Next build of Windows 10 for Phones Technical Preview coming to more models
Thanks to a process called "partition stitching," Microsoft can re-size the partition dynamically, allowing the update to be sent to more models. The "partition stitching" was tested last week by Microsoft. The company says that another week of engineering is needed to make sure that the next Technical Preview will be representative of Windows 10 for all of the units that will be allowed to install it.
The following is a list of Windows Phones that are expected to support the next Technical Preview of Windows 10 for Phones: Lumia 1020, Lumia 1320, Lumia 1520, Lumia 520, Lumia 525, Lumia 526, Lumia 530, Lumia 530 Dual Sim, Lumia 535, Lumia 620, Lumia 625, Lumia 630, Lumia 630 Dual Sim, Lumia 635, Lumia 636, Lumia 638, 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 532, Microsoft Lumia 532 Dual SIM, Microsoft Lumia 640 Dual SIM and the Microsoft Lumia 535 Dual SIM.
Microsoft cautions that the phones listed above are not 100% locked into receiving the preview. If a bug shows up on a particular handset during testing, that model might be removed from the list. If the Windows Phone model you own is on the list now, you might just want to keep your fingers crossed hoping that it stays there.
source: Windows via WindowsCentral