Update 2025-08-18 (PST) (AI summary of creator comment): - The successor must involve a change to the model's name.
Purely background updates that keep the exact same name will not count.
People are also trading
I believe in an interview Sam said he wanted to switch to a model where they make many small frequent changes while retaining the same name rather than a few large releases.
Not sure whether to put this under the GPT-5 (new) bucket or the other bucket.
I guess there's also a question of model targeting via the API versus the name of the system selected via the ChatGPT drop down.
In the case of the API datestamped GPT-5s seem like they would make sense.
@jessald I think I want to allow anything except the change being in the background and not modifying the name at all, bc i want to avoid the controversy/ambiguity that might lead to
@Bayesian So if they release gpt-5-2025-10-01 via API but the name shown in the ChatGPT dropdown doesn't change how does this resolve? Or maybe it doesn't until GPT-6 comes out in a year or two?

https://openai.com/index/introducing-gpt-5/
I believe they've moved to a new paradigm where they consider GPT-5 to be a system which integrates multiple models along with integrated software scaffolding.
So I think I would not consider a new model accessible via API as a GPT-5 successor. You would need something more like an operating system release like Windows 11 versus Windows 10 or something like that.
I think I've convinced myself that GPT-6 is the right answer.