October 21, 2026 / Latest Daily Edition / 1 story in this issue
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Pydantic Updates Agent Instructions Without Rewriting the Opening

An agent’s task state can change without changing the start of its next model request. Pydantic AI’s new append mode puts the update at the end of the conversation, preserving the earlier prefix for possible cache reuse.

Two paper strips compare rewriting Todo: done at the opening with retaining Todo: pending and appending Todo: done after history.
Diagram Punkthe update changes position; the earlier state stays in the prompt. Cache reuse is not guaranteed.
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Evidence: commit cd04b05 / October 21, 2026 / Daily Edition
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