AI Tools — Blog

Claude Opus 5.5 Explained: What's New, What It Costs, and Which Plans Include It
Anthropic's Claude Opus 5.5 matches Fable 5.1 on most work at 40% lower running cost than Opus 5. Here are the published benchmarks, the new $4/$20 API price list, how the Fable-style safeguards route flagged requests, what breaks when you migrate from Opus 5, and which Claude plans give you the model.

Claude Fable 5.1 Explained: What's New, What It Costs, and Which Plans Include It
Anthropic released Claude Fable 5.1 on 1 September 2026. This guide covers what changed versus Fable 5 – benchmarks, the five effort levels, 75% cheaper cache reads, fewer safeguard false positives and the new watermark – plus which Claude plans include it and where it fits alongside the software you already run.