IST-Unbabel Participation in the WMT20 Quality Estimation Shared Task

We present the joint contribution of IST and Unbabel to the WMT 2020 Shared Task on Quality Estimation.Our team participated on all tracks (Direct Assessment, Post-Editing Effort, Document-Level), encompassing a total of 14 submissions.Our submitted systems were developed by extending the OpenKiwi framework to a transformer-based predictorestimator architecture, and to cope with glassbox, uncertainty-based features coming from neural machine translation systems.