Today, OpenAI revealed in a press release that "OpenAI has recently begun training its next frontier model". It was commonly believed that GPT-5 had begun training in 2023, shortly after GPT-4 finished. For example, the market for a release this year went from 68% to 50% on the OpenAI press release today, and markets like this one implied a substantial chance of training beginning in 2023 earlier this year.

This market resolves YES if any reputable news source, such as The Information, indicates that OpenAI did in fact begin a training run for GPT-5 previously and abandoned it to start this training run. This could indicate that they ran into some sort of issue or simply that they decided to restart and train a cheaper model using the innovations made for GPT-4o, if those save a significant amount of compute.

"GPT-5" here means "a scaled up version of GPT-4"; if it is referred to by a codename but they mention that it has many more parameters than GPT-4 and is the model that would have been expected to be called GPT-5, I would still resolve YES.