Bass' deal is for two years and includes a team option for 2023, a source told MLB Network's Jon Morosi. He's guaranteed $5 million, and potentially more in incentives, according to MLB Network's Jon Heyman.
Bass, 33, spent last season with the Toronto Blue Jays, authoring a 3.51 ERA and 3.62 FIP with seven saves in 25 2/3 innings.
The veteran reliever has spent nine years in the big leagues with various clubs while also pitching overseas in Japan during 2016.
Bass owns a career 9-16 record with a 4.32 ERA in 373 innings.