Comment by atleastoptimal

My theory is that they're using a fine-tuned version of GPT-4-turbo in ChatGPT to fix the issue with everyone saying it was lazy. They fine-tuned it using responses from GPT-4.5-turbo, which they have internally. This synthetic data was probably based on a suite of questions which included self-identification, leading to it releasing its model name in the training data, and the new ChatGPT less lazy model is adopting the name via osmotic data leakage.