I suspect the YCombinator usage is iffy. YCombinator don't give advice on visas, but rather suggest you speak to YC alumni who've done it. While I'm sure there

I suspect the YCombinator usage is iffy. YCombinator don't give advice on visas, but rather suggest you speak to YC alumni who've done it. While I'm sure there are many reasons why they take that approach, I wouldn't be surprised if the legality was a big reason. Saying that many developers both for startups and for other industries like finance do go to the US and work 2-3 months without any issue. It's not clearly allowed, but nor is it clearly disallowed. The reason people suggest speaking to an attorney is that if you screw it up, not only will you get deported but you can be banned from re-entry not only to that country but many other countries. There's nothing like "denied entry" being stamped on your passport to get you stopped at every border crossing you cross for the rest of your life.