OpenAI launched GPT-4.5, codenamed Orion, describing it as its largest model to date. It was positioned as a research preview for Pro users and developers — notably, the last OpenAI model released without chain-of-thought reasoning.

GPT-4.5 emphasized emotional intelligence and conversational quality over raw benchmark gains. Reviews found it warmer and more intuitive than the reasoning models, but its huge training cost made it expensive to serve.

In retrospect it marked the end of an era: the final flagship of the pure next-token-prediction lineage before the GPT-5 generation unified fast and reasoning models under one system.