It sounds too close to Scarlett for me to believe this was not the goal whether they hired somebody else or not, and if they try and prove beyond a doubt no audio post processing was done. Just listen to famous musicians doing acoustic or no processing versions of their songs to see how much you can craft a voice or sound.
[Edit]
1. A movie that features an AI voice of a female voiced by Scarlett Johansson.
2. A real-life AI company, OpenAI, is trying to put a distinct voice to their AI product vs. a canned voice.
3. Sam Altman, CEO of OpenAI, contacting SJ to ask her to be the AI voice.
4. SJ refuses.
5. CEO of OpenAI tweets "her" the title of the movie in #1 above.
Audio processing with DSP methods and current audio engineering craft or training AI to make it sound like SJ would be the thing to prove. Get raw audio of actress and finished sound and compare how they steered it to the final product and compare a spectrograph of SJ if you can get the same words.My common sense and the above facts says OpenAI did whatever they did to get close enough to SJ's voice. SA pursued it a few times, no? It definitely sounds like her enough to me.