AuraFlow Sigma Scheduler

AuraFlow is the rectified-flow model that answered SD3's license collapse in July 2024 and then mostly got forgotten - fal shipped v0.2 under Apache 2.0, v0.2 genuinely beat FLUX Dev on prompt adherence, and then nothing more ever came. Its one lasting footprint in ComfyUI is that ModelSamplingAuraFlow node, whose name survived and got reused on models that have nothing to do with AuraFlow. If you're actually running the original weights, the AuraFlow Sigma Scheduler is the clean way to get its schedule right.

This is the simplest node in the Sigmax pack, and honestly that's the point. AuraFlow v0.2 uses a fixed unit-flow ratio of 1.73 and a 50-step recipe at CFG 3.5. There's exactly one mode - Official Fixed (1.73) - because there's exactly one schedule that matches the original model's expectations. No mode roulette, no dynamic shifts.

Inputs

• mode - one choice, Official Fixed (1.73). It exists so that the selection is explicit rather than silently assumed; the pack's design rule is "no silent generic fallback."
• steps - default 50, and that's the official recipe count. You can lower it, but you're leaving the verified recipe the moment you do.
• strict_source - keep it on to stay on the pinned source recipe.
• already_shifted - set true only if a model-sampling shift for AuraFlow has already been applied upstream in your workflow. Default false is correct for a normal ModelSamplingAuraFlow setup... which, to be clear, is the thing this node's schedule is replacing in the custom-sampling path. If you're already applying the shift, that's the "already shifted" case.
• start_step / end_step - slice the schedule.

Outputs are sigmas and schedule_info (the JSON recipe + warnings). sigmas goes to a custom sampler's external-sigma input.

Scope, stated plainly

The pack is unusually careful about this, and you should read the warning signs: support is limited to original AuraFlow v0.2 with the fixed 1.73 ratio and 50 steps. Finetunes, other AuraFlow versions, dynamic shifts, and any quality claim are explicitly out of scope. So if you've got AuraFlow v0.3 or some finetune, this node's schedule is not aimed at you - treat it as a starting point, not gospel.

Installing

Standard Sigmax install, once for the whole pack:

cd ComfyUI/custom_nodes
git clone https://github.com/rookiestar28/ComfyUI-Sigmax comfyui-sigmax

Restart ComfyUI and search the node menu for Sigmax; ComfyUI Manager also lists the pack as "ComfyUI-Sigmax". Python 3.10+ and ComfyUI 0.29.0+ required, no extra dependencies, no models to download.

Where people get tripped up

The single most common mistake is assuming this node is somehow tied to the ModelSamplingAuraFlow node or that the schedule should pass through another scheduler afterward. It shouldn't - connect sigmas directly to your custom-sampling path and leave the scheduler alone. The other trap is the name: just because your model looks like a flow-matching model and someone told you to use "AuraFlow shift" doesn't mean it wants AuraFlow's 1.73 ratio. The node is honest about only covering the original; you should be too.