ktransformers/kt-kernel/python/sft/weights.py

# Weight extraction and loading utilities for SFT
# SPDX-License-Identifier: Apache-2.0

from __future__ import annotations

import logging
import os
import time
from dataclasses import dataclass

import torch
import torch.nn as nn

from .arch import MOEArchConfig
from .conv3d_compat import _canonicalize_qwen3_vl_fused_expert_weights
from .dist_utils import _maybe_zero3_gathered_parameters

logger = logging.getLogger(__name__)

try:
    from safetensors import safe_open

    SAFETENSORS_AVAILABLE = True
except ImportError:
    SAFETENSORS_AVAILABLE = False
    safe_open = None


# =============================================================================
# Weight Extraction
# =============================================================================


def _require_materialized_expert_weight(name: str, weight: torch.Tensor) -> None:
    if weight.device.type == "meta" or getattr(weight, "_kt_zero_storage", False):
        raise RuntimeError(
            f"Cannot extract {name}: routed expert weight is an unmaterialized placeholder"
        )
    try:
        storage_bytes = weight.untyped_storage().nbytes()
    except (NotImplementedError, RuntimeError):
        return
    required_bytes = weight.numel() * weight.element_size()
    if required_bytes and storage_bytes < required_bytes:
        raise RuntimeError(
            f"Cannot extract {name}: routed expert weight is a zero-storage placeholder"
        )


def extract_moe_weights(
    moe_module: nn.Module, moe_config: MOEArchConfig
) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
    """
    Extract MoE expert weights from the module.

    Returns (gate_proj, up_proj, down_proj) with shape
    [expert_num, out_features, in_features].

    Supports two formats:
    - ModuleList of Linear experts (transformers v4 style)
    - Fused Parameters (transformers v5 style): single module with
      ``gate_up_proj`` [E, 2*I, H] and ``down_proj`` [E, H, I] tensors.
    """
    from .arch import detect_fused_experts

    experts = getattr(moe_module, moe_config.experts_attr)

    # Fused format (transformers v5): a single nn.Module with gate_up_proj/down_proj tensors
    if detect_fused_experts(experts):
        gate_up_parameter = getattr(experts, "gate_up_proj")
        down_parameter = getattr(experts, "down_proj")
        _require_materialized_expert_weight("gate_up_proj", gate_up_parameter)
        _require_materialized_expert_weight("down_proj", down_parameter)
        gate_up = gate_up_parameter.data
        down_fused = down_parameter.data
        vlm_weights = _canonicalize_qwen3_vl_fused_expert_weights(gate_up, down_fused, moe_config)
        if vlm_weights is not None:
            return vlm_weights
        # gate_up_proj is [E, 2*I, H], split into gate [E, I, H] and up [E, I, H]
        intermediate = gate_up.shape[1] // 2
        gate_proj = gate_up[:, :intermediate, :].contiguous()
        up_proj = gate_up[:, intermediate:, :].contiguous()
        # down_proj is already [E, H, I]
        down_proj = down_fused.contiguous()
        return gate_proj, up_proj, down_proj

    gate_name, up_name, down_name = moe_config.weight_names

    gather_params: list[torch.nn.Parameter] = []
    for expert in experts:
        for weight_name in (gate_name, up_name, down_name):
            proj = getattr(expert, weight_name, None)
            if proj is not None and hasattr(proj, "weight"):
                # Handle PEFT LoRA wrapped modules
                weight = proj.weight
                if isinstance(weight, torch.Tensor):
                    gather_params.append(weight)
                elif hasattr(weight, "data"):
                    gather_params.append(weight.data)

    with _maybe_zero3_gathered_parameters(gather_params):
        gate_weights = []
        up_weights = []
        down_weights = []

        for expert_idx, expert in enumerate(experts):
            # Handle PEFT LoRA wrapped modules - get weight tensor properly
            gate_proj = getattr(expert, gate_name)
            up_proj_mod = getattr(expert, up_name)
            down_proj_mod = getattr(expert, down_name)

