Garza also posted on his account, "Business side over! Hooray! Time to focus on what really matters 2013."
Garza signed his second straight one-year contract.
The 29-year-old made $9.5 million last season, going 5-7 with a 3.91 ERA before being sidelined with an elbow injury. He's scheduled to become a free agent for the first time in his career after the 2013 season. The Cubs are expected to make the deal official Friday when their annual fan convention commences.
The Cubs have two more players, pitchers James Russell and Jeff Samardzija, who also have filed for arbitration. They can still work out deals with the club before their respective arbitration hearings in February.
Information from The Associated Press was used in this report.