We investigated the use of crystalline coatings as the highly reflective coating of an Yb:YAG thin disk directly bonded onto a silicon carbide heatsink. Compared to commonly used ion-beam-sputtered coatings, it possesses lower optical losses and higher thermal conductivity, resulting in better heat management and laser outputs. We pumped the disk up to 1.15 kW at 969 nm and reached 665 W of average output power, and disk temperature of 107 °C with a highly multi-modal V-cavity. These promising results were reached with this novel design despite the adoption of a cheap silicon carbide substrate having more than 3 times lower thermal conductivity compared to frequently used CVD diamond.