Can you guess who didn't sign on to the group letter?

The most popular frontier lab leaders are warning against powerful open-weight AI models.

Nearly 200 US startups, including Y Combinator and Proton, warn a ban on Chinese open-weight AI would kill hundreds of them and hand the market to Anthropic.

Letter explaining support comes amid rift over AI development philosophies and governance

Can you guess who didn't sign on to the group letter?