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Correct answer: B. Its summary of the findings, and not the material it read
Explanation
The principle — delegation only pays if the worker's reading stays with the worker.
Why the key is correct — Anthropic is explicit about what crosses back: delegate the exploration so only the findings come back, and the subagent returns only the summary. What you receive is a report of what was found, not the material read to find it.
Why the others are wrong — the reading never arrives in your conversation; if it did, the delegation would have cost the very context it exists to save. Running several workers at once is something delegating makes possible, not what one worker hands back. And the worker is another Claude session, so what returns is not a cleverer answer than yours, only a shorter one.
Remember this — you get the findings, never the reading that produced them.
Sources — Anthropic's Claude Code subagents and common-workflows documentation.
Sources
“the subagent does that work in its own context and returns only the summary”
“Exploring a large codebase fills your context with file reads. Delegate the exploration so only the findings come back.”
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