Sigma has released the various performance tests/graphs for their new Sigma 135mm f/1.8 DG HSM Art lens on their global website. The lens looks absurdly sharp (according to Sigma, the diffraction MTF better represents real-life performance, even if almost everyone in the industry uses the geometric MTF, which tends to be sharper than reality).
Sigma has uploaded two official sample photos on their website. More sample photos and price info for the 135mm f/1.8 lens (via AP, for US pricing and pre-order options check Adorama and B&H):