A message below appeared in our Office 365 tenant last week on Friday.
Office 365 Feature Update: Deploy and use SharePoint Framework client side web parts
We are giving you the ability to deploy and use SharePoint Framework client side web parts in Office 365. You’ll begin seeing this change starting today. We are only rolling this out to First Release customers, at this time.
How does this affect me?
Developers can build client-side web parts using the SharePoint Framework. With this update, those developers can now use and test their parts in the context of SharePoint. Administrators can take those SharePoint Framework Client-side Solutions and deploy them via their App Catalog to make them available within their organization. Site owners can then use SharePoint Framework client-side web parts in Classic and Modern pages. Note: The SharePoint Framework is in Developer Preview. Elements of the developer interface may change between now and general availability, which may interrupt the function of parts built on the Developer Preview.
What do I need to do to prepare for this change?
There is no action you need to take to prepare for this change. Please click Additional Information to learn more.