Elevated error rates on Opus 4.6

Update timeline

1. investigating Mar 27, 2026, 06:59 AM UTC

   We are currently investigating this issue.

2. investigating Mar 27, 2026, 11:04 AM UTC

   We are continuing to investigate the ongoing incident.

3. investigating Mar 27, 2026, 11:21 AM UTC

   Sonnet 4.6 is also showing elevated errors.

4. investigating Mar 27, 2026, 12:09 PM UTC

   As of 5:00 PT / 12:00 UTC Sonnet 4.6 is now healthy. We are still working to fix Opus 4.6.

5. identified Mar 27, 2026, 01:34 PM UTC

   We have mitigated the main issue and the error rate for Opus 4.6 is hovering around 0.4% which is still high, but much better than the performance during the previous hours. We are waiting for a more permanent fix to land in the near future.

6. monitoring Mar 27, 2026, 01:46 PM UTC

   As of 6:40 PT / 13:40 UTC our error rate has returned to the baseline. We are still monitoring the current situation.

7. resolved Mar 27, 2026, 04:46 PM UTC

   This incident has been mitigated as of 9:30 PT / 16:30 UTC.

8. postmortem Mar 27, 2026, 05:36 PM UTC

   On March 26–27, 2026, customers experienced elevated error rates when using Claude Opus 4.6 and Claude Sonnet 4.6. The issue was caused by a networking performance degradation within our infrastructure that disrupted communication between components of our serving stack. We resolved the incident by migrating the affected workloads to healthy infrastructure, restoring normal service by 9:30 AM PT on March 27.