A Claude Code cache-resume bug re-bills a finished sub-agent's entire context on follow-up
An r/ClaudeAI user traced part of this week's quota burn to a specific defect: when a Claude Code sub-agent finishes and you send it a follow-up, Claude Code rebuilds the conversation in a form the prompt cache does not recognize, so the next request re-sends and re-pays for nearly everything that agent had read. It happens inside the 1-hour cache window, and messages sent while the agent is still working are cheap. The same user separately found sub-agent prompt cache lifetime defaults to 5 minutes against the main conversation's 1 hour and fixed that with a setting. Their weekly usage went 49% to 60% in one session while deliberately holding back. Filed with Anthropic, unconfirmed, but the workaround is concrete: message sub-agents while they are running, not after.
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