Osborne, 18, joins on a contract running until 2030 after a standout campaign in which he won Hearts B's Player of the Year and Players' Player of the Year awards for 2025-26.
Having switched from midfield to centre-back last season, he captained Hearts' Under-18s side to glory in the Scottish FA Youth Cup final and made 28 appearances for the club's B team in the Lowland Football League, the fifth tier of the Scottish game.
He has represented Scotland several times at youth level, most recently captaining his country in qualifying for the Uefa European Under-19 Championship.
Greenwood's route to a professional deal has been considerably quicker. The forward joined Chelsea from Wolverhampton Wanderers ahead of the 2025-26 season to link up with the club's Under-18s, having already gained Under-18 Premier League experience with Wolves the previous year, making seven appearances and scoring once while still of school age.
He made an immediate impact after switching clubs, helping Dan Hogan's Under-18s side lift both the southern and national titles in the Under-18 Premier League. Across all competitions last season, Greenwood made 23 appearances and scored nine goals, and he has represented England at Under-16 level.
Both signings form part of Chelsea's continued investment in academy recruitment, with Osborne arriving as a ball-playing defender rated highly north of the border and Greenwood joining a crowded but productive forward pool at Cobham as the club looks to develop the next generation of first-team talent.
Osborne's move follows significant interest from clubs across England and Europe, with Hearts having been keen to keep the defender on an improved contract before ultimately losing him to Chelsea's recruitment drive.
Greenwood's rapid progress, by contrast, has come entirely within Chelsea's own system since his arrival from Wolves, with the club moving quickly to tie him down on a professional deal as soon as he became eligible on his 17th birthday.