"There were a lot of reasons behind it," Thigpen said Monday, in confirming the decision a day after it was first reported by ESPN.com. "My agent talked to them, and I'm just glad to be here, and looking forward to the season."
Thigpen is now set to make a base salary of $1.5 million this season in the second year of a three-year contract he signed last summer.
The decision allowed the Bills to lower their salary cap number, and made it easier for the team to carry four quarterbacks when making their final cuts on Friday. It's a group that includes Tarvaris Jackson, who was acquired in a trade from Seattle last week, and receiver/Wildcat specialist Brad Smith.
Thigpen is competing with Jackson for the backup job behind Ryan Fitzpatrick.
The Bills also elected to keep Thigpen because he's far more familiar with the offense than Jackson, and more capable of stepping in early should Fitzpatrick get hurt.
And Smith's status is uncertain after he hurt his groin in a 38-32 preseason finale loss at Detroit on Thursday.
Buffalo opens the season at the New York Jets on Sunday.