o, i)
+
+        use_batched_format = (
+            self.activation_formats[0] == mk.FusedMoEActivationFormat.BatchedExperts
+        )
+        assert not use_batched_format, "batched format not supported"
+
+        in_dtype = hidden_states.dtype
+
+        run_cutlass_moe_w4a8_fp8(
+            output,
+            hidden_states,
+            w1,
+            w2,
+            topk_ids,
+            activation_callable,
+            global_num_experts,
+            expert_map,
+            self.w1_scale,
+            self.w2_scale,
+            a1q_scale,
+            a2_scale,
+            self.g1_alphas,  # per-channel scales
+            self.g2_alphas,  # per-channel scales
+            self.a_strides1,
+            self.a_strides2,
+            self.b_strides1,
+            self.b_strides2,
+            self.c_strides1,
+            self.c_strides2,
+            self.s_strides1,
+            self.s_strides2,
+            workspace13,
+            workspace2,
+            expert_num_tokens,
+            self.out_dtype if self.out_dtype is not None else in_dtype,
+            self.per_act_token_quant,
+            self.per_out_ch_quant,
+            use_batched_format,
+            topk_weights,
+            self.group_size,
+        )
+
+
+def cutlass_moe_w4a8_fp8(
+    a: torch.Tensor,
+    w1_q: torch.Tensor,
+    w2_q: torch.Tensor,
+    topk_weights: torch.Tensor,
+    topk_ids: torch.Tensor,
+    a_strides1: torch.Tensor,
+    a_strides2: torch.Tensor,
+    b_strides1: torch.Tensor,
+    b_strides2: torch.Tensor,
+    c_strides1: torch.Tensor,
+    c_strides2: torch.Tensor,
+    s_strides1: torch.Tensor,
+    s_strides2: torch.Tensor,
+    quant_config: FusedMoEQuantConfig,
+    activation: str = "silu",
+    expert_map: torch.Tensor | None = None,
+    apply_router_weight_on_input: bool = False,
+    global_num_experts: int = -1,
+    group_size: int = 128,
+) -> torch.Tensor:
+    """
+    This function computes a w4a8-quantized Mixture of Experts (MoE) layer
+    using two sets of quantized weights, w1_q and w2_q, and top-k gating
+    mechanism. The matrix multiplications are implemented with CUTLASS
+    mixed-dtype grouped gemm.
+
+    Parameters:
+    - a (torch.Tensor): The input tensor to the MoE layer.
+        Shape: [M, K]
+    - w1_q (torch.Tensor): The first set of fp8-quantized expert weights.
+        Shape: [num_experts, 2*N, K // packed_factor]
+    - w2_q (torch.Tensor): The second set of fp8-quantized expert weights.
+        Shape: [num_experts, K, N // packed_factor]
+    - topk_weights (torch.Tensor): The weights of each token->expert mapping.
+    - topk_ids (torch.Tensor): The token->expert mappings.
+    - a_strides1 (torch.Tensor): The input strides for the first gemm.
+        Shape: [num_experts]
+    - a_strides2 (torch.Tensor): The input strides for the second gemm.
+        Shape: [num_experts]
+    - b_strides1 (torch.Tensor): The packed layout for the first gemm weights.
+        Shape: [num_experts, 3]
+        dtype: torch.int32
+    - b_strides2 (torch.Tensor): The packed layout for the second gemm weights.
+        Shape: [num_experts, 3]
+        dtype: torch.int32
+    - c_strides1 (torch.Tensor): The output strides for the first gemm.
+        Shape: [num_experts]
+    - c_strides2 (torch.Tensor): The output strides for the second gemm.
+        Shape: [num_experts]
+    - s_strides1 (torch.Tensor): strides for the group-wise scales for the first gemm.
+        Shape: [num_experts, 2]
+        dtype: torch.int64
+    - s_strides2 (torch.Tensor): strides for the group-wise scales for the second gemm.
+        Shape: [num_experts, 2]
+        dtype: torch.int64
+    - per_act_token (Optional[bool]): Whether the scale is per-token or
+                                      per-tensor.
+    - activation (str): The activation function to use.
+    - expert_map (Optional[torch.Tensor]): In the case of Expert parallel,
+        every Rank is responsible for a subset of experts. expert_map is a
+        mapping from global expert-id to local expert-id. When expert_map[i]
+        is -1, it means that this Rank is not responsible for global
+        expert-id i.
+    - apply_router_weight_on_input (bool): When true, the topk weights are
+        applied directly on the inputs. This is only applicable when topk is 1.
+    - global_num_experts (int): The total number of experts.
+    - group_size (int): The number of weights per scale factor
+
+    Returns:
+    - torch.Tensor: The bf16 output tensor after applying the MoE layer.
+    """
+    assert quant_config is not None
+
+    num_experts = global_num_experts if global_num_experts != -1 else w1_q.size(0)
+
+    fn = mk.FusedMoEModularKernel(
+        MoEPrepareAndFinalizeNoEP(),
+        CutlassExpertsW4A8Fp8(
+            out_dtype=a.dtype,
+            a_strides1=a_strides1,
+            a_strides2=a_strides2,
+            b_strides1=b_strides1,
+            b_strides2=b_strides2,
+            c_strides1=c_strides1,
+            c_strides2=c_strides2,
+            s_strides1=s_strides1,
+            s_strides2=s_strides2,
+            quant_config=quant_config,
+            group_size=group_size,
+        ),
+    )
+
+    return fn(
+        a,
+        w1_q,
+        w2_q,
+        topk_weights,
+        topk_ids,
+        activation=activation,
+        global_num_experts=num_experts,
+        expert_map=expert_map,
+        apply_router_weight_on_input=apply_router_weight_on_input,
+    )

