Process Supervision Reward Models (PRMs) & Step-Level Monte Carlo Credit Assignment revolutionize mathematical reasoning by replacing sparse final trajectory scores with dense step-by-step verification; while Outcome Reward Models (ORMs) score only the final answer (failing to penalize hallucinated reasoning steps that stumble onto correct answers by chance), PRMs evaluate the rigorous correctness
r(st)∈[0,1] of every individual deduction step; automated weak supervision (Math-Shepherd framework) annotates step-level ground-truth by launching
K independent Monte Carlo rollouts from intermediate prefixes, assigning high process scores if rollout pass rates are high; during test-time inference, PRMs serve as heuristic value evaluators guiding Tree Search and Best-of-
N pruning.