Empirical finding: uni_pc is the closest match to upstream's
UniPCMultistep (same algorithm, just comfy's port), but its multistep
polynomial extrapolation works against you at high step counts when
the per-step clamp_denoised non-linearity compounds. At 38 steps it
produced bad output; at ~20 steps it works well and is noticeably
closer to the HF Space than dpmpp_2m at 38.
The earlier "uni_pc produces bad output, route around it" framing was
wrong -- the real issue was step count, not the sampler. Updated the
README to reflect that, and bumped the example workflow.
UniPC is multistep so 15-25 steps is the typical range for flow
models; pushing past 25 starts to amplify any per-step error
accumulation through the polynomial fit.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
