Assuming U.S. Senator Jeff Sessions resigns his Senate seat to become Attorney General, there will be no special election to replace him during 2017. Alabama law permits a Governor to call a special election in an odd year to fill a vacancy in the U.S. Senate, but it does not require the Governor to do that.
On January 5, Alabama Governor Robert Bentley said he won’t call a special election in 2017. Instead there will be a special election in November 2018, for the remaining two years of that term. This is disappointing, because last year a U.S. District Court had ruled that when Alabama holds a special congressional election, for that special election the normal 3% petition requirement must be eased. See this news story about the Governor’s decision. He isn’t holding a special election in 2017 in order to save money.