🔧 Model Sampling SD3 Advanced

This node patches a flow-matching model's timestep shift - the knob that decides whether the sampler spends its effort on big-picture composition or on fine detail. The stock ModelSamplingSD3 gives you a single shift value; this "Advanced" variant lets that shift change across the denoising range instead of staying constant. It's a niche tuning node, but if you're chasing the last bit of quality out of SD3, Flux, or a similar model, it's a lever worth knowing.

Why you'd reach for it

Flux, SD3, Z-Image and basically every modern architecture are flow-matching models, and they exposed a new knob the old SD 1.5/SDXL world didn't have: shift (a timestep shift). Roughly, it controls how sampling effort distributes between composition and detail, and it's model-specific - the right value for one checkpoint is wrong for another. A single constant shift is usually fine, but sometimes you want more composition emphasis early and more detail emphasis late. That's the gap this node fills: it lets the shift vary rather than committing to one number for the entire trajectory.

How it works

You feed a model in, it returns a patched model with modified sampling behavior. The controls: shift is the base shift value (same idea as stock ModelSamplingSD3). cut_off is a threshold along the sampling range - a split point between the "composition" and "detail" phases. shift_multiplier scales the shift on one side of that cut-off, so the effective shift isn't flat across the whole schedule. The honest summary: shift is the knob you'll actually move day to day; cut_off and shift_multiplier are cubiq's extension for shaping how that shift behaves across the denoise, and they're genuinely advanced-user territory - worth experimenting with, not worth agonizing over.

Inputs and outputs

One input, model, and one output, MODEL - you drop this into the pipe between your checkpoint loader and your sampler, exactly where the stock ModelSampling node would go. The settings are shift (default 3), cut_off (default 0.5), and shift_multiplier (default 2). If you only touch one thing, touch shift.

Installing it

From ComfyUI Essentials by cubiq (Matteo Spinelli, the IPAdapter author). ComfyUI Manager: search ComfyUI Essentials, install, restart. Or:

cd ComfyUI/custom_nodes
git clone https://github.com/cubiq/ComfyUI_essentials

then restart. It shows up as 🔧 Model Sampling SD3 Advanced under essentials/sampling, class ModelSamplingSD3Advanced+. The pack has been maintenance-only since April 2025.

Common issues

First, take your shift value from the model card if there is one - flow-matching shift is model-specific (Z-Image Turbo, for example, famously wants a higher shift than ComfyUI's default). Second, and this one burns people: some samplers and schedulers apply their own internal sigma shift and quietly ignore the one you set here. If moving shift seems to do nothing, check your scheduler before concluding the node is broken - a scheduler like bong_tangent overrides it. Finally, this is a subtle-quality lever, not a fix-everything node; if your images are outright broken, the problem is usually CFG or sampler choice, not shift.