Ray Traced Shadows

adamrice117

Hello, I'm watching an excellent tutorial on lighting by William Faucher here: https://www.youtube.com/watch?v=fSbBsXbjxPo

I'm wondering why in my Directional Light Details, the Cast Ray Traced Shadows is greyed out. All of my Project Settings are set correctly and I have a Geforce GTX 1080ti which supports ray tracing; it appears the shadows are quite soft and ray tracing is working. But I'm curious why this setting is greyed out and I can't Enable or Disable it as I please.

Any thoughts?

Thanks!