The other invitees are catcher Jordan Procyshen, outfielder Brian Bogusevic and right-handers Kyle Kendrick, Chandler Shepherd and Ben Taylor.
After the trade of Yoan Moncada to the White Sox for Chris Sale, Devers will be the Minor League position player Red Sox fans focus on the most in the coming year.
Travis was a standout performer last Spring Training for the Red Sox, but he suffered a season-ending torn ACL in his left knee while playing for Triple-A Pawtucket in May.
Castillo, who hasn't lived up to expectations after signing a seven-year, $72.