Claude Mythos Preview | Epoch AI

ECI

N/A

Anthropic

Apr. 7, 2026

Closed weights

Claude Mythos Preview is a closed-weights model from Anthropic, released April 7, 2026.

Claude Mythos Preview vs select alternatives

Domain	Benchmark	Claude Mythos Preview Anthropic Apr. 7, 2026 Closed weights	GPT-5.4 Pro OpenAI Mar. 5, 2026 Closed weights	Gemini 3.1 Pro Google DeepMind Feb. 19, 2026 Closed weights	Grok 4.20 xAI Feb. 17, 2026 Closed weights
Software engineering	METR Time HorizonsBest score 17 hr 25 min	17 hr 25 min	—	6 hr 24 min	—
	ExploitBench v0.1Best score 74%	74%	n/a	26%	n/a

Model metadata

General
Organization	Anthropic
Release date	Apr. 7, 2026
Model accessibility	Closed weights
Country	United States of America
Knowledge cutoff	Unknown
Provider notes	Claude Mythos Preview System Card

Pricing
Input price	—
Output price	—

Training
Parameters	Unknown
Training compute	Unknown
Training hardware	Unknown
Training time	Unknown
Training dataset size	Unknown