            # Get weight tensors, handling both regular Linear and PEFT LoRA wrapped
            def get_weight_tensor(mod, projection_name):
                weight = mod.weight
                if isinstance(weight, torch.Tensor):
                    tensor = weight
                elif hasattr(weight, "data"):
                    tensor = weight.data
                else:
                    raise ValueError(
                        f"Cannot extract weight from {type(mod)}, weight type={type(weight)}"
                    )
                _require_materialized_expert_weight(
                    f"expert {expert_idx} {projection_name}", tensor
                )
                return tensor.data

            gate_weights.append(get_weight_tensor(gate_proj, gate_name))
            up_weights.append(get_weight_tensor(up_proj_mod, up_name))
            down_weights.append(get_weight_tensor(down_proj_mod, down_name))

    gate_proj = torch.stack(gate_weights, dim=0)
    up_proj = torch.stack(up_weights, dim=0)
    down_proj = torch.stack(down_weights, dim=0)

    return gate_proj, up_proj, down_proj


def _clear_original_expert_weights(
    moe_module: nn.Module,
    moe_config: MOEArchConfig,
    full_weight_grad: bool = False,
    *,
    empty_placeholders: bool = False,
) -> None:
    """
    Clear original expert weights to free memory after KT weights are loaded.

    In full_weight_grad mode, gate_proj_buf/up_proj_buf/down_proj_buf serve as
    the authoritative copies for the optimizer. The original expert weights in
    the model tree are redundant and cause double-counting in count_parameters().
    Clear them just like in LoRA mode.
    """
    from .arch import detect_fused_experts

    experts = getattr(moe_module, moe_config.experts_attr, None)
    if experts is None:
        return

    def make_placeholder(parameter: torch.nn.Parameter) -> nn.Parameter:
        if empty_placeholders:
            fake_tensor = torch.empty(0, dtype=parameter.dtype, device="cpu")
        else:
            tiny_storage = torch.UntypedStorage(1, device="cpu")
            fake_tensor = torch.tensor([], dtype=parameter.dtype, device="cpu").set_(
                tiny_storage,
                storage_offset=0,
                size=parameter.shape,
                stride=[0] * len(parameter.shape),
            )
        placeholder = nn.Parameter(fake_tensor, requires_grad=False)
        placeholder._kt_zero_storage = True
        placeholder._kt_original_shape = tuple(parameter.shape)
        return placeholder

    # Fused format: replace gate_up_proj/down_proj tensors with zero-storage placeholders
    if detect_fused_experts(experts):
        for name in ("gate_up_proj", "down_proj"):
            param = getattr(experts, name, None)
            if not isinstance(param, torch.nn.Parameter):
                continue
            experts._parameters[name] = make_placeholder(param)
        return

    def _iter_weight_params():
        for expert in experts:
            for weight_name in moe_config.weight_names:
                proj = getattr(expert, weight_name, None)
                if proj is None or not hasattr(proj, "weight"):
                    continue

                parametrizations = getattr(proj, "parametrizations", None)
                parametrized_weight = (
                    getattr(parametrizations, "weight", None) if parametrizations is not None else None
                )
                if parametrized_weight is not None:
                    original = getattr(parametrized_weight, "original", None)
                    if isinstance(original, torch.nn.Parameter):
                        yield proj, parametrized_weight, "original", original
                        continue

                direct_weight = getattr(proj, "_parameters", {}).get("weight")
                if isinstance(direct_weight, torch.nn.Parameter):
                    yield proj, proj, "weight", direct_weight
                    continue

                # Fallback: `weight` can be a non-settable property (e.g. parametrizations) or a non-Parameter.
                weight_attr = getattr(proj, "weight", None)
                if isinstance(weight_attr, torch.nn.Parameter):
                    yield proj, proj, "weight", weight_attr

    gather_params: list[torch.nn.Parameter] = []
    for _, _, _, weight_param in _iter_weight_params():
        gather_params.append(weight_param)

    replaced_count = 0

    with _maybe_zero3_gathered_parameters(gather_params):
        for proj, container, param_name, weight_param in _iter_weight_params():
            new_param = make_placeholder(weight_param)
            replaced_count += 1

