Edit again: scratch the NYT, Variety has more details about the who-plays-what:
In Utopia, O'Byrne will play the mid-19th century Russia radical theorist and editor, Alexander Herzen.
Stephen Dillane essayed the part in London. Crudup will play literary critic Vissarion Belinsky. Hawke is the aristocrat-turned-anarchist Michael Bakunin and Hamilton will be the poet Nicholas Ogarev. Easton, Ehle, Harbour and Plimpton will be featured in multiple roles throughout the three-part work.