No, although it's better because it one less thing you'll have to worry about later. Once accepted, you can file online for an adjustment of status to B-1 witho

No, although it's better because it one less thing you'll have to worry about later. Once accepted, you can file online for an adjustment of status to B-1 without leaving the US and enjoy that status as soon as you submit -- although it will usually take a few months until your case is processed. You'll usually get 6 months and can reasonably extend for 10 months. Once accepted in YC, one can assume you can reasonably qualify for O-1 or EB-1, but because it takes longer to prepare such application, you best bet is to start with B-1.