GrapheneOS and CalyxOS are commonly compared as similar options for people looking for an alternative Android OS for their Pixel devices. Below are some of the reasons we recommend GrapheneOS over CalyxOS.
GrapheneOS extends the user profile feature, allowing you to end a current session. To do this, select *End Session* which will clear the encryption key from memory. GrapheneOS also provides [cross-profile notification forwarding](https://grapheneos.org/features#notification-forwarding). GrapheneOS plans to introduce nested profile support with better isolation in the future.
When Google Play services are used on GrapheneOS, they run as a user app and are contained within a user or work profile. Sandboxed Google Play is confined using the highly restrictive, default [`untrusted_app`](https://source.android.com/security/selinux/concepts) domain provided by [SELinux](https://en.wikipedia.org/wiki/Security-Enhanced_Linux). Permissions for apps to use Google Play Services can be revoked at any time.
microG is a partially open-source re-implementation of Google Play Services.[^1] On CalyxOS, it runs in the highly privileged [`system_app`](https://source.android.com/security/selinux/concepts) SELinux domain like regular Google Play Services, and it uses [signature spoofing](https://github.com/microg/GmsCore/wiki/Signature-Spoofing) to masquerade as Google Play Services. This is less secure than Sandboxed Google Play's approach, which does not need access to sensitive system APIs.
When using Sandboxed Play Services, you have the option to reroute location requests to the Play Services API back to the OS location API, which uses satellite based location services. With microG, you have the option to choose between different backend location providers, including *shifting trust* to another location backend, like Mozilla; using [DejaVu](https://github.com/n76/DejaVu), a location backend that locally collects and saves RF-based location data to an offline database which can be used when GPS is not available; or to simply not use a network location backend at all.
Network location providers like Play Services or Mozilla rely the on the MAC addresses of surrounding WiFi access points and Bluetooth devices being submitted for location approximation. Choosing a network location like Mozilla to use with microG provides little to no privacy benefit over Google because you are still submitting the same data and trusting them to not profile you.
Local RF location backends like DejaVu require that the phone has a working GPS first for the local RF data collected to be useful. This makes them less effective as location providers, as the job of a location provider is to assist location approximation when satellite based services are not working.
If your threat model requires protecting your location or the MAC addresses of nearby devices, rerouting location requests to the OS location API is probably the best option. The benefit brought by microG's custom location backend is minimal at best when compared to Sandboxed Play Services.
In terms of application compatibility, Sandboxed Google Play on GrapheneOS is always going to be more compatible as it is the same code as what is released by Google. microG is a reimplementation of these services. As a result of that it only supports the various parts that have been reimplemented, meaning some things such as [Google Play Games](https://play.google.com/googleplaygames) and [In-app Billing API](https://android-doc.github.io/google/play/billing/api.html) are not yet supported.
Larger apps, especially games, require Play Delivery to be installed, which is currently not implemented in microG. Authentication using [FIDO](../basics/multi-factor-authentication.md#fido-fast-identity-online) with online services on Android also relies on Play Services, and does not currently work with microG.
[^1]: It should be noted that microG still uses proprietary Google binaries for some of its components such as DroidGuard. Push notifications, if enabled, still go through Google's servers just like with Play Services. Outside of default microG setups like on CalyxOS, it is possible to run microG in the unprivileged [`untrusted app`](https://source.android.com/security/selinux/concepts) SELinux domain and without the signature spoofing patch. However, microG's functionality and compatibility, which is already not nearly as broad as Sandboxed Play Services, will greatly diminish.
Currently, eSIM activation is tied to a privileged proprietary application by Google. The app has the `READ_PRIVILEGED_PHONE_STATE` permission, giving Google access to your hardware identifiers such as the IMEI.
On CalyxOS, the app comes installed by default (regardless of whether you choose to have microG or not) and cannot be opted out. This means Google still has access to your hardware identifiers regardless of whether or not you need eSIM activation and can be accessed persistently.
Android 12 comes with special support for seamless app updates with [third-party app stores](https://android-developers.googleblog.com/2020/09/listening-to-developer-feedback-to.html). The popular Free and Open-Source Software (FOSS) repository [F-Droid](https://f-droid.org) doesn't implement this feature and requires a [privileged extension](https://f-droid.org/en/packages/org.fdroid.fdroid.privileged) to be included with the Android distribution in order to have unattended app installation.
