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.[1] In 2015 he was the FIM CEV Moto3 Junior World Championship runner-up.[2]
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, he 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.