In my experience, around the time the author describes as starting to not need plan mode is when erasing the chat history became an anti-feature. I found the agents were doing better when they had the context already, and with the history I no longer needed to micro-manage persisting various caveats and rejections to the plan artifact. The amount of prompt construction necessary went down overall.

By the time my plan’s done I’m usually between 200 and 350k context. Even if keeping that around gives a performance bump for the implementation (which I haven’t noticed to be the case) it balloons the cost. I would much rather put everything in a plan file and start fresh.

Plus, I usually plan with a more expensive model and guide implementation with a cheaper model (with smaller validation calls back to a more expensive model)