This is honestly irrelevant. Studios are always working on the next project in some capacity, and Polyphony Digital is no different. Large parts of the team don’t just sit around once a game ships.
After Gran Turismo 7 launched, smaller teams stayed behind to handle updates, bug fixes, live content, and esports support. That’s standard post-release work and doesn’t require the full studio.
The bulk of the core developers - engine programmers, gameplay engineers, graphics and technical artists - have almost certainly already moved on to early development for the next Gran Turismo. That’s where long-lead work like engine upgrades, next-gen rendering, physics evolution, and AI systems happen, and it starts years before anything is announced.
Gran Turismo never really stops. GT7 is being maintained, while the next entry is already being built in parallel.