Moto3 World Championship Arenas debuted in the Moto3 World Championship in the last race of the 2014 season in Valencia, as he was signed by Calvo Team to replace the injured
Eric Granado. In
2015, he was the FIM CEV Moto3 Junior World Championship runner-up.
Aspar Team (2016) In the
2016 Moto3 season, Arenas first made three appearances with the
Aspar Team, two as a
wild card entry and one as the substitute for the injured
Jorge Martín,
Peugeot MC Saxoprint (2016) In 2016, Arenas later joined the Peugeot MC Saxoprint team as the permanent replacement for
Alexis Masbou.
Aspar Team (2017–2020) In 2020, Arenas finished the
2020 Moto3 World Championship season as the world champion, taking 174 points with 3 wins and 5 podiums, edging out both
Tony Arbolino and
Ai Ogura by 4 points.
Moto2 World Championship Aspar Team (2021–2022) Arenas joined the
Aspar Moto2 team in the 2021 season. It was a relatively weak season for Arenas, spending most of it getting up to grips with the bike, scoring only 28 points in 18 races, and finishing 21st in the standings. The
2022 season was better, as Arenas collected 90 points, finishing 12th in the standings, with his season best result a 4th place from Rimini.
Red Bull KTM Ajo (2023) Earning a ride at a top team, Arenas competed for the
Red Bull KTM Ajo Moto2 team in the 2023 season. Arenas went on to finish the season 14th in the standings, collecting 85 points, and a season's best 3rd place in Catalonia, his first podium in the intermediate class. His teammate
Pedro Acosta won the title by a comfortable margin, 83 points.
Gresini Racing Moto2 (2024) Arenas officially joined
Gresini Racing Moto2 for the
2024 Moto2 season, where he was paired with teammate
Manuel González. == Personal life ==