Bosi is only the second British sport climber in history to redpoint a 9b (5.15b) graded sport climbing route (King Capella in 2021), and by 2023, was one of only a small group of climbers in the world to have completed a V17 (9A) boulder (Alphane in 2022, Burden of Dreams in 2023, and both Return of the Sleepwalker and Spots of Time in 2024).

Both parents took him and his 3-year-old brother Alexander to an indoor climbing centre in Newhaven, Edinburgh when he was 6 years old.

[2][3] In 2020–2021, Bosi became only the second British climber in history, after Steve McClure, to climb a 9b (5.15b) grade sport route with his repeat of Adam Ondra's La Capella, and followed up by his first free ascent of King Capella (a route initially considered a possible 9b+), both of which are in Siurana in Spain.

[5] That year, he also created Honey Badger in the English peak district, which he graded at 8C+ (V16).

[8] In April 2023, he made the first repeat of Nalle Hukkataival's Burden of Dreams, considered the world's first-ever V17 (9A) boulder, and which at the time of Bosi's repeat was still considered the world's hardest boulder.