Claude Opus 4.1 and Opus 4 degraded quality

Incident Report for Anthropic

Identified

From 17:30 UTC on Aug 25th to 02:00 UTC on Aug 28th, Claude Opus 4.1 experienced a degradation in quality for some requests. Users may have seen lower intelligence, malformed responses or issues with tool calling in Claude Code.

This was caused by a rollout of our inference stack, which we have since rolled back for Claude Opus 4.1. While we often make changes intended to improve the efficiency and throughput of our models, our intention is always to retain the same model response quality.

We’ve also discovered that Claude Opus 4.0 has been affected by the same issue and we are in the process of rolling it back.

Posted Aug 29, 2025 - 17:02 UTC

This incident affects: claude.ai, console.anthropic.com, api.anthropic.com, and Claude Code.