The main change in 1.6.2 is the addition of the SAT backend. The first iteration of this feature was written by Patrick Spracklen as a summer student project. All constraints in the language have a SAT encoding. MiniSat and Lingeling are fully supported as backend solvers: 1.6.2 can run them, parse the solution and collect some statistics from the solver.
In addition 1.6.2 fixes a few bugs. The most serious is a bug in Active CSE that could cause a negated global constraint to be deleted. Since Active CSE is switched on by default, I would recommend that all users of Savile Row should upgrade to 1.6.2. There are some efficiency improvements particularly in matrix operations.
Finally, the documentation has had some minor improvements, particularly the Essence’ tutorial.