            # Avoid `KeyError: attribute 'weight' already exists` for parametrized modules
            # where `weight` is a property and the real parameter lives elsewhere.
            container_params = getattr(container, "_parameters", {})
            if isinstance(container_params, dict) and param_name in container_params:
                container_params[param_name] = new_param
                continue

            if hasattr(container, param_name):
                logger.debug(
                    f"Skipping clearing expert weight {type(proj).__name__}.{param_name}: "
                    "attribute exists but is not a registered parameter."
                )
                continue

            try:
                setattr(container, param_name, new_param)
            except Exception as exc:
                logger.warning(f"Failed to clear expert weight {type(proj).__name__}.{param_name}: {exc}")

    logger.info(f"Replaced {replaced_count} expert weight params")


_KT_RANK_LOCAL_PARAMETER_NAMES = "_kt_rank_local_parameter_names"


def get_kt_expert_placeholders(model: nn.Module) -> dict[str, nn.Parameter]:
    """Resolve current placeholder identities from stable, cached FQNs."""
    placeholder_ids: set[int] = set()
    for module in model.modules():
        if not getattr(module, "_is_kt_moe_wrapper", False):
            continue

        experts_attr = getattr(module, "_experts_attr", None)
        experts = getattr(module, experts_attr, None) if isinstance(experts_attr, str) else None
        if not isinstance(experts, nn.Module):
            raise RuntimeError("KT MoE wrapper does not expose a valid expert subtree")

        placeholder_ids.update(
            id(parameter)
            for parameter in experts.parameters(recurse=True)
            if getattr(parameter, "_kt_zero_storage", False)
        )

    named_parameters: dict[str, nn.Parameter] = {}
    discovered: dict[str, nn.Parameter] = {}
    for fqn, parameter in model.named_parameters(remove_duplicate=False):
        if fqn in named_parameters and named_parameters[fqn] is not parameter:
            raise RuntimeError(
                f"Model parameter FQN {fqn!r} resolves to conflicting Parameter identities"
            )
        named_parameters[fqn] = parameter
        if id(parameter) not in placeholder_ids:
            continue
        if fqn in discovered and discovered[fqn] is not parameter:
            raise RuntimeError(f"KT expert placeholder FQN {fqn!r} resolves to conflicting Parameter identities")
        discovered[fqn] = parameter
    found_ids = {id(parameter) for parameter in discovered.values()}
    if found_ids != placeholder_ids:
        raise RuntimeError("KT expert placeholder is not registered in the model parameter tree")

    cached_names = getattr(model, _KT_RANK_LOCAL_PARAMETER_NAMES, None)
    if cached_names is None:
        cached_names = tuple(sorted(discovered))
        setattr(model, _KT_RANK_LOCAL_PARAMETER_NAMES, cached_names)
    elif (
        not isinstance(cached_names, tuple)
        or any(not isinstance(name, str) or not name for name in cached_names)
        or tuple(sorted(set(cached_names))) != cached_names
    ):
        raise RuntimeError("KT rank-local parameter-name cache is invalid")
    elif set(discovered).difference(cached_names):
        raise RuntimeError("KT expert placeholder inventory changed after its initial discovery")

    placeholders = {}
    for fqn in cached_names:
        parameter = named_parameters.get(fqn)
        if parameter is None:
            raise RuntimeError(f"Cached KT rank-local parameter FQN is no longer registered: {fqn!r}")
        placeholders[fqn] = parameter
    return placeholders


# =============================================================================
# kt_weight_path Loading Functions
# =============================================================================


@dataclass
class INT8ExpertWeights:
    """Container for INT8 expert weights with scales."""

    gate_proj: torch.Tensor
    gate_scale: torch.Tensor
    up_proj: torch.Tensor
    up_scale: torch.Tensor
    down_proj: torch.Tensor
    down_scale: torch.Tensor


@dataclass
class BlockFP8ExpertWeights:
    """Raw per-expert E4M3 weights and normalized block scales.

