[AMD][MXFP4] Reland "Online MXFP4 quantization 2/N - FP8 to MXFP4 requantization on AMD GPUs" (#28291)

Co-authored-by: Bowen Bao <bowenbao@amd.com>
Co-authored-by: HAI <hixiao@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>

docs_new/docs/advanced_features/quantization.mdx

@@ -883,7 +883,7 @@ Other layers (e.g. projections in the attention layers) have their weights quant
 
 SGLang running on AMD GPUs with hardware FP4 support (CDNA4 architecture, e.g. MI355x) supports the quantization method `--quantization quark_mxfp4`, that will quantize BF16 model weights to MXFP4 at load time, use dynamic MXFP4 quantization for activations and MXFP4 GEMMs instead of BF16 GEMMs.
 
-Example:
+Example (BF16 to MXFP4 requantization):
 
 ```bash
 sglang serve --model-path Qwen/Qwen3-30B-A3B \
@@ -891,6 +891,22 @@ sglang serve --model-path Qwen/Qwen3-30B-A3B \
     --quantization quark_mxfp4
 ```
 
+The option `--quantization quark_mxfp4` also supports converting FP8 dense and MOE models to MXFP4, following this logic:
+
+1. Load an FP8 weight tensor,
+2. Dequantize it to BF16,
+3. Requantize it to MXFP4
+
+progressively during weight loading.
+
+Example (FP8 to MXFP4 requantization):
+
+```bash
+sglang serve --model-path Qwen/Qwen3-30B-A3B-Instruct-2507-FP8 \
+    --tensor-parallel-size 1 \
+    --quantization quark_mxfp4
+```
+
 ### Intel® Neural Compressor online quantization method
 
 SGLang supports quantization methods based on the advanced algorithm [auto-round](https://github.com/intel/auto-round) in [Intel® Neural Compressor](https://github.com/intel/neural-compressor). You can simply specify `--quantization auto-round-int8` to use this feature. It will quantize the model on the fly to target format. More online quantization methods are on the way.

python/sglang/srt/configs/model_config.py

@@ -211,6 +211,9 @@ def get_dsa_index_n_heads(config: PretrainedConfig) -> int:
     return config.index_n_heads
 
 
+REQUANTIZATION_METHODS = ["quark_mxfp4"]
+
+
 def get_num_indexer_layers(config) -> int:
     """Layer count for the global indexer-topk capturer's host buffer.
 
@@ -1242,7 +1245,7 @@ class ModelConfig:
             log_str = f"quant={quant_method}"
 
             # Append interesting fields if they exist
-            for field in ["bits", "quant_algo", "fmt"]:
+            for field in ["bits", "quant_algo", "fmt", "requantization_method"]:
                 if field in quant_cfg:
                     log_str += f", {field}={quant_cfg[field]}"
 
@@ -1441,6 +1444,10 @@ class ModelConfig:
                         f"Using draft model's detected quantization: {quant_method}"
                     )
                     self.quantization = quant_method
+                elif self.quantization in REQUANTIZATION_METHODS:
+                    logger.info_once(
+                        f"Requantizing from quant_method='{quant_method}' to the requested online quantization='{self.quantization}'. Beware that requantization may incur a loss in accuracy, the requantized model should be re-validated/re-evaluated. More details at https://docs.sglang.io/advanced_features/quantization.html#online-quantization."
+                    )
                 else:
                     raise ValueError(
                         "Quantization method specified in the model config "

python/sglang/srt/layers/linear.py

@@ -76,6 +76,7 @@ WEIGHT_LOADER_V2_SUPPORTED = [
     "PetitNvFp4LinearMethod",
     "QuarkInt4Fp8LinearMethod",
     "HummingLinearMethod",
+    "QuarkLinearMethod",
 ]
 
 _is_cpu = is_cpu()

python/sglang/srt/layers/quantization/dequantization.py

@@ -0,0 +1,44 @@
+"""
+Utilities to manage the dequantization of weights.
+"""
+
+import torch
+
+from sglang.srt.layers.quantization.fp8_utils import (
+    block_quant_dequant,
+    inverse_transform_scale_ue8m0,
+)
+from sglang.srt.utils import set_weight_attrs
+
+
+def copy_missing_attrs(old: torch.Tensor, new: torch.Tensor) -> None:
+    """Copies any attrs present in `old` but not in `new` to `new`"""
+    new_attrs = set(dir(new))
+    attrs_to_set = {}
+    for attr in dir(old):
+        if attr not in new_attrs:
+            attrs_to_set[attr] = getattr(old, attr)
+    set_weight_attrs(new, attrs_to_set)
+
+
+def dequantize_fp8(
+    w_q: torch.Tensor,
+    w_s: torch.Tensor,
+    block_size: list[int],
+    format_ue8m0: bool = False,
+) -> torch.Tensor:
+    """
+    Dequantizes `w_q` to bfloat16.
+    """
+    if format_ue8m0:
+        # TODO this is only needed for Blackwell
+        w_s = inverse_transform_scale_ue8m0(w_s, mn=w_q.shape[-2])
+
+    w_dequant = block_quant_dequant(
+        w_q,
+        w_s,
+        block_size=block_size,
+        dtype=torch.bfloat16,
+    )
+
+    return w_dequant

python/sglang/srt/layers/quantization/fp8.py

@@ -461,8 +461,9 @@ class Fp8LinearMethod(LinearMethodBase):
         self.use_aiter_fp8_per_token = envs.SGLANG_USE_AITER_FP8_PER_TOKEN.get()
         self.use_per_token_if_dynamic = False
 
+    @staticmethod
     def validate_block_quant_shapes(
-        self,
+        quant_config,
         input_size: int,
         input_size_per_partition: int,
         output_size: int,
@@ -472,8 +473,8 @@ class Fp8LinearMethod(LinearMethodBase):
     ):
         tp_size = get_parallel().tp_size
         block_n, block_k = (
-            self.quant_config.weight_block_size[0],
+            quant_config.weight_block_size[0],
-            self.quant_config.weight_block_size[1],
+            quant_config.weight_block_size[1],
         )
 
         if skip_block_quant_check:
@@ -501,28 +502,36 @@ class Fp8LinearMethod(LinearMethodBase):
                             f"weight quantization block_n = {block_n}."
                         )
 
-    def create_weights(
+    @staticmethod
-        self,
+    def create_fp8_weight_(
         layer: torch.nn.Module,
+        block_quant: bool,
+        quant_config,
+        use_mxfp8: bool,
+        output_size_per_partition: int,
         input_size_per_partition: int,
         output_partition_sizes: List[int],
         input_size: int,
         output_size: int,
         params_dtype: torch.dtype,
+        weight_loader,
+        is_checkpoint_fp8_serialized: bool,
         skip_block_quant_check: bool = False,
         **extra_weight_attrs,
     ):
+        """
+        Registers weights into `layer`. This static method can be reused by other quantization methods that require loading FP8 checkpoints first (e.g. requantization to other formats as MXFP4).
+        """
         # Copy the layer attributes
-        output_size_per_partition = sum(output_partition_sizes)
         layer.logical_widths = output_partition_sizes
         layer.input_size_per_partition = input_size_per_partition
         layer.output_size_per_partition = output_size_per_partition
         layer.orig_dtype = params_dtype
-        weight_loader = extra_weight_attrs.get("weight_loader")
 
-        if self.block_quant:
+        if block_quant:
-            block_n, block_k = self.quant_config.weight_block_size
+            block_n, block_k = quant_config.weight_block_size
-            self.validate_block_quant_shapes(
+            Fp8LinearMethod.validate_block_quant_shapes(
+                quant_config,
                 input_size,
                 input_size_per_partition,
                 output_size,
@@ -530,10 +539,12 @@ class Fp8LinearMethod(LinearMethodBase):
                 output_partition_sizes,
                 skip_block_quant_check,
             )
+        else:
+            block_n, block_k = None, None
 
         # Create the weight
         weight_dtype = (
-            torch.float8_e4m3fn if self.is_checkpoint_fp8_serialized else params_dtype
+            torch.float8_e4m3fn if is_checkpoint_fp8_serialized else params_dtype
         )
         weight = ModelWeightParameter(
             data=torch.empty(
@@ -545,20 +556,14 @@ class Fp8LinearMethod(LinearMethodBase):
         )
         layer.register_parameter("weight", weight)
 
