Samsung still isn't updating the Galaxy S9 and Galaxy S9 Plus units sold in the United States on a monthly basis like the company initially promised, with most of them still being stuck on the February Android security patch nearly three months after the two smartphone models were commercialized. Sprint and Verizon's devices have only now started receiving the first update since their March 16 release, with that particular software package coming with the May security patch even though Samsung already repackaged the June one, though it's presumably yet to optimize it for the Galaxy S9 line.
AT&T's units haven't received a single update since hitting the market, whereas T-Mobile's are stuck on the March one, with the April upgrade rollout commencing last month before being put on an indefinite hold for unspecified reasons. The unlocked variants aren't faring much better, with all Galaxy S9 models sold in the U.S. hence being behind on updates compared to their unlocked Exynos counterparts, most of which are presently running the May security patch, with the June one being expected to debut in several weeks. Samsung's support pages list the Galaxy S9 and Galaxy S9 Plus as being eligible for monthly software maintenance but note that not all units may receive them as their availability will depend on the willingness of particular carriers to collaborate with Samsung so as to optimize and push out new firmware in a timely manner.
All Samsung's flagships released in recent times come with a promise of two major operating system jumps and three years' worth of security updates, though the company is still struggling on delivering the latter on a regular basis. While the Snapdragon variants of Galaxy-branded handsets aren't any harder to develop for than the Exynos models sold in most other parts of the world, the fact that U.S. carriers pre-load a wide variety of software onto their units often delays their timely releases, which is an issue that Samsung has yet to resolve.