litgpt/scripts/convert_lit_checkpoint.py

# Copyright Lightning AI. Licensed under the Apache License 2.0, see LICENSE file.

import gc
from collections import defaultdict
from functools import partial
from pathlib import Path
from pprint import pprint
from typing import Dict, Optional, Union

import torch
from lightning.fabric.utilities.load import _NotYetLoadedTensor as NotYetLoadedTensor

from litgpt import Config
from litgpt.scripts.convert_hf_checkpoint import layer_template, load_param
from litgpt.utils import extend_checkpoint_dir, incremental_save, lazy_load


def copy_weights_falcon(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "transformer.word_embeddings.weight",
        "transformer.h.{}.attn.qkv.weight": "transformer.h.{}.self_attention.query_key_value.weight",
        "transformer.h.{}.attn.proj.weight": "transformer.h.{}.self_attention.dense.weight",
        "transformer.h.{}.mlp.fc.weight": "transformer.h.{}.mlp.dense_h_to_4h.weight",
        "transformer.h.{}.mlp.proj.weight": "transformer.h.{}.mlp.dense_4h_to_h.weight",
        "transformer.ln_f.bias": "transformer.ln_f.bias",
        "transformer.ln_f.weight": "transformer.ln_f.weight",
        "lm_head.weight": "lm_head.weight",
    }
    # the original model definition is different for each size
    if "7b" in config.name:
        weight_map.update(
            {
                "transformer.h.{}.norm_1.bias": "transformer.h.{}.input_layernorm.bias",
                "transformer.h.{}.norm_1.weight": "transformer.h.{}.input_layernorm.weight",
            }
        )
    elif "40b" in config.name or "180B" in config.name:
        weight_map.update(
            {
                "transformer.h.{}.norm_1.bias": "transformer.h.{}.ln_attn.bias",
                "transformer.h.{}.norm_1.weight": "transformer.h.{}.ln_attn.weight",
                "transformer.h.{}.norm_2.bias": "transformer.h.{}.ln_mlp.bias",
                "transformer.h.{}.norm_2.weight": "transformer.h.{}.ln_mlp.weight",
            }
        )
    else:
        raise NotImplementedError

    for from_name, param in lit_weights.items():
        name_template, layer_idx = layer_template(from_name)
        to_name = weight_map[name_template].format(layer_idx)
        param = load_param(param, from_name, None)
        if from_name.endswith((".attn.qkv.weight", ".attn.qkv.bias")):
            # Reassemble [q, q, ..., k, k, ..., v, v, ...] --> [q, k, v, q, k, v, ...]
            param = qkv_reassemble(param, config)
        if saver is not None:
            param = saver.store_early(param)
        state_dict[to_name] = param


def copy_weights_gpt_neox(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "gpt_neox.embed_in.weight",
        "transformer.h.{}.norm_1.bias": "gpt_neox.layers.{}.input_layernorm.bias",
        "transformer.h.{}.norm_1.weight": "gpt_neox.layers.{}.input_layernorm.weight",
        "transformer.h.{}.attn.qkv.bias": "gpt_neox.layers.{}.attention.query_key_value.bias",
        "transformer.h.{}.attn.qkv.weight": "gpt_neox.layers.{}.attention.query_key_value.weight",
        "transformer.h.{}.attn.proj.bias": "gpt_neox.layers.{}.attention.dense.bias",
        "transformer.h.{}.attn.proj.weight": "gpt_neox.layers.{}.attention.dense.weight",
        "transformer.h.{}.norm_2.bias": "gpt_neox.layers.{}.post_attention_layernorm.bias",
        "transformer.h.{}.norm_2.weight": "gpt_neox.layers.{}.post_attention_layernorm.weight",
        "transformer.h.{}.mlp.fc.bias": "gpt_neox.layers.{}.mlp.dense_h_to_4h.bias",
        "transformer.h.{}.mlp.fc.weight": "gpt_neox.layers.{}.mlp.dense_h_to_4h.weight",
        "transformer.h.{}.mlp.proj.bias": "gpt_neox.layers.{}.mlp.dense_4h_to_h.bias",
        "transformer.h.{}.mlp.proj.weight": "gpt_neox.layers.{}.mlp.dense_4h_to_h.weight",
        "transformer.ln_f.bias": "gpt_neox.final_layer_norm.bias",
        "transformer.ln_f.weight": "gpt_neox.final_layer_norm.weight",
        "lm_head.weight": "embed_out.weight",
    }

