https://wccftech.com/rocket-league-f2p-ps-plus-switch-online-requirement-dropped/

Rocket League is going to free-to-play before the end of September, and on the PS4 and Nintendo Switch you won’t even have to sign up for a subscription to PlayStation Plus or Nintendo Switch Online. Free will truly mean free! Unfortunately, it seems the same won’t be true on Xbox One – Psyonix’s new FAQ mentions PS Plus and Switch Online not being needed, but Xbox Live Gold is curiously excluded.

PlayStation Plus on PlayStation 4 and Nintendo Switch Online will no longer be required for online play on those platforms.