Bridge Input (MODEL)

Bridge Input (MODEL) looks like a mistake until you get the mental model. A MODEL socket on an input bridge - but the whole point of these bridges is that an outside agent injects values, and you can't inject a diffusion model over HTTP. Right. So this node isn't about injecting; it's about naming a place.

In ComfyBridgeIO's design, every Bridge Input node is a contract: the name widget tags a spot, the Python client's schema extraction (bridge.get_schema()) reports that spot to the agent, and scalars get patched at runtime. Complex types - MODEL, CLIP, VAE, CONDITIONING, IMAGE, LATENT - can't be serialized into a JSON patch, so their bridges are landmarks. You wire an actual model into the optional value input (usually from a Checkpoint Loader / UNET Loader), the value output feeds the sampler, and the graph now has a named node that says "the model is this far into the pipeline, right here."

Why bother? Two reasons. First, structure for the agent: when a workflow has a MODEL bridge, the schema the client extracts tells the agent exactly where the checkpoint enters, so it can make decisions ("swap the model by patching the loader's ckpt_name" or "this path is model-dependent"). Second, readability - the same reason the plumbing layer exists (see the KB's writeup on value nodes and reroutes). A named tap beats a naked wire when a human or an agent is trying to understand the graph.

Install

cd ComfyUI/custom_nodes
git clone https://github.com/cbpark84/ComfyBridgeIO

Restart ComfyUI, or ComfyUI Manager → search ComfyBridgeIO → Install. No model files in this pack (bring your own checkpoint, obviously), no heavy deps. The optional Python client (pip install -e in the repo) wants aiohttp, websockets, Pillow. The README's clone line points at nicekate/ComfyBridgeIO - stale, the repo is cbpark84 as above.

Common issues

Don't expect the client to conjure a model. An unwired Bridge Input (MODEL) outputs nothing, and the sampler downstream fails. Wire the loader into it inside ComfyUI. And if your goal was "let the agent swap checkpoints," know the bridge doesn't do that by itself - you'd still patch the loader's filename, which is a STRING field, not this socket.