Scrum-half Smith, 34, looks set for his last season in New Zealand having signed long-term with Toyota Verblitz.
Fly-half Barrett, 31, could still return home to play after 2024 following his spell with the same club.
Barrett took a sabbatical to join Japanese club Suntory Sungoliath in 2021 before returning to New Zealand.
All Blacks full-back Damian McKenzie played in Japan last season while fly-half Richie Mo'unga has signed up for the 2024 campaign.