ChatGPT 5.2 Instant vs Claude Sonnet 4.5: Fast Professional AI Assistants Compared ChatGPT 5.2 Instant and Claude Sonnet 4.5 are often chosen by professionals who want speed without sacrificing credibility, because both models promise fast responses while still being suitable for business communication, technical drafting, and analytical summaries that may circulate internally or externally. They are not positioned as experimental reasoning extremes, and they are not lightwei