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Claude Mythos 5.1

Anthropic · Released Sep 1, 2026 · 54 days ago · Closed weights
Latest Claude Mythos

Restricted Claude model for advanced cybersecurity and biology research workflows

Context window
1M
tokens in · 128K out
Since the last one
84 days
after Claude Mythos 5
Lab announcement ↗Open in the timeline

Since Claude Mythos 5

2 releases in the Claude Mythos line.

Claude Mythos 5Jun 9, 202684dClaude Mythos 5.1Sep 1, 2026
Released84 days later
Context1Msame
BENCHMARKS

Not in the Epoch Capabilities Index. Epoch benchmarks what it can run, so this is a gap in coverage, not a poor result.

Anthropic's past year

12 release days in the past year, about one every 30 days. The next is expected around Nov 17, 2026. Forecasts ↗

NovDecJanFebMarAprMayJunJulAugSepOctNov

Specifications

RELEASE DATESep 1, 2026
WEIGHTSClosed weights
CONTEXT WINDOW1M
MAX OUTPUT128K
REASONINGNot listed
TOOL CALLINGNot listed
INPUTStext, image/jpeg, image/png, image/gif, image/webp, application/pdf
OUTPUTStext

Models.dev record ↗

Specifications and prices from Models.dev; availability and limits may differ by provider. Benchmarks from Epoch AI (CC BY 4.0), LiveBench and the other sources named above.