Microsoft is now releasing build 12400 of the Windows Phone 8.1 OS preview

Microsoft has thrown the switch on a new release of the Preview for Developers and Windows Phone 8.1. Starting at 1 PM ET, those who are enrolled in the free Preview for Developers program are receiving build 12400 of the OS, which is a small jump from the previous 12397.

Currently, it is not known what changes are brought with the latest release, though it is most likely fixes for stability and other optimizations.

The update is 21 MB in size.

We are updating this article as more information comes in.


Reader comments

Microsoft is now releasing build 12400 of the Windows Phone 8.1 OS preview



when there is a mtstery, we need Sherlock, where is him? when we dont need him, he just appeared, now we need him, and he is gone..


No is not for both. Preview is always one in front. They said weeks ago that they had nearly signed off on GDR1

Also, Cyan, Black, Amber; they're firmware updates... The OS updates can go on and go on independently of the firmware ones.

That's because you're continiing to get access to updates before they're officially released to the rest. WP8.1 and Cyan are done, but there will still be bug fixes and whatnot in the intrim of the next major update.

I'm pretty sure they are different numbers, this is OS update, Cyan is a firmware update that will only apply to fomerly Nokia now Microsoft Mobile Lumia devices. So technically its version number doesn't matter.

I need help, I had WP8.1 Developer's Preview on my phone. Last night, the 8.1+Cyan update was ready to download for my Lumia 625. This morning I began downloading it. At 5% download, it suddenly vanished and since then it keeps just saying your phone is up to date. And I no where see this new update available too. I'm from India, device is carrier unlocked.

Right now I'm experiencing a similar thing on my Lumia 720 running Dev Preview. I'm searching for updates and it says your phone is up to date. Right now the OS version is 12397... Region is United States.

Same here in Canada. Lumia 1020 with OS version 12397. It says "your phone is up to date". I guess Microsoft pull off the update.

Same here, I am in the United Kingdom with HTC 8S and with Dev Preview OS Ver 12397 and it says "Your phone is up to date". I don't understand!

I still sit blank. The problem is, I have a 625, and it should have picked up the cyan update by now, but it hasn't. It then is also not picking up this new DP update. I tried turning off and on the developer preview app. The update that vanished at 5% download leaves me mid way, as when I was updating, I had 2.5GB+ storage in the internal, fully charged battery and moreover device plugged into the charger.

From what I can tell you need to use Nokia Software Recovery Tool to bring your phone back to WP8, then update to Cyan, basically get rid of the Dev Preview before installing Cyan.

This happened to me on a previous update.  In my case it turned out to be a internal storage issue.  Make sure you have enough free storage space.

This may be because of following:
• u didn't kept at least 1.5 GB free in PHONE memory.
• Too many background tasks.
• Low battery level issues.
• Your phone might have hung up during the process and might have disturbed the download.

I suggest 3 things:
• go to nearby service center and ask for technical and update support.
• reset your phone and try phone update again. It might work.
• wait for some time and keep trying u might get lucky to escape the bug.

I would highly recommend 2nd option, and rest is up to you.

I have 2.5GB internal space, no bg task, fully charged battery and it was working fine, when the update vanished mid way. Reset may work, but that data loss is too much for me to restore on a limited data plan on my 3G

Do download apps via PC and install them quickly via 'files'. U will save your download usage by hundreds. Even after reset you can download them again with 1 tap and no internet this time.

Try plugging your phone into a PC and after about 5 mins, restart the phone then try the update again

I had the same issue,but don't worry keep checking the update it will show up.It has to do with congestion.I have Cyan now.

Same problem to me it stopped then I tried to download then it vanished showing your phone is up to date.

Ohh.. Then I guess, it is some problem with Microsoft's server or their back end and I'm definitely not gonna reset my phone for that...

I had live chat with microsoft support, and they said something of the existing 8.1 on my phone is preventing the download of cyan. So, I'll need to use Nokia Software Recovery and then redo the update process... :'(

The Bing apps didn't get updated either, as far as I know... +720 The main point for me going 'dev' was so I can load apps onto SD... I'm not really worried about the rest, including Cortana, I don't feel that'll be so great on 512mb devices...

Okay, signed in still nothing, so obviously not released yet in UK or whatever, I'm grateful for your advice though...

and I don't have to say something, and Cortana understands of what I'm saying with this update!

Dear Blackberry if u want us to use yr bbm on windows phn, come like a humble child and let us use it. Don't take our exam. Do it in simple manner and be wise. U r creating a drama and thats it like mcdonnald did in Moscow at the time of openig first outlet. There r othr open options. MS pls interfere don't spoil yr reputation. I m doing correctly and no positives.

I owned the Galaxy "Nexus" a while back, and it's so frustrating how long Verizon takes with these updates. I wouldn't hold my breath for Fall, either. Maybe Spring of next year...

This is a problem that has always been in Windows Phone. (At least for me.) The cellular radio being enabled keeps the phone "alert" at all times, but while disabled, it isn't as responsive.


At least the random "reverting from wifi to cellular data" issue hasn't happened in a while.

I was so excited, thought it was Cyan for my Icon... oh well... hope this brings something good!

Hahaha yes! They are mean! Internal gossips says that MSFT is calling it the "trolling update", just to keep us busy while the carriers do their respective "tests" on the firmware update. jaja

Hope it fixes the audio issue through headphones where you get a notification and then only the left speaker / earbud only works and you're stuck with mono sound vice stereo. The only way to fix it is a soft reset.

I have had it a few times with my Lumia 822. My daughter has a 810 and this happens to her a lot. I assume its because she is getting notifications and always either listening to music or watching videos at the same time.

Oh wow, I thought I was the only one with this issue! Lumia 925 here. Only a reboot fixes it for me :(

That was happening to me when listening to audio and if a call would come it. One of the minor updates seems to have fixed it a month ago or so, it hasn't happened in a while now.

Haven't had that issue, but another problem I'd like them to fix about the sound is the fact that you can't adjust the music and alarms sounds individually when on earphones or Bluetooth. Sometimes I listen to really calm music and every loud alarms make me jump, and when I listen to louder music I often don't ear the alarms.

Have this issue with my 820 while watching videos with the Videos app. Doesn't happen when watching via MoliPlayerPro after a fresh reboot without starting Videos app. Problem with Videos app.

That is a safety thing to prevent you from accidently popping your eardrums the next time you plug in headphones or ear buds.  I, personally, appreciate this feature.

Would love to see a change log or bug fix log.....Hate updates that dont give heads up on fixes...but, i'll take it, hope it does not break anything...

Any changes noticed by anyone ?


+720 Pakistan
Got update for my phone but during installation either it was failed or stopped and now saying phone is up to date

I hope this fixes some things with 8.1. My phone was working perfectly ever since I upgraded to 12397 and all of a sudden today it just took a huge crap on itself. My notfications aren't working at all and some of the sounds like the camera shutter or the lock sound don't play anymore even though they're enabled. This might give that sort of stuff a reset, but I doubt it.

That may be true but we havent seen any updates since 7.8 came out in very early 2013, so I'm considering it dead. Kinda sad for my poor LG Quantum. It was a nice phone.

Downloading now on HTC 8X T-mobile! Even little bug fix updates are very welcome! Keep em coming!

Just got the update on my HTC 8x, so it definitely can't have any thing to do with cyan as the cyan update is for Lumia phones not HTC phones.