On the news page of this site, which is where we announce each release, each new platform and any change to the plans. You can follow it with the RSS feed in any feed reader.
When you request access, you can also tick a separate box for our newsletter: product updates and early-access news, at most once a month. You are subscribed only after you confirm by email, and every newsletter mail has a link to unsubscribe. The news page also says plainly what is still missing in each release, the same way this site says that nothing is released today.
Each announcement carries its date and says which platforms and plans it covers. To ask for an invitation to try early builds, see early access.