how's Sonnet vs Opus in terms of daily coding?

For doing 'boring' day to day things in python I find them more or less the same. For doing non-trivial things in Rust, Opus is much better. Sonnet is much more prone to producing garbage that is just completely wrong in those cases. However I find Gemini 2.5 Pro better than both for harder programming problems.

I guess it depends? It seems a limited offering if you're planning to go all-in on agents, but on the other hand one of the most common complaints about Claude Code is that its costs are unpredictable and weird.

Your mileage may vary dramatically, but I don't think I would subscribe to Pro just for this. It's a "nice to have" on top of my existing Pro subscription whose services are the bulk of the value I'm paying for.