GitHub incident: spurious 401s hit 15% of API traffic before mitigation

GitHub resolved an incident in which sporadic authentication failures affected roughly 15% of its API traffic. The API began returning erroneous 401 Unauthorized responses, which had a knock-on effect: app integrations interpreted the errors as expired credentials and triggered unnecessary re-authentication flows. The Issues service also experienced degraded performance during the same window.

GitHub traced the problem to a faulty component in its infrastructure, mitigated the degradation in stages (Issues first, then API requests), and is monitoring for stability. A full root cause analysis is promised but not yet published.

The incident is a reminder of how authentication errors propagate beyond simple request failures. Because 401s carry semantic meaning — ‘your credentials are bad’ rather than ‘something broke on our end’ — downstream integrations and CI/CD pipelines that depend on GitHub’s API can cascade into token-refresh storms or false credential alerts even during a short-lived infrastructure fault.