I expect Pi is mostly used with OpenAI plans, and OpenAI has a dedicated compaction endpoint you should probably be using with their models instead of a compaction prompt.

There is a compaction routing plugin, as well as a general OAI compatibility plugin that simulates some of their harness features (ie. code_mode/batching tools) that also includes their compaction.

That said, from reading the pi subreddit I don't see people referencing these much.