There is no compensation in Matlab's SUM. For small arrays (there was a limit at 88999 elements, but this might change with the Matlab release) the sum is computed directly. For bigger arrays the sum is divided in parts and distributed over different threads.
If you need a compensated sum, try:
This offers a Kahan-compensation, Knuth's method with intermediate 128 and 192 bit precision, an 80bit accumulator and Knuth with 160 bits (the last two are not supported by all compilers and platforms).