Microsoft has just released a new version of the Client Side Object Model (CSOM) for SharePoint Online (SPO) http://dev.office.com/blogs/new-sharepoint-csom-version-released-for-Office-365-august-2016. As you can read in the blog published at dev.office.com:
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This new CSOM version, as usual, is only available por SPO and you can download it from NuGet.
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This new version of the SPO CSOM brings mainly new classes to work with Project Online.