XtcProbability

XtcProbability enables the XTC (eXclude Top Choices) sampler. With probability XtcProbability at each step, XTC removes the top candidate tokens, forcing the engine to sample from the tail. Useful for injecting diversity without raising temperature.

Quick reference
Type float
Default -1.0 (disabled)
Range 0.0 – 1.0, or -1.0 to disable
Category Advanced / diversity
Field on SamplerParameters.XtcProbability

What it does

At each generation step, with probability XtcProbability, XTC fires: the engine excludes all tokens whose probability is above XtcThreshold, and samples from whatever remains. This nudges the model into less-obvious paths without changing temperature.

  • -1.0 (default) — disabled.
  • 0.1 – 0.3 — XTC fires on 10–30 % of steps. Mild diversity boost.
  • 0.5 – 0.8 — XTC fires often. Strong variety; risk of incoherence.

When to change it

Scenario Value
Default (disabled) -1.0
Light creativity boost 0.1 – 0.2
Alternative to high temperature 0.3 – 0.5
Experimental variety push 0.5+

XTC is a recent addition. Prefer conventional Temperature + TopP tuning first. Reach for XTC when you want variety specifically when the model is confident — standard sampling tightens those steps; XTC breaks them.

Example

var preset = new Qwen25Preset();
preset.SamplerParameters.XtcProbability = 0.2f;
preset.SamplerParameters.XtcThreshold = 0.1f;
// On ~20 % of steps, tokens above 0.1 probability are excluded.

using var api = AsposeLLMApi.Create(preset);
string reply = await api.SendMessageAsync("Suggest three fictional startup names.");
Console.WriteLine(reply);

Interactions

  • XtcThreshold — minimum probability a token must have to be considered for exclusion.
  • Temperature — orthogonal. XTC works at any temperature.
  • TopP — still applied; XTC runs within what TopP keeps.

What’s next

DynatempExponent XtcThreshold