GitHub publishes root cause for the August 18 Actions Larger Runners failure, an expired certificate whose runtime enablement had been paused on purpose

Sources: GitHub status incident gx7js8bd0jpz, GitHub status incident bmpybhnrky3x
Summary: Two Actions incidents on 2026-08-18 affected Larger Runners, with status-page windows of 07:40 to 11:42 UTC and 09:36 to 10:23 UTC. GitHub wrote the root cause analysis into both incident records on 2026-08-21 at 22:46 UTC, which is why a four-day-old incident is today's outage item. The stated cause is an expired certificate. The certificate had been rotated in KeyVault, and only the runtime enablement step was left paused, a deliberate choice made to avoid repeating an earlier incident that the enablement step itself had caused. The analysis text opens with a February date that matches neither incident record nor either status-page window, and this block dates the incident from the record. Both analyses name a replacement of the Actions authentication path as in progress.
Why it matters: The certificate had been rotated in KeyVault and only the runtime enablement step was paused, deliberately, to avoid repeating an earlier incident that step had caused, so the safeguard against one failure mode produced another.
Follow-up: Track whether GitHub's replacement of the Actions authentication path lands.