vllm/model_executor/layers/fused_moe/modular_kernel.py

@@ -367,7 +367,7 @@ class FusedMoEPrepareAndFinalize(ABC):
 class FusedMoEPermuteExpertsUnpermute(ABC):
     """
     An abstract base class for the [Permute-Experts-Unpermute] step described
-    above.
+        above.
     """
 
     def __init__(

vllm/model_executor/layers/quantization/compressed_tensors/compressed_tensors.py

@@ -256,7 +256,7 @@ class CompressedTensorsConfig(QuantizationConfig):
                     if format is not None
                     else is_activation_quantization_format(quant_format)
                 )
-                # TODO(czhu): w4a8fp8 is in packed-quantized format
+                # w4a8fp8 is in packed-quantized format
                 # but needs input activation quantization
                 input_activations = quant_config.get("input_activations")
                 if act_quant_format or input_activations:

vllm/model_executor/layers/quantization/compressed_tensors/compressed_tensors_moe.py

@@ -33,6 +33,7 @@ from vllm.model_executor.layers.fused_moe.config import (
     FusedMoEQuantConfig,
     fp8_w8a8_moe_quant_config,
     int4_w4a16_moe_quant_config,
+    int4_w4afp8_moe_quant_config,
     int8_w8a8_moe_quant_config,
     int8_w8a16_moe_quant_config,
     nvfp4_moe_quant_config,
@@ -79,7 +80,11 @@ from vllm.model_executor.layers.quantization.utils.marlin_utils_fp4 import (
 from vllm.model_executor.layers.quantization.utils.marlin_utils_fp8 import (
     prepare_moe_fp8_layer_for_marlin,
 )
-from vllm.model_executor.layers.quantization.utils.quant_utils import swizzle_blockscale
+from vllm.model_executor.layers.quantization.utils.quant_utils import (
+    convert_bf16_scales_to_fp8,
+    convert_packed_uint4b8_to_signed_int4_inplace,
+    swizzle_blockscale,
+)
 from vllm.model_executor.layers.quantization.utils.w8a8_utils import (
     all_close_1d,
     normalize_e4m3fn_to_e4m3fnuz,
@@ -204,6 +209,11 @@ class CompressedTensorsMoEMethod(FusedMoEMethodBase):
             return CompressedTensorsW8A8Int8MoEMethod(
                 weight_quant, input_quant, layer.moe_config
             )
+        elif quant_config._is_fp8_w4a8_sm90(weight_quant, input_quant):
+            logger.info_once("Using CompressedTensorsW4A8Fp8MoEMethod")
+            return CompressedTensorsW4A8Fp8MoEMethod(
+                weight_quant, input_quant, layer.moe_config
+            )
         elif quant_config._is_dynamic_token_w4a8_int(weight_quant, input_quant):
             return CompressedTensorsW4A8Int8MoEMethod(
                 weight_quant, input_quant, layer.moe_config
@@ -2428,3 +2438,331 @@ class CompressedTensorsW4A8Int8MoEMethod(CompressedTensorsMoEMethod):
             apply_router_weight_on_input,
             int(_act_kind(activation)),
         )
+
+
+class CompressedTensorsW4A8Fp8MoEMethod(CompressedTensorsMoEMethod):
+    def __init__(
+        self,
+        weight_quant: QuantizationArgs,
+        input_quant: QuantizationArgs,
+        moe: FusedMoEConfig,
+        layer_name: str | None = None,
+    ):
+        super().__init__(moe)
+        self.weight_quant = weight_quant
+        self.input_quant = input_quant
+
+        self.group_size = self.weight_quant.group_size
+        self.num_bits = self.weight_quant.num_bits
+        self.packed_factor = 32 // self.num_bits
+
+        assert self.weight_quant.symmetric, (
+            "Only symmetric quantization is supported for W4A8 MoE"
+        )
+        assert self.weight_quant.actorder != "group"
+        assert self.group_size == 128, "Only group size 128 supported for W4A8 MoE"
+
+        self.disable_expert_map = False
+        self.layer_name = layer_name
+
+        from vllm.model_executor.layers.quantization.input_quant_fp8 import QuantFP8
+        from vllm.model_executor.layers.quantization.utils.quant_utils import (