    for from_name, param in lit_weights.items():
        name_template, layer_idx = layer_template(from_name)
        to_name = weight_map[name_template].format(layer_idx)
        param = load_param(param, from_name, None)
        if from_name.endswith((".attn.qkv.weight", ".attn.qkv.bias")):
            # Reassemble [q, q, ..., k, k, ..., v, v, ...] --> [q, k, v, q, k, v, ...]
            param = qkv_reassemble(param, config)
        if saver is not None:
            param = saver.store_early(param)
        state_dict[to_name] = param


def copy_weights_llama(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    untie_weights: bool = False,
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "model.embed_tokens.weight",
        "transformer.h.{}.norm_1.weight": "model.layers.{}.input_layernorm.weight",
        "transformer.h.{}.norm_1.bias": "model.layers.{}.input_layernorm.bias",
        "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.o_proj.weight",
        "transformer.h.{}.norm_2.weight": "model.layers.{}.post_attention_layernorm.weight",
        "transformer.h.{}.norm_2.bias": "model.layers.{}.post_attention_layernorm.bias",
        "transformer.ln_f.weight": "model.norm.weight",
        "transformer.ln_f.bias": "model.norm.bias",
        "lm_head.weight": "lm_head.weight",
    }
    if config.mlp_class_name == "LLaMAMoE":
        weight_map.update(
            {
                "transformer.h.{}.mlp.gate.weight": "model.layers.{}.block_sparse_moe.gate.weight",
                "transformer.h.{}.mlp.experts.{}.fc_1.weight": "model.layers.{}.block_sparse_moe.experts.{}.w1.weight",
                "transformer.h.{}.mlp.experts.{}.fc_2.weight": "model.layers.{}.block_sparse_moe.experts.{}.w3.weight",
                "transformer.h.{}.mlp.experts.{}.proj.weight": "model.layers.{}.block_sparse_moe.experts.{}.w2.weight",
            }
        )
    elif config.mlp_class_name in ("LLaMAMLP", "GemmaMLP"):
        weight_map.update(
            {
                "transformer.h.{}.mlp.fc_1.weight": "model.layers.{}.mlp.gate_proj.weight",
                "transformer.h.{}.mlp.fc_2.weight": "model.layers.{}.mlp.up_proj.weight",
                "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.down_proj.weight",
            }
        )
    else:
        raise NotImplementedError

    for from_name, param in lit_weights.items():
        if from_name == "lm_head.weight" and untie_weights:
            continue
        name_template, *ids = layer_template(from_name, num_matches=2)
        param = load_param(param, from_name, None)
        if from_name.endswith(".attn.qkv.weight"):
            to_names = (
                "model.layers.{}.self_attn.q_proj.weight".format(*ids),
                "model.layers.{}.self_attn.k_proj.weight".format(*ids),
                "model.layers.{}.self_attn.v_proj.weight".format(*ids),
            )
            params = param.split(
                (
                    config.n_head * config.head_size,
                    config.n_query_groups * config.head_size,
                    config.n_query_groups * config.head_size,
                )
            )
        else:
            to_names = (weight_map[name_template].format(*ids),)
            params = (param,)

        for to_name, param in zip(to_names, params):
            if saver is not None:
                param = saver.store_early(param)
            state_dict[to_name] = param


def copy_weights_gemma_2(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    untie_weights: bool = False,
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "model.embed_tokens.weight",
        "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.o_proj.weight",
        "transformer.h.{}.mlp.fc_1.weight": "model.layers.{}.mlp.gate_proj.weight",
        "transformer.h.{}.mlp.fc_2.weight": "model.layers.{}.mlp.up_proj.weight",
        "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.down_proj.weight",
        "transformer.h.{}.norm_1.weight": "model.layers.{}.input_layernorm.weight",
        "transformer.h.{}.post_attention_norm.weight": "model.layers.{}.post_attention_layernorm.weight",
        "transformer.h.{}.norm_2.weight": "model.layers.{}.pre_feedforward_layernorm.weight",
        "transformer.h.{}.post_mlp_norm.weight": "model.layers.{}.post_feedforward_layernorm.weight",
        "transformer.ln_f.weight": "model.norm.weight",
        "lm_head.weight": "lm_head.weight",
    }

