Claude Fable 5.1: same price, stronger at long-running coding and multistep research

What's new in Claude Fable 5.1

Anthropic updated its platform docs for Claude Fable 5.1. Pricing matches Fable 5, with cache reads at a quarter of the cost. The focus is stronger long-running agentic coding, multistep research, and document, spreadsheet, and slide work. Three breaking changes: forced tool use now errors, earlier models can't read its thinking blocks, and editing earlier turns invalidates thinking blocks. Five additive features include mid-conversation effort changes, turn-scoped system messages, and readable progress between tool calls—some marked beta. The post doesn't include benchmark scores or latency figures.

Why it matters: Anthropic ships Claude Fable 5.1 with a 4x cache cost reduction and three breaking changes developers need to watch. Solid product update with direct cost and workflow impact for Claude-heavy users. Not scoring higher because it's a docs-only release so far — no independent be...