ModelMergeAdd_motorway_edition

Merging is how a huge chunk of the CivitAI catalog gets made: take two checkpoints, interpolate their weights, done. Most of those merges are blends - a bit of this, a bit of that. ModelMergeAdd is the least subtle member of the family: it adds two models at full strength, both directions, no ratio knob. This is its Motorway-ed clone.

What it actually does

Under the hood it's weight-patch math, not a new checkpoint on disk. It takes every key patch from model2's diffusion_model, adds it to a clone of model1 with strength 1.0 on both sides, and hands back a model that behaves as if model1 and model2 were summed. All widget-free on the model side - the only real controls are the two key strings.

Why does that matter if you can't turn the knob? Because adding two full models directly usually produces mush - the weights are dense and overlapping, so a plain add smears both. The classic place it genuinely shines is as a building block in the "add the difference" trick: if model C differs from model B by some style delta, you can add that delta onto model A. You rarely reach for ModelMergeAdd alone; you reach for it when you're composing with other merge nodes in a longer chain. The community's warning from the merge culture applies here more than anywhere: a model's description will usually tell you it's a merge, and merges "combine strengths of their parents at the cost of some consistency" - plain adds cost the most consistency.

The inputs

• INPUT_model1_key (default model1) and INPUT_model2_key (default model2) - the two models to add. Order doesn't change the math here (it's symmetric), but keep it consistent for when you swap in a different merge node.
• OUTPUT_MODEL_key (default MODEL) - where the summed model lands for the sampler to read.

Everything is keyed through the MOTORWAY 🚌💨 - the clone instantiates stock ModelMergeAdd, pulls both models out, runs the merge, stores the result. No behavior lost.

Install

One install covers the whole pack. ComfyUI Manager, search "ComfyUI_agilly1989_motorway", or:

cd ComfyUI/custom_nodes
git clone https://github.com/agilly1989/ComfyUI_agilly1989_motorway

Restart ComfyUI. No requirements.txt, no model downloads.

Troubleshooting

• If the result looks like noise soup, that's not a bug - a raw full-strength add is usually garbage. Reach for ModelMergeSimple (ratio blend) or ModelMergeSubtract (difference) instead unless you specifically want the add.
• 'MotorwayClass' object has no attribute 'hash_' = a model key isn't in the Motorway; check the loaders ran and the key spelling matches (case-sensitive).
• Pack caveats: BETA, and the newest published version (1.1.7) disabled clone generation, so on a fresh install these _motorway_edition nodes may be missing from the menu. They're present in the 1.1.0–1.1.6 builds comfy.icu indexed.