    for from_name, param in lit_weights.items():
        if from_name == "lm_head.weight" and untie_weights:
            continue
        name_template, *ids = layer_template(from_name, num_matches=2)
        param = load_param(param, from_name, None)
        if from_name.endswith(".attn.qkv.weight"):
            to_names = (
                "model.layers.{}.self_attn.q_proj.weight".format(*ids),
                "model.layers.{}.self_attn.k_proj.weight".format(*ids),
                "model.layers.{}.self_attn.v_proj.weight".format(*ids),
            )
            params = param.split(
                (
                    config.n_head * config.head_size,
                    config.n_query_groups * config.head_size,
                    config.n_query_groups * config.head_size,
                )
            )
        else:
            to_names = (weight_map[name_template].format(*ids),)
            params = (param,)

        for to_name, param in zip(to_names, params):
            if saver is not None:
                param = saver.store_early(param)
            state_dict[to_name] = param


def copy_weights_gemma_3(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    untie_weights: bool = False,
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "model.embed_tokens.weight",
        "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.o_proj.weight",
        "transformer.h.{}.mlp.fc_1.weight": "model.layers.{}.mlp.gate_proj.weight",
        "transformer.h.{}.mlp.fc_2.weight": "model.layers.{}.mlp.up_proj.weight",
        "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.down_proj.weight",
        "transformer.h.{}.norm_1.weight": "model.layers.{}.input_layernorm.weight",
        "transformer.h.{}.post_attention_norm.weight": "model.layers.{}.post_attention_layernorm.weight",
        "transformer.h.{}.norm_2.weight": "model.layers.{}.pre_feedforward_layernorm.weight",
        "transformer.h.{}.post_mlp_norm.weight": "model.layers.{}.post_feedforward_layernorm.weight",
        "transformer.ln_f.weight": "model.norm.weight",
        "lm_head.weight": "lm_head.weight",
        "transformer.h.{}.attn.norm_q.weight": "model.layers.{}.self_attn.q_norm.weight",
        "transformer.h.{}.attn.norm_k.weight": "model.layers.{}.self_attn.k_norm.weight",
    }

    for from_name, param in lit_weights.items():
        if from_name == "lm_head.weight" and untie_weights:
            continue
        name_template, *ids = layer_template(from_name, num_matches=2)
        param = load_param(param, from_name, None)
        if from_name.endswith(".attn.qkv.weight"):
            to_names = (
                "model.layers.{}.self_attn.q_proj.weight".format(*ids),
                "model.layers.{}.self_attn.k_proj.weight".format(*ids),
                "model.layers.{}.self_attn.v_proj.weight".format(*ids),
            )
            params = param.split(
                (
                    config.n_head * config.head_size,
                    config.n_query_groups * config.head_size,
                    config.n_query_groups * config.head_size,
                )
            )
        else:
            to_names = (weight_map[name_template].format(*ids),)
            params = (param,)

        for to_name, param in zip(to_names, params):
            if saver is not None:
                param = saver.store_early(param)
            state_dict[to_name] = param


def copy_weights_phi(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "model.embed_tokens.weight",
        "transformer.h.{}.norm_1.weight": "model.layers.{}.input_layernorm.weight",
        "transformer.h.{}.norm_1.bias": "model.layers.{}.input_layernorm.bias",
        "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.dense.weight",
        "transformer.h.{}.attn.proj.bias": "model.layers.{}.self_attn.dense.bias",
        "transformer.h.{}.mlp.fc.weight": "model.layers.{}.mlp.fc1.weight",
        "transformer.h.{}.mlp.fc.bias": "model.layers.{}.mlp.fc1.bias",
        "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.fc2.weight",
        "transformer.h.{}.mlp.proj.bias": "model.layers.{}.mlp.fc2.bias",
        "transformer.ln_f.weight": "model.final_layernorm.weight",
        "transformer.ln_f.bias": "model.final_layernorm.bias",
        "lm_head.weight": "lm_head.weight",
        "lm_head.bias": "lm_head.bias",
    }
    if config.name.lower().startswith(("phi-3", "phi-4")):
        weight_map.update(
            {
                "transformer.h.{}.attn.qkv.weight": "model.layers.{}.self_attn.qkv_proj.weight",
                "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.o_proj.weight",
                "transformer.h.{}.norm_2.weight": "model.layers.{}.post_attention_layernorm.weight",
                "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.down_proj.weight",
                "transformer.ln_f.weight": "model.norm.weight",
            }
        )
        gate_up_proj_weights = defaultdict(dict)

