Extended thinking is simplified to two options—thinking and thinking_effort (low, medium, high, xhigh, or max)—with Claude 5 models thinking by default, while Fable 5 always thinks regardless of configuration.

Simplified extended thinking to thinking and thinking_effort (low, medium, high, xhigh, or max). Claude 5 models think by default; -o thinking 0 disables thinking for Sonnet 5 and Opus 5, while Fable 5 always thinks. -R/--hide-reasoning now omits reasoning from responses and logs. The thinking_budget, thinking_display, and thinking_adaptive options have been removed. #80

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