Claude Sonnet 4.5 saw an error spike on April 20, 2026
This incident appears to have been model-specific. It is useful as a reminder that Claude can feel broken for some developers even while the broader site remains reachable.
Published: Apr 20, 2026, 2:14 AM EDT
Updated: Apr 21, 2026, 8:40 AM EDT
Incident started: Apr 20, 2026, 1:03 AM EDT
Crowd spike noticed: Apr 20, 2026, 1:10 AM EDT
Resolved: Apr 20, 2026, 2:14 AM EDT
Affected surface: Claude Sonnet 4.5 model requests
Official incident messaging described a Claude Sonnet 4.5 error spike that was later resolved after the model returned to baseline behavior.
- The official language pointed to a model-layer error spike instead of a whole-platform outage.
- This kind of incident matters most to API users and power users tied to one model family.
- A detector needs to distinguish model instability from broader Claude.ai or auth failures.
A reviewed note on the April 20, 2026 Sonnet 4.5 incident where the issue looked model-specific rather than a full Claude platform outage.
Review the methodology page for how crowd reports are deduplicated and the status lag explainer for how independent reports differ from provider updates.
If you want the broader archive context, go back to the Claude outage history page.
Related notes in the same incident category: