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Android 7.0 or newer. Play keeps you updated automatically; the APK is there if you would rather not use Play. It is built from the same source, but it is not the same file: Google re-signs the Play copy, so neither installs over the other — to switch, make a backup, uninstall, install the other and restore. Play can also be several versions behind the APK. Desktop builds are unsigned for now, so your system may warn on first run.
Every release publishes SHA256SUMS.txt alongside the files.
Checking takes one command and proves the file you have is the file that was
built:
sha256sum -c SHA256SUMS.txt --ignore-missingOn macOS use shasum -a 256; on Windows,
Get-FileHash in PowerShell.
Z is on Google Play as Z Messenger. The Play build comes from the same source but is not the APK above: Google re-signs it with the key it holds (Play App Signing) and serves its own split of it, so it cannot be checked against the published checksums. The APK above can be, and it can be rebuilt from the source and compared, as reproducible builds describes.
Google Play and the Google Play logo are trademarks of Google LLC.
The source is published and the protocol is fully specified, so you can build from the repository rather than trusting a binary at all. Personal self-hosting of the relay is expressly permitted; see self-hosting.