Brother of Mackem skipper Steve Caldwell, Gary is captain at Easter Road, and this deal has been on the cards for months.
Hibs fans have been bracing themselves to see the Scotland international central defender move to the Glasgow giants, and it has been the worst kept secret in Scottish football.
The imminent departure prompted a section of the Hibernian supporters to jeer the 23-year-old during their defeat to Aberdeen at Easter Road last week.
Strachan : "He's coming here in the summer and there will be no deals done now."