Blazor has been split into two versions, there is a server side and a client side version, both that share the same component model. The server side version went GA a last week with .Net core 3.0, the client side is looking like it will GA in April 2020. The reason given is that their not happy with the size of the payloads required for now, the aim to have everything compiled to webAssembly by then, not just the mono runtime that's running as an IL interpreter at the moment.

The server side version is interesting, it ships DOM updates to the client from the server over a websocket (musch like OOUI https://github.com/praeclarum/Ooui). Not something that I'd use for production, but for quick internal projects which have the feel of a client side SPA, but while not requiring you to build the API layer it's quite neat.