+            GroupShape,
+        )
+
+        self.quant_fp8 = QuantFP8(static=False, group_shape=GroupShape.PER_TOKEN)
+
+    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.num_experts = num_experts
+        layer.orig_dtype = params_dtype
+        layer.weight_block_size = None
+
+        # requirement for CUTLASS reorder_tensor
+        assert hidden_size % 256 == 0, f"{hidden_size=} must be divisible by 256"
+        assert intermediate_size_per_partition % 256 == 0, (
+            f"{intermediate_size_per_partition=} must be divisible by 256"
+        )
+        # storage type, pack 8xint4 into int32
+        params_dtype = torch.int32
+
+        # WEIGHTS
+        w13_weight_packed = torch.nn.Parameter(
+            torch.empty(
+                num_experts,
+                2 * intermediate_size_per_partition,
+                hidden_size // self.packed_factor,
+                dtype=params_dtype,
+            ),
+            requires_grad=False,
+        )
+        layer.register_parameter("w13_weight_packed", w13_weight_packed)
+        set_weight_attrs(w13_weight_packed, extra_weight_attrs)
+
+        w2_weight_packed = torch.nn.Parameter(
+            torch.empty(
+                num_experts,
+                hidden_size,
+                intermediate_size_per_partition // self.packed_factor,
+                dtype=params_dtype,
+            ),
+            requires_grad=False,
+        )
+        layer.register_parameter("w2_weight_packed", w2_weight_packed)
+        set_weight_attrs(w2_weight_packed, extra_weight_attrs)
+
+        # SCALES
+        # weight_scale refers to the group-wise scales
+        # they are initially loaded as bf16, we will convert to fp8
+        # after loading
+        w13_weight_scale = torch.nn.Parameter(
+            torch.ones(
+                num_experts,
+                2 * intermediate_size_per_partition,
+                hidden_size // self.group_size,
+                dtype=layer.orig_dtype,
+            ),
+            requires_grad=False,
+        )
+        layer.register_parameter("w13_weight_scale", w13_weight_scale)
+
+        w2_weight_scale = torch.nn.Parameter(
+            torch.ones(
+                num_experts,
+                hidden_size,
+                intermediate_size_per_partition // self.group_size,
+                dtype=layer.orig_dtype,
+            ),
+            requires_grad=False,
+        )
+        layer.register_parameter("w2_weight_scale", w2_weight_scale)
+        # Add PER-GROUP quantization for FusedMoE.weight_loader.
+        extra_weight_attrs.update(
+            {"quant_method": FusedMoeWeightScaleSupported.GROUP.value}
+        )
+        set_weight_attrs(w13_weight_scale, extra_weight_attrs)
+        set_weight_attrs(w2_weight_scale, extra_weight_attrs)
+
+        # weight shapes
+        w2_weight_shape = torch.nn.Parameter(
+            torch.empty(num_experts, 2), requires_grad=False
+        )
+        layer.register_parameter("w2_weight_shape", w2_weight_shape)
+        set_weight_attrs(w2_weight_shape, extra_weight_attrs)
+        w13_weight_shape = torch.nn.Parameter(
+            torch.empty(num_experts, 2), requires_grad=False
+        )
+        layer.register_parameter("w13_weight_shape", w13_weight_shape)
+        set_weight_attrs(w13_weight_shape, extra_weight_attrs)
+
+        # don't use input scales
+        layer.w13_input_scale = None
+        layer.w2_input_scale = None
+
+    def process_weights_after_loading(self, layer):
+        device = layer.w13_weight_packed.device
+
+        # STRIDES
+        # A, C
+        self.a_strides1_c_strides2 = torch.full(
+            (layer.local_num_experts,),
+            layer.hidden_size,
+            device=device,
+            dtype=torch.int64,
