The ArcGIS 10.4 release is now available for all who have current licenses. You can download the software from your my.esri.com account.
The new release includes new geoprocessing tools and updates, Python 2.7.10 with additional third-party libraries including SciPy, pandas, Sympy, and nose, and other updates to Mapping, Editing, Geodata/Geodatabases, and Network Analyst. For more info, visit the 10.4 What’s New page.
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