Teamday

Chat & Reasoning Model · Anthropic

Claude Fable 5.1

Claude Fable 5.1 is Anthropic's most capable widely released model, released September 1, 2026 as the successor to Claude Fable 5 in the same tier at the same base price — with cache hits 4x cheaper ($0.25 vs $1 per 1M tokens). It has a 1M-token context window and up to 128K output tokens. In Teamday it is the pick for the hardest, longest-running work on the Claude Code harness — Claude Opus 5.5 is the recommended default — with reasoning effort selectable from low up to max.

Use Claude Fable 5.1 in Teamday →All models

At a glance (verified 2026-09-05)

Vendor
Anthropic
Type
Chat & Reasoning Model
Context window
1M tokens
Pricing
Base: $10 in / $0.25 cache hits / $50 out per 1M tokens. Cache writes: $12.50 5m / $20 1h.

Best for

Long-horizon agentic workAutonomous codingDeep researchMulti-hour missions

How to use Claude Fable 5.1 in Teamday

Pick Claude Fable 5.1 in Teamday's chat model picker on the Claude Code harness — it replaced Claude Fable 5 as the pick for the hardest missions, while Claude Opus 5.5 is the recommended default for most work.

Harness: claude-code →Max →Daisy →

Frequently asked questions

How much does Claude Fable 5.1 cost?

Base API pricing is $10 per 1M input tokens, $0.25 for cache hits, and $50 per 1M output tokens; cache writes cost $12.50 (5-minute) or $20 (1-hour) per 1M tokens. That is the same base price as Claude Fable 5, with cache hits 4x cheaper ($0.25 vs $1).

What changed from Claude Fable 5 to Claude Fable 5.1?

Same tier, same base price, three breaking API changes: forced tool use (tool_choice any or tool) returns an error, thinking blocks are bound to the model that produced them, and editing earlier turns of a conversation invalidates its thinking blocks. Claude Fable 5 stays callable as a legacy model.

Can I use Claude Fable 5.1 in Teamday?

Yes — it is available on Teamday's Claude Code harness for the hardest, longest-running work, with selectable reasoning effort (low, medium, high, xhigh, max; high is the default). Claude Opus 5.5 is the recommended default for most work at 2.5x lower prices.

Related

Claude Fable 5.1 is one of the models Teamday's AI employees already run — no API keys, no infrastructure.

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