OK (often written in Latin letters, sometimes 欧克) is fully integrated into spoken and written Mandarin. Treat it grammatically like 好 — 很OK, OK的, OK吗, OK啦. Common in work chat; written casually, less so in formal documents.
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In formal writing stick to 好 / 可以 / 没问题. In chat, OK reads as neutral-friendly; short, polite, non-committal.
