The update comes with firmware version G930W8VLS8CTI1 for Galaxy S7 and G935W8VLS8CTI1 for the S7 Edge and weighs just 70MB in size. The Exynos variant devices in the UK are receiving this new update with a slight change firmware version: G93xFXXU8ETI2.
The update is being rolled out in phases where Canada, UK are the first ones. All carriers in Canada have picked up the latest update. This is an early phase of the rollout, so we expect the update to reach other regions soon.
It is a very rare case when a company rolls out an update to a phone that is over 4 years old. Recently, Samsung announced that it will now provide 3 major OS updates. Google and OnePlus also provide 3 years of Android updates. So, these companies are setting a new benchmark for providing updates. [source]

Samsung Galaxy S7 and Galaxy S7 Edge receiving new update with September 2020 security patch - 50