GTA+ is a monthly subscription, priced at $7.99, that Rockstar offers for GTA Online on PS5 and Xbox Series X|S. It grants a recurring $500,000 in-game deposit, access to a rotating set of vehicles and properties, bonus missions, and exclusive discounts. It has nothing to do with single-player content.
For GTA 6, the only confirmed connection is a pre-order bonus. If you pre-order the Standard or Ultimate Edition on the PlayStation Store before November 20, 2026, you get one month of GTA+ for free, which you can check on the price page. That is it. There is no announced integration of GTA+ with the single-player campaign, and no details on whether GTA+ will extend to a future online mode for GTA 6. Rockstar has not said anything beyond the pre-order perk.
If you are asking because you want GTA 6 benefits, hold off. The free month is a nice add-on, but it only works for GTA Online on current-gen consoles. Any talk of GTA+ becoming a core part of GTA 6 is speculation. The subscription will likely evolve, but until Rockstar announces an online mode for GTA 6, GTA+ remains a GTA Online service.