Remember the good old days when BlackBerry used to release beta OS builds to developers? Well, they're back. BlackBerry has rather quietly updated the BlackBerry Dev Alpha downloads page with beta builds of BlackBerry 10.3.3.746 so developers may test their apps against that build to ensure all remains working fine.
Just as before, the OS builds are not full builds of the OS, they are watermarked with your PIN and are certainly not recommended to be downloaded unless you are a developer. One problem has already popped up in the forums, wherein the SD Card Drivers for the OS would not install for someone who unknowingly installed one of the beta builds.
That warning aside and knowing some will entirely ignore it, you can hit the link below to grab the OS for your specific device. Z10, Z30, Q5, Q10, Leap, Passport, Classic and finally, Dev Alpha C are all supported.
Update - BlackBerry has now outlined the details via the Inside BlackBerry Developer Blog. Here's what they had to say about the releases.
Get your applications ready for BlackBerry 10 OS 10.3.3! We've just released beta autoloaders for 10.3.3, which you can get from the software update page.
There have not been any changes or additions to APIs in 10.3.3, so your applications that support 10.3.2 should also work fine on 10.3.3. But here is your chance to try it for yourself.
Similar to the previous beta releases, these autoloaders contain a reduced set of BlackBerry 10 applications compared to a full OS release and are intended for application testing, not regular use.
BlackBerry OS 10.3.2 included anti-theft protection that prevented downgrading of the OS. This is also present in 10.3.3, which means that you won't be able to downgrade to 10.3.2 after installing a 10.3.3 autoloader. Your device will remain on the limited 10.3.3 beta until the gold release of 10.3.3. Before loading you should also make note of the BlackBerry ID account used on the device because you'll need to log back into the same one after the load is complete.
So go ahead and load your test devices but consider these restrictions if you were thinking of loading this on your primary BlackBerry 10 device.