After finishing season 2 I did some research -- first the good news: Apple has signed the dotted line and there WILL be two more seasons and a 'conclusion'.
As for season 3. I didn't read the books... this will probably make more sense to you. Apparently the first two seasons of SILO was based on one book... might have been more than one book like a trilogy, I'm not sure...... and now in season 3 it will be based on the second book which is basically related but a different tale than the first book. Speculation is that they will kind of merge the two books for the coming two seasons.... unlike what was done in the books.
When the final episode of season 2 began I figured it out quickly but it was a shock at first. Didn't expect a prelude.
As for Apple TV... I think they're doing very well. I don't watch a lot of TV but the last couple, maybe 3 years, I've watched a few series.... started with Longmire which I loved and then on Waterfields suggestion watched "Bosch" which was also great. Neither of those were Apple TV productions... but then I moved to Apple TV for no other reason than I had it but had never watched it.

Most of their content doesn't interest me much but those few I have watched have been great. Very high quality productions. I'm going to start another tonight that just came out.... episode 3 isn't even released yet. It's called "Prime Target" and caught my attention... we'll see.

- JamesJM