A rebuilt version of Sites was launched on November 22, 2016. The Sites API cannot access or modify Sites made with this version, but can still access classic Sites.

Access and modify classic Google Sites content programmatically

Create new sites or copy existing sites
Retrieve, create, modify, and delete pages, attachments, and other content.
Upload and download attachments and files.
Modify sharing permissions across a site
Review the revision history across the site.