MtoA 1.2.7.3 ships with Arnold 4.2.13.
If you want to take advantage of the improvements in Arnold 4.2.14.0 (like the increase in the maximum number of threads from 128 to 256), here’s what you need to do:
- Download Arnold 4.2.14.0 and extract the archive
- Replace Arnold (libai.so, ai.dll, libai.dylib), kick, and maketx in the MtoA bin folder with the versions from the Arnold 4.2.14.0 download
- Replace the Arnold Python bindings in the MtoA scripts/arnold folder with the Python bindings from the Arnold python/arnold folder. For example, replace this folder:
C:\solidangle\mtoadeploy\2016-1.2.7.3\scripts\arnoldwith the python\arnold folder from the Arnold 4.2.14.0 download. For example:
C:\solidangle\arnold\Arnold-4.2.14.0-windows\python\arnold
You must update the Arnold Python bindings, otherwise MtoA won’t load. That’s because Arnold 4.2.14.0 included a number of API changes, including the removal of some API (like AiLicenseSetServer). The older Python bindings still refer to the removed API, so there will be Python errors that prevent MtoA from loading.
Arnold Support Corner 
So there is no need for a new mtoa release anytime soon? Is this the only way to update to 4.2.14.0
This is how you update MtoA 1.2.7.3 to use Arnold 4.2.14.0
This blog post is not making any statement or prediction about possible future updates of MtoA.