-        # If checkpoint is serialized fp8, load them.
+        if is_checkpoint_fp8_serialized:
-        # Otherwise, wait until process_weights_after_loading.
+            if block_quant:
-        if self.is_checkpoint_fp8_serialized:
+                if hasattr(quant_config, "activation_scheme"):
-            # WEIGHT SCALE
+                    assert quant_config.activation_scheme == "dynamic"
-            if self.block_quant:
+                elif hasattr(quant_config, "linear_activation_scheme"):
-                if hasattr(self.quant_config, "activation_scheme"):
+                    assert quant_config.linear_activation_scheme == "dynamic"
-                    assert self.quant_config.activation_scheme == "dynamic"
+
-                elif hasattr(self.quant_config, "linear_activation_scheme"):
+                scale_dtype = torch.uint8 if use_mxfp8 else torch.float32
-                    assert self.quant_config.linear_activation_scheme == "dynamic"
-                if self.use_mxfp8 and not self.is_checkpoint_fp8_serialized:
-                    raise ValueError(
-                        "MXFP8 requires fp8-serialized checkpoint for linear layers."
-                    )
-                scale_dtype = torch.uint8 if self.use_mxfp8 else torch.float32
                 scale_init = torch.zeros if scale_dtype == torch.uint8 else torch.empty
                 scale = BlockQuantScaleParameter(
                     data=scale_init(
@@ -570,7 +575,7 @@ class Fp8LinearMethod(LinearMethodBase):
                     output_dim=0,
                     weight_loader=weight_loader,
                 )
-                scale.format_ue8m0 = self.use_mxfp8
+                scale.format_ue8m0 = use_mxfp8
                 if scale_dtype != torch.uint8:
                     scale[:] = torch.finfo(torch.float32).min
                 layer.register_parameter("weight_scale_inv", scale)
@@ -584,11 +589,11 @@ class Fp8LinearMethod(LinearMethodBase):
 
             # INPUT ACTIVATION SCALE
             if (
-                hasattr(self.quant_config, "activation_scheme")
+                hasattr(quant_config, "activation_scheme")
-                and self.quant_config.activation_scheme == "static"
+                and quant_config.activation_scheme == "static"
             ) or (
-                hasattr(self.quant_config, "linear_activation_scheme")
+                hasattr(quant_config, "linear_activation_scheme")
-                and self.quant_config.linear_activation_scheme == "static"
+                and quant_config.linear_activation_scheme == "static"
             ):
                 scale = PerTensorScaleParameter(
                     data=torch.empty(len(output_partition_sizes), dtype=torch.float32),
@@ -599,6 +604,37 @@ class Fp8LinearMethod(LinearMethodBase):
                 layer.register_parameter("input_scale", scale)
             else:
                 layer.register_parameter("input_scale", None)
+        elif use_mxfp8:
+            raise ValueError(
+                "MXFP8 requires fp8-serialized checkpoint for linear layers."
+            )
+
+    def create_weights(
+        self,
+        layer: torch.nn.Module,
+        input_size_per_partition: int,
+        output_partition_sizes: List[int],
+        input_size: int,
+        output_size: int,
+        params_dtype: torch.dtype,
+        skip_block_quant_check: bool = False,
+        **extra_weight_attrs,
+    ):
+        Fp8LinearMethod.create_fp8_weight_(
+            layer,
+            block_quant=self.block_quant,
+            quant_config=self.quant_config,
+            use_mxfp8=self.use_mxfp8,
+            output_size_per_partition=sum(output_partition_sizes),
+            input_size_per_partition=input_size_per_partition,
+            output_partition_sizes=output_partition_sizes,
+            weight_loader=extra_weight_attrs.get("weight_loader"),
+            skip_block_quant_check=skip_block_quant_check,
+            input_size=input_size,
+            output_size=output_size,
+            is_checkpoint_fp8_serialized=self.is_checkpoint_fp8_serialized,
+            params_dtype=params_dtype,
+        )
 
     def process_weights_after_loading_block_quant(self, layer: Module) -> None:
         if self.convert_mxfp8_to_block:
@@ -1044,22 +1080,30 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             )
         return False
 
-    def create_weights(
+    @staticmethod
-        self,
+    def create_fp8_moe_weight_(
         layer: Module,
         num_experts: int,
         hidden_size: int,
         intermediate_size_per_partition: int,
+        block_quant: bool,
+        quant_config,
+        use_mxfp8: bool,
+        is_checkpoint_fp8_serialized: bool,
+        is_fp4_expert: bool,
         params_dtype: torch.dtype,
         with_bias: bool = False,
         fp4_scale_dtype: Optional[torch.dtype] = None,
         **extra_weight_attrs,
     ):
-        self.with_bias = with_bias
+        """
+        Registers weights into `layer`. This static method can be reused by other quantization methods that require loading FP8 checkpoints first (e.g. requantization to other formats as MXFP4).
+        """
         from sglang.srt.layers.moe.fused_moe_triton import FusedMoeWeightScaleSupported
 
-        if self.quant_config.is_checkpoint_fp8_serialized:
+        if is_checkpoint_fp8_serialized:
             params_dtype = torch.uint32 if _use_hip_int4 else torch.float8_e4m3fn
+
         tp_size = get_parallel().tp_size
 
         w13_up_dim, w2_up_dim, weight_padded = get_moe_weight_sizes(
@@ -1069,10 +1113,10 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             is_packed=False,
         )
 
-        if self.block_quant:
+        if block_quant:
             block_n, block_k = (
-                self.quant_config.weight_block_size[0],
+                quant_config.weight_block_size[0],
-                self.quant_config.weight_block_size[1],
+                quant_config.weight_block_size[1],
             )
 
             padding_size = get_moe_padding_size(_use_aiter)
@@ -1095,7 +1139,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
                         )
 
         # WEIGHTS
-        if self.is_fp4_expert:
+        if is_fp4_expert:
             w13_weight = torch.nn.Parameter(
                 torch.empty(
                     num_experts,
@@ -1165,7 +1209,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
         set_weight_attrs(w2_weight, extra_weight_attrs)
 
         # BIAS (optional, e.g. GPT-OSS)
-        if self.with_bias:
+        if with_bias:
             w13_up_dim = (
                 2 * intermediate_size_per_partition
                 if layer.moe_runner_config.is_gated
@@ -1186,7 +1230,7 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             set_weight_attrs(w2_weight_bias, extra_weight_attrs)
 
         # WEIGHT_SCALES
-        if self.is_fp4_expert:
+        if is_fp4_expert:
             fp4_block_k = 32
             if fp4_scale_dtype is None:
                 fp4_scale_dtype = torch.float8_e8m0fnu if _use_aiter else torch.float32
@@ -1210,8 +1254,8 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             )
             layer.register_parameter("w13_weight_scale_inv", w13_weight_scale)
             layer.register_parameter("w2_weight_scale_inv", w2_weight_scale)
-        elif self.block_quant:
+        elif block_quant:
-            scale_dtype = torch.uint8 if self.use_mxfp8 else torch.float32
+            scale_dtype = torch.uint8 if use_mxfp8 else torch.float32
             scale_init = torch.zeros if scale_dtype == torch.uint8 else torch.ones
             w13_weight_scale = torch.nn.Parameter(
                 scale_init(
@@ -1232,13 +1276,12 @@ class Fp8MoEMethod(FusedMoEMethodBase):
                 requires_grad=False,
             )
             # w13_weight and w2_weight are always requanted together
-            w13_weight_scale.format_ue8m0 = self.use_mxfp8
+            w13_weight_scale.format_ue8m0 = use_mxfp8
-            w2_weight_scale.format_ue8m0 = self.use_mxfp8
+            w2_weight_scale.format_ue8m0 = use_mxfp8
             layer.register_parameter("w13_weight_scale_inv", w13_weight_scale)
             layer.register_parameter("w2_weight_scale_inv", w2_weight_scale)
-            assert self.quant_config.activation_scheme == "dynamic"
+
-            if get_moe_runner_backend().is_cutlass():
+            assert quant_config.activation_scheme == "dynamic"
-                self._ensure_cutlass_buffers_initialized(layer)
 
         else:
             # Allocate 2 scales for w1 and w3 respectively.
@@ -1273,13 +1316,14 @@ class Fp8MoEMethod(FusedMoEMethodBase):
         # to ensure the weight scales are loaded in properly
         extra_weight_attrs.update(
             {"quant_method": FusedMoeWeightScaleSupported.BLOCK.value}
-            if self.block_quant
+            if block_quant
             else {"quant_method": FusedMoeWeightScaleSupported.TENSOR.value}
         )
+
         # If loading fp8 checkpoint, pass the weight loaders.
         # If loading an fp16 checkpoint, do not (we will quantize in
         #   process_weights_after_loading()
-        if self.quant_config.is_checkpoint_fp8_serialized:
+        if quant_config.is_checkpoint_fp8_serialized:
             set_weight_attrs(w13_weight_scale, extra_weight_attrs)
             set_weight_attrs(w2_weight_scale, extra_weight_attrs)
 
@@ -1291,8 +1335,8 @@ class Fp8MoEMethod(FusedMoEMethodBase):
                 set_weight_attrs(w2_weight_scale1, extra_weight_attrs)
 
         # INPUT_SCALES
-        if self.quant_config.activation_scheme == "static":
+        if quant_config.activation_scheme == "static":
-            if not self.quant_config.is_checkpoint_fp8_serialized:
+            if not quant_config.is_checkpoint_fp8_serialized:
                 raise ValueError(
                     "Found static activation scheme for checkpoint that "
                     "was not serialized fp8."
@@ -1314,6 +1358,38 @@ class Fp8MoEMethod(FusedMoEMethodBase):
             layer.w13_input_scale = None
             layer.w2_input_scale = None
 
