ChatGPT-User represents an on-demand visit triggered by a real user action inside ChatGPT, not bulk crawling. OpenAI documents it as the agent used when ChatGPT needs to retrieve a page to answer a user's request, and notes that because these fetches are user-initiated, robots.txt rules may not apply.
OpenAI documents four bots with different jobs: GPTBot (training), OAI-SearchBot (search results), ChatGPT-User (live user-initiated fetches), and OAI-AdsBot (ad validation, added in 2026, not used for training). Knowing which is which prevents you from blocking the wrong one.