When should you use Fast mode for Claude Opus 5?

Fast mode suits exploration, rapid drafting, and lower-risk iterative loops where getting a response back quickly matters more than minimizing cost per token, since it runs at roughly 2.5 times the speed of standard mode at about double the price.

It's less suited to workloads where cost efficiency is the primary concern, or where the specific platform being used doesn't yet support it - currently it's a Claude API-only research preview, unavailable through Amazon Bedrock, Google Cloud, or Microsoft Foundry.

Because it's a research preview rather than a fully stable feature, teams should also weigh that its availability, pricing, or exact performance characteristics could still change as Anthropic continues developing it, unlike Opus 5's standard mode.

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