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How To Guide G998U and G998U1 Firmware Links and Flashing Discussion Here

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Jul 12, 2021
Samsung Galaxy S21 Ultra
That one did it, file name SM-G998U1_1_20210621202237_97lvcfggiq_fac.zip.enc4
Can you share a screenshot of your Software Version Page? Also if your original device is from Verizon and you have verizon sim card installed the device Will update to show that the device is U1 but it will continue to show VZW/VZW/VZW as soon as you install verizon Sim card in it. Samsung has not enabled ability to go from one carrier specific to another carrier specific device yet. It also took a long time for S20 to get that feature based on historical threads I read.


May 2, 2011


May 2, 2011
Still on Verizon but planning on switching. Was trying to get all the Verizon bloat off in anticipation of my switching carriers.

So do I need to do a factory reset after I switch carriers?


Jul 12, 2021
Samsung Galaxy S21 Ultra
Still on Verizon but planning on switching. Was trying to get all the Verizon bloat off in anticipation of my switching carriers.

So do I need to do a factory reset after I switch carriers

OK this original device is from Verizon. I suggest you wait until you get new Sim. You need to make sure you do not insert Verizon sim so that Verizon Bloat is not activated again.
Okay, post deleted, but it's probably worth noting that you don't know what the G998W is. Because it's the same phone as the U and U1. During the One UI 3.0 Beta on the S20 Ultra, I flashed G988U on my G988W, and when the beta continued onto the U1, I flashed those firmware files as well. The Canadian S20/S21 is just a non branded T-Mobile with more supported radio bands in the firmware.

If you actually look at the carrier info for the S20 Unlocked U/U1/W firmware, they all say XAC and XAA at the bottom no matter whether it's U/U1/W. They are all the same phone and Samsung even uses the same firmware merged, just different radio bands, and because Canadian radio bands support ALL bands, it makes the W firmware the a merge of both U and U1, so it's actually the better choice from what you have posted because it supports every U/U1/W the best. So your post is relevant to the W models whether you want to accept it or not.

That's why I included a link to the firmware, because it's the same device, same flashing process, completely same procedure, so this thread IS relevant to the W models even if you said U and U1 only, the W is also included in that even if you didn't say it was, doesn't make it true.

Also the only difference between U and U1 is U is unlocked but INCLUDES carrier bloat, U1 is unlocked and has NO carrier bloat.

So, closing info here.

U1 is unlocked, no carrier bloat, US radio bands
U is unlocked, HAS carrier bloat, US radio bands
W is unlocked, no carrier bloat, ALL radio bands

You just need to make sure it's the SM-G998W for AXC and it's the best choice with no bloat.
Just because you clearly didn't know this about the W phones, doesn't mean you gotta get all snappy, I'm just trying to help the community.
Both U and U1 only support single sim, I can't find the SIM card manager in settings, would G998W support dual sim?


Senior Member
Feb 1, 2011
Samsung Galaxy Note II
HTC 10
My G998U with baseband G998U1UEU1ATLI, Sac23 rom, unlocked from Samsung, rooted, on Verizon, still XAA. I want to change the CSC to VZW for wifi calling etc but I don't want to update the firmware or receive OTAs or do anything that could result in an updated bootloader and remove root. Is this possible? I assume I would have to use an old CSC file that matches bootloader v1? And to not have bloat, I'd have to change to U1 as well right? Where would I find the right one to use? The kernel says it's still UAG from Jan 31. I assume it's from before the bootloader got updated to v2

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    For those who aren't already aware, G998U is the model number of all of the US carrier versions of the S21 Ultra. The G998U1 is the model number of the same device, but sold by Samsung SIM unlocked and with no carrier bloatware. Firmware is 100% interchangeable among these models: any U or U1 firmware version can be flashed to any U or U1 device at any time, assuming that you're not trying to downgrade the bootloader. A "U to U" or "U1 to U1" flash does not require a factory reset, but changing from one firmware to the other will require one. Also, U firmware is identical for the 4 base files (AP, BL, CP, CSC) for each individual build, no matter which carrier it comes from. So if you download 2 different carrier versions of the exact same build, the 4 base files will be identical. Where the firmware differs is in the USERDATA file - that's where the carrier bloatware and customizations reside.

