Claude Opus 4.6 changelog

Fast mode removed for Claude Opus 4.6

Requests to claude-opus-4-6 with speed fast now run at standard speed and standard rates instead of returning an error.

Who is affected:

Apps using fast mode on Claude Opus 4.6.

What to do:

Move fast mode traffic to Claude Opus 4.8.

Anthropic confirms three changes degraded Claude Code quality

Anthropic traced user reports of worse Claude Code answers to a lower default effort (March 4 to April 7), a bug that dropped older reasoning every turn (March 26 to April 10) and a verbosity prompt change (April 16 to 20). The API was not affected, and Anthropic reset usage limits for all subscribers on April 23.

Who is affected:

Claude Code, Agent SDK and Cowork users on Sonnet 4.6, Opus 4.6 and Opus 4.7 between March and April 2026.

Action needed:

Update Claude Code to 2.1.116 or later.

Max 5x users report quota exhausted in 1.5 hours, Claude Code team points to 1M-context cache misses

A GitHub issue reported a Max 5x quota exhausted within 1.5 hours of moderate use on Opus 4.6 with 1M context. Claude Code's Boris Cherny replied that stale sessions over an hour old cause full cache misses with the 1M window and that Anthropic was investigating a 400k default. The thread drew 759 points and 660 comments.

Who is affected:

Claude Max subscribers using 1M-context sessions in Claude Code.

Action needed:

Run /clear before resuming sessions idle for over an hour, or set CLAUDE_CODE_AUTO_COMPACT_WINDOW=400000.