Is this update for all Apple watches?

Hi there, Gelmer125!
Thanks for reaching out to the Apple Support Communities! That is a great question you have about the current watchOS update and availability and I’m happy to assist! Check out this link to watchOS 5 - Apple. Specifically:

watchOS 5 compatibility.

watchOS 5 requires iPhone 5s or later with iOS 12 or later, and one of the following Apple Watch models:

Apple Watch Series 1
Apple Watch Series 2
Apple Watch Series 3
Apple Watch Series 4

watchOS 5 is not compatible with the first-generation Apple Watch.

Find your Apple Watch model