I didn't ask but pretty sure it's compatible. My Note 9 is compatible.

Will work as "Compatible with Fi" or "Designed for Fi" (can do network switching)?

I guess it depends on where you are and how well Tmobile works. For me, I get great Tmobile coverage.

Damn I was really hoping for network switching functionality. Do you think it's worth using on Fi without it?

I spoke with Google FI chat as well. It will work but will be limited to the Tmobile network, which is fine for me.

Not a huge surprise, but I just spoke with Fi's live chat and they said S10 phones will work. Figured I'd share this here.

Google Fi will work with Galaxyy S10/S10+/S10e