+    def create_weights(
+        self,
+        layer: Module,
+        num_experts: int,
+        hidden_size: int,
+        intermediate_size_per_partition: int,
+        params_dtype: torch.dtype,
+        with_bias: bool = False,
+        **extra_weight_attrs,
+    ):
+        Fp8MoEMethod.create_fp8_moe_weight_(
+            layer=layer,
+            num_experts=num_experts,
+            hidden_size=hidden_size,
+            intermediate_size_per_partition=intermediate_size_per_partition,
+            block_quant=self.block_quant,
+            quant_config=self.quant_config,
+            use_mxfp8=self.use_mxfp8,
+            is_checkpoint_fp8_serialized=self.quant_config.is_checkpoint_fp8_serialized,
+            is_fp4_expert=self.is_fp4_expert,
+            params_dtype=params_dtype,
+            with_bias=with_bias,
+            **extra_weight_attrs,
+        )
+
+        if (
+            not self.is_fp4_expert
+            and self.block_quant
+            and get_moe_runner_backend().is_cutlass()
+        ):
+            self._ensure_cutlass_buffers_initialized(layer)
+
     def process_weights_after_loading_block_quant(self, layer: Module) -> None:
         # AMD FP4 experts: use aiter's native MXFP4 MoE path
         if _use_aiter and self.is_fp4_expert:

python/sglang/srt/layers/quantization/fp8_utils.py

@@ -1378,6 +1378,8 @@ def block_quant_dequant(
     block_n, block_k = block_size[0], block_size[1]
     *_, n, k = x_q_block.shape
 
+    # NOTE: This is very memory inefficient, results in *16384 memory requirement for scales
+    # with block_size = [128, 128].
     # ... n_scale k_scale -> ... (n_scale block_n) (k_scale block_k)
     x_scale_repeat = x_s.repeat_interleave(block_n, dim=-2).repeat_interleave(
         block_k, dim=-1

python/sglang/srt/layers/quantization/online_quantization.py

@@ -0,0 +1,23 @@
+# Adapted from https://github.com/vllm-project/vllm/pull/31914
+import torch
+from torch.utils._python_dispatch import TorchDispatchMode
+
+
+class CopyNumelCounter(TorchDispatchMode):
+    """
+    Tracks total number of elements modified with `copy_`. Useful for keeping
+    track of weight loading where underlying weights can be arbitrarily
+    transformed (such as with `narrow`) before calling copy.
+    """
+
+    def __init__(self):
+        super().__init__()
+        self.copied_numel = 0
+
+    def __torch_dispatch__(self, func, types, args=(), kwargs=None):
+        if kwargs is None:
+            kwargs = {}
+        out = func(*args, **kwargs)
+        if func == torch.ops.aten.copy_.default:
+            self.copied_numel += args[0].numel()
+        return out

python/sglang/srt/layers/quantization/quark/quark.py

@@ -14,6 +14,7 @@ from sglang.srt.layers.quantization.base_config import (  # noqa: E501
     QuantizationConfig,
     QuantizeMethodBase,
 )
+from sglang.srt.layers.quantization.fp8 import Fp8Config, Fp8LinearMethod
 from sglang.srt.layers.quantization.kv_cache import BaseKVCacheMethod
 from sglang.srt.layers.quantization.quark.schemes import (
     QuarkLinearScheme,
@@ -55,13 +56,14 @@ class QuarkConfig(QuantizationConfig):
 
     def __init__(
         self,
-        quant_config: Optional[dict[str, Any]] = None,
+        quant_config: dict[str, Any] | None = None,
         hf_config: "PretrainedConfig | None" = None,
         kv_cache_group: Optional[list[str]] = None,
         kv_cache_config: Optional[dict[str, Any]] = None,
         pack_method: str = "reorder",
         is_prequantized: bool = False,
         online_scheme: Optional[str] = None,
+        dequantization_config: Optional[QuantizationConfig] = None,
     ):
         super().__init__()
         if kv_cache_group is None:
@@ -79,23 +81,39 @@ class QuarkConfig(QuantizationConfig):
         if quant_config is None:
             raise ValueError("Either quant_config or online_scheme must be provided")
 
+        self.online_scheme = online_scheme
         self.quant_config = quant_config
         self.kv_cache_group = kv_cache_group
         self.kv_cache_config = kv_cache_config
         self.pack_method = pack_method
         self.exclude_layers = cast(list[str], self.quant_config.get("exclude", []))
         self.is_prequantized = is_prequantized
-
+        self.dequantization_config = dequantization_config
         self.packed_modules_mapping = self.quant_config["packed_modules_mapping"]
-        self._quantized_layers = set()
+        self._online_quantized_layers = set()
 
-    @property
+        if isinstance(self.dequantization_config, Fp8Config):
-    def quantized_layers(self) -> tuple[list[str], int]:
+            self.weight_block_size = self.dequantization_config.weight_block_size
-        # Extract unique layer types (last part after ".")
+
-        layer_types = sorted(
+    def log_online_quantization(self) -> None:
-            set(name.split(".")[-1] for name in self._quantized_layers)
+        """
+        Log which layers are using online quantization, as well as a count for each layer type.
+        """
+        # Count layers per type (last two parts after ".")
+        type_counts: dict[str, int] = {}
+        for name in self._online_quantized_layers:
+            parts = name.split(".")
+            layer_type = ".".join(parts[-2:]) if len(parts) >= 2 else parts[-1]
+            type_counts[layer_type] = type_counts.get(layer_type, 0) + 1
+
+        type_counts = dict(sorted(type_counts.items()))
+        count = len(self._online_quantized_layers)
+
+        type_summary = ", ".join(f"{t}: {c}" for t, c in type_counts.items())
+        logger.info_once(
+            f"Online {self.online_scheme} quantization: "
+            f"quantized {count} layers in total ({type_summary})."
         )
-        return layer_types, len(self._quantized_layers)
 
     def get_linear_method(self) -> "QuarkLinearMethod":
         return QuarkLinearMethod(self)
@@ -124,13 +142,17 @@ class QuarkConfig(QuantizationConfig):
         self, layer: torch.nn.Module, prefix: str
     ) -> Optional["QuantizeMethodBase"]:
         # Check if the layer is skipped for quantization.
-
         if should_ignore_layer(
             prefix,
             ignore=self.exclude_layers,
             fused_mapping=self.packed_modules_mapping,
         ):
             if isinstance(layer, LinearBase):
+                if self.dequantization_config is not None:
+                    # In case of online requantization, "exclude" means keeping the original precision.
+                    # NOTE: Only FP8 supported for now.
+                    return Fp8LinearMethod(quant_config=self.dequantization_config)
+                else:
                     return UnquantizedLinearMethod()
             elif isinstance(layer, RadixAttention):
                 return QuarkKVCacheMethod(self)
@@ -139,17 +161,17 @@ class QuarkConfig(QuantizationConfig):
         if isinstance(layer, LinearBase):
             scheme = self.get_linear_scheme(layer=layer, layer_name=prefix)
             layer.scheme = scheme
-            self._quantized_layers.add(prefix)
+            self._online_quantized_layers.add(prefix)
             return QuarkLinearMethod(self)
 
         if isinstance(layer, RadixAttention):
-            self._quantized_layers.add(prefix)
+            self._online_quantized_layers.add(prefix)
             return QuarkKVCacheMethod(self)
 
         from sglang.srt.layers.moe.fused_moe_triton.layer import FusedMoE
 
         if isinstance(layer, FusedMoE):
-            self._quantized_layers.add(prefix)
+            self._online_quantized_layers.add(prefix)
             layer.scheme = self.get_moe_scheme(layer, prefix)
             return QuarkFusedMoEMethod(self)
 
@@ -157,6 +179,33 @@ class QuarkConfig(QuantizationConfig):
 
     @classmethod
     def from_config(cls, config: dict[str, Any]) -> "QuarkConfig":
+        if config["quant_method"] != "quark":
+            assert "requantization_method" in config
+
+            if (
+                config["quant_method"] == "fp8"
+                and config["requantization_method"] == "quark_mxfp4"
+                and config["activation_scheme"] == "dynamic"
+            ):
+                hf_config = config["hf_config"]
+                quant_config = QuarkConfig._create_online_mxfp4_config(
+                    model_type=hf_config.model_type
+                )
+                dequantization_config = Fp8Config.from_config(config)
+                quark_config = cls(
+                    quant_config=quant_config,
+                    hf_config=hf_config,
+                    is_prequantized=False,
+                    dequantization_config=dequantization_config,
+                    online_scheme=config["requantization_method"],
+                )
+            else:
+                raise NotImplementedError(
+                    f"Requantization into {config['requantization_method']} is not supported, from the original quant_method={config['quant_method']} and activation_scheme={config['activation_scheme']}. "
+                )
+
+            return quark_config
+
         export_config = config.get("export")
         if export_config is None:
             raise ValueError(
@@ -241,7 +290,17 @@ class QuarkConfig(QuantizationConfig):
             "re:.*embed_tokens",
         ]
 
