Default verbosity via a one-line system instruction

The prompt

All questions should be answered comprehensively with details, unless the user requests a concise response specifically.

Expected result

Detailed, thorough answers by default across an entire session, without repeating "be detailed" in every message — until the user explicitly asks for something shorter.

Why it works

A one-line system instruction sets a durable default for the whole conversation instead of a per-message request, and explicitly carves out the override condition so the model knows exactly when to switch to concise mode.