AI agents write 30% more code, but finished work barely moves

A Harvard working paper tracking ~700 firms and 700,000 workers from 2021 to 2026 found that after adopting coding agents, lines of code rose 30% and pull requests 23%, while resolved Jira issues showed no significant change. The gap traces to review: time from PR to merge grew 49% (to 10.5 days) and the share of PRs with changes requested nearly doubled from 13% to 25%.

• Lines of code +30%, commits +20%, pull requests +23% per engineer per month
• Resolved Jira issues +0.12 — not significant, upper bound ~12%
• Time from PR to merge rose 3.45 days, or 49% longer
• Share of PRs with changes requested rose from 13% to ~25%, review comments per PR +35%