+        )
+        self.a_strides2 = torch.full(
+            (layer.local_num_experts,),
+            layer.intermediate_size_per_partition,
+            device=device,
+            dtype=torch.int64,
+        )
+        self.c_strides1 = torch.full(
+            (layer.local_num_experts,),
+            2 * layer.intermediate_size_per_partition,
+            device=device,
+            dtype=torch.int64,
+        )
+
+        # S (group-wise scales)
+        # sizeof(StrideS) = 16 bytes, so we need to use 2xint64 to encode it
+        self.s_strides1 = torch.zeros(
+            (layer.local_num_experts, 2), device=device, dtype=torch.int64
+        )
+        self.s_strides1[:, 0] = 2 * layer.intermediate_size_per_partition
+
+        self.s_strides2 = torch.zeros(
+            (layer.local_num_experts, 2), device=device, dtype=torch.int64
+        )
+        self.s_strides2[:, 0] = layer.hidden_size
+
+        # encode and reorder weight tensors, and get the layout to pass to
+        # the grouped gemm kernel. `b_strides1/2` specifies the entire layout
+        convert_packed_uint4b8_to_signed_int4_inplace(layer.w13_weight_packed)
+        w13_weight_shuffled, self.b_strides1 = (
+            ops.cutlass_encode_and_reorder_int4b_grouped(layer.w13_weight_packed)
+        )
+        replace_parameter(layer, "w13_weight_packed", w13_weight_shuffled)
+        convert_packed_uint4b8_to_signed_int4_inplace(layer.w2_weight_packed)
+        w2_weight_shuffled, self.b_strides2 = (
+            ops.cutlass_encode_and_reorder_int4b_grouped(layer.w2_weight_packed)
+        )
+        replace_parameter(layer, "w2_weight_packed", w2_weight_shuffled)
+
+        # convert bf16 scales to (fp8_scales, channel_scales)
+        w13_weight_scale, w13_weight_chan_scale = convert_bf16_scales_to_fp8(
+            self.quant_fp8, layer.w13_weight_scale
+        )
+        w2_weight_scale, w2_weight_chan_scale = convert_bf16_scales_to_fp8(
+            self.quant_fp8, layer.w2_weight_scale
+        )
+
+        # register channel scales
+        layer.register_parameter(
+            "w13_weight_chan_scale",
+            torch.nn.Parameter(w13_weight_chan_scale, requires_grad=False),
+        )
+        layer.register_parameter(
+            "w2_weight_chan_scale",
+            torch.nn.Parameter(w2_weight_chan_scale, requires_grad=False),
+        )
+
+        # The scales are stored as (E, N, K // 128) but the kernel expects
+        # (E, K // 128, N) in row-major format, so we need to permute the last 2 dims
+        # and make it contiguous
+        w13_weight_scale_packed = ops.cutlass_pack_scale_fp8(
+            w13_weight_scale.permute(0, 2, 1).contiguous()
+        )
+        replace_parameter(layer, "w13_weight_scale", w13_weight_scale_packed)
+        w2_weight_scale_packed = ops.cutlass_pack_scale_fp8(
+            w2_weight_scale.permute(0, 2, 1).contiguous()
+        )
+        replace_parameter(layer, "w2_weight_scale", w2_weight_scale_packed)
+
+    def maybe_make_prepare_finalize(
+        self,
+        routing_tables: tuple[torch.Tensor, torch.Tensor, torch.Tensor] | None = None,
+    ) -> mk.FusedMoEPrepareAndFinalize | None:
+        return super().maybe_make_prepare_finalize(routing_tables)
+
+    def get_fused_moe_quant_config(
+        self, layer: torch.nn.Module
+    ) -> FusedMoEQuantConfig | None:
+        # Store quantization scales; both per-group and per-channel
+        # Note we haven't specified the group size here because
+        # the quant config logic assumes group-wise scaling
+        # and channel-wise scaling are exclusive.
+        return int4_w4afp8_moe_quant_config(
+            w1_scale=layer.w13_weight_scale,  # group scale
+            w2_scale=layer.w2_weight_scale,  # group scale
