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The standalone "# Communicating with the user" prompt section (for Opus 4.6 users) and the "# Output efficiency" prompt section (for other users) were both removed from the system prompt assembly. Their guidance is now covered by the tighter communication style instructions and the new numeric length anchors.
Evidence
Both "Communicating with the user" and "Output efficiency" strings are absent from v2.1.100 (confirmed via search)
Strings lifted out of the shipped bundle, so the claim above can be checked against them.