On 20 January 2016, Microsoft announced the availability of SharePoint Server 2016 Release Candidate (RC), but it was not included InfoPath 2016 and SharePoint Designer 2016 as SharePoint Server 2013 RC!
So the SharePoint Designer 2013 will still be used, against
- SharePoint Server 2013.
- SharePoint Server 2016.
- SharePoint Online.
Note: The support for InfoPath 2013 and SharePoint Designer 2013 will match the support lifecycle for SharePoint Server 2016, running
until 2026.
For more details check SharePoint designer 2016 and InfoPath 2016 in SharePoint server 2016, what’re the alternatives?