The Reward Horizon Problem: Learning From Delayed Feedback

People increasingly use language models to pursue objectives that are realized over long time horizons. However, post-training rewards are typically computed over short horizons, which creates a mismatch between the reward signal and the ultimate objective. For example, while a short-horizon training signal may reward code that runs, does it reward code that stays stable? We study this reward horizon problem in a software engineering setting, where the consequences of a code change may not be observed for several days or months. Using code corrections as a source of delayed feedback, we find substantial differences between the signals available at short and long horizons. Short-horizon feedback omits information about long-horizon objectives and encodes a different distribution of label sources. We then analyze how critic models trained on long-horizon outcomes may distill some of this delayed feedback into short-horizon rewards.