    The lists intentionally remain unstacked: native FP8 packing consumes one
    expert pointer at a time and releases these checkpoint tensors after the
    synchronous C++ load completes.
    """

    gate_proj: list[torch.Tensor]
    gate_scale: list[torch.Tensor]
    up_proj: list[torch.Tensor]
    up_scale: list[torch.Tensor]
    down_proj: list[torch.Tensor]
    down_scale: list[torch.Tensor]
    block_size: tuple[int, int] = (128, 128)


def _checkpoint_tensor_files(
    checkpoint_files: list[str],
    sharded_metadata: dict | None,
) -> dict[str, str]:
    """Return tensor key -> absolute checkpoint file without loading tensors."""

    base_dir = os.path.dirname(checkpoint_files[0])
    weight_map = (
        sharded_metadata.get("weight_map")
        if isinstance(sharded_metadata, dict)
        else None
    )
    if weight_map:
        return {
            key: os.path.join(base_dir, filename)
            for key, filename in weight_map.items()
        }

    result: dict[str, str] = {}
    for file_path in checkpoint_files:
        with safe_open(file_path, framework="pt") as handle:
            for key in handle.keys():
                result[key] = file_path
    return result


def load_block_fp8_experts_from_checkpoint_files(
    checkpoint_files: list[str],
    sharded_metadata: dict | None,
    layers_prefix: str,
    moe_config: MOEArchConfig,
    layer_idx: int,
    hidden_size: int,
    block_size: tuple[int, int] = (128, 128),
) -> BlockFP8ExpertWeights:
    """Load raw block-FP8 routed experts without stacking or dequantizing.

    Native FP8 SFT currently accepts only non-fused, CPU-resident E4M3FN
    matrices with one inverse scale per 128x128 block. Scale tensors from
    checkpoints may be BF16 or FP32; the returned scale lists are always FP32.
    """

    if not SAFETENSORS_AVAILABLE:
        raise ImportError("safetensors is required for native FP8 expert loading")
    if not checkpoint_files:
        raise FileNotFoundError("checkpoint_files is empty")
    if tuple(block_size) != (128, 128):
        raise ValueError(
            "native FP8 SFT requires weight_block_size=[128, 128], "
            f"got {tuple(block_size)}"
        )

    hidden_size = int(hidden_size)
    intermediate_size = int(moe_config.intermediate_size)
    if hidden_size % 128 or intermediate_size % 128:
        raise ValueError(
            "native FP8 SFT requires hidden and routed intermediate dimensions "
            f"divisible by 128, got hidden_size={hidden_size}, "
            f"intermediate_size={intermediate_size}"
        )

    gate_name, up_name, down_name = moe_config.weight_names
    experts_prefix = (
        f"{layers_prefix}.{layer_idx}.{moe_config.moe_layer_attr}."
        f"{moe_config.experts_attr}"
    )
    tensor_files = _checkpoint_tensor_files(checkpoint_files, sharded_metadata)
    fused_keys = (
        f"{experts_prefix}.gate_up_proj",
        f"{experts_prefix}.gate_up_proj.weight",
        f"{experts_prefix}.down_proj",
        f"{experts_prefix}.down_proj.weight",
    )
    if any(key in tensor_files for key in fused_keys):
        raise ValueError(
            "native FP8 SFT requires non-fused per-expert checkpoint weights; "
            f"layer {layer_idx} contains fused gate_up/down tensors"
        )

    projection_specs = {
        "gate": (gate_name, (intermediate_size, hidden_size)),
        "up": (up_name, (intermediate_size, hidden_size)),
        "down": (down_name, (hidden_size, intermediate_size)),
    }
    keys: list[str] = []
    for expert_idx in range(int(moe_config.expert_num)):
        base = f"{experts_prefix}.{expert_idx}"
        for projection_name, _ in projection_specs.values():
            keys.extend(
                (
                    f"{base}.{projection_name}.weight",
                    f"{base}.{projection_name}.weight_scale_inv",
                )
            )

    missing = [key for key in keys if key not in tensor_files]
    if missing:
        preview = ", ".join(missing[:3])
        suffix = " ..." if len(missing) > 3 else ""
        raise FileNotFoundError(
            f"layer {layer_idx} is missing {len(missing)} native FP8 tensors: "
            f"{preview}{suffix}"
        )

