Both the Samsung Galaxy S9 and Galaxy S9 Plus on Verizon are now beginning to receive updates, bringing the Android Security patch level up to August 2018. Specifically, the patch will bring the Samsung Galaxy S9 to software version 'R16NW.G960USQS3ARG8' and the latter Samsung Galaxy S9 Plus will be pushed to 'R16NW.G965USQS3ARG8.' Since this update only delivers security enhancements and bug fixes, there aren't likely to be any changes on the user-facing side of the software with this update.
For clarity, this is actually the August 1 version of the security patch. That means that there are at least 15 new fixes in this update. According to the most recent security bulletin, the update should include at least three fixes indexed as being at the 'Critical' severity level. Each of those is marked as a vulnerability allowing for remote code execution (RCE), meaning they effectively would have allowed code to be executed at a distance under certain conditions. However, the remaining twelve patches are also rated in the 'High' severity level category. Three are related to 'elevation of privileges' vulnerabilities while four are marked as potentially allowing a denial of services. The later August 5 Android Security patch also contained a number Qualcomm-specific fixes, including three marked as 'Critical.' Since the update that is currently rolling out is noted as being for the first of those, it's not immediately apparent whether or not Samsung has included those fixes alongside others with the rollout of the earlier patch.
Bearing all of that in mind, it should also make the devices receiving the update much more secure as well as fixing any minor bugs that may be lingering since the devices' launch. So Verizon subscribers who own a Galaxy S9 or S9 Plus will want to update their software as quickly as possible. That's easy enough to accomplish by navigating to the Settings app and scrolling down to the 'System Updates' submenu. Tapping 'Check for system updates' should get the process started. Although it may take some time to arrive on every user's device, going through those steps can sometimes trigger the impending update earlier than waiting for it to arrive over the air.