Anthropic: Claude Fable 5.1 (batch)

anthropic/claude-fable-5.1:batch · AnthropicNot yet established

Tokenizer lineage (measured): Claude
Evidence confidence: Moderate
Declared tokenizer tag: Claude
Entered catalogue: 1 September 2026
Last tested: Not yet measured
Measurement: Variant: inherits its base model’s measurement

Evidence

✓ inherited from anthropic/claude-fable-5.1: a serving variant shares its base model's tokenizer

Compare with Anthropic: Claude Fable 5.1

This entry is a serving variant of Anthropic: Claude Fable 5.1. A variant shares its base model's tokenizer by construction, so the measurement lives on the base record and this page inherits it.

Identity statement

Anthropic: Claude Fable 5.1 (batch) is Anthropic's model. Its measured tokenizer sits with the Claude group, which is evidence that it builds on the Claude tokenizer. Tokenizer reuse is normal engineering, open vocabularies travel between labs, and this says nothing against Anthropic's authorship of the model itself.

Evidence stack

Signals of different kinds, weighed together

Signal	Result	Reference
Tokenizer signature	Not measured	–
API surface	No other entry shares this exact contract	api_bb74210f
Context and output	1,000,000 context · 128,000 max output	declared
Reasoning contract	Mandatory · efforts max, xhigh, high, medium, low · default high	declared
Serving providers observed	None recorded yet	–

Declared record

What the catalogue claims about this model

Claude Fable 5.1 improves on Claude Fable 5 across the board, with the biggest gains in agentic coding, long-running agentic workflows, and knowledge work: long code refactors, front-end and visual...

Modalities: text+image+file->text
Declared tokenizer: Claude
Prompt price: $5.00 / M tokens
Completion price: $25.0 / M tokens

Supported parameters

include_reasoningmax_tokensreasoningreasoning_effortresponse_formatstopstructured_outputstool_choicetoolsverbosity

defaults: {}

Catalogue entry

History

Every observation, kept as taken

1 September 2026Enters the OpenRouter catalogue declared as Claude.

Cite this page as the evidence record for Anthropic: Claude Fable 5.1 (batch): the URL is stable, measurements are dated, and revisions append to the history above. Method: tokenizer fingerprinting, v1, 50 strings.