Behaviour where the same input can produce different outputs across multiple runs. LLMs exhibit this by design, requiring testers to shift from exact-match checks to presence/absence assertions. So what? Non-determinism means a regression test can "fail" without the answer being wrong — a fundamental difference from testing traditional software. Example: Running the same summarisation prompt twice may return the same meaning in different words. Editorial note: This definition has been inferred from how the term was used in the source material.
"The maximum time you expect your application to take to respond to a specific request or action." — Demi Van Malcot
