fix klein lora loading.

src/diffusers/loaders/lora_conversion_utils.py

@@ -2443,6 +2443,191 @@ def _convert_non_diffusers_flux2_lora_to_diffusers(state_dict):
     return converted_state_dict
 
 
+def _convert_kohya_flux2_lora_to_diffusers(state_dict):
+    def _convert_to_ai_toolkit(sds_sd, ait_sd, sds_key, ait_key):
+        if sds_key + ".lora_down.weight" not in sds_sd:
+            return
+        down_weight = sds_sd.pop(sds_key + ".lora_down.weight")
+
+        # scale weight by alpha and dim
+        rank = down_weight.shape[0]
+        default_alpha = torch.tensor(rank, dtype=down_weight.dtype, device=down_weight.device, requires_grad=False)
+        alpha = sds_sd.pop(sds_key + ".alpha", default_alpha).item()
+        scale = alpha / rank
+
+        scale_down = scale
+        scale_up = 1.0
+        while scale_down * 2 < scale_up:
+            scale_down *= 2
+            scale_up /= 2
+
+        ait_sd[ait_key + ".lora_A.weight"] = down_weight * scale_down
+        ait_sd[ait_key + ".lora_B.weight"] = sds_sd.pop(sds_key + ".lora_up.weight") * scale_up
+
+    def _convert_to_ai_toolkit_cat(sds_sd, ait_sd, sds_key, ait_keys, dims=None):
+        if sds_key + ".lora_down.weight" not in sds_sd:
+            return
+        down_weight = sds_sd.pop(sds_key + ".lora_down.weight")
+        up_weight = sds_sd.pop(sds_key + ".lora_up.weight")
+        sd_lora_rank = down_weight.shape[0]
+
+        default_alpha = torch.tensor(
+            sd_lora_rank, dtype=down_weight.dtype, device=down_weight.device, requires_grad=False
+        )
+        alpha = sds_sd.pop(sds_key + ".alpha", default_alpha)
+        scale = alpha / sd_lora_rank
+
+        scale_down = scale
+        scale_up = 1.0
+        while scale_down * 2 < scale_up:
+            scale_down *= 2
+            scale_up /= 2
+
+        down_weight = down_weight * scale_down
+        up_weight = up_weight * scale_up
+
+        num_splits = len(ait_keys)
+        if dims is None:
+            dims = [up_weight.shape[0] // num_splits] * num_splits
+        else:
+            assert sum(dims) == up_weight.shape[0]
+
+        # check if upweight is sparse
+        is_sparse = False
+        if sd_lora_rank % num_splits == 0:
+            ait_rank = sd_lora_rank // num_splits
+            is_sparse = True
+            i = 0
+            for j in range(len(dims)):
+                for k in range(len(dims)):
+                    if j == k:
+                        continue
+                    is_sparse = is_sparse and torch.all(
+                        up_weight[i : i + dims[j], k * ait_rank : (k + 1) * ait_rank] == 0
+                    )
+                i += dims[j]
+            if is_sparse:
+                logger.info(f"weight is sparse: {sds_key}")
+
+        ait_down_keys = [k + ".lora_A.weight" for k in ait_keys]
+        ait_up_keys = [k + ".lora_B.weight" for k in ait_keys]
+        if not is_sparse:
+            ait_sd.update(dict.fromkeys(ait_down_keys, down_weight))
+            ait_sd.update({k: v for k, v in zip(ait_up_keys, torch.split(up_weight, dims, dim=0))})  # noqa: C416
+        else:
+            ait_sd.update({k: v for k, v in zip(ait_down_keys, torch.chunk(down_weight, num_splits, dim=0))})  # noqa: C416
+            i = 0
+            for j in range(len(dims)):
+                ait_sd[ait_up_keys[j]] = up_weight[i : i + dims[j], j * ait_rank : (j + 1) * ait_rank].contiguous()
+                i += dims[j]
+
+    # Detect number of blocks from keys
+    num_double_layers = 0
+    num_single_layers = 0
+    for key in state_dict.keys():
+        if key.startswith("lora_unet_double_blocks_"):
+            block_idx = int(key.split("_")[4])
+            num_double_layers = max(num_double_layers, block_idx + 1)
+        elif key.startswith("lora_unet_single_blocks_"):
+            block_idx = int(key.split("_")[4])
+            num_single_layers = max(num_single_layers, block_idx + 1)
+
+    ait_sd = {}
+
+    for i in range(num_double_layers):
+        # Attention projections
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_img_attn_proj",
+            f"transformer.transformer_blocks.{i}.attn.to_out.0",
+        )
+        _convert_to_ai_toolkit_cat(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_img_attn_qkv",
+            [
+                f"transformer.transformer_blocks.{i}.attn.to_q",
+                f"transformer.transformer_blocks.{i}.attn.to_k",
+                f"transformer.transformer_blocks.{i}.attn.to_v",
+            ],
+        )
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_txt_attn_proj",
+            f"transformer.transformer_blocks.{i}.attn.to_add_out",
+        )
+        _convert_to_ai_toolkit_cat(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_txt_attn_qkv",
+            [
+                f"transformer.transformer_blocks.{i}.attn.add_q_proj",
+                f"transformer.transformer_blocks.{i}.attn.add_k_proj",
+                f"transformer.transformer_blocks.{i}.attn.add_v_proj",
+            ],
+        )
+        # MLP layers (Flux2 uses ff.linear_in/linear_out)
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_img_mlp_0",
+            f"transformer.transformer_blocks.{i}.ff.linear_in",
+        )
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_img_mlp_2",
+            f"transformer.transformer_blocks.{i}.ff.linear_out",
+        )
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_txt_mlp_0",
+            f"transformer.transformer_blocks.{i}.ff_context.linear_in",
+        )
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_double_blocks_{i}_txt_mlp_2",
+            f"transformer.transformer_blocks.{i}.ff_context.linear_out",
+        )
+
+    for i in range(num_single_layers):
+        # Single blocks: linear1 -> attn.to_qkv_mlp_proj (fused, no split needed)
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_single_blocks_{i}_linear1",
+            f"transformer.single_transformer_blocks.{i}.attn.to_qkv_mlp_proj",
+        )
+        # Single blocks: linear2 -> attn.to_out
+        _convert_to_ai_toolkit(
+            state_dict,
+            ait_sd,
+            f"lora_unet_single_blocks_{i}_linear2",
+            f"transformer.single_transformer_blocks.{i}.attn.to_out",
+        )
+
+    # Handle optional extra keys
+    extra_mappings = {
+        "lora_unet_img_in": "transformer.x_embedder",
+        "lora_unet_txt_in": "transformer.context_embedder",
+        "lora_unet_time_in_in_layer": "transformer.time_guidance_embed.timestep_embedder.linear_1",
+        "lora_unet_time_in_out_layer": "transformer.time_guidance_embed.timestep_embedder.linear_2",
+        "lora_unet_final_layer_linear": "transformer.proj_out",
+    }
+    for sds_key, ait_key in extra_mappings.items():
+        _convert_to_ai_toolkit(state_dict, ait_sd, sds_key, ait_key)
+
+    remaining_keys = list(state_dict.keys())
+    if remaining_keys:
+        logger.warning(f"Unsupported keys for Kohya Flux2 LoRA conversion: {remaining_keys}")
+
+    return ait_sd
+
+
 def _convert_non_diffusers_z_image_lora_to_diffusers(state_dict):
     """
     Convert non-diffusers ZImage LoRA state dict to diffusers format.

