AI / Claude OPUS5 Interview questions

What is the difference between disabling thinking on Opus 5 vs Fable 5?

On Claude Opus 5, thinking can be explicitly disabled with thinking: {"type": "disabled"}, but only at effort level high or below - attempting this at xhigh or max effort returns an HTTP 400 error, since those higher effort levels require thinking to stay on.

On Claude Fable 5 and Claude Mythos 5, adaptive thinking is always on with no disabled mode available at any effort level at all - it's simply not a configuration option the way it is, with restrictions, on Opus 5.

This reflects a broader pattern across Anthropic's current lineup: Opus 5 offers a genuine, if now restricted, choice about whether thinking runs, while the Mythos-tier models treat always-on adaptive thinking as a fixed characteristic rather than a togglable setting.

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On Claude Fable 5 and Mythos 5, disabling thinking is: not available at any effort level - thinking is always on

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the default behavior unless explicitly enabled

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available at every effort level with no restriction

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On Opus 5, attempting to disable thinking at xhigh or max effort: silently succeeds with no error

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automatically downgrades the request to high effort

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returns an HTTP 400 error

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More Related questions...

What is Claude Opus 5? When was Claude Opus 5 released? What is the pricing for Claude Opus 5? What is the API model string for Claude Opus 5? What is Claude Fable 5? Describe the effort parameter in Claude Opus 5? What is Fast mode for Claude Opus 5? What is the context window size for Claude Opus 5? What is the maximum output token limit for Claude Opus 5? Define thinking (reasoning) in the context of Claude Opus 5? What is the prompt caching minimum for Claude Opus 5? Describe mid-conversation tool changes in Claude Opus 5? What is automatic fallback on the Claude API? List the platforms where Claude Opus 5 is available? What is Claude Opus 5's position in Anthropic's Claude Max and Claude Pro plans? What is Claude Mythos 5? How do you enable thinking on Claude Opus 5? What is the default effort level for Claude Opus 5? Describe subagent delegation in Claude Opus 5? How do you migrate an application from Claude Opus 4.8 to Claude Opus 5? What is the difference between Claude Opus 5 and Claude Opus 4.8? How does Claude Opus 5 compare to Claude Fable 5 in capability and price? Why is thinking on by default a breaking change when migrating to Claude Opus 5? What is the difference between the effort parameter and response verbosity in Claude Opus 5? When should you use Fable 5 instead of Opus 5? How does Claude Opus 5's self-verification behavior differ from Claude Opus 4.8? What is the difference between disabling thinking on Opus 5 vs Fable 5? Why does max_tokens behave differently on Claude Opus 5 compared to Claude Opus 4.8? How does Claude Opus 5's narration behavior affect agentic prompting? What is the difference between Opus 5 and Opus 4.8 rate limits? When should you use Fast mode for Claude Opus 5? How does Opus 5 handle disabling thinking at xhigh or max effort? What is the difference between Claude Opus 5's Priority Tier support and Claude Opus 4.8's? Why should you avoid carrying over "double-check your work" instructions to Claude Opus 5? How does Claude Opus 5's prompt caching minimum affect short system prompts? How do Opus 5 and Fable 5 differ in calibrating thinking depth? When should you scope, rather than remove, a verification instruction? How does Opus 5's release cadence compare to Opus 4.5 and 4.1? Explain how the effort parameter governs Claude Opus 5's output beyond just reasoning? How can you optimize prompts when migrating from Opus 4.8 to Opus 5? How do you troubleshoot an Opus 5 response truncated at max_tokens? Explain the execution flow of mid-conversation tool changes in Claude Opus 5? How can you optimize agentic narration behavior in Claude Opus 5 through prompting? Which is better for long-horizon autonomous coding: Opus 5 or Fable 5? How do you troubleshoot an HTTP 400 error disabling thinking on Opus 5? Explain the tradeoffs of using Claude Opus 5's Fast mode versus standard mode? How can you optimize cost migrating high-volume workloads to Opus 5? Explain the artifacts that can appear in Claude Opus 5's output when thinking is disabled? How do you troubleshoot over-verification behavior in a Claude Opus 5 agentic workflow? Explain how Opus 5's positioning versus Fable 5 reflects Anthropic's strategy?

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