Published by Steve Litchfield at 11:07 UTC, March 28th 2015

It's been six weeks since the first build of Windows 10 for phones was released for 'Insiders' , and we've been chatting about it off and on, on the AAWP Insight podcast , with our Lumia 630's 'upgraded'. We now have more information from the horse's mouth about progress towards the next major test build and the devices for which it will be enabled - for the brave!

From the Microsoft blog post:

When we sent out the first build of Windows 10 Technical Preview for phones on February 12th, the list of phones was very limited. As I wrote in the accompanying blog post, the reason for this is that we had to select from the set of phones that had sufficient system partition sizes configured by the manufacturer. This was necessary for us to be able to in-place upgrade the phones. I also talked about a feature we were working on called “partition stitching” that would allow us to re-size the system partition dynamically, allowing us to do the upgrade on a larger set of phones... Here’s a quick update on where we are: The partition stitching feature code came into our main code branch late last week. The Storage and Filesystems Team had been working on this in their branch and it passed all of their quality evaluations.

We spent this week testing on individual devices, as well as providing the builds with this feature to our internal rings so that we all could test it on our own phones which had been previously not usable. I’ve been thrilled to get my beloved Lumia 1020 on Windows 10!

This testing will allow us to support A LOT more phones for the next flight. I get a ton of questions every day on Twitter about when your favorite phones will be usable, and I’m happy to report that the vast majority will be supported with the next flight (full list below.)

We’ll also have support for phones that didn’t have China Mobile Operator support in the last build, so that’s great news too for our Windows Insiders in China. Bottom line is that this is a preliminary list, but as Windows Insiders I wanted to give you the visibility even though it’s not 100% locked: Lumia 1020

Lumia 1320

Lumia 1520

Lumia 520, Lumia 525, Lumia 526, Lumia 530, Lumia 530 Dual Sim, Lumia 535, Lumia 532, Lumia 532 Dual SIM, Lumia 535 Dual SIM

Lumia 620, Lumia 625, Lumia 630, Lumia 630 Dual Sim, Lumia 635, Lumia 636, Lumia 638, Lumia 640 Dual SIM

Lumia 720, Lumia 730, Lumia 730 Dual SIM, Lumia 735

Lumia 810, Lumia 820, Lumia 822, Lumia 830

Lumia 920, Lumia 925, Lumia 928

Lumia ICON

Microsoft Lumia 430, Microsoft Lumia 435, Microsoft Lumia 435 Dual SIM, Microsoft Lumia 435 Dual SIM DTV

The system partitioning issue sounds rather complicated, but the post makes it clear that a workaround is in place now. In terms of timescale, the post goes on to talk about "at least one more week of engineering", so I guess we're looking at the second week in April. Still, this is effectively a whole new OS we're talking about, so best get it right.

The absence of, notably, the Lumia 930 from the list is a little worrying, though note that other devices may also get pulled from the compatibility list as further testing is done if bugs or issues are found. I'm sure the devices will all be back on the list by the time of the final builds in May and June. The 930's different from the 1520 in that it has an AMOLED pentile screen and I'm wondering if the screen tech and refresh rates are the issue identified in this build.

Anyway, watch this space for more Windows 10 coverage, I'm eyeing up the editorial 1520s for the next Insider build!

PS. Note that if there's a catastrophic problem with the new preview, it's possible to get back to the previous Windows Phone 8.1 Update 1 using the Microsoft recovery tool here.

PPS. Here's the original video from Joe Belfiore giving an overview of what's new and changed in Windows 10 for phones (so far):