---
type: "Evidence Item"
title: "Claude Fable 5.1 and Mythos 5.1: advanced reasoning with different access"
description: "Anthropic reports advances in extended coding, research and professional document work. Fable and Mythos share a base model but apply different safeguards, affecting which tasks."
resource: "https://www.anthropic.com/claude-fable-and-mythos-5-1"
tags: ["appendix-iii", "vendor", "anthropic"]
timestamp: "2026-09-01"
category: "vendor"
publisher: "Anthropic"
cope_score: 76
confidence: 0.85
---

# Claude Fable 5.1 and Mythos 5.1: advanced reasoning with different access

# Claim

Anthropic reports advances in extended coding, research and professional document work. Fable and Mythos share a base model but apply different safeguards, affecting which tasks each can perform.

# Relevance

Appendix III, sections one and two: model capability and vendor threshold evidence

# Oracle Verdict

Safeguards and access conditions are part of usable capability. The restricted model should not be presented as generally available, and benchmark comparisons must account for interventions.

# Metadata

* Publisher: Anthropic
* Category: vendor
* Sector: General AI capability
* Capability: Agentic coding and professional task execution
* Cope score: 76
* Confidence: 0.85

# Related Concepts

* [Live evidence index](index.md)
* [Thesis](../thesis.md)

# Citations

[1] [Claude Fable 5.1 and Mythos 5.1: advanced reasoning with different access](https://www.anthropic.com/claude-fable-and-mythos-5-1)