    tensors: dict[str, torch.Tensor] = {}
    keys_by_file: dict[str, list[str]] = {}
    for key in keys:
        keys_by_file.setdefault(tensor_files[key], []).append(key)
    for file_path, file_keys in keys_by_file.items():
        with safe_open(file_path, framework="pt") as handle:
            for key in file_keys:
                tensors[key] = handle.get_tensor(key)

    output: dict[str, list[torch.Tensor]] = {
        "gate_proj": [],
        "gate_scale": [],
        "up_proj": [],
        "up_scale": [],
        "down_proj": [],
        "down_scale": [],
    }
    fp8_dtype = torch.float8_e4m3fn
    for expert_idx in range(int(moe_config.expert_num)):
        base = f"{experts_prefix}.{expert_idx}"
        for label, (projection_name, expected_shape) in projection_specs.items():
            weight_key = f"{base}.{projection_name}.weight"
            scale_key = f"{base}.{projection_name}.weight_scale_inv"
            weight = tensors[weight_key]
            scale = tensors[scale_key]
            expected_scale_shape = (
                expected_shape[0] // 128,
                expected_shape[1] // 128,
            )
            if weight.device.type != "cpu" or weight.dtype != fp8_dtype:
                raise ValueError(
                    f"{weight_key} must be CPU torch.float8_e4m3fn, got "
                    f"{weight.dtype} on {weight.device}"
                )
            if tuple(weight.shape) != expected_shape:
                raise ValueError(
                    f"{weight_key} shape mismatch: expected {expected_shape}, "
                    f"got {tuple(weight.shape)}"
                )
            if scale.device.type != "cpu" or scale.dtype not in {
                torch.bfloat16,
                torch.float32,
            }:
                raise ValueError(
                    f"{scale_key} must be a BF16 or FP32 CPU tensor, got "
                    f"{scale.dtype} on {scale.device}"
                )
            if tuple(scale.shape) != expected_scale_shape:
                raise ValueError(
                    f"{scale_key} shape mismatch for 128x128 blocks: expected "
                    f"{expected_scale_shape}, got {tuple(scale.shape)}"
                )
            output[f"{label}_proj"].append(weight.contiguous())
            output[f"{label}_scale"].append(
                scale.to(dtype=torch.float32, device="cpu").contiguous()
            )

    logger.info(
        "Loaded layer %d native FP8 routed experts: experts=%d, block_size=%s",
        layer_idx,
        moe_config.expert_num,
        block_size,
    )
    return BlockFP8ExpertWeights(**output, block_size=(128, 128))


def _find_safetensor_files(kt_weight_path: str) -> list[str]:
    if not os.path.isdir(kt_weight_path):
        raise FileNotFoundError(f"kt_weight_path directory not found: {kt_weight_path}")

    safetensor_files = []
    for file in sorted(os.listdir(kt_weight_path)):
        if file.endswith(".safetensors"):
            safetensor_files.append(os.path.join(kt_weight_path, file))

    if not safetensor_files:
        raise FileNotFoundError(f"No safetensors files found in {kt_weight_path}")

    return safetensor_files


def _load_kt_weight_index(kt_weight_path: str) -> dict[str, str]:
    if not SAFETENSORS_AVAILABLE:
        raise ImportError("safetensors is required for loading kt_weight_path")

    index = {}
    safetensor_files = _find_safetensor_files(kt_weight_path)

    for file_path in safetensor_files:
        with safe_open(file_path, framework="pt") as f:
            for key in f.keys():
                index[key] = file_path

    logger.info(f"Indexed {len(index)} tensors from {len(safetensor_files)} safetensors files")
    return index


def _dequant_fp8_experts(
    weights: list[torch.Tensor], scales: list[torch.Tensor | None], block_size: tuple[int, int]
) -> torch.Tensor:
    """Dequantize a list of FP8 expert weights and stack them (batched, vectorized).

