V2 #deltachat is rolling out after weeks of internal testing, a major milestone revising how end-to-end encryption works and bringing more beautiful contact and group profiles, direct access to chat-shared apps in the title bar and a "new email" action with setting a subject for those using a classic server.
Best of all, users and developers don't need to co-ordinate anything for upgrading to V2 despite the massive security rework behind the scenes :)