-        if model_type == "qwen3_5_moe":
+        # Exclusion for accuracy adapted from
+        # https://huggingface.co/amd/DeepSeek-V3.2-mxfp4/blob/main/config.json
+        if model_type in ["deepseek_v3", "deepseek_v32"]:
+            exclude.extend(
+                [
+                    "re:.*model.layers.61.*",
+                    "re:.*self_attn.*",
+                    "re:.*mlp.gate$",
+                ]
+            )
+        elif model_type == "qwen3_5_moe":
             # Exclusion for accuracy adapted from
             # https://huggingface.co/amd/Qwen3.5-397B-A17B-MXFP4/blob/main/config.json
             exclude.extend(
@@ -470,6 +529,7 @@ class QuarkConfig(QuantizationConfig):
                 weight_config,
                 input_config,
                 is_checkpoint_mxfp4_serialized=self.is_prequantized,
+                dequantization_config=self.dequantization_config,
             )
         if self._is_fp8_w8a8(weight_config, input_config):
             is_fp8_w8a8_supported = self._check_scheme_supported(
@@ -520,6 +580,7 @@ class QuarkConfig(QuantizationConfig):
                 weight_config,
                 input_config,
                 is_checkpoint_mxfp4_serialized=self.is_prequantized,
+                dequantization_config=self.dequantization_config,
             )
         elif self._is_mx_w4a8(weight_config, input_config):
             logger.info_once("Using Quark MXFP4-W/FP8-A MoE scheme")
@@ -569,10 +630,14 @@ class QuarkLinearMethod(LinearMethodBase):
 
     def __init__(self, quantization_config: QuarkConfig):
         self.quantization_config = quantization_config
+        self.quant_config = quantization_config
 
     def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
         layer.scheme.process_weights_after_loading(layer)
 
+        if self.quantization_config.online_scheme is not None:
+            self.quantization_config.log_online_quantization()
+
     def create_weights(
         self,
         layer: torch.nn.Module,
@@ -625,6 +690,9 @@ class QuarkFusedMoEMethod(FusedMoEMethodBase):
     def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
         layer.scheme.process_weights_after_loading(layer)
 
+        if self.quantization_config.online_scheme is not None:
+            self.quantization_config.log_online_quantization()
+
     def create_weights(
         self,
         layer: torch.nn.Module,

python/sglang/srt/layers/quantization/quark/schemes/quark_w4a4_mxfp4.py

@@ -1,11 +1,19 @@
 # SPDX-License-Identifier: Apache-2.0
 
 import logging
+import threading
 from typing import Any, Callable, Optional
 
 import torch
 
 from sglang.srt.layers.parameter import GroupQuantScaleParameter, PackedvLLMParameter
+from sglang.srt.layers.quantization import QuantizationConfig
+from sglang.srt.layers.quantization.dequantization import (
+    copy_missing_attrs,
+    dequantize_fp8,
+)
+from sglang.srt.layers.quantization.fp8 import Fp8Config, Fp8LinearMethod
+from sglang.srt.layers.quantization.online_quantization import CopyNumelCounter
 from sglang.srt.layers.quantization.quark.schemes import QuarkLinearScheme
 from sglang.srt.utils import is_hip
 from sglang.srt.utils.common import direct_register_custom_op, mxfp_supported
@@ -162,12 +170,14 @@ class QuarkW4A4MXFP4(QuarkLinearScheme):
         weight_quant_spec: dict[str, Any],
         input_quant_spec: dict[str, Any],
         is_checkpoint_mxfp4_serialized: bool = True,
+        dequantization_config: QuantizationConfig | None = None,
     ):
         self.out_dtype = torch.get_default_dtype()
         self.qscheme = "per_group"
         self.weight_quant_spec = weight_quant_spec
         self.input_quant_spec = input_quant_spec
         self.is_checkpoint_mxfp4_serialized = is_checkpoint_mxfp4_serialized
+        self.dequantization_config = dequantization_config
 
         if not self.is_checkpoint_mxfp4_serialized:
             if not mxfp_supported():
@@ -176,7 +186,7 @@ class QuarkW4A4MXFP4(QuarkLinearScheme):
                     "FP4 hardware support (gfx95x, e.g. MI355x)."
                 )
             logger.info_once(
-                "Using online MXFP4 quantization from a higher precision checkpoint. Beware that this optimization may degrade prediction quality - please validate your model accuracy. More details at https://docs.sglang.io/advanced_features/quantization.html#online-quantization."
+                "Using online MXFP4 quantization in dense linear layers from a higher precision checkpoint. Beware that this optimization may degrade prediction quality - please validate your model accuracy. More details at https://docs.sglang.io/advanced_features/quantization.html#online-quantization."
             )
 
     @classmethod
@@ -204,9 +214,67 @@ class QuarkW4A4MXFP4(QuarkLinearScheme):
 
         layer.logical_widths = output_partition_sizes
 
+        # If dequantization_config is provided, we need to create FP8 weights first
+        # for dequantization from FP8 checkpoint to MXFP4
+        if self.dequantization_config is not None:
+            if not isinstance(self.dequantization_config, Fp8Config):
+                raise NotImplementedError(
+                    f"Requantization in QuarkW4A4MXFP4 from {self.dequantization_config.__class__.__name__} is not supported, only Fp8Config is supported."
+                )
+            # Create FP8 weights for re-quantization from FP8 checkpoint
+            # Extract necessary parameters from dequantization_config
+            self.weight_block_size = self.dequantization_config.weight_block_size
+
+            if self.dequantization_config.use_mxfp8:
+                raise NotImplementedError(
+                    "use_mxfp8=True is not supported in Quark MXFP4 requantization."
+                )
+
+            block_quant = self.weight_block_size is not None
+
+            if not block_quant:
+                raise NotImplementedError(
+                    "Only block_quant=True is supported in Quark MXFP4 requantization, got block_quant=False."
+                )
+
+            layer._fp8_weight_loaded_numel = 0
+            layer._load_device = torch.get_default_device()
+            layer._fp8_weight_loading_lock = threading.Lock()
+            layer._fp8_weight_materialized = False
+
+            # Wrap the weight loader to handle FP8->MXFP4 conversion
+            fp8_to_mxfp4_weight_loader = self.get_online_fp8_to_mxfp4_weight_loader(
+                layer, weight_loader
+            )
+
+            # Create FP8 MoE weight parameters on meta device to avoid device memory overhead during weight loading, as the resulting model uses MXFP4 using less device memory.
+            # The weight loader handles progressive FP8 weight materialization on device.
+            with torch.device("meta"):
+                Fp8LinearMethod.create_fp8_weight_(
+                    layer=layer,
+                    block_quant=block_quant,
+                    quant_config=self.dequantization_config,
+                    use_mxfp8=False,
+                    output_size_per_partition=output_size_per_partition,
+                    input_size_per_partition=input_size_per_partition,
+                    output_partition_sizes=output_partition_sizes,
+                    weight_loader=fp8_to_mxfp4_weight_loader,
+                    is_checkpoint_fp8_serialized=True,
+                    params_dtype=params_dtype,
+                    skip_block_quant_check=False,
+                    input_size=kwargs.get("input_size", input_size_per_partition),
+                    output_size=kwargs.get("output_size", output_size_per_partition),
+                )
+
+            # NOTE: ideally, weight_loader should be refactored to be aware of `param_name`.
+            layer.weight._param_name = "weight"
+            layer.weight_scale_inv._param_name = "weight_scale_inv"
+        else:
             original_weight_loader = weight_loader
             if not self.is_checkpoint_mxfp4_serialized:
-            weight_loader = self.get_online_mxfp4_weight_loader(layer, weight_loader)
+                weight_loader = self.get_online_mxfp4_weight_loader(
+                    layer, weight_loader
+                )
 