    Args:
        weights: list of [out, in] float8_e4m3fn tensors (one per expert)
        scales: list of [out//bs_m, in//bs_n] scale_inv tensors (one per expert, may be None)
        block_size: (bs_m, bs_n)

    Returns:
        Stacked BF16 tensor of shape [num_experts, out, in]
    """
    has_scales = scales[0] is not None
    if not has_scales:
        return torch.stack(weights, dim=0).to(torch.bfloat16).cpu().contiguous()

    bs_m, bs_n = block_size
    n = len(weights)
    out_features, in_features = weights[0].shape

    # Stack all experts: [N, out, in] fp8 -> reshape to blocks -> bf16
    w = torch.stack(weights, dim=0)  # [N, out, in] fp8
    w = w.reshape(n, out_features // bs_m, bs_m, in_features // bs_n, bs_n)
    w = w.to(torch.bfloat16)

    # Stack all scales: [N, out//bs_m, in//bs_n] -> bf16, broadcast multiply
    s = torch.stack(scales, dim=0).to(torch.bfloat16)  # [N, out//bs_m, in//bs_n]
    w = w * s[:, :, None, :, None]

    return w.reshape(n, out_features, in_features).contiguous()


def load_experts_from_checkpoint_files(
    checkpoint_files: list[str],
    sharded_metadata: dict | None,
    layers_prefix: str,
    moe_config: MOEArchConfig,
    layer_idx: int,
    block_size: tuple[int, int] | None = None,
) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
    if not SAFETENSORS_AVAILABLE:
        raise ImportError("safetensors is required for loading experts from checkpoint files")

    if not checkpoint_files:
        raise FileNotFoundError("checkpoint_files is empty")

    t0 = time.time()

    weight_map = None
    base_dir = os.path.dirname(checkpoint_files[0])
    if sharded_metadata is not None:
        weight_map = sharded_metadata.get("weight_map", None)

    gate_name, up_name, down_name = moe_config.weight_names
    experts_prefix = f"{layers_prefix}.{layer_idx}.{moe_config.moe_layer_attr}.{moe_config.experts_attr}"
    fused_gate_up_key = f"{experts_prefix}.gate_up_proj"
    fused_down_key = f"{experts_prefix}.down_proj"
    is_fused = weight_map is not None and fused_gate_up_key in weight_map

    if is_fused:
        keys = [fused_gate_up_key, fused_down_key]
    else:
        keys = []
        for expert_idx in range(moe_config.expert_num):
            base = f"{experts_prefix}.{expert_idx}"
            keys.append(f"{base}.{gate_name}.weight")
            keys.append(f"{base}.{gate_name}.weight_scale_inv")
            keys.append(f"{base}.{up_name}.weight")
            keys.append(f"{base}.{up_name}.weight_scale_inv")
            keys.append(f"{base}.{down_name}.weight")
            keys.append(f"{base}.{down_name}.weight_scale_inv")

    keys_by_file: dict[str, list[str]] = {}
    mapped_count = 0
    unmapped_count = 0
    for key in keys:
        if weight_map is not None:
            filename = weight_map.get(key)
            if filename is None:
                unmapped_count += 1
                continue
            mapped_count += 1
            file_path = os.path.join(base_dir, filename)
        else:
            file_path = checkpoint_files[0]
        keys_by_file.setdefault(file_path, []).append(key)

    print(
        f"[kt_moe] Layer {layer_idx}: key mapping done in {time.time()-t0:.1f}s — "
        f"total_keys={len(keys)}, mapped={mapped_count}, unmapped={unmapped_count}, "
        f"files_to_open={len(keys_by_file)}",
        flush=True,
    )

    t1 = time.time()
    tensor_map: dict[str, torch.Tensor] = {}
    for file_idx, (file_path, file_keys) in enumerate(keys_by_file.items()):
        with safe_open(file_path, framework="pt") as f:
            available_keys = set(f.keys())
            for key in file_keys:
                if key in available_keys:
                    tensor_map[key] = f.get_tensor(key)
        if file_idx == 0:
            print(
                f"[kt_moe] Layer {layer_idx}: first file loaded ({os.path.basename(file_path)}, "
                f"{len(file_keys)} keys) in {time.time()-t1:.1f}s",
                flush=True,
            )

    print(
        f"[kt_moe] Layer {layer_idx}: all files loaded in {time.time()-t1:.1f}s — "
        f"tensor_map has {len(tensor_map)} tensors",
        flush=True,
    )

