Claude Opus 5 changelog

Every change to Claude Opus 5 that Modelpeers has recorded, newest first, each with the source it came from. The record starts Jul 24, 2026.

All (14)Releases (3)Retiring (1)Breaking changes (3)Quality (2)Benchmarks (5)

August 2026

Claude Code and Opus 5

2 products from Anthropic

Default changeAug 28, 2026

Claude Code default model for seat-based Enterprise switches to Opus 5

Claude Code 2.1.251 changed the default model for seat-based Enterprise subscriptions to Opus 5, matching other premium plans.

Who is affected:: Claude Code users on seat-based Enterprise plans.
What to do:: Pick a model with /model if you want a different default.

July 2026

Claude Code and Opus 5

2 products from Anthropic

Default changeJul 24, 2026

Claude Code makes Opus 5 the default Opus model

Claude Code 2.1.219 added Claude Opus 5 as the default Opus model and removed Opus 4.7 from fast mode. Anthropic also made Opus 5 the default model on Claude Max.

Who is affected:: Claude Code users on the opus alias or the Max plan.
What to do:: Pin claude-opus-4-8 with /model if you need the previous model.

Claude Opus 5

Model at Anthropic

Breaking changeJul 24, 2026

Claude Opus 5 rejects disabled thinking at xhigh and max effort

On Claude Opus 5, sending thinking disabled together with effort xhigh or max returns a 400 error.

Who is affected:: Code moving from Claude Opus 4.8 to Opus 5 that turns thinking off.
What to do:: Use effort high or below when thinking is disabled.

8 incidents are listed on the Claude Opus 5 page. Get this changelog in a feed reader with the RSS feed.