[chrisbroadfoot]

"The team also tested their approach on a collection of 30 challenges in DeepMind Lab using a more powerful 36-core 4-GPU machine. The resulting AI significantly outperformed the original AI that DeepMind used to tackle the challenge, which was trained on a large computing cluster."

Well, they presumably tested the same CPU with 4 GPUs (2080 Ti I think) - maybe they wanted to compare.