    for from_name, param in lit_weights.items():
        if from_name == "lm_head.weight" and config.name.startswith("Phi-4"):
            continue
        name_template, layer_idx = layer_template(from_name)
        param = load_param(param, from_name, None)
        if from_name.endswith((".attn.qkv.weight", ".attn.qkv.bias")):
            if config.name.lower().startswith(("phi-3", "phi-4")):
                to_names = (weight_map[name_template].format(layer_idx),)
                params = (param,)
            else:
                weight_type = from_name.split(".")[-1]  # weight or bias
                to_names = (
                    f"model.layers.{{}}.self_attn.q_proj.{weight_type}".format(layer_idx),
                    f"model.layers.{{}}.self_attn.k_proj.{weight_type}".format(layer_idx),
                    f"model.layers.{{}}.self_attn.v_proj.{weight_type}".format(layer_idx),
                )
                params = param.split(
                    (
                        config.n_head * config.head_size,
                        config.n_query_groups * config.head_size,
                        config.n_query_groups * config.head_size,
                    )
                )
        elif from_name.endswith((".fc_1.weight", ".fc_2.weight")):
            weight = load_param(param, from_name, None)
            weight_name = from_name.split(".")[-2]
            gate_up_proj_weights[layer_idx][weight_name] = weight
        else:
            to_names = (weight_map[name_template].format(layer_idx),)
            params = (param,)

        for to_name, param in zip(to_names, params):
            if saver is not None:
                param = saver.store_early(param)
            state_dict[to_name] = param

    if config.name.lower().startswith(("phi-3", "phi-4")):
        for layer_idx in list(gate_up_proj_weights):
            fc_1_weight = gate_up_proj_weights[layer_idx]["fc_1"]
            fc_2_weight = gate_up_proj_weights[layer_idx]["fc_2"]
            weight = torch.concat([fc_1_weight, fc_2_weight], dim=0)
            layer_name = f"model.layers.{layer_idx}.mlp.gate_up_proj.weight"
            state_dict[layer_name] = weight
            del gate_up_proj_weights[layer_idx]


def copy_weights_qwen_2_5(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    untie_weights: bool = False,
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "model.embed_tokens.weight",
        "transformer.h.{}.norm_1.weight": "model.layers.{}.input_layernorm.weight",
        "transformer.h.{}.norm_2.weight": "model.layers.{}.post_attention_layernorm.weight",
        "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.o_proj.weight",
        "transformer.h.{}.mlp.fc_1.weight": "model.layers.{}.mlp.gate_proj.weight",
        "transformer.h.{}.mlp.fc_2.weight": "model.layers.{}.mlp.up_proj.weight",
        "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.down_proj.weight",
        "transformer.ln_f.weight": "model.norm.weight",
        "lm_head.weight": "lm_head.weight",
    }

    for from_name, param in lit_weights.items():
        if from_name == "lm_head.weight" and untie_weights:
            continue
        name_template, *ids = layer_template(from_name, num_matches=2)
        param = load_param(param, from_name, None)
        if from_name.endswith((".attn.qkv.weight", ".attn.qkv.bias")):
            weight_type = from_name.split(".")[-1]  # weight or bias
            to_names = (
                "model.layers.{}.self_attn.q_proj.{}".format(*ids, weight_type),
                "model.layers.{}.self_attn.k_proj.{}".format(*ids, weight_type),
                "model.layers.{}.self_attn.v_proj.{}".format(*ids, weight_type),
            )
            params = param.split(
                (
                    config.n_head * config.head_size,
                    config.n_query_groups * config.head_size,
                    config.n_query_groups * config.head_size,
                )
            )
        else:
            to_names = (weight_map[name_template].format(*ids),)
            params = (param,)

        for to_name, param in zip(to_names, params):
            if saver is not None:
                param = saver.store_early(param)
            state_dict[to_name] = param


