Season 4 expires on Thursday, June 15th.
There is also a Season 5 XP Collectible at Level 74 on the S4 FP (2,126,000 XP)
*This is from Zirksee’s Twitter account
I kinda guessed that there would be before it was confirmed cause of this tweet… https://twitter.com/MUTLeaks23/status/1558221893592834049?cxt=HHwWgoCzjc6j9Z8rAAAA