The Rock Band 4 development team has announced that the rhythm game will be delisted in just a few days, so if you haven't played it yet and you want to, make sure you pick it up sooner rather than later.
In a message on the game's Discord server (as spotted by ResetEra user Big Yoshi), the folks behind Rock Band 4 say that because the "core licenses" for the game's music are expiring, Rock Band 4 will be removed from both the PlayStation and Xbox storefronts.
As is often the case with digital delisting, if you've already bought the game, then you can continue to download and play it at your leisure, and naturally, that goes for if you've got a boxed copy of Rock Band 4 as well.

You might be wondering what's going to happen to Rock Band 4's plethora of DLC songs, and sadly, the same applies to them: as soon as they hit their ten-year milestone, they'll be taken down, but until then, you'll still be able to pick them up.
Rock Band 4 was originally released back in 2015, and at time of writing, it's still the most recent mainline entry in the series. Like previous Rock Band titles, the game sees players teaming up on instrument peripherals to take on a variety of songs across different genres (despite the name).
It's also the last game in the series (assuming it continues in any form, that is) to be developed by original creator Harmonix, which was purchased by Epic Games back in 2021 and which is now responsible for the very Rock Band-esque Fortnite Festival.

News of Rock Band 4's delisting comes just a couple of months after original Guitar Hero studio RedOctane's announcement that it will make its triumphant return to the world of rhythm games, and that its first post-reunion game is already in the works.
If you do want to check out Rock Band 4 before its delisting on October 5th, you can do so right now via the PlayStation or Xbox stores.