What is the difference between Claude Opus 5 and Claude Opus 4.8?

The most consequential functional difference is that Claude Opus 5 runs with thinking on by default, while Opus 4.8 ran without thinking unless a request explicitly enabled it - this alone changes both typical token cost and answer quality on unconfigured requests.

Opus 5 also lowers the prompt-caching minimum to 512 tokens (from 1,024), uses a separate rate-limit bucket rather than the shared Opus 4.x pool, adds mid-conversation tool changes and automatic fallback as new beta capabilities, and drops support for Priority Tier, a feature some enterprise customers relied on with Opus 4.8.

On raw capability, Anthropic reports Opus 5 achieving markedly better results on agentic and reasoning-heavy benchmarks like Frontier-Bench, at the same $5/$25 per-million-token pricing as Opus 4.8 - so the upgrade is framed primarily as a capability and efficiency gain rather than a price change.

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