Advancing the State of the Art in Open Domain Dialog Systems through the Alexa Prize. - Chandra Khatri; Behnam Hedayatnia; Anu Venkatesh; Jeff Nunn; Yi Pan 001; Qing Liu 003; Han Song; Anna Gottardi; Sanjeev Kwatra; Sanju Pancholi; Ming Cheng; Qinglang Chen; et al. (CoRR, 2018)