"Differential sync brings the ability to sync only the parts of large files that have changed, not the entire file. This makes the file synchronization process faster for these files. Currently OneDrive supports differential sync for Office 2016 files. Later this year, Microsoft will bring the ability to leverage differential sync to all file types stored in OneDrive and SharePoint."
"To complement these large uploads, we announced availability of differential sync for PC and Mac, bringing the ability to sync only the parts of large files that have changed, not the entire file."
"Differential sync brings the ability to sync only the parts of large files that have changed, not the entire file. This makes the file synchronization process faster for these files. Currently OneDrive supports differential sync for Office 2016 files. Later this year, Microsoft will bring the ability to leverage differential sync to all file types stored in OneDrive and SharePoint."
https://mspoweruser.com/microsoft-announce-onedrive-improvem...
Edit: It went live on November 4th 2019:
"To complement these large uploads, we announced availability of differential sync for PC and Mac, bringing the ability to sync only the parts of large files that have changed, not the entire file."
https://techcommunity.microsoft.com/t5/Microsoft-OneDrive-Bl...