# Claude Mythos 5.1: SI Model Safety Record

> Claude Mythos 5.1 is an SI model from Anthropic. The Containment Board lists it as a flagship model of Anthropic, which gets B+ overall. Sources linked.

Source: https://enterrsi.si/encyclopedia/claude-mythos-5-1/
Updated: 2026-11-08

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RSI Encyclopedia · Model

# Claude Mythos 5.1

Claude Mythos 5.1 is an SI model from Anthropic. The Containment Board lists it as a flagship model of Anthropic, which gets B+ overall.

Developer
:   Anthropic

Type
:   SI model

Rogue Log cases
:   0

Lab grade
:   B+

## What the sources document

This entry only states what the sources on enterrsi.si document. Release dates, sizes and other specifications are left out unless a source here gives them.

## Grade context

The Containment Board grades labs, not single models. Anthropic gets **B+** overall, rank 1 of 11, on the commitments that decide whether its models can be tested, contained and stopped. See the [full report card](https://enterrsi.si/containment-board/anthropic/).

- Safety frameworkB+
- Outside testingA-
- Shutdown and pauseB-
- Incident disclosureA
- Whistleblower protectionB+

The model

Model
:   Claude Mythos 5.1

Developer
:   Anthropic

On the board
:   Yes, as a flagship

Highest Rogue Scale level
:   None recorded

Developer

[Anthropic **Lab**](https://enterrsi.si/encyclopedia/anthropic/)

Other Anthropic models

- [Claude Opus 5.5](https://enterrsi.si/encyclopedia/claude-opus-5-5/)
- [Claude Fable 5.1](https://enterrsi.si/encyclopedia/claude-fable-5-1/)
- [Claude Mythos 5](https://enterrsi.si/encyclopedia/claude-mythos-5/)
- [Claude Mythos Preview](https://enterrsi.si/encyclopedia/claude-mythos-preview/)
- [Claude Opus 4.7](https://enterrsi.si/encyclopedia/claude-opus-4-7/)
- [Claude Opus 4.6](https://enterrsi.si/encyclopedia/claude-opus-4-6/)
- [Claude Opus 4](https://enterrsi.si/encyclopedia/claude-opus-4/)
- [Claude Haiku 4.5](https://enterrsi.si/encyclopedia/claude-haiku-4-5/)

Related terms

[Frontier model **Term**](https://enterrsi.si/encyclopedia/frontier-model/)

Cite this entry

"Claude Mythos 5.1." The RSI Encyclopedia, enterrsi.si, November 8, 2026. https://enterrsi.si/encyclopedia/claude-mythos-5-1/

Free to cite under CC BY 4.0 with a link to enterrsi.si.

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