Answer
Under-23. Saka played for Arsenal's Under-23 team before joining the first team. The Under-23 team, also known as the reserves, is a development squad for young players who are not yet ready for the first team. Saka joined the Under-23 team in 2017 and quickly became one of their most promising players. He made his debut for the first team in 2018 and has since become a regular starter.