Arnold for 3ds Max is provided by the MAXtoA plug-in.
This version of MAXtoA is included with 3ds Max 2018 Update 3.
September 28, 2017
This is a bugfix releasing, using the Arnold 22.214.171.124 core, and is MAXtoA build 859.
Get the installer on Solid Angle Downloads.
See the Arnold 126.96.36.199 release notes for the full list of enhancements and fixes.