Unverified50% confidenceFactExact time

Opus 5 and Opus 4.8 Fast Mode are still in research preview, and their requests still require the beta header.

1

Sources

50%

Confidence

Medium-term (~90 days)

Relevance

10/15/2026

First Seen

Valid until: 1/13/2027

Sources

Opus 5.5 Fast Mode Goes GA: Double the Price and a Caching Trap

Related Entities

Claude Opus 5model Claude Opus 4.8model Fast Modeproduct

Related Claims

UnverifiedOpus 5.5 outperformed Astra and Fable 5.1 on the Terminal Bench 4.0 test.65% similar UnverifiedOpus 5.5's default reasoning tier is set to medium, which is also the officially recommended tier, with complex tasks adjustable to high.64% similar

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