The announcement was made on the Rocket League blog. This change will come at the same time as the game goes free-to-play. And this also coincides with it leaving Steam and being available on the Epic Games Store instead. All of this is set to happen sometime after the next update drops, which is currently scheduled for mid September.
Psyonix previously said that when Rocket League makes the jump to free-to-play, you’ll not lose any progress. You’ll also be able to keep your progress regardless of which platform you play on from that point on. Cross-platform play is already a thing, and with cross progression, this means you can play on any platform you prefer at any given time. Overall, this is a good thing for those who play the game on consoles. But as mentioned earlier, once the game becomes free-to-play, it will no longer be available to new players on Steam. Existing owners on the other hand will still be able to play as usual. So if you’re a PC player who insists on having it on Steam and don’t mind paying for what will soon be a free game, you can get it for RM38. (Source: Psyonix)