In a year that saw Big Law eagerly ship up to Boston, Washington, D.C.-based Arent Fox is arriving in Beantown in a merger with local, 55-lawyer Posternak Blankstein & Lund.

The merger, which the firms announced Tuesday, will officially go live Jan. 1, 2019, marking a major northeast expansion for Arent Fox and offering the latest evidence of Boston’s hot legal market.