alt Hacker NewsIt was announced in April, but it was leaked in March (CMS bug) at which point external partners were already using it, and the most common rumored date for training competition is 2026-02-07 (I think Feb is likely, but that specific date is just rumor).
> the first early version of Claude Mythos Preview was made available for internal use on February 24. [...] Based on these findings, we decided to release the model to a small number of partners to prioritize its use for cyber defense.
https://www-cdn.anthropic.com/7624816413e9b4d2e3ba620c5a5e09... (pg. 13)