ComfyUI Extension: comfyui-model-diff-to-lora

<h1 align="center">Model Diff to LoRA for ComfyUI</h1> <p align="center"> Bake any chain of LoRAs (and any other model edits) into a single distributable <code>.safetensors</code> LoRA.<br> Load 3 LoRAs at the strengths you want, run this node, and walk away with one combined LoRA file you can ship anywhere. </p> <p align="center"> <a href="https://buymeacoffee.com/lorasandlenses"><img src="https://img.shields.io/badge/Buy%20me%20a%20coffee-FFDD00?style=for-the-badge&logo=buy-me-a-coffee&logoColor=black" alt="Buy Me A Coffee"></a> </p>

---

What it does

Give the node two MODEL objects:

• model_before — your unmodified base model
• model_after — the same base with whatever LoRAs (and/or other edits) loaded onto it

The node walks every trainable weight, computes the per-tensor difference, runs SVD to factor each diff into low-rank LoRA up / down matrices, and saves the result as a standard .safetensors LoRA file.

The output LoRA, applied at strength 1.0 to the original base, reproduces the "after" model's behaviour. So whatever combination of LoRAs you had loaded gets baked into one portable file.

Primary use case: combine multiple LoRAs into one

The most common reason to reach for this node:

[Load Checkpoint] ──► model_before
       │
       ▼
[LoRA Loader: identity.safetensors @ 1.0]
       │
       ▼
[LoRA Loader: style.safetensors @ 0.7]
       │
       ▼
[LoRA Loader: details.safetensors @ 0.5] ──► model_after
       │
       └─────────────────────► Model Diff to LoRA ──► combined.safetensors
                                          ▲
                                          │
                  model_before ────────────┘

You experiment with stacking LoRAs at the strengths that produce the look you want — identity at 1.0, style at 0.7, details at 0.5 — and once you're happy, this node bakes that exact combination into a single file. Now you can:

• Share one LoRA instead of "use these three with these strengths"
• Get back to the same look with one drop-down instead of three loaders + three strength sliders
• Use the combined LoRA as the base for further mixing
• Save a "preset" of your favourite multi-LoRA stack

Other things it captures

It's not LoRAs-only. The node captures any difference between the two MODEL objects, so it also handles:

• Block-level scaling (e.g. layer-scaler nodes that boost / suppress specific transformer blocks)
• External merges — if you merged two checkpoints in another tool and want a small LoRA that captures the merge delta rather than shipping a whole new checkpoint
• IP-Adapter and other patch-style edits — anything ComfyUI applies as a model_patcher.patches entry gets correctly baked in
• Custom one-off patches — useful for sharing edits with someone who doesn't have your patch code

Inputs

| Input | Type | Purpose | |---|---|---| | enabled | BOOLEAN | Run the extraction when queued. Default on; it auto-disables after a successful save so it sits dormant until you re-enable it. | | model_before | MODEL | The baseline (unmodified) model | | model_after | MODEL | The same model with whatever edits applied | | output_rank | INT | Target LoRA rank (default 64, range 4–256; higher = more faithful, larger file) | | output_path | STRING | Save directory. Leave empty for ComfyUI/output/extracted_loras. Remembers the last path you used. | | output_name | STRING | Filename prefix for the saved .safetensors (a timestamp is appended). Remembers the last name you used. |

The SVD device is chosen automatically — CUDA if a GPU is available, otherwise CPU. Layers whose difference is essentially numerical noise are skipped automatically (internal threshold) to keep the file small.

Outputs

| Output | Type | Purpose | |---|---|---| | lora_path | STRING | Absolute path to the saved file | | info | STRING | Multi-line summary: layers extracted / skipped, compression ratio, SVD device, file size |

Install

1. Drop the comfyui-model-diff-to-lora folder into ComfyUI/custom_nodes/.
2. Restart ComfyUI.
3. Add the Model Diff to LoRA node from the loaders/lora category.
4. Wire model_before and model_after, set output_rank, and click Queue (enabled is on by default).

No pip installs needed beyond what ComfyUI already ships with.

Notes

• Rank choice. Higher output_rank = larger file but closer reproduction of the diff. For most edits, rank 16–32 captures >95% of the signal; for very subtle edits, rank 4 may be enough. Default is 64.
• Noise threshold. Layers whose difference is essentially numerical noise are skipped automatically so the file stays small — this is handled internally, nothing to configure.
• GPU SVD. The device is selected automatically: CUDA when a GPU is available, otherwise CPU. On big models (Flux, SDXL) CPU SVD can take minutes while CUDA is typically seconds to tens of seconds.
• Auto-disable. enabled is on by default and turns itself off after a successful save, so the node won't silently re-extract on your next Queue — flip it back on when you want to run again.
• The node honours patches. ComfyUI applies LoRAs and other modifications as model_patcher.patches rather than baking them into weights. This node detects patches on the input MODEL objects and applies them via comfy.lora.calculate_weight() before computing the diff — so your chained LoRAs and runtime patches are correctly captured.

Support

If this saves you time or unlocks a workflow you couldn't ship before, consider buying me a coffee:

<a href="https://buymeacoffee.com/lorasandlenses"><img src="https://img.shields.io/badge/Buy%20me%20a%20coffee-FFDD00?style=for-the-badge&logo=buy-me-a-coffee&logoColor=black" alt="Buy Me A Coffee"></a>

License

MIT.