Treble's compatibility system isn't very relevant to us right now. There's a new Android release every month: a monthly, quarterly or yearly release. The devices we currently support (Pixels) receive each of these updates officially. Most Android devices do not get the monthly or quarterly updates, only the yearly ones. Other devices rely on partial backports of security patches (Android Security Bulletins) to an initial release, which are provided for ~3-4 years after the initial yearly release. If we supported typical Android devices with that situation, then we'd at least partially rely on Treble to provide the latest OS version. Pixels are currently the only devices meeting our hardware security requirements listed at https://grapheneos.org/faq#future-devices. Having proper updates for 7 years from launch is just part of that, most of the requirements are for hardware-based security features like the secure element features, hardware memory tagging, pointer authentication, USB controller support for blocking new connections and disabling USB data, etc.
GrapheneOS uses the 6.1 and 6.6 long term support branches of the Linux kernel with 6.12 as the next one that's likely going to be used to replace 6.6 for on-device virtual machines and the emulator with Android 16.
But they're drivers that are not upstreamed and which therefore make it hard to move to a newer kernel, right?
It's no harder than it would be dealing with them if they were upstream. Google ports all the Pixel drivers to newer LTS branches and a recent branch of the mainline kernel themselves.
With the recent Android 15 QPR2 release last month (March 2025), 6th/7th generation Pixels moved from the 5.10 branch to 6.1 and 8th generation Pixels moved from 5.15 to 6.1. 6th, 7th, 8th and 9th generation Pixels share the same kernel and kernel driver source tree now. They have them ported to 6.6 and mainline kernels too, it's just not ready to ship yet. 6.6 is used for virtual machines run on the devices and the emulator. 6.12 will be what's used for Android 16.
You can see at https://android.googlesource.com/kernel/google-modules/aoc/+... that they still port the 6th gen Pixel drivers to newer mainline kernels. They're ported to 6.13 and probably moving along to 6.14 soon. It doesn't mean they're going to ship them. Only LTS branches make sense to ship and they need long term stabilization first. The likely model is going to become ~12 months of stabilization and then ~12 months of usage since LTS kernel branches are moving back to 2 years of support. It was essentially increased to 6 years for 6th gen Pixels having 5 years of support, but they moved along to upgrading to newer LTS branches for 8th gen Pixels moving to 7 years of support. Greg KH works for and with Google on the LTS kernel maintenance / testing so it's actually quite Android centric rather than server centric. Long term support desktop/server distributions historically maintain their own LTS branches so they're not really the ones involved in that for the most part.
Drivers that are upstream don't actually get much free maintenance and testing. People making API changes blindly update the drivers without testing them. They get lots of updates and refactoring, but not much ongoing maintenance. Maintainers still need to deal with it. It's very common for upstream drivers to continuously regress. They can go a long time without actually working properly across releases due to how few people use them. Most people are using distributions with frozen package versions like Debian, not a rolling, and people using a rolling release like Arch Linux can use an LTS kernel branch to avoid a lot of this. The drivers for embedded hardware and things not used much by enthusiasts on desktops often break without it being noticed.
Android made a Generic Kernel Image system with ABI stability for drivers which does not benefit Pixels because they update the drivers to match the latest GKI kernel they ship. Similarly, Pixels don't really need the Treble HAL ABI forwards compatibility because they update all the vendor code to the latest monthly, quarterly and yearly OS releases anyway. It's helpful that drivers don't need to add all the new standard features to keep providing working support for new OS versions though. It's nice having it all nearly all neatly standardized and stable. We like Treble because of the sandboxing. The forwards compatibility benefits are largely unrealized because the vendors needing it aren't doing updates much anyway. Qualcomm is moving to 8 years of full update support for Snapdragon to partially match Pixels anyway.
First: I did momentarily forget that you're only targeting Pixel devices that are actively getting updates from Google. In light of that, so long as Google stays on top of maintaining those devices, yeah in your case that's probably fine. I'm somewhat accustomed to less responsible vendors and a lot of my views are shaped by that.
