How do you migrate an application from Claude Opus 4.8 to Claude Opus 5?

The baseline step is simple: change the model identifier from claude-opus-4-8 to claude-opus-5 in API requests, since most existing requests continue to work without further changes.

Beyond that string swap, it's worth explicitly checking a small number of behavior changes that can affect correctness or cost: thinking now runs by default and shares the max_tokens budget with the visible reply, disabling thinking is restricted to effort high or below, effort levels were recalibrated, and Opus 5 draws from a separate rate-limit bucket rather than the combined Opus 4.x pool.

On the prompting side, it's also worth reviewing prompts for outdated verbosity or verification instructions carried over from Opus 4.8, since Opus 5's different default behavior around response length and self-verification can interact with those older instructions in ways that waste tokens rather than helping.

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