Nico's original title was 'WP10: a branch for everyone'. Which sounds good, but there are significant technical hurdles to overcome in implementing a lot of what follows and is linked to, so 'everyone' is way too broad! As usual, if you follow your nose through linked articles and tips, don't blame us if something goes wrong - AAWP offers no support and everything is at your own risk.
Having said that, with huge input from Nico:
Despite the evolution of WP10 versions over time, here’s a case where “one size does not fit all”. Each Lumia device performs better, in terms of speed and battery life, depending on which WP10 version is installed. There are currently available via OTA or OTC Updater the following branches to download:
- Branch 1607, up to build 14393.2551 (Anniversary Update, AU)
- Branch 1703, up to build 15063.1868 (Creators Update, CU)
- Branch 1709, up to build build 15254.603 (Fall Creators Update, FCU, security to January 2020)
As a rule of thumb, later Windows 10 Mobile branches (1703 and 1709) are over the top for old processors and compromise even some basic functionality. In general, by 'stopping' at the lowest branch (1607), rather than pressing on, the phone is faster and with better battery life, but you lose access to some apps (e.g. latest versions of Unigram (Telegram) and MSN apps like News, Weather and Money, which are all compiled by the developers against later SDKs).
Also, as Steve suggested, FCU is no big deal, so “don’t obsess over missing out on Fall Creators Update (FCU), you’re not missing much - on Mobile, at least”.
In past articles on AAWP, moving to Windows 10 Mobile for some Lumias has been explicitly covered, but here’s a useful recap by model, based on my (Nico's) personal experience, with the related links to AAWP (Steve’s) articles, where available:
Lumia 520, 620, 625, 720: installation of WP10 is theoretically possible, but the phone OS is not-responsive at all (crashes, stuttering performance overall). These are Dual-Core models with paltry 512 MB RAM. Stay on WP8.1.
Lumia 435: although Dual-Core, it has 1GB RAM, so WP10 is working all right up to branch 1607, and no further (also consider the smallish battery BV-5J of just 1560 mAh).
Lumia 820: it has 1GB RAM, so WP10 installation is possible, up to branch 1607, but the battery life is so heavily compromised in everyday use that I strongly suggest you stay on WP8.1.
NB. Note that Windows Phone 8.1 - as you'll know, but it's worth stating - is not tenable in terms of reinstalling applications or discovering new ones since the Store no longer works. Yes, you can go uber-geek and side load applications under a developer environment, but we'll leave that for another article, another day. In general, if you have an 8.1-recommended phone and it's working and loaded with apps, then be happy(ish) and don't under any circumstances break or reset the device!
Lumia 920, 925, 1020: they share the same S4 CPU and 1GB RAM. You should install WP10 up to branch 1607 and no further. Venture beyond this and nasty things happen, including Maps losing all its street depictions!
NB. Yes, the Lumia 1020 has - technically - 2GB RAM, but half of this is effectively partitioned for camera use and you can't rely on it to help with OS operation.
Lumia 1320: despite having good specs on paper (Dual Core 1.7 GHz, 1GB RAM), WP10 does not perform well on this device. Lag everywhere, battery drain is shocking, as in the Lumia 820, depleting fast after just 10-20 minutes of use. The brightness control is broken, and Glance Screen is lost for good. Definitely stay on WP8.1.
Lumia 530: it’s a Quad-core processor, but with only 512MB RAM and a paltry 3.64 GB of phone storage, which makes any update impossible. Must remain on WP8.1.
Lumia 532: with a Quad-Core 1.2 GHz CPU and 1GB RAM, you can install WP10 up to branch 1607, and the device remains fluid and snappy.
Lumia 535: You can install WP10 up to branch 1703, but the device becomes slow and you need patience to open some apps, so I suggest to stop at branch 1607. And even so, battery drain is very heavy. There is however a trick: you can replace its small battery (BL-L4A, 1905 mAh) with that of the Lumia 830, a beefier 2200 mAh (BV-L4A model), to get more juice for WP10.
Lumia 540: You can install WP10 up to branch 1703, since it has the same CPU and RAM as the Lumia 535: the device responds, overall, better to WP10 than the Lumia 535.
Lumia 630: it has only 512MB RAM, but here you can install WP10 up to branch 1703 and the OS performance is still responding well. There are however lags and delays while starting apps. Patience is required, so I guess branch 1607 is the better choice here.
Lumia 635: WP10 is responding very well up to latest branch 1709, just expect some worrying battery drain.
Lumia 640, 640 XL: For them, branch 1703 was officially the last supported OS version, but you can install the latest 1709. However, the 640 XL shows some lag with 1709. At the same time, Lumia 640 XL, with its Li-Ion 3000 mAh battery (one of the biggest, together with the 3400 mAh of Lumia 1320 and Lumia 1520), is not much affected by battery drain problems under version 1709. As for me, I'd rather keep Lumia 640 and 640 XL to branch 1703. After all, as Steve pointed out, "Don't obsess over missing out on Fall Creators Update (FCU), you're not missing much... in terms of front end functionality, Fall Creators Update just brings in some more emoji and a little more eye candy in the UI. That's it.
Lumia 735: you can install the latest branch 1709 but beware - again - of battery drain issues.
Lumia 830: despite having same the CPU and RAM as the Lumia 735, WP10 gives me (Nico) huge battery drain even in the low branch 1607: definitely, a showstopper. Stay on WP8.1 update 2 (out of the box for this model). Yet Steve suggests to upgrade Lumia 830 (and the 735, for which all this also applies) to WP10 latest branch 1709 with this caveat “they work just fine for casual use right up to the very latest Fall Creators Update (1709)”.
Lumia 930, 1520: you can install the latest branch 1709 and the devices are as smooth as silk, just with the usual minor battery drain issues.
NB. Battery drain is a common theme above. The chipsets and battery capacities were designed for a much lighter OS (8.1) - and most phones have some issues under Windows 10 Mobile, there's just too much going on in terms of OS and not enough battery to keep it all going, in some cases through a heavy day, in others, even past tea-time. This is to be expected when hacking phones 'up' though.
Lumia 550, 650, 950, 950 XL, Alcatel IDOL 4 Pro, HP Elite X3: these are all fully update-able, officially, to the latest branch, 1709, so no hacking is needed.
NB. The IDOL 4 Pro would have stopped at 1607 officially, since Alcatel just didn't care, but AAWP managed to get a few Microsoft staffers on board with trying to add the phone to the official compatibility lists for 1703 and 1709 - I suspect that such access and opportunity wouldn't be possible today!