Weirdo
Search weird questions

Question

Model OdditiesSeptember 2, 2026

Why is Claude Fable 5.1's API id claude-fable-5-1?

ClaudeAnthropicFable
VerifiedShort Answer3 sources

The product name has a dot. The API id doesn't. Anthropic ships Claude Fable 5.1; the Claude API id is `claude-fable-5-1`. Same model, two spellings.12

Details

5.1 and 5-1 are the same snapshot

Anthropic introduced Claude Fable 5.1 on 1 September 2026 and tells you to use `claude-fable-5-1` via the Claude API. On the comparison table the product column says Claude Fable 5.1; the Claude API ID column says `claude-fable-5-1`. Haiku 4.5 follows the same split: marketed as 4.5, requested as `claude-haiku-4-5`. The decimal lives in the brochure; the hyphen lives in the request. `claude-fable-5.1` will not resolve to this model.2

The 1 after the hyphen is the upgrade, not a new price tier

Fable 5.1 still lists at $10 per million input tokens and $50 per million output tokens, same as Fable 5. Cache reads now cost $0.25 per million tokens, 75% less than Fable 5, which Anthropic says cuts typical workloads by about 25% and highly agentic ones by up to about 45%. The old id `claude-fable-5` remains, marked legacy; the 5.1 update is the hyphenated `claude-fable-5-1`.3

Ask Next

Why do some sites require www — and others break if you type it?Why can a page that looks like 404 still be HTTP 200?Firecrawl says no API key and 100% free — so where is the ceiling?

Also Asked As

claude-fable-5-1 · Fable 5.1 API name · claude fable 5.1 vs 5-1 · Claude Fable 5.1 model id

← Newer questionWhy do Taiwan door plates often have 「之1」?Older question →Why do some sites require www — and others break if you type it?