Anthropic Release notes and new features

Claude Fable 5.1 and Claude Mythos 5.1 launch

Anthropic launched Claude Fable 5.1 and Claude Mythos 5.1, designed for coding and knowledge work.

• Claude Fable 5.1 and Claude Mythos 5.1 launchGA
• Claude API adds turn-scoped system messages in betaBeta
• Claude API thinking.display adds an updates mode in betaBeta
• Claude Enterprise Admin, Analytics and Compliance API guides add anthropic-version
• Claude Fable 5.1 and Mythos 5.1 require 30-day data retention
• Claude Fable 5.1 output carries text watermarks and C2PA Content Credentials
• Per-message effort changes enter beta on the Claude APIBeta
• Claude Fable 5.1 and Mythos 5.1 reject tool_choice any and tool
• Claude Fable 5.1 launches alongside Claude Mythos 5.1 with 1M token contextGA
• Claude Fable 5.1 thinking blocks only replay to the same or newer models
• Prompt cache reads on Claude Fable 5.1 and Mythos 5.1 drop to $0.25 per MTokPricing

Claude Fable 5.1 and Claude Mythos 5.1 launched

Anthropic launched Claude Fable 5.1 and Claude Mythos 5.1, described as its most advanced models for coding and knowledge work.