The OpenAI API is currently advertising their preview to my clients as `gpt-4-1106-preview`. I've been calling the Q4 2023 4-series stuff `4.5` or `4.5-preview` to distinguish it from the pre-big-announcement stuff.

I don't recall if I saw any press calling anything `4.5`, but it's a different model in some important ways (one suspects better/cheaper quantization at a minimum) and since they've used `.5` for point releases in the past it seemed the most consistent with their historical versioning.