             # WEIGHT
             # Both serialized and online quantization use packed uint8 format
@@ -270,6 +338,119 @@ class QuarkW4A4MXFP4(QuarkLinearScheme):
 
         return online_mxfp4_weight_loader
 
+    def get_online_fp8_to_mxfp4_weight_loader(
+        self,
+        layer,
+        original_weight_loader: Callable,
+    ) -> Callable:
+        """
+        Wrap the original weight loader to perform FP8 to MXFP4 requantization.
+
+        This loader handles:
+        1. Loading FP8 weights and weight_scale_inv parameters
+        2. Waiting for all shards (e.g., q_proj, k_proj, v_proj) to be loaded
+        3. Dequantizing FP8 -> BF16
+        4. Requantizing BF16 -> MXFP4
+        """
+
+        def online_fp8_to_mxfp4_weight_loader(
+            param: torch.nn.Parameter,
+            loaded_weight: torch.Tensor,
+            shard_id: int | str | None = None,
+        ):
+            param_name = getattr(param, "_param_name", None)
+
+            is_weight_or_weight_scale = "weight" in param_name
+            is_weight = param_name == "weight"
+            is_weight_scale_inv = param_name == "weight_scale_inv"
+
+            # Sanity multi-threaded load check.
+            assert torch.cuda.current_device() == layer._load_device.index
+
+            with layer._fp8_weight_loading_lock:
+                # Materialize FP8 parameters on first load on device (there may be several shards for a single layer parameter, e.g. q_proj, k_proj, v_proj).
+
+                if is_weight_or_weight_scale and not layer._fp8_weight_materialized:
+
+                    # Sanity check.
+                    assert layer.weight.device.type == "meta"
+
+                    materialized_tensor = layer.weight.__class__(
+                        data=torch.empty_like(
+                            layer.weight.data, device=layer._load_device
+                        ),
+                        input_dim=1,
+                        output_dim=0,
+                        weight_loader=layer.weight._weight_loader,
+                    )
+                    copy_missing_attrs(layer.weight, materialized_tensor)
+                    layer.weight = materialized_tensor
+
+                    # Sanity check.
+                    assert layer.weight_scale_inv.device.type == "meta"  # Sanity check.
+
+                    materialized_tensor = layer.weight_scale_inv.__class__(
+                        data=torch.empty_like(
+                            layer.weight_scale_inv.data, device=layer._load_device
+                        ),
+                        input_dim=1,
+                        output_dim=0,
+                        weight_loader=layer.weight_scale_inv._weight_loader,
+                    )
+                    copy_missing_attrs(layer.weight_scale_inv, materialized_tensor)
+                    layer.weight_scale_inv = materialized_tensor
+
+                    # Mark as materialized to prevent other threads from doing it again.
+                    layer._fp8_weight_materialized = True
+
+                if is_weight:
+                    param = layer.weight
+                elif is_weight_scale_inv:
+                    param = layer.weight_scale_inv
+
+            kwargs = {}
+            if shard_id is not None:
+                kwargs["loaded_shard_id"] = shard_id
+
+            # Track how much data we are actually loading (`narrow` used in weight loader)
+            copy_numel_counter = CopyNumelCounter()
+            with copy_numel_counter:
+                original_weight_loader(param, loaded_weight, **kwargs)
+
+            with layer._fp8_weight_loading_lock:
+                if is_weight_or_weight_scale:
+                    layer._fp8_weight_loaded_numel += copy_numel_counter.copied_numel
+
+                target_numel = layer.weight.numel() + layer.weight_scale_inv.numel()
+
+                # Perform requantization outside the lock (but only if we're the chosen thread)
+                if layer._fp8_weight_loaded_numel == target_numel and hasattr(
+                    layer, "weight_scale_inv"
+                ):
+                    assert layer.weight.device.type != "meta"
+
+                    # FP8 -> BF16 dequantization.
+                    weight_bf16 = dequantize_fp8(
+                        layer.weight,
+                        layer.weight_scale_inv,
+                        block_size=self.weight_block_size,
+                    )
+
+                    # BF16 -> MXFP4 requantization.
+                    weight_mxfp4, weight_mxfp4_scale = dynamic_mxfp4_quant(weight_bf16)
+
+                    layer.weight = torch.nn.Parameter(weight_mxfp4, requires_grad=False)
+                    layer.weight_scale = torch.nn.Parameter(
+                        weight_mxfp4_scale, requires_grad=False
+                    )
+
+                    # Clean up FP8 parameters and tracking attributes
+                    del layer.weight_scale_inv
+                    del layer._load_device
+                    del weight_bf16
+
+        return online_fp8_to_mxfp4_weight_loader
+
     def apply_weights(
         self,
         layer: torch.nn.Module,

python/sglang/srt/layers/quantization/quark/schemes/quark_w4a4_mxfp4_moe.py

@@ -3,12 +3,20 @@
 from __future__ import annotations
 
 import logging
+import threading
 from typing import TYPE_CHECKING, Any
 
 import torch
 
 from sglang.srt.layers.moe import MoeRunner, MoeRunnerBackend, MoeRunnerConfig
 from sglang.srt.layers.moe.utils import get_moe_weight_sizes
+from sglang.srt.layers.quantization.base_config import QuantizationConfig
+from sglang.srt.layers.quantization.dequantization import (
+    copy_missing_attrs,
+    dequantize_fp8,
+)
+from sglang.srt.layers.quantization.fp8 import Fp8Config, Fp8MoEMethod
+from sglang.srt.layers.quantization.online_quantization import CopyNumelCounter
 from sglang.srt.layers.quantization.quark.schemes import QuarkMoEScheme
 from sglang.srt.utils import (
     get_bool_env_var,
@@ -51,10 +59,12 @@ class QuarkW4A4MXFp4MoE(QuarkMoEScheme):
         weight_config: dict[str, Any],
         input_config: dict[str, Any],
         is_checkpoint_mxfp4_serialized: bool = True,
+        dequantization_config: QuantizationConfig | None = None,
     ):
         self.weight_quant = weight_config
         self.input_quant = input_config
         self.is_checkpoint_mxfp4_serialized = is_checkpoint_mxfp4_serialized
+        self.dequantization_config = dequantization_config
 
         weight_qscheme = self.weight_quant.get("qscheme")
         input_qscheme = self.input_quant.get("qscheme")
@@ -96,6 +106,61 @@ class QuarkW4A4MXFp4MoE(QuarkMoEScheme):
 
         from sglang.srt.layers.moe.fused_moe_triton import FusedMoeWeightScaleSupported
 
+        original_weight_loader = extra_weight_attrs.get("weight_loader")
+        with_bias = extra_weight_attrs.pop("with_bias", False)
+        self.with_bias = with_bias
+
+        # Handle FP8 to MXFP4 requantization
+        if self.dequantization_config is not None:
+            if not isinstance(self.dequantization_config, Fp8Config):
+                raise NotImplementedError(
+                    f"Requantization in QuarkW4A4MXFp4MoEMethod from {self.dequantization_config.__class__.__name__} is not supported, only Fp8Config is supported."
+                )
+
+            if self.dequantization_config.use_mxfp8:
+                raise NotImplementedError(
+                    "use_mxfp8=True is not supported in Quark MXFP4 requantization."
+                )
+
+            block_quant = self.dequantization_config.weight_block_size is not None
+
+            if not block_quant:
+                raise NotImplementedError(
+                    "Only block_quant=True is supported in Quark MXFP4 requantization, got block_quant=False."
+                )
+
+            # `_fp8_loaded_numel` is used to trigger FP8 -> MXFP4 requantization once all weights are loaded.
+            # `_fp8_materialized` is used to ensure only one thread materializes weights from meta device.
+            layer._fp8_loaded_numel = 0
+            layer._fp8_materialized = False
+            layer._load_device = torch.get_default_device()
+            layer._fp8_loading_lock = threading.Lock()
+
+            # Custom weight loader handling FP8->MXFP4 conversion.
+            fp8_to_mxfp4_weight_loader = self.get_online_fp8_to_mxfp4_weight_loader(
+                layer, original_weight_loader
+            )
+
+            extra_weight_attrs["weight_loader"] = fp8_to_mxfp4_weight_loader
+            # Create FP8 MoE weight parameters on meta device to avoid device memory overhead during weight loading, as the resulting model uses MXFP4 using less device memory.
+            # The weight loader handles progressive FP8 weight materialization on device.
+            with torch.device("meta"):
+                Fp8MoEMethod.create_fp8_moe_weight_(
+                    layer=layer,
+                    num_experts=num_experts,
+                    hidden_size=hidden_size,
+                    intermediate_size_per_partition=intermediate_size_per_partition,
+                    block_quant=block_quant,
+                    quant_config=self.dequantization_config,
+                    use_mxfp8=False,
+                    is_checkpoint_fp8_serialized=True,
+                    is_fp4_expert=False,
+                    params_dtype=params_dtype,
+                    with_bias=with_bias,
+                    **extra_weight_attrs,
+                )
+            return
+
         w13_up_dim, w2_down_dim, weight_padded = get_moe_weight_sizes(
             intermediate_size_per_partition,
             is_aiter_moe=_use_aiter,
@@ -112,40 +177,61 @@ class QuarkW4A4MXFp4MoE(QuarkMoEScheme):
             },
         )
 
-        params_dtype = torch.uint8
-
-        original_weight_loader = extra_weight_attrs.get("weight_loader")
-
         if self.is_checkpoint_mxfp4_serialized:
             weight_loader = original_weight_loader
+            weight_device = torch.get_default_device()
+            weight_dtype = torch.uint8
         else:
+            # Online quantization: use original dtype and meta device
             weight_loader = self.get_online_weight_loader(layer, original_weight_loader)
+            weight_device = torch.device("meta")
+            weight_dtype = params_dtype
+
+        params_dtype = torch.uint8
+
+        layer._load_device = torch.get_default_device()
+        layer._w13_loaded_numel = 0
+        layer._w2_loaded_numel = 0
 
         extra_weight_attrs["weight_loader"] = weight_loader
 
-        # WEIGHTS — always uint8 (packed mxfp4), always on device
+        # WEIGHTS
+        w13_shape = (
+            num_experts,
+            2 * intermediate_size_per_partition,
+            hidden_size // 2 if self.is_checkpoint_mxfp4_serialized else hidden_size,
+        )
         w13_weight = torch.nn.Parameter(
             torch.empty(
-                num_experts,
+                w13_shape,
-                w13_up_dim,
+                dtype=weight_dtype,
-                hidden_size // 2,
+                device=weight_device,
-                dtype=params_dtype,
             ),
             requires_grad=False,
         )
         layer.register_parameter("w13_weight", w13_weight)
+
         set_weight_attrs(w13_weight, extra_weight_attrs)
 
-        w2_weight = torch.nn.Parameter(
+        w2_shape = (
-            torch.empty(
             num_experts,
             hidden_size,
-                w2_down_dim,
+            (
-                dtype=params_dtype,
+                intermediate_size_per_partition // 2
+                if self.is_checkpoint_mxfp4_serialized
+                else intermediate_size_per_partition
+            ),
+        )
+        w2_weight = torch.nn.Parameter(
+            torch.empty(
+                w2_shape,
+                dtype=weight_dtype,
+                device=weight_device,
             ),
             requires_grad=False,
         )
         layer.register_parameter("w2_weight", w2_weight)
+
         set_weight_attrs(w2_weight, extra_weight_attrs)
 
         # WEIGHT_SCALES
@@ -180,7 +266,7 @@ class QuarkW4A4MXFp4MoE(QuarkMoEScheme):
 
     def get_online_weight_loader(self, layer, original_weight_loader):
         """
-        Wrap the original weight loader to perform online MXFP4 quantization.
+        Wrap the original weight loader to perform online MXFP4 quantization for MoE layers.
         """
 
         def online_mxfp4_moe_weight_loader(
@@ -195,29 +281,290 @@ class QuarkW4A4MXFp4MoE(QuarkMoEScheme):
                     "Online MXFP4 quantization for MoE is only supported on AMD GPUs."
                 )
 
-            # Materialize on device the loaded weight.
+            # Determine which weight parameter we're loading (w13 or w2)
-            loaded_weight = loaded_weight.to(param.device)
+            is_w13 = "w13" in weight_name
+            is_w2 = "w2" in weight_name
 
-            # Quantize the high-precision shard loaded_weight to MXFP4.
+            # Initialize weight on device if first load
-            qweight, weight_scale = dynamic_mxfp4_quant(loaded_weight)
+            if is_w13 and layer._w13_loaded_numel == 0:
-
+                layer.w13_weight = torch.nn.Parameter(
-            original_weight_loader(param, qweight, weight_name, shard_id, expert_id)
+                    torch.empty_like(param.data, device=layer._load_device),
-
+                    requires_grad=False,
-            if "w13" in weight_name:
-                scale_param = layer.w13_weight_scale
-                scale_weight_name = "w13_weight_scale"
-            else:
-                # w2.
-                scale_param = layer.w2_weight_scale
-                scale_weight_name = "w2_weight_scale"
-
-            scale_param.weight_loader(
-                scale_param, weight_scale, scale_weight_name, shard_id, expert_id
                 )
+                param = layer.w13_weight
+            elif is_w2 and layer._w2_loaded_numel == 0:
+                layer.w2_weight = torch.nn.Parameter(
+                    torch.empty_like(param.data, device=layer._load_device),
+                    requires_grad=False,
+                )
+                param = layer.w2_weight
+
+            # Move to device for faster quantization
+            loaded_weight = loaded_weight.to(layer._load_device)
+
+            if is_w13:
+                param = layer.w13_weight
+            elif is_w2:
+                param = layer.w2_weight
+
+            # In case TP>1, the weight loader logic uses narrow so we cannot directly rely on `param.shape` or `loaded_weight.shape`.
+            copy_numel_counter = CopyNumelCounter()
+            with copy_numel_counter:
+                original_weight_loader(
+                    param, loaded_weight, weight_name, shard_id, expert_id
+                )
+
+            if is_w13:
+                layer._w13_loaded_numel += copy_numel_counter.copied_numel
+                target_loaded_numel = layer.w13_weight.numel()
+                current_loaded = layer._w13_loaded_numel
+            elif is_w2:
+                layer._w2_loaded_numel += copy_numel_counter.copied_numel
+                target_loaded_numel = layer.w2_weight.numel()
+                current_loaded = layer._w2_loaded_numel
+            else:
+                raise ValueError("Expected w13 or w2.")
+
+            assert (
+                current_loaded <= target_loaded_numel
+            ), f"target_loaded_numel={target_loaded_numel}, current_loaded={current_loaded}"
+
+            # Delay online quantization until all tensor shards (e.g. w1 and w3) are loaded, to avoid having to re-quantize later on.
+            if is_w13 and layer._w13_loaded_numel == target_loaded_numel:
+                self._quantize_w13_online(layer, dynamic_mxfp4_quant)
+            elif is_w2 and layer._w2_loaded_numel == target_loaded_numel:
+                self._quantize_w2_online(layer, dynamic_mxfp4_quant)
 
