GitHub Availability Report: December 2025

Source: GitHub Blog

December 2025 Incident Summary

In December, we experienced five incidents that resulted in degraded performance across GitHub services.

December 08 19:51 UTC (lasting 1 hour 15 minutes)

Impact – Between Nov 26 2025 02:24 UTC and Dec 8 2025 20:26 UTC, enterprise administrators could not view agent‑session activity on the Enterprise AI Controls page.

• Users were unable to list agent‑session activity in the AI Controls view.
• Viewing activity in audit logs, navigating to individual agent‑session logs, or managing AI agents was not affected.

Root cause – A misconfiguration introduced in a change deployed on Nov 25 unintentionally prevented data from being published to an internal Kafka topic that feeds the AI Controls page.

Mitigation – The configuration issue was corrected on Dec 8.

Follow‑up actions –

• Improving monitoring for data‑pipeline dependencies.
• Enhancing pre‑deployment validation to catch configuration issues before they reach production.

December 15 17:43 UTC (lasting 39 minutes)

Impact – From 15:15 UTC to 18:22 UTC, Copilot Code Review suffered a degradation: 46.97 % of pull‑request review requests failed, showing the error:

“Copilot encountered an error and was unable to review this pull request. You can try again by re‑requesting a review.”

The remaining requests completed successfully.

Root cause – Elevated response times in an internal, model‑backed dependency caused request timeouts and back‑pressure in the review‑processing pipeline, leading to queue growth and failed reviews.

Mitigation –

• Temporarily bypassed fix suggestions to reduce latency.
• Increased worker capacity to drain the backlog.
• Rolled out a model‑configuration change that reduced end‑to‑end latency.

Queue depth and success rates returned to normal and stayed stable through peak traffic.

Follow‑up actions –

• Increased baseline worker capacity.
• Added instrumentation for worker utilization and queue health.
• Improving automatic load‑shedding, fallback behavior, and alerting to shorten detection and mitigation times.

December 18 16:33 UTC (lasting 1 hour 8 minutes)

Impact – From 08:15 UTC to 17:11 UTC, some GitHub Actions runners experienced intermittent API‑call timeouts, causing failures during runner setup and workflow execution.

• Approximately 1.5 % of jobs on larger and standard hosted runners in the West US region (≈ 0.28 % of all Actions jobs) were impacted.

Root cause – Network packet loss between West US runners and one of GitHub’s edge sites.

Mitigation – By 17:11 UTC all traffic was rerouted away from the affected edge site, eliminating the timeouts.

Follow‑up actions – Working on earlier detection of cross‑cloud connectivity issues and faster mitigation paths.

December 18 17:36 UTC (lasting 1 hour 33 minutes)

Impact – Between 16:25 UTC and 19:09 UTC, the service underlying Copilot policies was degraded. Users, organizations, and enterprises could not update any Copilot policies. No other GitHub or Copilot services were affected.

Root cause – A database migration introduced a schema drift.

Mitigation – Synchronized the schema to restore normal operation.

Follow‑up actions – Hardened the service against schema drift and are investigating deployment‑pipeline improvements to shorten future mitigation times.

December 22 22:31 UTC (lasting 1 hour 46 minutes)

Impact – From 22:01 UTC to 22:32 UTC, unauthenticated requests to github.com were degraded, resulting in slow or timed‑out page loads and API calls. Unauthenticated requests from Actions jobs (e.g., release downloads) were also impacted. Authenticated traffic remained unaffected.

Root cause – A severe spike in traffic, primarily to search endpoints.

Mitigation – Identified and mitigated the traffic surge; automated traffic‑management restored full service.

Follow‑up actions –

• Improved limiters for high‑load endpoints.
• Continuing work to proactively detect large traffic changes, enhance resilience of critical request flows, and reduce time‑to‑mitigation.

Stay Updated

• Follow our status page for real‑time updates and post‑incident recaps.
• Learn more about our work in the engineering section of the GitHub Blog.

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