Valve's VACnet solution is definitely interesting. It uses AI, deep learning and is server side. It's hard to tell how effective that has been for them compared to traditional client side detection systems; I don't imagine they'll share any results.

The fact that it's completely hidden from cheat developers gives them a huge advantage though. In the past, any client side algorithm or detection method could be reversed engineered by cheat developers and patched before lunch time. Now they're working against Valve completely in the dark.