Checkpoint Pair Cycler Loader (Nukun)

Sometimes one checkpoint isn't the unit you want to batch over - you want pairs. Two different checkpoints fed into the same graph, crossed against each other, every combination tested. That's the "all-with-all" matrix, and doing it by hand in ComfyUI means managing two loaders, two counters, and praying they stay in sync.

NukunCheckpointPairCyclerLoader turns the whole matrix into a single pair_index. One number steps through every ordered pair of checkpoints in a folder, and the node handles the indexing so you don't have to.

How the matrix works

Give it a checkpoint_folder - the dropdown only lists checkpoint subfolders, and each folder is a separate choice - and it builds an ordered matrix of N × N pairs from the checkpoints inside. The indexing is the thing to get your head around: MODEL_2 advances fastest, one step per pair_index increment, while MODEL_1 advances only after a full pass through the folder.

And the matrix is full: it includes self-pairs and reversed pairs. So with models A, B, C you'll get A×A, A×B, A×C, then B×A, B×B, ... - every ordered combination, which matters if your workflow treats the two model inputs asymmetrically (say, one drives a reference, one drives composition).

Two extra inputs shape the sweep:

• model_index_start / model_index_end - restrict the matrix to an inclusive global index range, e.g. 20..49. Handy when you're resuming a long run that died at pair 20, or splitting a giant matrix across multiple queues.
• vae_name - checkpoint keeps the VAE from MODEL_2 (which is the last model loaded), or pick an external VAE to override the shared output.

What comes out

The full bus: MODEL_1/CLIP_1 and MODEL_2/CLIP_2, a shared VAE, and the metadata you need for filenames - modelname_1, modelname_2, and a combined_modelname that joins them as modelname_1__x__modelname_2 (filename-safe, directly usable as a save prefix). pair_index, model_index_1, model_index_2, and total_pairs come out too, and total_pairs is the one that matters for chunking: it tells you the size of the full matrix so you know where your wrap point is.

The README's tip for long runs: set pair_index to increment-wrap, and wrap it over the reduced total_pairs value when you're using an index range. That way the counter loops cleanly inside your restricted slice.

Installing it

Same one-time pack install:

cd ComfyUI/custom_nodes
git clone https://github.com/OnekoSL/Nukun_ComfyUI_Nodes.git

Restart ComfyUI or install via ComfyUI Manager ("Nukun").

The honest caveat

The all-with-all matrix is a blunt instrument - for 10 checkpoints that's 100 runs, 50 of them A×A self-pairs you may not care about. That's not a defect, it's the design: it guarantees complete coverage. If you only want directed A/B tests without the self-pairs, you're better off with the single CheckpointCyclerLoader and a second fixed loader. But when you genuinely want every combination tested and can let the queue run overnight, this node is the cleanest way to get it - one counter, zero index math on your part.