In MLB, the National League and American League didn't have unified rules until 2022, when the National League finally adopted the designated hitter rule.
It was part of the 2022-2026 collective bargaining agreement. I wouldn't expect it to ever go away, since it effectively created another high-pay player for NL teams.
How can you talk shit to AL fans about pitchers hitting now? Have any stats gotten more similar between the leagues, where the DH diverged them before?