    t2 = time.time()
    if is_fused:
        gate_up = tensor_map.get(fused_gate_up_key)
        down = tensor_map.get(fused_down_key)
        if gate_up is None or down is None:
            raise FileNotFoundError(f"Missing fused expert weights for layer {layer_idx}")
        gate_up = gate_up.cpu().to(torch.bfloat16).contiguous()
        down = down.cpu().to(torch.bfloat16)
        vlm_weights = _canonicalize_qwen3_vl_fused_expert_weights(gate_up, down, moe_config)
        if vlm_weights is not None:
            gate_proj, up_proj, down_proj = vlm_weights
        else:
            intermediate = gate_up.shape[1] // 2
            gate_proj = gate_up[:, :intermediate, :].contiguous()
            up_proj = gate_up[:, intermediate:, :].contiguous()
            down_proj = down.contiguous()
        del gate_up
        print(
            f"[kt_moe] Layer {layer_idx}: fused expert format — "
            f"split gate_up_proj [{gate_proj.shape}] + down [{down_proj.shape}]",
            flush=True,
        )
        print(
            f"[kt_moe] Layer {layer_idx}: done — dtype={gate_proj.dtype}, "
            f"shape={gate_proj.shape}, dequant=0.0s, total={time.time()-t0:.1f}s",
            flush=True,
        )
        return gate_proj, up_proj, down_proj

    gate_weights = []
    up_weights = []
    down_weights = []
    gate_scales = []
    up_scales = []
    down_scales = []
    for expert_idx in range(moe_config.expert_num):
        base = f"{experts_prefix}.{expert_idx}"
        gate_key = f"{base}.{gate_name}.weight"
        up_key = f"{base}.{up_name}.weight"
        down_key = f"{base}.{down_name}.weight"
        if gate_key not in tensor_map or up_key not in tensor_map or down_key not in tensor_map:
            raise FileNotFoundError(f"Missing expert weights for layer {layer_idx}, expert {expert_idx}")
        gate_weights.append(tensor_map[gate_key])
        up_weights.append(tensor_map[up_key])
        down_weights.append(tensor_map[down_key])
        gate_scales.append(tensor_map.get(f"{base}.{gate_name}.weight_scale_inv"))
        up_scales.append(tensor_map.get(f"{base}.{up_name}.weight_scale_inv"))
        down_scales.append(tensor_map.get(f"{base}.{down_name}.weight_scale_inv"))

    # Check if weights are FP8 and need dequantization
    t2 = time.time()
    is_fp8 = gate_weights[0].dtype == torch.float8_e4m3fn
    if is_fp8:
        if block_size is None:
            block_size = (128, 128)
        print(
            f"[kt_moe] Layer {layer_idx}: FP8 expert weights detected, "
            f"dequantizing with block_size={block_size} "
            f"(has_scales={gate_scales[0] is not None})",
            flush=True,
        )
        gate_proj = _dequant_fp8_experts(gate_weights, gate_scales, block_size)
        up_proj = _dequant_fp8_experts(up_weights, up_scales, block_size)
        down_proj = _dequant_fp8_experts(down_weights, down_scales, block_size)
    else:
        gate_proj = torch.stack(gate_weights, dim=0).cpu().to(torch.bfloat16).contiguous()
        up_proj = torch.stack(up_weights, dim=0).cpu().to(torch.bfloat16).contiguous()
        down_proj = torch.stack(down_weights, dim=0).cpu().to(torch.bfloat16).contiguous()

    print(
        f"[kt_moe] Layer {layer_idx}: done — dtype={gate_proj.dtype}, shape={gate_proj.shape}, "
        f"dequant={time.time()-t2:.1f}s, total={time.time()-t0:.1f}s",
        flush=True,
    )
    return gate_proj, up_proj, down_proj


def load_experts_from_kt_weight_path(
    kt_weight_path: str,
    layer_idx: int,
    num_experts: int,
    hidden_size: int,
    intermediate_size: int,
) -> INT8ExpertWeights:
    """Load INT8 preprocessed expert weights from kt_weight_path for a specific layer."""
    if not SAFETENSORS_AVAILABLE:
        raise ImportError("safetensors is required for loading kt_weight_path")

    index = _load_kt_weight_index(kt_weight_path)

