Izan Almansa was born in Murcia, Spain. He father, Steve Horton, was an American professional basketball player for CB Murcia. Almansa grew up in Spain playing association football and dreamed of playing professionally. Almansa did not start playing basketball until he was 9 years old. He joined the UCAM Murcia youth ranks and was already 6'1" at age 12. In his final season with UCAM he helped lead the Team Infantil squad to a 6th place finish at the Spanish National Championship-the club's best performance ever at the Infantil level-while averaging 18 points and 18 rebounds per game. In the summer of 2019, Almansa was recruited by Real Madrid. He played two seasons with Real Madrid Cadete.
In 2021, Almansa signed with the Overtime Elite, a professional basketball league for high school-aged players. In the 2021-2022 season, he played for Team OTE and averaged 6.4 points and 5.0 rebounds per game. In 2022-2023, Almansa was drafed by YNG Dreamerz. Almansa became a focal point of his team's offense and averaged 9.3 points and 8.6 rebounds per game.
This past season Almansa played for the Ignite of the NBA G League. He started 16 games and showed that he could hold his own in a professional setting. He averaged 8.2 points and 6.9 rebounds per game and is widely regarded as a first round prospect in the 2024 NBA Draft.