I got an Internship offer from a HFT (over email, said "We'd love to make you an offer" and organized a call soon), very happy and I think I'll go for them over all my other options. I'm worried though that they might change their mind anytime before the official contract is sent, and I don't know how likely that is. 

Anyone have any idea? I have interviews next week with a couple of other companies, one that's also in the same league and that I could potentially pick as well. I think I will keep my current interviews, but should I also keep applying to other places/take pending OAs?