Some macOS Actions jobs routing to Ubuntu instead
Incident
Report for GitHub
Resolved
Between December 9th, 2025 21:07 UTC and December 10th, 2025 14:52 UTC, 177 macos-14-large jobs were run on an Ubuntu larger runner VM instead of MacOS runner VMs. The impacted jobs were routed to a larger runner with incorrect metadata. We mitigated this by deleting the runner.
The routing configuration is not something controlled externally. A manual override was done previously for internal testing, but left incorrect metadata for a large runner instance. An infrastructure migration caused this misconfigured runner to come online which started the incorrect assignments. We are removing the ability to manually override this configuration entirely, and are adding alerting to identify possible OS mismatches for hosted runner jobs.
As a reminder, hosted runner VMs are secure and ephemeral, with every VM reimaged after every single job. All jobs impacted here were originally targeted at a GitHub-owned VM image and were run on a GitHub-owned VM image.
The routing configuration is not something controlled externally. A manual override was done previously for internal testing, but left incorrect metadata for a large runner instance. An infrastructure migration caused this misconfigured runner to come online which started the incorrect assignments. We are removing the ability to manually override this configuration entirely, and are adding alerting to identify possible OS mismatches for hosted runner jobs.
As a reminder, hosted runner VMs are secure and ephemeral, with every VM reimaged after every single job. All jobs impacted here were originally targeted at a GitHub-owned VM image and were run on a GitHub-owned VM image.
Update
We've applied a mitigation to ensure all macOS jobs route to macOS fulfillers and are monitoring for full recovery.
Investigating
We are investigating reports of degraded performance for Actions
This incident affected: Actions.
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