☁️BizyAir ModelSamplingSD3

This is the smaller, simpler sibling of BizyAir ModelSamplingFlux: one input, shift (default 3), applied to a BIZYAIR_MODEL before sampling. It's the cloud-run equivalent of ComfyUI's stock ModelSamplingSD3 node, built for SD3-family rectified-flow architectures where Flux's width/height-aware version doesn't apply, this one just takes a flat shift value with no resolution dependency baked in.

What shift is actually doing

On rectified-flow models, the noise schedule doesn't need the kind of aggressive reshaping that DDPM-style models (SD 1.5, SDXL) benefit from from Karras or exponential scheduling, in fact heavily reshaping the sigma curve is a documented failure mode on this model family rather than merely a worse choice. What replaced schedule-tuning as the main lever is this: a single shift value that determines how sampling effort is distributed between early composition steps and later detail steps. Push shift higher and the model spends relatively more of its schedule on structure before committing to fine detail; lower it and detail resolves earlier. It's a coarser, more direct knob than fiddling with the scheduler dropdown ever was on these architectures, and it's genuinely worth tuning per model rather than assuming the default is universally right, different SD3-family checkpoints and finetunes have published different recommended shift values.

One landmine worth knowing about

Not every scheduler actually respects this node's output the way you'd expect. Some schedulers apply their own internal sigma shift and simply ignore whatever value a ModelSamplingSD3-style node upstream set, which means you can change shift here, get no visible difference in the output, and reasonably conclude the node isn't working, when the actual cause is a scheduler further downstream silently overriding it. If tuning shift seems to do nothing at all, check what scheduler your sampler is using before concluding this node is broken.

Where it fits

Output is BIZYAIR_MODEL, a patched model, wire it in place of the raw model output between your BizyAir loader/LoRA chain and your BizyAir_KSampler or BizyAir_KSamplerAdvanced. This only makes sense on architectures that actually use the rectified-flow shift mechanism, applying it to a model outside that family (a DDPM-style SD 1.5/SDXL checkpoint, for instance) isn't the right tool, those architectures tune through sampler and scheduler choice instead.

Installing it

Through ComfyUI Manager: search "BizyAir", install, restart. Or clone directly:

cd ComfyUI/custom_nodes && git clone https://github.com/siliconflow/BizyAir.git

You need a BizyAir/SiliconFlow API key before this executes, set via the "click to login" prompt on first use. Signup goes through phone-number verification, and some users outside China have reported friction getting that step to accept a non-Chinese number, worth planning for ahead of time.

Common issues

If changing shift produces no visible difference, check your scheduler before anything else, per the landmine above, some schedulers override this value entirely. If output looks off-balance between composition and detail, that's the actual shift value to adjust, and it's worth checking whatever recommendation the specific checkpoint's own documentation gives rather than assuming 3 is universally correct.

As with every node in this pack, a run that stalls or errors with no clear workflow-level cause almost always traces back to the API key. Separately: if BizyAir shows up in your custom_nodes folder without you having installed it, that's a known ComfyUI Manager quirk (misresolving an unrelated missing-node error on an older shared workflow), not malware, and it's safe to remove through the Manager.