A Primer on Post-Training Reasoning Data

This primer is the first to pull the scattered post-training reasoning-data literature into one place, synthesizing over 150 public studies and system reports that previously lived across dataset papers, RL write-ups, and lab reports. It organizes the field around four questions: what data objects exist, what makes them useful, how they are constructed, and how they scale. The key reframing is that a reasoning-data item is more than a prompt-response pair: it packages a problem or state, model behavior, judging feedback, and attribution metadata, with usefulness defined relative to the verifier and the rest of the corpus rather than in isolation.