Definition
Plain language
A separate model or program that grades whether an answer is correct.
As stated in the literature
A model or deterministic checker that scores candidate outputs, used to provide reward signals or filter rollouts in training and evaluation.
Also called: verifiers
Why it matters: Verifiers are how systems turn a noisy generator into a reliable end-to-end pipeline, and a strong verifier often matters more than a stronger generator.
For example, a code generator might produce 10 candidate solutions and a verifier runs each against the test suite to pick the one that passes.
Heard on the show
“It observes which recipes happen to lead to dishes the diners — meaning the verifier — actually like, and shifts the chef's habits to use those recipes more often.”Episode 011 — When RL Actually Teaches Agents Something New, And When It Doesn't