def copy_weights_olmo2(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    untie_weights: bool = False,
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "model.embed_tokens.weight",
        "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.o_proj.weight",
        "transformer.h.{}.attn.norm_q.weight": "model.layers.{}.self_attn.q_norm.weight",
        "transformer.h.{}.attn.norm_k.weight": "model.layers.{}.self_attn.k_norm.weight",
        "transformer.h.{}.norm_2.weight": "model.layers.{}.post_attention_layernorm.weight",
        "transformer.h.{}.norm_2.bias": "model.layers.{}.post_attention_layernorm.bias",
        "transformer.h.{}.post_mlp_norm.weight": "model.layers.{}.post_feedforward_layernorm.weight",
        "transformer.ln_f.weight": "model.norm.weight",
        "transformer.ln_f.bias": "model.norm.bias",
        "lm_head.weight": "lm_head.weight",
    }
    if config.mlp_class_name in ("LLaMAMLP", "GemmaMLP"):
        weight_map.update(
            {
                "transformer.h.{}.mlp.fc_1.weight": "model.layers.{}.mlp.gate_proj.weight",
                "transformer.h.{}.mlp.fc_2.weight": "model.layers.{}.mlp.up_proj.weight",
                "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.down_proj.weight",
            }
        )
    else:
        raise NotImplementedError

    for from_name, param in lit_weights.items():
        if from_name == "lm_head.weight" and untie_weights:
            continue
        name_template, *ids = layer_template(from_name, num_matches=2)
        param = load_param(param, from_name, None)
        if from_name.endswith(".attn.qkv.weight"):
            to_names = (
                "model.layers.{}.self_attn.q_proj.weight".format(*ids),
                "model.layers.{}.self_attn.k_proj.weight".format(*ids),
                "model.layers.{}.self_attn.v_proj.weight".format(*ids),
            )
            params = param.split(
                (
                    config.n_head * config.head_size,
                    config.n_query_groups * config.head_size,
                    config.n_query_groups * config.head_size,
                )
            )
        else:
            to_names = (weight_map[name_template].format(*ids),)
            params = (param,)

        for to_name, param in zip(to_names, params):
            if saver is not None:
                param = saver.store_early(param)
            state_dict[to_name] = param


def copy_weights_qwen_3(
    config: Config,
    state_dict: Dict[str, torch.Tensor],
    lit_weights: Dict[str, Union[torch.Tensor, NotYetLoadedTensor]],
    untie_weights: bool = False,
    saver: Optional[incremental_save] = None,
) -> None:
    weight_map = {
        "transformer.wte.weight": "model.embed_tokens.weight",
        "transformer.h.{}.norm_1.weight": "model.layers.{}.input_layernorm.weight",
        "transformer.h.{}.norm_2.weight": "model.layers.{}.post_attention_layernorm.weight",
        "transformer.h.{}.attn.proj.weight": "model.layers.{}.self_attn.o_proj.weight",
        "transformer.h.{}.attn.norm_q.weight": "model.layers.{}.self_attn.q_norm.weight",
        "transformer.h.{}.attn.norm_k.weight": "model.layers.{}.self_attn.k_norm.weight",
        "transformer.ln_f.weight": "model.norm.weight",
        "lm_head.weight": "lm_head.weight",
    }
    if config.mlp_class_name == "LLaMAMoE":
        weight_map.update(
            {
                "transformer.h.{}.mlp.gate.weight": "model.layers.{}.mlp.gate.weight",
                "transformer.h.{}.mlp.experts.{}.fc_1.weight": "model.layers.{}.mlp.experts.{}.gate_proj.weight",
                "transformer.h.{}.mlp.experts.{}.fc_2.weight": "model.layers.{}.mlp.experts.{}.up_proj.weight",
                "transformer.h.{}.mlp.experts.{}.proj.weight": "model.layers.{}.mlp.experts.{}.down_proj.weight",
            }
        )
    elif config.mlp_class_name == "LLaMAMLP":
        weight_map.update(
            {
                "transformer.h.{}.mlp.fc_1.weight": "model.layers.{}.mlp.gate_proj.weight",
                "transformer.h.{}.mlp.fc_2.weight": "model.layers.{}.mlp.up_proj.weight",
                "transformer.h.{}.mlp.proj.weight": "model.layers.{}.mlp.down_proj.weight",
            }
        )
    else:
        raise NotImplementedError

