Spawning a subagent in Claude Code feels free. It isn't. We measured it across a real review pipeline, and the number that matters is one almost nobody talks about: each subagent costs roughly 436,000 tokens in fixed overhead before it does any useful work.
This post explains where that number comes from, how to reproduce the measurement on your own setup, and what it changes about how you should split work between agents.
The experiment
We run a weekly review pipeline over a catalog of digital products (Markdown-heavy repos: rules files, skills, templates). The pipeline embeds each product's full content into a reviewer prompt and asks for structured findings.
We ran the same product, same full content, two ways:
