GPT-4o is available for me on ChatGPT, with the text+attachment input (as a Plus user from Germany). It's crazy fast. The voice for the audio conversation in the app is still the old one, and doesn't let you interrupt it.
It is. I've got it already, but I'm a bit of a gpt4 power user. I hit my rate limit biweekly or so and run up close to it every day. I'd bet maybe they prioritized people that were costing them money.
It might be just by sign-up order. I signed up for pro basically as soon as I could, but I never hit limits, and only really use it once or twice a day, sometimes not at all.
Is it? I can't use it yet at least