GPT-4 to GPT-5: What Actually Changed

By C.W. Jameson · Published 10 January 2026 · Last reviewed 10 February 2026

GPT-5 is not GPT-4 with more parameters. The architecture and training approach changed in observable ways.

A technical analysis of the differences between GPT-4 and GPT-5: reasoning, coding, multimodal, and agentic capabilities.