Available directly from the Mac App Store or through the Software Update function in the Mac App Store, the update is now available to download on the compatible devices.
Release notes for the update are sparse, saying only that the update will improve stability and reliability of the MacBook Pro with Touch Bar, although the update is recommended for all 2018 models.
The macOS High Sierra 10.13.6 Supplemental Update 2 improves the stability and reliability of MacBook Pro with Touch Bar (2018) computers, and is recommended for all users.
For detailed information about the security content of this update, please visit: https://support.apple.com/kb/HT201222
Build numbers for this update are 17G2037/15P6805. There isn’t an equivalent macOS Mojave beta update for 2018 MacBook Pro users.