         return online_mxfp4_moe_weight_loader
 
+    def get_online_fp8_to_mxfp4_weight_loader(self, layer, original_weight_loader):
+        """
+        Wrap the original weight loader to perform FP8 to MXFP4 requantization for MoE layers.
+
+        This loader handles:
+        1. Loading FP8 weights (w13_weight, w2_weight) and weight_scale_inv parameters
+        2. Waiting for all experts to be loaded
+        3. Dequantizing FP8 -> BF16 using weight_scale_inv
+        4. Requantizing BF16 -> MXFP4
+        """
+
+        def online_fp8_to_mxfp4_moe_weight_loader(
+            param: torch.nn.Parameter,
+            loaded_weight: torch.Tensor,
+            weight_name: str,
+            shard_id: str,
+            expert_id: int,
+        ):
+            is_w13_weight = "w13_weight" in weight_name and "scale" not in weight_name
+            is_w2_weight = "w2_weight" in weight_name and "scale" not in weight_name
+            is_w13_scale = "w13_weight_scale_inv" in weight_name
+            is_w2_scale = "w2_weight_scale_inv" in weight_name
+
+            # Sanity multi-threaded load check.
+            assert torch.cuda.current_device() == layer._load_device.index
+
+            # Materialize FP8 parameters on first load from meta device. Adds a small but manageable overhead compared to materializing one by one - but weights are loaded in order layer by layer so it is fine.
+            with layer._fp8_loading_lock:
+
+                if not layer._fp8_materialized:
+                    # w13_weight
+                    assert layer.w13_weight.device.type == "meta"
+                    materialized = torch.nn.Parameter(
+                        torch.empty_like(
+                            layer.w13_weight.data, device=layer._load_device
+                        ),
+                        requires_grad=False,
+                    )
+                    copy_missing_attrs(layer.w13_weight, materialized)
+                    layer.w13_weight = materialized
+
+                    # w13_weight_scale_inv
+                    materialized = torch.nn.Parameter(
+                        torch.empty_like(
+                            layer.w13_weight_scale_inv.data, device=layer._load_device
+                        ),
+                        requires_grad=False,
+                    )
+                    copy_missing_attrs(layer.w13_weight_scale_inv, materialized)
+                    layer.w13_weight_scale_inv = materialized
+
+                    # w2_weight
+                    assert layer.w2_weight.device.type == "meta"
+                    materialized = torch.nn.Parameter(
+                        torch.empty_like(
+                            layer.w2_weight.data, device=layer._load_device
+                        ),
+                        requires_grad=False,
+                    )
+                    copy_missing_attrs(layer.w2_weight, materialized)
+                    layer.w2_weight = materialized
+
+                    # w2_weight_scale_inv
+                    assert layer.w2_weight_scale_inv.device.type == "meta"
+                    materialized = torch.nn.Parameter(
+                        torch.empty_like(
+                            layer.w2_weight_scale_inv.data, device=layer._load_device
+                        ),
+                        requires_grad=False,
+                    )
+                    copy_missing_attrs(layer.w2_weight_scale_inv, materialized)
+                    layer.w2_weight_scale_inv = materialized
+
+                    # Mark as materialized to prevent other threads from doing it again.
+                    layer._fp8_materialized = True
+
+                if is_w13_weight:
+                    param = layer.w13_weight
+                elif is_w2_weight:
+                    param = layer.w2_weight
+                elif is_w13_scale:
+                    param = layer.w13_weight_scale_inv
+                elif is_w2_scale:
+                    param = layer.w2_weight_scale_inv
+
+            # Track how much data we are actually loading (`narrow` used in weight loader)
+            copy_numel_counter = CopyNumelCounter()
+            with copy_numel_counter:
+                original_weight_loader(
+                    param, loaded_weight, weight_name, shard_id, expert_id
+                )
+
+            with layer._fp8_loading_lock:
+                layer._fp8_loaded_numel += copy_numel_counter.copied_numel
+
+                total_target_numel = (
+                    layer.w13_weight.numel()
+                    + layer.w2_weight.numel()
+                    + layer.w13_weight_scale_inv.numel()
+                    + layer.w2_weight_scale_inv.numel()
+                )
+
+                # Sanity check
+                assert layer._fp8_loaded_numel <= total_target_numel
+
+                # Perform dequantization and requantization only when all data is loaded AND no other threads are still loading.
+                if layer._fp8_loaded_numel == total_target_numel:
+                    if dynamic_mxfp4_quant is None:
+                        raise NotImplementedError(
+                            "MXFP4 quantization for MoE is only supported on AMD GPUs."
+                        )
+
+                    assert layer.w13_weight.device.type == "cuda"
+                    assert layer.w13_weight_scale_inv.device.type == "cuda"
+                    assert layer.w13_weight.dtype != torch.uint8
+
+                    # Dequantize and requantize w13
+                    w13_bf16 = dequantize_fp8(
+                        layer.w13_weight,
+                        layer.w13_weight_scale_inv,
+                        block_size=self.dequantization_config.weight_block_size,
+                    )
+
+                    qw13_weight_list = []
+                    w13_weight_scale_list = []
+                    for expert_idx in range(w13_bf16.shape[0]):
+                        # NOTE: dynamic_mxfp4_quant does not accept 3D inputs.
+                        qweight, weight_scale = dynamic_mxfp4_quant(
+                            w13_bf16[expert_idx]
+                        )
+                        qw13_weight_list.append(qweight)
+                        w13_weight_scale_list.append(weight_scale)
+
+                    qw13_weight = torch.stack(qw13_weight_list)
+                    w13_weight_scale = torch.stack(w13_weight_scale_list)
+
+                    # Dequantize and requantize w2
+                    w2_bf16 = dequantize_fp8(
+                        layer.w2_weight,
+                        layer.w2_weight_scale_inv,
+                        block_size=self.dequantization_config.weight_block_size,
+                    )
+
+                    qw2_weight_list = []
+                    w2_weight_scale_list = []
+                    for expert_idx in range(w2_bf16.shape[0]):
+                        # NOTE: dynamic_mxfp4_quant does not accept 3D inputs.
+                        qweight, weight_scale = dynamic_mxfp4_quant(w2_bf16[expert_idx])
+                        qw2_weight_list.append(qweight)
+                        w2_weight_scale_list.append(weight_scale)
+
+                    qw2_weight = torch.stack(qw2_weight_list)
+                    w2_weight_scale = torch.stack(w2_weight_scale_list)
+
+                    # Replace FP8 parameters with MXFP4 parameters
+                    layer.w13_weight = torch.nn.Parameter(
+                        qw13_weight, requires_grad=False
+                    )
+                    layer.w13_weight_scale = torch.nn.Parameter(
+                        w13_weight_scale, requires_grad=False
+                    )
+                    layer.w2_weight = torch.nn.Parameter(
+                        qw2_weight, requires_grad=False
+                    )
+                    layer.w2_weight_scale = torch.nn.Parameter(
+                        w2_weight_scale, requires_grad=False
+                    )
+
+                    # Clean up FP8 parameters and tracking attributes
+                    del layer.w13_weight_scale_inv
+                    del layer.w2_weight_scale_inv
+                    del layer._fp8_materialized
+                    del layer._load_device
+                    del layer._fp8_loading_lock
+
+        return online_fp8_to_mxfp4_moe_weight_loader
+
+    def _quantize_w13_online(self, layer, dynamic_mxfp4_quant):
+        qw13_weight = torch.empty(
+            layer.w13_weight.shape[0],
+            layer.w13_weight.shape[1],
+            layer.w13_weight.shape[2] // 2,
+            dtype=torch.uint8,
+            device=layer._load_device,
+        )
+
+        for expert in range(layer.w13_weight.shape[0]):
+            qweight, weight_scale = dynamic_mxfp4_quant(layer.w13_weight.data[expert])
+            assert qw13_weight[expert].shape == qweight.shape
+            assert qw13_weight[expert].dtype == qweight.dtype
+            qw13_weight[expert] = qweight
+
+            assert layer.w13_weight_scale[expert].shape == weight_scale.shape
+            assert layer.w13_weight_scale[expert].dtype == weight_scale.dtype
+            layer.w13_weight_scale[expert] = weight_scale
+
+        layer.w13_weight = torch.nn.Parameter(qw13_weight, requires_grad=False)
+
+    def _quantize_w2_online(self, layer, dynamic_mxfp4_quant):
+        qw2_weight = torch.empty(
+            layer.w2_weight.shape[0],
+            layer.w2_weight.shape[1],
+            layer.w2_weight.shape[2] // 2,
+            dtype=torch.uint8,
+            device=layer._load_device,
+        )
+
+        for expert in range(layer.w2_weight.shape[0]):
+            qweight, weight_scale = dynamic_mxfp4_quant(layer.w2_weight.data[expert])
+            qw2_weight[expert] = qweight
+            layer.w2_weight_scale[expert] = weight_scale
+
+        layer.w2_weight = torch.nn.Parameter(qw2_weight, requires_grad=False)
+
     def process_weights_after_loading(self, layer: torch.nn.Module) -> None:
+        if (
+            not self.is_checkpoint_mxfp4_serialized
+            or self.dequantization_config is not None
+        ):
+            # Quantization already happened during weight loading.
+            # This covers both:
+            # - Online quantization from BF16/FP16 -> MXFP4
+            # - Requantization from FP8 -> MXFP4
+            assert layer.w13_weight.dtype == torch.uint8
+            assert layer.w2_weight.dtype == torch.uint8
+            assert layer.w13_weight_scale.dtype == torch.uint8
+            assert layer.w2_weight_scale.dtype == torch.uint8
+
         # Pre-shuffle weight scales
         s0, s1, _ = layer.w13_weight_scale.shape
         w13_weight_scale = layer.w13_weight_scale.view(s0 * s1, -1)

python/sglang/srt/layers/quantization/quark/utils.py

@@ -206,5 +206,9 @@ def quark_post_load_weights(self_attn: nn.Module, w: torch.Tensor, quant_format:
             w_vc, w_s_vc = b_dynamic_mxfp4_quant(w_vc)
             w_s_kc = w_s_kc.transpose(1, 2).contiguous().transpose(1, 2)
             w_s_vc = w_s_vc.contiguous().transpose(1, 2)
+        else:
+            raise ValueError(
+                f"Unexpected w.dtype: {w.dtype} (should be bfloat16 or uint8)"
+            )
 
         return w_kc, w_s_kc, w_vc, w_s_vc

python/sglang/srt/model_loader/utils.py

@@ -309,7 +309,21 @@ def maybe_executor_submit(
     if func_kwargs is None:
         func_kwargs = {}
     if use_async:
-        futures.append(executor.submit(func, *func_args, **func_kwargs))
+        # CRITICAL: Capture current CUDA device and restore it in worker thread.
+        # torch.cuda.current_device() is thread-local and is NOT correctly passed to threads.
+        # This may result in errors in case the `func` relies on torch current device to be already correctly specified.
+        # See details in https://github.com/pytorch/pytorch/issues/56588.
+        current_device = (
+            torch.cuda.current_device() if torch.cuda.is_available() else None
+        )
+
+        def device_aware_wrapper(*args, **kwargs):
+            # Set CUDA device in worker thread to match parent thread
+            if current_device is not None:
+                torch.cuda.set_device(current_device)
+            return func(*args, **kwargs)
+
+        futures.append(executor.submit(device_aware_wrapper, *func_args, **func_kwargs))
     else:
         func(*func_args, **func_kwargs)
 

python/sglang/srt/model_loader/weight_utils.py

@@ -40,7 +40,7 @@ from pydantic import BaseModel, ConfigDict, ValidationInfo, model_validator
 from tqdm.auto import tqdm
 
 from sglang.srt.configs.load_config import LoadConfig
-from sglang.srt.configs.model_config import ModelConfig
+from sglang.srt.configs.model_config import REQUANTIZATION_METHODS, ModelConfig
 from sglang.srt.distributed import (
     get_world_group,
 )
@@ -276,6 +276,12 @@ def get_quant_config(
         )
         if not modelopt_mixed_config_incomplete:
             hf_quant_config["packed_modules_mapping"] = packed_modules_mapping
+            hf_quant_config["hf_config"] = model_config.hf_config
+
+            # This is only used by quantization methods that support requantization (e.g. from fp8 to mxfp4).
+            if model_config.quantization in REQUANTIZATION_METHODS:
+                hf_quant_config["requantization_method"] = model_config.quantization
+
             return quant_cls.from_config(hf_quant_config)
 
