GPT 5 is likely just going to be a router model that decides whether to send the prompt to 4o, 4o mini, 4.5, o3, or o3 mini.
Even by their poor standards at naming it would be weird to introduce a completely new type/concept, that can loop in models including the 4 / 4.5 series, while naming it part of that same series.
My bet: probably something weird like "oo1", or I suspect they might try to give it a name that sticks for people to think of as "the" model - either just calling it "ChatGPT", or coming up with something new that sounds more like a product name than a version number (OpenCore, or Central, or... whatever they think of)
https://www.theverge.com/news/611365/openai-gpt-4-5-roadmap-...
> “We hate the model picker as much as you do and want to return to magic unified intelligence,”
> “a top goal for us is to unify o-series models and GPT-series models by creating systems that can use all our tools, know when to think for a long time or not, and generally be useful for a very wide range of tasks,”
> the company plans to “release GPT-5 as a system that integrates a lot of our technology, including o3,”
He even slips up and says "integrates" in the last quote.
When he talks about "unifying", he's talking about the user experience not the underlying model itself.