A lil somethin somethin: You can find the details for this event on the announcement page here.
Crusader Kings III, Update 1.5.1.1: Now available!
We have been working to enhance our Update 1.5.1 thanks to your feedback & bug reports.
Thank you for supporting CK3, we can't wait to show you what we have in store next!

Here’s the changelog 1.5.1.1:
###################
# Game Balance
###################
- Vassals can no longer join factions if they have a Truce with their liege
###################
# Localization
#... Read more