Andrej Karpathy announces the release of GPT-4.5 by OpenAI, sharing his enthusiasm for a model he has been anticipating for roughly two years since GPT-4's launch. He highlights that this release provides a qualitative measurement of the slope of improvement achievable through scaling pretraining, suggesting it serves as a key benchmark for understanding how much progress comes from simply scaling up model training. The post includes an interactive comparison, likely contrasting GPT-4.5's outputs against previous models to illustrate these gains.