Cesium Klentaq AC is a cold-sensitive double mutant of Klentaq1 (5"-exonuclease deficient Taq polymerase with improved fidelity and thermostability). Due to its suppressed activity at low temperatures this enzyme is designed for hot start PCR performance.
https://academic.oup.com/nar/article/31/21/6139/1042365?ijkey=14VyrBEWenGT2&keytype=ref