Keep in mind that these are just rumors and speculations, and there's no official confirmation on Gran Turismo 8. Fans of the series will have to wait for an official announcement from Polyphony Digital or Sony Interactive Entertainment.
Below is a report detailing the current status of the franchise and the anticipated timeline for a potential eighth installment.
The most recent mainline entry is Gran Turismo 7 (released March 2022), followed by the Gran Turismo 7 Spec II update (November 2023). Any "GT8" content online is either fan speculation, rumor, or mislabeled.