src/diffusers/loaders/lora_pipeline.py

@@ -43,6 +43,7 @@ from .lora_conversion_utils import (
     _convert_bfl_flux_control_lora_to_diffusers,
     _convert_fal_kontext_lora_to_diffusers,
     _convert_hunyuan_video_lora_to_diffusers,
+    _convert_kohya_flux2_lora_to_diffusers,
     _convert_kohya_flux_lora_to_diffusers,
     _convert_musubi_wan_lora_to_diffusers,
     _convert_non_diffusers_flux2_lora_to_diffusers,
@@ -5673,6 +5674,13 @@ class Flux2LoraLoaderMixin(LoraBaseMixin):
             logger.warning(warn_msg)
             state_dict = {k: v for k, v in state_dict.items() if "dora_scale" not in k}
 
+        is_kohya = any(".lora_down.weight" in k for k in state_dict)
+        if is_kohya:
+            state_dict = _convert_kohya_flux2_lora_to_diffusers(state_dict)
+            # Kohya already takes care of scaling the LoRA parameters with alpha.
+            out = (state_dict, metadata) if return_lora_metadata else state_dict
+            return out
+
         is_peft_format = any(k.startswith("base_model.model.") for k in state_dict)
         if is_peft_format:
             state_dict = {k.replace("base_model.model.", "diffusion_model."): v for k, v in state_dict.items()}