It’s up to MS. There are 4 possible ways (that I can think of). They are listed in what I consider the liklihood. I’m not sure how MS usually deals with beta’s of OSs.
1. People that are signed up with MS. I’m not sure how MS does it, but for example with Apple Developers pay to join Apple Developer Connection, and Apple Sends them every beta.
2. Only people inside MS, but it will probably be leaked like the last two alphas.
3. No one because it won’t be ready 😉
4. MS will release it to anyone that freely registers online.