     # In case of bitsandbytes/QLoRA, get quant config from the adapter model.

test/registered/quant/test_quark_mxfp4.py

@@ -1,4 +1,5 @@
 import io
+import os
 import re
 import unittest
 
@@ -10,6 +11,7 @@ import time
 from types import SimpleNamespace
 
 import requests
+import torch
 
 from sglang.srt.utils import kill_process_tree
 from sglang.srt.utils.common import is_cuda_alike, mxfp_supported
@@ -18,15 +20,22 @@ from sglang.test.test_utils import (
     DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH,
     DEFAULT_URL_FOR_TEST,
     CustomTestCase,
+    is_in_ci,
     popen_launch_server,
 )
 
 
 class TestOnlineQuantizationMemoryLoad(CustomTestCase):
     runner_args = []
+    environment = {}
 
     @classmethod
     def setUpClass(cls):
+        if torch.cuda.device_count() < cls.tp:
+            raise unittest.SkipTest(
+                f"test requires {cls.tp} devices, only {torch.cuda.device_count()} are available."
+            )
+
         if not mxfp_supported():
             raise unittest.SkipTest(
                 "online MXFP4 quantization requires an AMD ROCm device with "
@@ -55,6 +64,14 @@ class TestOnlineQuantizationMemoryLoad(CustomTestCase):
             return_stdout_stderr=(cls.stdout, cls.stderr),
         )
 
+        cls.original_envs = {}
+        for env_name, env_value in cls.environment.items():
+            original_env = os.environ.get(env_name, None)
+            if original_env is not None:
+                cls.original_envs[env_name] = os.environ.get(env_name, None)
+
+            os.environ[env_name] = env_value
+
         url = cls.base_url + "/health"
         timeout = DEFAULT_TIMEOUT_FOR_SERVER_LAUNCH
         start_time = time.perf_counter()
@@ -108,6 +125,9 @@ class TestOnlineQuantizationMemoryLoad(CustomTestCase):
 
     @classmethod
     def tearDownClass(cls):
+        for env_name, env_value in cls.original_envs.items():
+            os.environ[env_name] = env_value
+
         kill_process_tree(cls.process.pid)
         cls.stdout.close()
         cls.stderr.close()
@@ -153,6 +173,7 @@ class TestOnlineQuantizationMemoryLoad(CustomTestCase):
 
 class TestOnlineQuantizationMemoryLoadDense(TestOnlineQuantizationMemoryLoad):
     model = "Qwen/Qwen3-8B"
+    tp = 1
 
     def test_peak_memory(self):
         # Original Qwen/Qwen3-8B BF16 model: 15.268 GiB
@@ -171,6 +192,7 @@ class TestOnlineQuantizationMemoryLoadMOE(TestOnlineQuantizationMemoryLoad):
     # - ibm-granite/granite-3.0-3b-a800m-base: dtype issue with fp16 in AITER MOE MLP activation
     # so using a large model here.
     model = "Qwen/Qwen3-30B-A3B-Instruct-2507"
+    tp = 1
     # TODO: test TP>=2 with an other model (Qwen/Qwen3-30B-A3B-Instruct-2507 crashes in this case as 768/2 = 384, and 384/32 = 12 not divisible by BLOCK_SIZE_N=8. in fused_dynamic_mxfp4_quant_moe_sort.
 
     def test_peak_memory(self):
@@ -184,5 +206,117 @@ class TestOnlineQuantizationMemoryLoadMOE(TestOnlineQuantizationMemoryLoad):
         self._test_gsm8k(accuracy_threshold=0.89)
 
 
+class TestFP8ToMXFP4DenseTP1(TestOnlineQuantizationMemoryLoad):
+    tp = 1
+    model = "Qwen/Qwen3-8B-FP8"
+
+    def test_peak_memory(self):
+        # Original Qwen/Qwen3-8B-FP8 model: 8.801 GiB (TP=1, peak_memory_before_load)
+        self._test_peak_memory(
+            threshold=6.5, test_start=False, add_peak_memory_before_load=True
+        )
+
+    def test_gsm8k(self):
+        # Original Qwen/Qwen3-8B-FP8 reference accuracy: ~0.92
+        self._test_gsm8k(accuracy_threshold=0.868)
+
+
+class TestFP8ToMXFP4DenseTP2(TestOnlineQuantizationMemoryLoad):
+    tp = 2
+    model = "Qwen/Qwen3-8B-FP8"
+
+    def test_peak_memory(self):
+        # Original Qwen/Qwen3-8B-FP8 model: 4.663 GiB (TP=2, peak_memory_before_load)
+        self._test_peak_memory(
+            threshold=4.2, test_start=False, add_peak_memory_before_load=True
+        )
+
+    def test_gsm8k(self):
+        # Original Qwen/Qwen3-8B-FP8 reference accuracy: ~0.92
+        self._test_gsm8k(accuracy_threshold=0.868)
+
+
+class TestFP8ToMXFP4MOETP1(TestOnlineQuantizationMemoryLoad):
+    model = "Qwen/Qwen3-30B-A3B-Instruct-2507-FP8"  # FP8 model
+    tp = 1
+
+    def test_peak_memory(self):
+        # Original Qwen/Qwen3-30B-A3B-Instruct-2507-FP8 model: 29.103 GiB (TP=1, peak_memory_before_load)
+        self._test_peak_memory(
+            threshold=18.5, test_start=False, add_peak_memory_before_load=True
+        )
+
+    def test_gsm8k(self):
+        # Original Qwen/Qwen3-30B-A3B-Instruct-2507-FP8 reference accuracy: ~0.948
+        self._test_gsm8k(accuracy_threshold=0.92)
+
+
+@unittest.skipIf(is_in_ci(), "local test only")
+class TestDeepSeekFP8ToMXFP4(TestOnlineQuantizationMemoryLoad):
+    # Loading should take ~51.65 seconds on TP=8 on MI355X.
+    # model = "deepseek-ai/DeepSeek-V3.2"  # FP8 model
+    model = "deepseek-ai/DeepSeek-V3.2"
+    tp = 8
+
+    def test_peak_memory(self):
+        # Original deepseek-ai/DeepSeek-V3.2 model: 80.366 GiB (TP=8, peak_memory_before_load)
+        self._test_peak_memory(
+            threshold=70, test_start=True, add_peak_memory_before_load=False
+        )  # TP=8
+
+    def test_gsm8k(self):
+        # Original deepseek-ai/DeepSeek-V3.2 reference accuracy: ~0.948
+        self._test_gsm8k(accuracy_threshold=0.94)
+
+
+@unittest.skipIf(is_in_ci(), "local test only")
+class TestKimiK2FP8ToMXFP4(TestOnlineQuantizationMemoryLoad):
+    model = "moonshotai/Kimi-K2-Instruct-0905"  # FP8 model
+    tp = 8
+
+    # Same as in test/registered/amd/test_kimi_k2_instruct.py
+    runner_args = [
+        "--decode-attention-backend",
+        "triton",
+        "--prefill-attention-backend",
+        "aiter",
+        "--trust-remote-code",
+    ]
+
+    # Same as in test/registered/amd/test_kimi_k2_instruct.py, getting an error otherwise.
+    environment = {"SGLANG_ROCM_FUSED_DECODE_MLA": "0"}
+
+    def test_peak_memory(self):
+        # Original moonshotai/Kimi-K2-Instruct-0905 model: 121.020 GiB (TP=8, peak_memory_before_load)
+        self._test_peak_memory(
+            threshold=82, test_start=True, add_peak_memory_before_load=False
+        )  # TP=8
+
+    def test_gsm8k(self):
+        # Original moonshotai/Kimi-K2-Instruct-0905 reference accuracy: ~0.962
+        self._test_gsm8k(accuracy_threshold=0.96)
+
+
+@unittest.skipIf(is_in_ci(), "local test only")
+class TestMiniMaxFP8ToMXFP4(TestOnlineQuantizationMemoryLoad):
+    model = "MiniMaxAI/MiniMax-M2.1"  # FP8 model
+
+    tp = 2
+    # NOTE: this test is failing in FP16 (default dtype of the original MiniMax-M2.1 model).
+    # Hence the usage of `--dtype bfloat16`
+    # NOTE: this test requires the following fix for TP>1: https://github.com/sgl-project/sglang/pull/18310
+    runner_args = ["--trust-remote-code", "--dtype", "bfloat16"]
+
+    def test_peak_memory(self):
+        # Original MiniMaxAI/MiniMax-M2.1 model: 107.375 GiB (TP=2, peak_memory_before_load)
+        self._test_peak_memory(
+            threshold=72, test_start=True, add_peak_memory_before_load=False
+        )  # TP=2
+
+    def test_gsm8k(self):
+        # Original MiniMaxAI/MiniMax-M2.1 reference accuracy: 0.954
+        self._test_gsm8k(accuracy_threshold=0.92)
+
+
 if __name__ == "__main__":
     unittest.main()