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

iBowToAndroid

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Nov 9, 2010
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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

Notes:

- DON'T QUOTE THE OP WHEN YOU REPLY, kthx

- 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
 
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iBowToAndroid

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Flashing the U1 right away when my Devices arrives :geek:
That's why I post it :)

That, and so that anyone interested can dig through the firmware for anything interesting.

I'm uploading in order of model number, so Ultra is last unfortunately - and my upload speed is only 10 Mbps. Should be up in the next few hours though
 

iBowToAndroid

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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
 

jcrompton

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Nov 30, 2004
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Thanks for doing this ! My phone arrives Wed and of course I wanna flash the U Home CSC to my unlocked U1 device so I can get the AT&T calling features. Are the ones you've uploaded the latest firmwares?

And thanks again for always taking time to do this!!!
 

crowax

Member
Oct 9, 2010
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Sorry for the possible silly question, but I am coming back to the Galaxy after 4 years on the Pixel and haven't been flashing for a while.

I am getting an Ultra from T-Mobile. If I flash the U1 (to remove the bloat) and then follow the instructions above, it says it will put the carrier files on there. Will that just put the bloat back on? I guess I was wondering if it would make it "stock" going forward. I just wanted to figure that out before I set the phone up since it requires a factory reset. Thanks!
 

iBowToAndroid

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Sorry for the possible silly question, but I am coming back to the Galaxy after 4 years on the Pixel and haven't been flashing for a while.

I am getting an Ultra from T-Mobile. If I flash the U1 (to remove the bloat) and then follow the instructions above, it says it will put the carrier files on there. Will that just put the bloat back on? I guess I was wondering if it would make it "stock" going forward. I just wanted to figure that out before I set the phone up since it requires a factory reset. Thanks!
No, that's not what it says - I think you're mis-reading. Flashing U1 removes bloat, period. If you want the bloat gone, you have no need to do anything else other than simply flashing U1 firmware
 
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crowax

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No, that's not what it says - I think you're mis-reading. Flashing U1 removes bloat, period. If you want the bloat gone, you have no need to do anything else other than simply flashing U1 firmware
Oh perfect. I checked again after your post and my confusion was at
"the correct procedure for switching from one carrier's firmware to another is". I was thinking it was the procedure to switch from a carrier firmware to any other firmware including U1. So the re-adding of the carrier files didn't make sense.

Thank you very much for your quick answer!
 

bANONYMOUS

Senior Member
Dec 30, 2011
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I do have my own thread about these firmwares, I was just including the Canadian bloat free firmware because you only have the US firmwares. The links are to samfw because they update them regularly so people can get the latest releases where as your links are the current version you linked so if you don't update them then they'll be out of date versions. Do you get paid from your Android File Host links or something? What's the issue? No need to be hostile, just trying to help provide information

EDIT:
Also, when you're flashing between different carrier firmware's, you should only use CSC and not HOME_CSC because keeping the user data sometimes includes the bloat apps preinstalled.
The rule of thumb is if you're CHANGING anything, start fresh with CSC
If you're UPDATING from the same carrier firmware to a newer version, use HOME_CSC.
So for anyone using this guide, it's not recommended to use HOME_CSC when converting over to the bloat free firmware as it's a different carrier release. Not saying it won't work, it's just not recommended, almost like a dirty flash so it could cause stability issues down the road after a few OTA's or something.
 
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bANONYMOUS

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Canada, Earth.
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.
 

iBowToAndroid

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Then why are you mad I included it when it's the same device? I don't get why you're being salty about it. I'm just trying to help out.
1. Not mad at all

2. It's the same device internally, yes. But this thread is about software - not hardware. And the software being discussed is the USA firmware, not the Canadian firmware.
 

alfredtv

Senior Member
Jun 8, 2005
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sorry I've also been out of the firmware game for a while too. I have a U1 from Samsung unlocked S21 Ultra and need to put the ATT carrier firmware on it. If I'm reading this right, I'm using Odin and flashing the XAA U1 firmware without a sim, when it reboots and reads updated SIM carrier setting at reboot then I am shutting it down and immediately attempting to install the ATT U1 firmware (all BL, AP, CP, CSC (non HOME CSC)? I don't see where I would select USERDATA but I need the ATT options (was going to exchange it but I got all the incentives)
 

iBowToAndroid

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Nov 9, 2010
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sorry I've also been out of the firmware game for a while too. I have a U1 from Samsung unlocked S21 Ultra and need to put the ATT carrier firmware on it. If I'm reading this right, I'm using Odin and flashing the XAA U1 firmware without a sim, when it reboots and reads updated SIM carrier setting at reboot then I am shutting it down and immediately attempting to install the ATT U1 firmware (all BL, AP, CP, CSC (non HOME CSC)? I don't see where I would select USERDATA but I need the ATT options (was going to exchange it but I got all the incentives)
1. If your phone is already running U1 firmware, there's no need to flash it again

2. If you don't see the USERDATA slot, you have a very old version of Odin
 
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alfredtv

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Jun 8, 2005
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It is running U1 but I need the ATT bloatware.....I'm on FirstNet and the only way it will connect correctly is if it's running the ATT built in config files. So I'm trying to go from clean to dirty!!