First of all congratulations on figuring yourself out!
Second of all, it depends. Do you know their views on bi people? I’d see if you can kind of broach the topic and see what their views of bi people are first, to see if you’d be cool coming out to them. If positive, then go ahead! If negative..do you really want to be friends with people who don’t accept who you are? However, people’s minds can change once they meet someone who is bi. So if their reaction isn’t great and you’re feeling brave, you could tell them “Well, I’m bi, and these stereotypes/ideas you have about bi people are wrong.” Maybe they’ll change their mind. But if not, then don’t keep around friends who don’t accept you. It’s not worth it.
You don’t have to tell them if you don’t want to either. It’s entirely up to you as to when (or if) you come out. But my first advice is always to check if they’d be cool with bi people by broaching the topic. Perhaps mention that one of your friends in Austrailia was bi, or that you saw a bi person on tv, in order to bring up the topic naturally so it doesn’t feel forced. Good luck.