    for from_name, param in lit_weights.items():
        if from_name == "lm_head.weight" and untie_weights:
            continue
        name_template, *ids = layer_template(from_name, num_matches=2)
        param = load_param(param, from_name, None)
        if from_name.endswith(".attn.qkv.weight"):
            weight_type = from_name.split(".")[-1]  # weight or bias
            to_names = (
                "model.layers.{}.self_attn.q_proj.{}".format(*ids, weight_type),
                "model.layers.{}.self_attn.k_proj.{}".format(*ids, weight_type),
                "model.layers.{}.self_attn.v_proj.{}".format(*ids, weight_type),
            )
            params = param.split(
                (
                    config.n_head * config.head_size,
                    config.n_query_groups * config.head_size,
                    config.n_query_groups * config.head_size,
                )
            )
        else:
            to_names = (weight_map[name_template].format(*ids),)
            params = (param,)

        for to_name, param in zip(to_names, params):
            if saver is not None:
                param = saver.store_early(param)
            state_dict[to_name] = param


def qkv_reassemble(param: Union[torch.Tensor, NotYetLoadedTensor], config: Config) -> torch.Tensor:
    """Reassemble from a normal to an interleaved placement in a QKV matrix.
    [Q, Q, ..., K, K, ..., V, V, ...] --> [Q, K, V, Q, K, V, ...]
    """
    q, k, v = param.split(
        (
            config.n_head * config.head_size,
            config.n_query_groups * config.head_size,
            config.n_query_groups * config.head_size,
        )
    )
    qs = q.split(config.n_head // config.n_query_groups * config.head_size)
    ks = k.split(config.head_size)
    vs = v.split(config.head_size)
    interleaved = [t for group in zip(qs, ks, vs) for t in group]
    return torch.cat(interleaved)


def check_conversion_supported(lit_weights: Dict[str, torch.Tensor]) -> None:
    if any("lora" in wn for wn in lit_weights):
        raise ValueError("Checkpoints with LoRA weights cannot be converted. Call `scripts/merge_lora.py` first.")
    if any("adapter" in wn or "gating_factor" in wn for wn in lit_weights):
        raise NotImplementedError("Converting adapter models is not supported.")


@torch.inference_mode()
def convert_lit_checkpoint(checkpoint_dir: Path, output_dir: Path) -> None:
    """Convert a LitGPT trained checkpoint into a Hugging Face Transformers checkpoint."""
    checkpoint_dir = extend_checkpoint_dir(checkpoint_dir)
    pprint(locals())

    config = Config.from_file(checkpoint_dir / "model_config.yaml")

    output_dir.mkdir(parents=True, exist_ok=True)
    output_path = output_dir / "model.pth"

    if "falcon" in config.name:
        copy_fn = partial(copy_weights_falcon, config)
    elif config.name.startswith("Gemma-2"):
        copy_fn = partial(copy_weights_gemma_2, config)
    elif config.name.lower().startswith("phi"):
        copy_fn = partial(copy_weights_phi, config)
    elif config.name.lower().startswith(("qwen2.5", "qwq", "qwen2")):
        copy_fn = partial(copy_weights_qwen_2_5, config)
    elif config.name.lower().startswith("olmo-2-"):
        copy_fn = partial(copy_weights_olmo2, config)
    elif config.name.lower().startswith("qwen3"):
        copy_fn = partial(copy_weights_qwen_3, config)
    elif config.mlp_class_name in ("LLaMAMLP", "GemmaMLP", "LLaMAMoE"):
        untie_weights = "Gemma" in config.name
        copy_fn = partial(copy_weights_llama, config, untie_weights=untie_weights)
    else:
        copy_fn = partial(copy_weights_gpt_neox, config)

    # initialize a new empty state dict to hold our new weights
    sd = {}
    with incremental_save(output_path) as saver:
        lit_weights = lazy_load(checkpoint_dir / "lit_model.pth")
        lit_weights = lit_weights.get("model", lit_weights)
        check_conversion_supported(lit_weights)
        copy_fn(sd, lit_weights, saver=saver)
        gc.collect()
        saver.save(sd)