Cox opted out of his minor-league deal with the Royals to become a free agent Thursday, Mark Feinsand of MLB.com reports.
Cox has pitched primarily with Triple-A Omaha this season, posting an underwhelming 4.03 ERA and 1.62 WHIP with a 29:17 K:BB in 29 innings. He put together some relatively effective innings in the majors in 2023 and could contribute to a big-league bullpen for the last few months of the season.