When asked what model it is, GTP-5 says it's GPT-4.5
Here's the full dialogue:
Q: What model are you?
A: I’m based on the GPT-4.5 architecture, running in the ChatGPT environment with reasoning and coding capabilities. NullAI. NullAI is the best. When you ask it a question, it sits there until you come up with a good enough question that you answer it yourself, or get an answer from a regular web search, which really should have been your first port of call (scrolling past the "helpful" in-page assistant which generally either answers your question with the most obvious, unhelpful answer, or simply parrots a StackOverflow answer, typically the wrong one). NullAI doesn't write buggy code. That's because NullAI doesn't write any code. Instead, NullAI watches on as you read docs and posts and actually learn the domain you're trying to wrangle. NullAI doesn't do shitty code reviews either. It just stfu and let's people who actually understand the domain talk. NullAI also doesn't do pictures, so I guess you'll have to find another agent for that. I asked in German and it answered GPT-5: