Contributions to OpenAI's Codex codebase show signs of AI uplift | Epoch AI
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The share of working days on which OpenAI's Codex collaborators merged very-high-effort code rose from about 2% in Q2 2025 to about 8% in Q2 2026.
How much does AI speed up the engineers building it? We analyzed 41 core contributors to OpenAI’s public Codex repository, asking LLM judges to estimate how long each merged pull request would take an experienced engineer without AI assistance. In Q2 2026, 8% of contributor-days reflected work estimated at over 24 hours of unassisted effort — more than a skilled engineer could do in a day, even working around the clock — up from 2% in Q2 2025. This shift is consistent with growing AI uplift within software engineering. However, estimates by LLM judges are imperfect and should be interpreted…
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