With version 4.0 of the api out, is there an end-of-life for the 3.x version?
The two API version will co-exist until 4.0 functionality matrix has all the designated 3.x features added to the 4.x API.
The current scheduled date is January 1, 2019.
See also http://downloads.esri.com/support/product%20life%20cycle/online_gis/ArcGISWebMappingAPIs_PLC.pdf
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