boobkake22-ComfyUI-SamplingPlanner/docs/comfy-sampler-parity.md

Comfy sampler parity notes

Retrieved: 2026-06-27.

These notes compare ComfyUI's native KSamplerAdvanced path with the modular SamplerCustomAdvanced path for Wan 2.2 two-stage high/low expert sampling.

Source references

• Official ComfyUI KSamplerAdvanced node documentation: https://docs.comfy.org/built-in-nodes/KSamplerAdvanced
• Official ComfyUI KSamplerAdvanced implementation: https://github.com/Comfy-Org/ComfyUI/blob/master/nodes.py
• Official ComfyUI KSampler sigma slicing implementation: https://github.com/Comfy-Org/ComfyUI/blob/master/comfy/samplers.py
• Official ComfyUI SamplerCustomAdvanced implementation: https://github.com/Comfy-Org/ComfyUI/blob/master/comfy_extras/nodes_custom_sampler.py
• Official ComfyUI SamplerCustomAdvanced node documentation: https://docs.comfy.org/built-in-nodes/SamplerCustomAdvanced

What KSampler Advanced does

KSamplerAdvanced is an all-in-one wrapper. It creates or suppresses initial noise, constructs the scheduler curve through Comfy's KSampler, applies start_at_step and end_at_step, and optionally forces the last sigma to zero when return_with_leftover_noise is disabled.

For a legacy two-KSampler high/low Wan branch:

High KSampler:
  add_noise = enable
  start_at_step = 0
  end_at_step = split
  return_with_leftover_noise = enable

Low KSampler:
  add_noise = disable
  start_at_step = split
  end_at_step >= steps
  return_with_leftover_noise = disable

The effective sigma slices are:

high sigmas = full_sigmas[:split + 1]
low sigmas  = full_sigmas[split:]

The handoff sigma is intentionally present in both slices. Removing it from the low slice, or forcing the high slice to terminal zero, does not match KSampler Advanced continuation semantics.

What SamplerCustomAdvanced does

SamplerCustomAdvanced is lower level. It receives an already-built NOISE, GUIDER, SAMPLER, SIGMAS, and LATENT, then calls the guider directly with those objects. That gives the planner exact curve control, but it means the workflow must recreate the parts KSampler Advanced used to own:

• high stage should use RandomNoise;
• low stage should use DisableNoise;
• low stage must receive the high stage output, not denoised_output;
• each stage should use CFGGuider for KSampler parity, not BasicGuider;
• the guider models must be the plan-shifted high/low expert models;
• the sampler object should come from KSamplerSelect with the same sampler name used by the legacy KSampler branch;
• the sigmas should come directly from Sampling Planner's Sigma Breakout.

denoised_output is an x0 estimate. It is useful for inspection, but it is not the partially sampled latent at the shared Wan expert handoff sigma.

Design conclusion

When the plan reports curve_mode: exact, prefer KSampler Breakout for regression testing against known-good two-KSampler workflows. This keeps native ComfyUI in charge of the schedule slicing and leftover-noise behavior.

Use Sigma Breakout with SamplerCustomAdvanced when the plan is piecewise, mixed-budget, priority-adjusted, or otherwise cannot be represented by ordinary KSampler Advanced controls.

Sampler-specific caution: Comfy's internal KSampler.calculate_sigmas has special count handling for a small set of samplers such as dpm_2, dpm_2_ancestral, uni_pc, and uni_pc_bh2. The KSampler Breakout node checks for this and rejects incompatible exact-curve routes. For custom-sampler routes, Sigma Breakout remains authoritative.