    numa_count = 0
    test_key_prefix = f"blk.{layer_idx}.ffn_gate_exps.0.numa."
    for key in index.keys():
        if key.startswith(test_key_prefix) and key.endswith(".weight"):
            numa_idx = int(key.split("numa.")[1].split(".")[0])
            numa_count = max(numa_count, numa_idx + 1)

    if numa_count == 0:
        raise FileNotFoundError(
            f"No weights found for layer {layer_idx} in {kt_weight_path}. "
            f"Expected keys like 'blk.{layer_idx}.ffn_gate_exps.0.numa.0.weight'"
        )

    logger.info(f"Loading INT8 weights for layer {layer_idx}: {num_experts} experts, {numa_count} NUMA partitions")

    gate_weights_list = []
    gate_scales_list = []
    up_weights_list = []
    up_scales_list = []
    down_weights_list = []
    down_scales_list = []

    for expert_idx in range(num_experts):
        gate_w_parts = []
        gate_s_parts = []
        for numa_idx in range(numa_count):
            w_key = f"blk.{layer_idx}.ffn_gate_exps.{expert_idx}.numa.{numa_idx}.weight"
            s_key = f"blk.{layer_idx}.ffn_gate_exps.{expert_idx}.numa.{numa_idx}.scale"

            if w_key not in index:
                raise FileNotFoundError(f"Weight key not found: {w_key}")

            with safe_open(index[w_key], framework="pt") as f:
                gate_w_parts.append(f.get_tensor(w_key))
                gate_s_parts.append(f.get_tensor(s_key))

        gate_w = torch.cat(gate_w_parts, dim=0)
        gate_s = torch.cat(gate_s_parts, dim=0)
        gate_w = gate_w.view(intermediate_size, hidden_size)

        gate_weights_list.append(gate_w)
        gate_scales_list.append(gate_s)

        up_w_parts = []
        up_s_parts = []
        for numa_idx in range(numa_count):
            w_key = f"blk.{layer_idx}.ffn_up_exps.{expert_idx}.numa.{numa_idx}.weight"
            s_key = f"blk.{layer_idx}.ffn_up_exps.{expert_idx}.numa.{numa_idx}.scale"

            if w_key not in index:
                raise FileNotFoundError(f"Weight key not found: {w_key}")

            with safe_open(index[w_key], framework="pt") as f:
                up_w_parts.append(f.get_tensor(w_key))
                up_s_parts.append(f.get_tensor(s_key))

        up_w = torch.cat(up_w_parts, dim=0)
        up_s = torch.cat(up_s_parts, dim=0)
        up_w = up_w.view(intermediate_size, hidden_size)

        up_weights_list.append(up_w)
        up_scales_list.append(up_s)

        down_w_parts = []
        down_s_parts = []
        for numa_idx in range(numa_count):
            w_key = f"blk.{layer_idx}.ffn_down_exps.{expert_idx}.numa.{numa_idx}.weight"
            s_key = f"blk.{layer_idx}.ffn_down_exps.{expert_idx}.numa.{numa_idx}.scale"

            if w_key not in index:
                raise FileNotFoundError(f"Weight key not found: {w_key}")

            with safe_open(index[w_key], framework="pt") as f:
                down_w_parts.append(f.get_tensor(w_key))
                down_s_parts.append(f.get_tensor(s_key))

        down_w = torch.cat(down_w_parts, dim=0)
        down_s = torch.cat(down_s_parts, dim=0)
        down_w = down_w.view(hidden_size, intermediate_size)

        down_weights_list.append(down_w)
        down_scales_list.append(down_s)

    gate_proj = torch.stack(gate_weights_list, dim=0)
    gate_scale = torch.stack(gate_scales_list, dim=0)
    up_proj = torch.stack(up_weights_list, dim=0)
    up_scale = torch.stack(up_scales_list, dim=0)
    down_proj = torch.stack(down_weights_list, dim=0)
    down_scale = torch.stack(down_scales_list, dim=0)

    return INT8ExpertWeights(
        gate_proj=gate_proj,
        gate_scale=gate_scale,
        up_proj=up_proj,
        up_scale=up_scale,
        down_proj=down_proj,
        down_scale=down_scale,
    )