+            g1_alphas=layer.w13_weight_chan_scale,
+            g2_alphas=layer.w2_weight_chan_scale,
+            per_act_token_quant=True,  # always use dynamc per-token
+            per_out_ch_quant=True,  # always use per-channel
+        )
+
+    def select_gemm_impl(
+        self,
+        prepare_finalize: mk.FusedMoEPrepareAndFinalize,
+        layer: torch.nn.Module,
+    ) -> mk.FusedMoEPermuteExpertsUnpermute:
+        assert self.moe_quant_config is not None
+        assert (
+            prepare_finalize.activation_format == FusedMoEActivationFormat.Standard
+        ), "BatchedExperts not supported"
+
+        from vllm.model_executor.layers.fused_moe import CutlassExpertsW4A8Fp8
+
+        experts: FusedMoEPermuteExpertsUnpermute
+
+        logger.debug("CutlassExpertsW4A8Fp8(%s)", self.__class__.__name__)
+        experts = CutlassExpertsW4A8Fp8(
+            out_dtype=self.moe.in_dtype,
+            a_strides1=self.a_strides1_c_strides2,
+            a_strides2=self.a_strides2,
+            b_strides1=self.b_strides1,
+            b_strides2=self.b_strides2,
+            c_strides1=self.c_strides1,
+            c_strides2=self.a_strides1_c_strides2,
+            s_strides1=self.s_strides1,
+            s_strides2=self.s_strides2,
+            quant_config=self.moe_quant_config,
+            group_size=self.group_size,
+        )
+
+        num_dispatchers = prepare_finalize.num_dispatchers()
+        self.disable_expert_map = (
+            num_dispatchers > 1 or not experts.supports_expert_map()
+        )
+
+        return experts
+
+    def apply(
+        self,
+        layer: torch.nn.Module,
+        x: torch.Tensor,
+        router_logits: torch.Tensor,
+        top_k: int,
+        renormalize: bool,
+        use_grouped_topk: bool = False,
+        topk_group: int | None = None,
+        num_expert_group: int | None = None,
+        global_num_experts: int = -1,
+        expert_map: torch.Tensor | None = None,
+        custom_routing_function: Callable | None = None,
+        scoring_func: str = "softmax",
+        routed_scaling_factor: float = 1.0,
+        e_score_correction_bias: torch.Tensor | None = None,
+        apply_router_weight_on_input: bool = False,
+        activation: str = "silu",
+        enable_eplb: bool = False,
+        expert_load_view: torch.Tensor | None = None,
+        logical_to_physical_map: torch.Tensor | None = None,
+        logical_replica_count: torch.Tensor | None = None,
+    ):
+        if enable_eplb:
+            raise NotImplementedError(
+                "EPLB not supported for `CompressedTensorsW4A8Fp8MoEMethod` yet."
+            )
+        assert self.moe_quant_config is not None
+        topk_weights, topk_ids, _ = layer.select_experts(
+            hidden_states=x,
+            router_logits=router_logits,
+        )
+
+        from vllm.model_executor.layers.fused_moe.cutlass_moe import (
+            cutlass_moe_w4a8_fp8,
+        )
+
+        return cutlass_moe_w4a8_fp8(
+            x,
+            layer.w13_weight_packed,
+            layer.w2_weight_packed,
+            topk_weights,
+            topk_ids,
+            quant_config=self.moe_quant_config,
+            activation=activation,
+            global_num_experts=global_num_experts,
+            expert_map=None if self.disable_expert_map else expert_map,
+            a_strides1=self.a_strides1_c_strides2,
+            a_strides2=self.a_strides2,
+            b_strides1=self.b_strides1,
+            b_strides2=self.b_strides2,
+            c_strides1=self.c_strides1,
+            c_strides2=self.a_strides1_c_strides2,
+            s_strides1=self.s_strides1,
+            s_strides2=self.s_strides2,
+            group_size=self.group_size,
+        )
+
+    @property
+    def supports_eplb(self) -> bool:
+        return False