GrapheneOS does not include F-Droid, because all updates have to be manually installed, which poses a security risk. However, you can use the [Neo Store](../android.md#neo-store) client for F-Droid which does support seamless (background) app updates in Android 12. GrapheneOS officially recommends [Sandboxed Google Play](https://grapheneos.org/usage#sandboxed-google-play) instead. Many FOSS Android apps are also in Google Play but sometimes they are not (like [NewPipe](../video-streaming.md)).
CalyxOS includes the [privileged extension](https://f-droid.org/en/packages/org.fdroid.fdroid.privileged), which may lower device security. Seamless app updates should be possible with [Aurora Store](https://auroraoss.com) in Android 12.
- **Hardened WebView:** Vanadium WebView requires [64-bit](https://en.wikipedia.org/wiki/64-bit_computing) processes on the [WebView](https://developer.android.com/reference/android/webkit/WebView) process and disables legacy [32-bit](https://en.wikipedia.org/wiki/32-bit_computing) processes. It uses hardened compiler options such as [`-fwrapv`](https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html) and [`-fstack-protector-strong`](https://gcc.gnu.org/onlinedocs/gcc-4.9.3/gcc/Optimize-Options.html), which can help protect against [stack buffer overflows](https://en.wikipedia.org/wiki/Stack_buffer_overflow). [API](https://en.wikipedia.org/wiki/API)s such as the [battery status API](https://chromestatus.com/feature/4537134732017664) are disabled for privacy reasons. All system apps on GrapheneOS use the Vanadium WebView which means that apps which use WebView will also benefit from Vanadium's hardening. The [Vanadium patch set](https://github.com/GrapheneOS/Vanadium) is a lot more comprehensive than CalyxOS's [Chromium patch set](https://gitlab.com/CalyxOS/chromium-patches) which is derived from it.
- **Hardened Kernel:** GrapheneOS kernel includes some hardening from the [linux-hardened](https://github.com/GrapheneOS/linux-hardened) project and the [Kernel Self Protection Project (KSPP)](https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project). CalyxOS uses the [same kernel](https://calyxos.org/docs/development/build/kernel/) as regular Android with some minor modifications.
- **Hardened Memory Allocator:** GrapheneOS uses the [hardened malloc](https://github.com/GrapheneOS/hardened_malloc) subproject as its memory allocator. This focuses on hardening against [memory heap corruption](https://en.wikipedia.org/wiki/Memory_corruption). CalyxOS uses the default AOSP [Scudo Malloc](https://source.android.com/devices/tech/debug/scudo), which is generally [less effective](https://twitter.com/danielmicay/status/1033671709197398016). Hardened Malloc has uncovered vulnerabilities in AOSP which have been [fixed](https://github.com/GrapheneOS/platform_system_core/commit/be11b59725aa6118b0e1f0712572e835c3d50746) by GrapheneOS such as [CVE-2021-0703](https://nvd.nist.gov/vuln/detail/CVE-2021-0703).
- **Secure Exec Spawning:** GrapheneOS [spawns](https://en.wikipedia.org/wiki/Spawn_(computing)) fresh processes as opposed to using the [Zygote model](https://ayusch.com/android-internals-the-android-os-boot-process) used by AOSP and CalyxOS. The Zygote model weakens [Address Space Layout Randomization](https://en.wikipedia.org/wiki/Address_space_layout_randomization) (ASLR) and is considered [less secure](https://wenke.gtisc.gatech.edu/papers/morula.pdf). Creating [fresh processes](https://grapheneos.org/usage#exec-spawning) is safer but will have some performance penalty when launching a new application. These penalties are not really noticeable unless you have an [old device](https://support.google.com/nexus/answer/4457705) with slow storage such as the Pixel 3a/3a XL as it has [eMMC](https://en.wikipedia.org/wiki/MultiMediaCard#eMMC).
**Please note that these are just a few examples and are not an extensive list of GrapheneOS's hardening**. For a more complete list, please read GrapheneOS' [official documentation](https://grapheneos.org/features).
