The 6-foot-3, 172-pound Kasdorf, 24, will likely begin next season with the AHL Rochester Americans.
Kasdorf, an afterthought in the blockbuster 2015 Evander Kane with the Jets, joined the Sabres in March after finishing his NCAA career with R.P.I. He played his only pro game April 8, making 26 saves in a 4-1 home loss to Columbus.
The Winnipeg native, a sixth-round pick by the Jets in 2011, is expected to share time with Linus Ullmark with the Amerks in 2016-17.
Kasdorf is guaranteed $200,000 next season and will receive $575,000 in the NHL and $100,000 in the minors, according to generalfanager.com.
The Sabres also officially announced they have re-signed another restricted free agent, forward Dan Catenacci, to a one-year, two-way deal.