That said, I'm not wholly convinced that Google's downstream kernels are as good as running from upstream. AFAICT, for example, GrapheneOS is currently shipping a kernel for the Pixel 6 that's 3 minor versions behind. Trying to track things through the Android development process is... unintuitive... to me, so forgive me if I've missed something... If I go to https://github.com/GrapheneOS/device_google_raviole-kernels_... , grab a .ko file that shows as being committed yesterday, and run modinfo on it, I get a version of 6.1.131 which https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.1.1... says is from March 13 and has been superseded by 6.1.134 at this writing (from checking https://www.kernel.org/ ). Contrast https://archlinux.org/packages/core/x86_64/linux-lts/ which says that Arch's LTS kernel is at 6.12.23 which is the latest of that line. EDIT: Actually, the much better comparison is that Debian 12 is shipping 6.1.133 according to https://packages.debian.org/stable/kernel/linux-image-arm64 now. So the super stable slow moving distro is in fact still ahead of Android, even slightly lagging as it is.
As to breakage/testing... Yes, someone has to test new versions. Ideally that'd be a CI farm flashing and testing devices, but I appreciate that it's not exactly a trivial problem. Nonetheless, if that results in Graphene not shipping the latest bugfixes, I feel like that's an extremely awkward position to be in.
Pixels only recently started moving to new LTS releases and will likely be moving to a new LTS release each year going forward. Moving the older generations to 6.1 to match current devices was done in March 2025. They'll likely move along together to a new branch each year going forward.
Linux kernel LTS revisions are nothing like LTS revisions of most other projects. They're largely untested patches blindly applied by the LTS maintainers based on patches to mainline being marked for stable backports. If the patches apply cleanly, they ship. If they don't apply cleanly, they largely don't ship. Whether it works is an open question.
> GrapheneOS is currently shipping a kernel for the Pixel 6 that's 3 minor versions behind
That's not quite right.
We're shipping the latest Linux 6.1 and Linux 6.6 GKI LTS branch releases from Greg KH. They're currently in between 2 upstream revisions upstream, not on a specific one. The devices all use both 6.1 and 6.6, not just 6.1. They use 6.1 for bare metal and 6.6 for virtual machines. Even the Pixel 6 has been ported to 6.13 by Google but that doesn't mean that's a stable enough kernel ready to ship.
The Android kernel branches also have a bunch of backports not included in the kernel.org LTS releases, including security patches and improvements they decided were important. Google does their own backporting and fixes in the GKI branch and Greg KH merges those into the GKI LTS branch. The kernel branch we use is the combination of the Google GKI backporting/fixes with the kernel.org backporting. The kernel.org LTS releases are far messier than you realize, and combining these things is messy too.
Linux LTS kernels are not very well tested and have tons of regressions. Quickly updating to the new LTS versions is problematic and we regularly encounter major regressions, especially in certain areas like f2fs and USB. We still update right away to the new GKI LTS versions. We're currently on the latest GKI LTS releases for each branch.
You'd have to ask Greg KH why there are still delays despite Google supporting it. It still seems to be him doing most of the kernel.org LTS and also GKI LTS work by himself, without nearly as much review or help by others as you would think. This is also tied into the severe regressions regularly happening with the LTS releases. Those can be security regressions too. Immediately updating to them is not necessarily a great idea with how much goes wrong at the moment.
They unfortunately sometimes lag behind the kernel.org releases. We used to merge the latest upstream kernel.org LTS releases ourselves but Greg KH convinced us we don't need to do that anymore and should just use the GKI LTS branch instead. We're not completely happy with it since it's not fully kept in sync but we're using our resources elsewhere at the moment.
> Actually, the much better comparison is that Debian 12 is shipping 6.1.133 according to https://packages.debian.org/stable/kernel/linux-image-arm64 now. So the super stable slow moving distro is in fact still ahead of Android, even slightly lagging as it is.
Debian is usually further behind than Greg KH's GKI LTS branch. Comparing at a snapshot in time doesn't mean much. GKI LTS branch should really be kept in sync but the GKI ABI stability system makes maintenance hard and is entirely worthless for Pixels. We would prefer if the whole GKI system did not exist. For Pixels, the kernel image and all the drivers are built with the same kernel source tree for Pixels so the whole system for driver ABI compatibility is just making things more complex and worse.
> As to breakage/testing... Yes, someone has to test new versions. Ideally that'd be a CI farm flashing and testing devices, but I appreciate that it's not exactly a trivial problem. Nonetheless, if that results in Graphene not shipping the latest bugfixes, I feel like that's an extremely awkward position to be in.
We do heavily test them. Our community helps with it. We OFTEN find regressions in the new LTS kernels. It often takes months before the issues we find and work around get fixed upstream. It's worth noting that due to mistreatment we've largely stopped helping them except for firmware, hardware or things we don't want to maintain downstream for some reason. It would be better if everyone collaborated on maintaining LTS kernels but instead it's largely 1 person and a couple others doing it with support from Google for testing, etc.