- Why Claude switched models in your conversation with Opus 5 or Opus 5.5Claude Opus 5 and Opus 5.5 improve on Claude Opus 4.8 across the board… Frontier LLM development (Opus 5.5 only)
Opus 5.5 has classifiers similar to Fable models for a small… These classifiers cause Claude to fall back from Opus 5.5 to Opus 5
- Claude Code model configurationOpus 5.5, claude-opus-5-5
Fable 5.1, claude-fable-5-1
Opus 5, claude-opus-5
Sonnet… 5.5: claude --model claude-opus-5-5
For Fable 5.1: claude --model claude-fable-5-1
For Opus… 5.5: echo 'export ANTHROPIC_MODEL="claude-opus-5-5"' >> ~/.zshrc
Fable 5.1: echo 'export ANTHROPIC_MODEL
- How large is the context window on paid Claude plans?5.5
1M tokens
Claude Opus 5
1M tokens
Claude Opus 4.8
500K tokens… 5.5
1M tokens
Claude Opus 5
1M tokens
Claude Opus 4.8
1M tokens… 5.5
1M tokens
Claude Opus 5
1M tokens
Claude Opus 4.8
1M tokens
- Change the model, effort, and thinking settingsThe effort selector is available for Claude Opus 5.5, Fable 5.1, Opus 5, Sonnet 5, Fable 5, Opus 4.7,… Thinking cannot be turned off in Claude when using Claude Opus 5.5, Claude Fable 5.1, or Claude Opus… On Opus 5.5 and Fable 5.1, thinking is always on at every effort level, including on the Claude API
- How up-to-date is Claude's training data?While we're constantly updating Claude's data, each model has a knowledge cutoff:
Claude Opus 5.5… Claude Opus 5 was trained on data up until May 2026… Claude Opus 3 was trained on data up until August 2023
- Real-time cyber safeguards on Claude Opus and SonnetNote: This article applies only to Opus and Sonnet class models, but doesn’t apply to Claude Opus 5.5… We'll soon be expanding the Cyber Verification Program to include Opus 5.5 and Mythos class models… 5
dataSharingEnabledProvider: "ANTHROPIC"
Advanced AI
Sonnet 5
Opus 4.7
Opus 4.8
- Preserved thinking: changing how the Messages API handles thinking blocks to protect against distillationOn Claude Fable 5.1 and Claude Opus 5.5, new API accounts can no longer edit the context around a thinking… Accounts created before then
Claude Fable 5.1
Applies
Doesn't apply
Claude Opus… 5.5
Applies
Doesn't apply
This covers Claude Platform organizations, Amazon Bedrock accounts
- Enable and use web search5.5
Fable 5.1
Opus 5
Sonnet 5
Fable 5
Opus 4.8
Opus 4.7
Sonnet… internet to provide you with up-to-date information and insights when using the following models:
Opus… 4.6
Opus 4.6
Haiku 4.5
Web search expands Claude's knowledge with real-time data, helping
- How Claude marks AI-generated content5.5
Claude Opus 5
Claude Opus 4.8… Claude Opus 4.7
Claude Opus 4.6
Claude… Opus 4.5
Claude Sonnet 5
Claude Sonnet 4.6
- Release notesSeptember 22, 2026
Claude Opus 5.5 launch
We just launched Claude Opus 5.5, the first model in our… For more information, see our blog post: Introducing Claude Opus 5.5… new Claude 5.5 family
