OpenAIAnthropicGooglexAIPerplexity
← Back to all updatesPublished ·Anthropic• Minor
Claude Fable 5 and Claude Mythos 5 support only adaptive thinking mode.
The read
Builders must remove disabled thinking, manual thinking budgets, and assistant prefill or requests return 400 errors.
The frame
For migrations from Claude Mythos Preview, integrations need adaptive thinking only and no assistant prefill.
Primary source
Anthropic →Keep reading
See what Nova3 builds →Related updates
- Jul 26, 2026OpenAI updated GPT-5.5 Instant to improve conversational quality in decision, advice, planning, research, and shopping tasks.
- Jul 25, 2026Enterprise and Edu users can find skills under Plugins, on the Skills tab in the Plugin Directory.
- Jul 25, 2026Anthropic removed modelcard language for Claude Fable 5 and Claude Mythos 5.
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