A distinction must be drawn between working during a startup program, which requires a work visa, and attending the program and not working. For the latter, there are several options, including, most commonly, the B-1 visa/status.
Out of curiosity, what percentage of YC founders just go to the office hours and dinner and not work for the duration of the program? Is this encouraged?
I can't comment on that but the issue here is what constitutes work and actively participating in YC doesn't even if this participation results in benefit to a company.
Work in the context of immigration means participating in the local economy. A person visiting SF to attend YC is not working for a U.S. company, they are not participating in the local economy, they’re on a business trip conducting business.
Sure, you can describe it that way if you want but that’s not the spirit of immigration law. A founder of a company (registered in the U.S. or overseas) visiting YC to raise money is not working in the local economy by the spirit of immigration law. A founder who registered a Delaware c-corp through stripe atlas is not working in the U.S. when they go to SF to raise money. That’s what business visas exist for.
I am a US citizen but have a few non-US citizen friends who might join if accepted.