Metric alerts was a special case as it needs some more Kafka consumers to be set up. We also want to ensure stability for self-hosted Sentry versions as the upgrade cycle for them is much slower (and sometimes people never upgrade them once setup).
You can assume sentry.io to be running on latest master of getsentry/sentry or something very close to that (barring weekends as we don’t usually deploy on weekends).
I don’t expect metric alerts to be available on the upcoming 20.10.0 release as we only have 2 days to make it happen but it should be out by 20.11.0.