I guess Anthropic knows this. They show you this warning:

--- Switch model? Your next response will be slower and use more tokens

This conversation is cached for the current model. Switching to Opus 4.8 (1M context) means the full history gets re-read on your next message. ---

Reminds me a bit of airline booking sites ("We noticed you didn't add insurance").

I mean, this is real. Your KV cache lives for an hour since the last token (on anthropic pro/Max at least, today at least, this has degraded in the past). So once you pay, say, 50k input and 50k output Opus tokens, you don't pay for cache reads of the 100k context while it builds. Switch to another model, you'll start with the cost of 100k input tokens on the smaller model to get that context loaded and its unique KV cache set.

The post may have some real insight here, where this 100k working context is actually better than trying to summarize it's findings into a plan. It's also right that the handoff is a perfect time to edit the context (removing planning instructions). But it doesn't mention it's a trade-off: the plan is smaller, so it's a cheaper "on-boarding" of the next model. Send quite plausible that this is worth it for 1-off tasks. If it's right, this is basically "plans are useless, planning is everything" for LLMs.

My problem is, I think the plans are useful. I want to review and edit them. I want them to give context for the upcoming code review (even if humans aren't reviewing). LLMs are notoriously bad at explaining why they're doing something in the moment. Humans are notoriously bad at accepting there's no reason why. I think the humans have it right here, and to bridge this gap want my PRs, my docs, and my comments teeming with reasons why.

(NB: ranted to long, reposting at top level)