Anthropic is facing criticism from across Silicon Valley for failing to sign an open letter defending open-weight AI models.

The new alliance sharpens the divide between firms selling closed models and companies that benefit from cheaper, customizable AI.

Anthropic is the only major AI lab that hasn't signed the open-weights letter. In June it argued the same case, when Washington pulled Fable 5.

Dario Amodei of Anthropic opposes a ban on open models, advocating instead for mandatory safety testing amid rising AI competition.