GPT-5.5 Pro spends extra compute on hard assistant tasks—dense documents, strict instructions, and long back-and-forth where mistakes are costly. Our tests show gains in instruction following and comprehension over standard GPT-5.5. Empathy stays cool. Creative writing gets worse under heavier reasoning: parallel internal drafts and compressed scratchpads produce drier, sometimes tone-fractured prose. Use it when correctness on a high-stakes ask matters more than warmth or literary quality.