IST-Unbabel 2021 Submission for the Quality Estimation Shared Task Chrysoula Zerva author Daan van Stigt author Ricardo Rei author Ana C Farinha author Pedro Ramos author José G C. de Souza author Taisiya Glushkova author Miguel Vera author Fabio Kepler author André F T Martins author 2021-11 text Proceedings of the Sixth Conference on Machine Translation Loic Barrault editor Ondrej Bojar editor Fethi Bougares editor Rajen Chatterjee editor Marta R Costa-jussa editor Christian Federmann editor Mark Fishel editor Alexander Fraser editor Markus Freitag editor Yvette Graham editor Roman Grundkiewicz editor Paco Guzman editor Barry Haddow editor Matthias Huck editor Antonio Jimeno Yepes editor Philipp Koehn editor Tom Kocmi editor Andre Martins editor Makoto Morishita editor Christof Monz editor Association for Computational Linguistics Online conference publication zerva-etal-2021-ist https://aclanthology.org/2021.wmt-1.102/ 2021-11 961 972