Appendix B — Practical verifier design checklist

Question Why it matters Failure if ignored Book anchor
What object is verified? Fixes the reward interface. The claim exceeds the evidence. Chapter 2
What evidence is consumed? Makes the verifier auditable. Hidden inputs shape reward silently. Chapter 2
What remains off-screen? Bounds the claim. The model optimizes unmeasured behavior. Chapters 7, 10
Is the reward binary, graded, or dense? Determines credit assignment. Correct checks become weak training signal. Chapters 3 and 5
Are extraction and normalization specified? Prevents format reward. Formatting becomes the task. Chapters 2 and 4
Are hidden tests or audit checks separate? Reduces direct overfitting. The policy learns the test suite. Chapter 7
Has the high-reward tail been audited? Tests optimizer-selected outputs. Best-of-\(N\) amplifies exploits. Chapters 6 and 7
Is verifier drift tracked across checkpoints? Measures validity under optimization. The verifier is only valid for the base policy. Chapter 10
Are tools and environment state logged? Makes agentic reward debuggable. Harness bugs become reward hacks. Chapter 9
Is the verifier versioned? Makes results reproducible. Patches cannot be tied to behavior changes. Chapters 7 and 10
Is test-time search separated from policy gain? Clarifies what improved. A system gain is misreported as model learning. Chapters 6 and 10
Are tax regressions checked? Prevents narrow benchmark optimization. Accuracy rises while deployment quality falls. Chapter 10