vllm/model_executor/layers/quantization/compressed_tensors/schemes/compressed_tensors_w4a8_fp8.py

@@ -128,14 +128,15 @@ class CompressedTensorsW4A8Fp8(CompressedTensorsScheme):
             ),
         )
 
-        # TODO(czhu): allocate the packed fp8 scales memory here?
-        # the scales will be expanded by 8x via `cutlass_pack_scale_fp8`
+        # After loading, we will transform bf16 -> fp8 ->
+        # expand by 8x via `cutlass_pack_scale_fp8`
+        # and construct per-channel fp32 scales.
         weight_scale_args = {
             "weight_loader": weight_loader,
             "data": torch.empty(
                 output_size_per_partition,
                 scales_and_zp_size,
-                dtype=torch.float8_e4m3fn,
+                dtype=params_dtype,
             ),
         }
 
@@ -152,17 +153,9 @@ class CompressedTensorsW4A8Fp8(CompressedTensorsScheme):
             data=torch.empty(2, dtype=torch.int64), weight_loader=weight_loader
         )
 
-        # per-channel scales
-        weight_chan_scale = ChannelQuantScaleParameter(
-            data=torch.empty((output_size_per_partition, 1), dtype=torch.float32),
-            output_dim=0,
-            weight_loader=weight_loader,
-        )
-
         layer.register_parameter("weight_packed", weight)
         layer.register_parameter("weight_scale", weight_scale)
         layer.register_parameter("weight_shape", weight_shape)
-        layer.register_parameter("weight_chan_scale", weight_chan_scale)
 
         self.kernel = kernel_type(
             mp_linear_kernel_config,