I work on Claude Code. You've got the basic mechanism right, but to be super clear, this only applies to background agents that are actively working. They get a summary call about every 30 seconds, and idle background agents don't. These summaries are used for both you and Claude Code to track what each background agent is working on, without reading transcripts.

Your 16.4% sounds like it was for a team running mostly background agents, and doesn't seem like a typical session. (Feel free to send me the session ID at [email protected] and we can dig further.)

Last week, across Claude Code users who send us telemetry, agent_summary was about 2% of cost at API list prices and just under 4% of requests. In the terminal, where nearly all of these calls happen, it was about 6% of cost.

That said, we agree that's a lot for a status line. We just rolled out a fix for the most expensive case, summaries that miss the prompt cache (2.1.311+), and right now we're working on a much cheaper mode that sends short notes to a smaller model instead of the full transcript.