Oracle offers Extended Support for Solaris 11.4 now till at least 2037

In 2023 Oracle has changed the Extended Support for Solaris 10 and Solaris 11.3
from January 2025 to January 2027.

Now Oracle adds another 3 years to Solaris 11.4 to November 2037.
This is a long term commitment I'm not aware of any other OS vendor.
New features are delivered every quarter using SRUs.

You can find all the Support dates in

http://www.oracle.com/us/support/library/lifetime-support-hardware-301321.pdf