One UI 9.5 Beta Build Spotted for Galaxy S26 Ultra

The first One UI 9.5 beta build for the Galaxy S26 Ultra appeared on November 4, 2026, according to a post on X. It’s S948BXXU6ZZK3, and it moves the bootloader from version 5 to version 6. You can’t install it yet. It’s a test build, and Samsung hasn’t opened the beta.

A second post about 20 minutes later listed the same build and placed it on Samsung’s test server. There’s a second build worth your attention too, because the November security update seems to make the same bootloader jump.

Three Galaxy S26 Ultra builds side by side

Here’s how the two test builds compare with the newest public firmware in our feed for the SM-S948B.

Build	What it is	Bootloader	Source
S948BXXU5BZJA	Public One UI 9, October 5 patch	5	Our firmware tracker
S948BXXS6BZK1	November security test build, based on One UI 9	6	Post on X
S948BXXU6ZZK3	One UI 9.5 beta test build	6	Posts on X

Our tracker follows public releases, and neither test build is in it yet. So these two rows rest on posts on X, and our tracker will confirm them when they go public. Another post lists the same November build and says testing has begun.

Both posts talk about the Galaxy S26 series, but S948 is the Ultra’s model code. Neither one lists a build for the Galaxy S26 or S26 Plus.

Reading the One UI 9.5 build number

The ending tells you more than the rest of the string. In S948BXXS6BZK1, the B is the One UI 9 letter on this phone, Z is 2026 and K is November. The beta build has a Z in that first slot, and its third string, S948BXXU6CZK3, ends in CZK3.

C is the letter One UI 9.5 should take on the S26 Ultra, as we explained in our One UI 9.5 post. The 6 is the bootloader version, and our firmware version guide breaks down the other characters.

Why bootloader 6 matters even if you skip the beta

Odin won’t flash firmware with a lower bootloader version than the one on your phone. If the November update reaches you with bootloader 6, today’s bootloader 5 builds stop being an option for a manual rollback.

The November build reportedly shares its bootloader with the beta build. A test build can still change before release, so check the fifth character from the end of the final build number before you install. If you like keeping a way back, that’s the digit to watch.

When the One UI 9.5 beta could start

Samsung hasn’t given a date. The first report hopes for the end of November, and SamMobile points to late November or early December.

Last year is the best yardstick we have. The first One UI 8.5 build for the Galaxy S25 was reportedly spotted on November 25, so this one is three weeks ahead. The One UI 8.5 beta itself opened on December 8. SamMobile thinks the head start could still shrink to about a week by the time the beta opens.

Android Authority expects the stable version to debut on the Galaxy S27 series. If you want to be ready for the beta, we walked through the sign-up in our guide to joining the One UI 9 beta. Until the next program opens, keep an eye on our November update tracker for the security build.