[energy123]

> If you plan on using this much at all then the primary thing to avoid is API-based pay per use.

I find there's a niche where API pay-per-use is cost effective. It's for problems that require (i) small context and (ii) not much reasoning.

Coding problems with 100k-200k context violates (i). Math problems violate (ii) because they generate long reasoning streams.

Coding problems with 10k-20k context are well suited, because they generate only ~5k output tokens. That's $0.03-$0.04 per prompt to GPT-5 under flex pricing. The convenience is worth it, unless you're relying on a particular agentic harness that you don't control (I am not).

For large context questions, I send them to a chat subscription, which gives me a budget of N prompts instead of N tokens. So naturally, all the 100k-400k token questions go there.