If you are running a self-hosted version, you can find the version in the bottom left corner of any page.
Sentry cloud mostly runs on the latest master of https://github.com/getsentry/sentry. See this thread for reference. New alert type: Metric Alerts
If you want to document, you can probably looks at releases and use the latest version from it. Https://github.com/getsentry/sentry/releases