    Manual Odin flashing is designed for those who:

    - want to manually update to a newer version of U firmware on their U device, either because they don't want to wait for their carrier's OTA or because OTAs aren't working on their device, or a different carrier got a new feature/patch before they did
    - want to flash U1 firmware to their U device
    - want to convert from U1 firmware to carrier U firmware
    - want to convert from one carrier's U firmware (with all apps and bloatware) to a different carrier's U firmware (with all apps and bloatware)

    For those who aren't already aware, anyone can now download firmware for almost any Samsung device any time that they want, via the various firmware download tools posted here on XDA like SamFirm or Frija. There are threads and info about them here on XDA so I won't waste time explaining - do a search if you're not already familiar with these tools. But they only provide whatever the latest/newest/current version is - nothing older. I pay for a subscription to a site that gets the official releases (usually) before they hit the firmware download tools, so that's where my files come from.

    This is not a "beginner's guide to Odin flashing" -type post/thread, so I won't list basic, step-by-step flashing instructions. My threads are geared towards those who already know what they're doing. If you're new to manually flashing Samsung firmware (or haven't done it in a long time), I recommend you consult one of those "beginner's" guides- there are tons of them here on XDA.

    Happy flashing!

    U firmware: https://www.androidfilehost.com/?w=files&flid=322089
    U1 firmware: https://www.androidfilehost.com/?w=files&flid=322090



    - I have lots of threads just like this one for other Samsung flagships, if it interests you. For those who have already made use of my previous threads for a different device and are upgrading to an S21, welcome back :)

    - My zips are compressed extra small for space and bandwidth savings. The default Windows extractor can't handle it, so you'll need a 3rd party tool like 7zip, WinRAR, etc

    - it's quite time consuming to download the files, zip them up, and upload them to AFH. And, I do threads like this for every single Sx and Note x model, so I won't be uploading every single version. The only full builds that I upload are ones where I get access to a new bootloader and/or Android version early, before they hit the firmware download tools.

    - My naming method for folders on AFH is: build - bootloader - Android version
    So "SAT - 1 - 9.0" means the full build number ends in SAT, it's bootloader version 1, and it's Android 9.0. When bootloader and Android versions increment, the first build to have those changes will have its folder notated appropriately.

    - HOME CSC file keeps data intact; using the other CSC will wipe data. Flashing USERDATA will also wipe data.

    - Since AT&T doesn't allow their firmware to be publicly available (for any of their devices), I'll try to always upload at least one USERDATA per bootloader increment for AT&T (and Cricket, if they get this model). I'll also upload any full builds if AT&T is the only carrier to get that specific build, because you won't be able to find the files anywhere else.

    - For identifying USERDATAS, and to know what region/CSC to use in the firmware download tools if you're downloading yourself:

    AIO = Cricket (not available via firmware download tools)
    ATT = AT&T (not available via firmware download tools)
    BST = Boost Mobile
    CCT = Xfinity Mobile (Comcast)
    CHA = Spectrum Mobile (Charter)
    DSH = Dish Network
    SPR = Sprint
    TMB = T-Mobile
    TMK = Metro PCS
    USC = US Cellular
    VZW = Verizon (available via firmware download tools, but Manual Entry is required - Auto will not work)
    XAA = U1 firmware

    - the correct procedure for switching from one carrier's firmware to another carrier's firmware is:
    1. Flash full U1 firmware package including non HOME CSC
    2. Upon boot, insert a SIM of the carrier whose firmware you want
    3. Watch for the popup that says "reboot to apply new carrier settings" etc, and do it
    4. After that restart completes, reboot back to Download mode and flash the full U firmware package, with the USERDATA file of the carrier whose firmware you want
    I've seen nothing about the May update for the G998U1. Older phones are getting it but we haven't.
    Have the Verizon version, what is the benefits of flashing to U1?
    The only benefits I can think of would be enabling Samsung features that Verizon disables, like the Spam Filter, and removing some of the bloat that might be impossible to remove on the VZ version.
    I would think you would have most features since the U1 firmware is sold by Samsung to work on networks like T-Mobile. However, all I can verify for you is that I got my wifi calling and I have a 5G icon with 305Mb on speed test. This is after flashing U1.

    I had the same issue. Out of the box, without even turning the phone on, I flashed the U1 firmware on my T-mobile S21 ultra but the device just kept saying "NO SIM"

    If you have a T-mobile device, turn it on with an active sim card first with the original U firmware. Don't need to go through the setup, just have to let it find a LTE/5G signal. After that you can power down and flash U1 firmware and won't have any SIM issues.

    Hope this might help anyone who might run into the same issues we did
    Initial U firmware and AT&T USERDATA are posted, along with U1 firmware. U firmware is not yet accessible in the firmware download tools like SamFirm and Frija, but if anyone wants a different carrier's USERDATA (for flashing bloatware to a U1 device or for converting a U device from one carrier's bloatware to a different one), let me know and I'll get it for you