Epoch AI had three AI models estimate how long an experienced engineer without AI would need for each pull request merged by 41 core contributors to OpenAI's public Codex repository. Contributor-days with more than 24 estimated hours of work rose from 2% in Q2 2025 to 8% in Q2 2026. Source.
Those hours are counterfactual estimates, not time sheets. Without AI, engineers would build less or differently, so Epoch treats the result as an upper bound on time saved, notes longer work is not necessarily more valuable, and calls it suggestive rather than causal evidence of uplift.
Terms in this piece · Glossary
LLM — A large language model — the neural network behind tools like Claude and ChatGPT, trained on huge amounts of text to predict what comes next.
