Claude Fable 5

Fable is a fourth naming tier, introduced above Opus. Where Opus 5 is the recommended default, Fable 5 is what the documentation points you to “for workloads that need the highest available capability” — specifically framed around long-running agents.

What sets it apart

Adaptive thinking is always on. Opus 5 and Sonnet 5 support adaptive thinking; Fable 5 does not let you turn it off. There is no thinking parameter and no non-thinking mode.

It is the slowest current model, which is the trade being made. For an agent running for hours, latency per turn matters less than not going off the rails on turn four hundred.

It is twice the price of Opus 5 — $10 in, $50 out per million tokens — and shares its pricing exactly with Claude Mythos 5.

The tokenizer caveat

Fable 5 uses the tokenizer introduced with Claude Opus 4.7. The same text produces roughly 30% more tokens than on Claude Sonnet 4.6 and earlier. Comparing $10/MTok against an older model’s $5/MTok therefore understates the real gap; the honest comparison multiplies the older model’s rate by about 1.3 first.

Its 1M-token context window is measured in those tokens too — around 555,000 words, against roughly 750,000 words for the same nominal window on Opus 4.6.

Specifications

Property	Value
Claude API ID	claude-fable-5
Amazon Bedrock ID	anthropic.claude-fable-5
Google Cloud ID	claude-fable-5
Context window	1M tokens (~555K words)
Max output	128K tokens
Adaptive thinking	Yes, always on
Extended thinking parameter	No
Reliable knowledge cutoff	January 2026

Pricing

Rate	Price per million tokens
Input	$10
Output	$50
5-minute cache write	$12.50
1-hour cache write	$20
Cache read	$1
Batch input / output	$5 / $25

Lifecycle

Active, tentative retirement not sooner than 9 June 2027.

Not yet covered here

Anthropic has published a post titled “Redeploying Claude Fable 5”. This reference has not yet read and summarised it, so nothing about its contents is claimed on this page. It is listed under sources so you can read it directly. If you know what changed, send it over.