England prop Stevens will join the Guinness Premiership title contenders on 19 January next year.
That is the exact date Stevens is available to play again on completion of a two-year drugs ban following a failed doping test in December 2008., and the former Bath forward said: "I have many great memories and friends in Bath, but there is something special happening at Saracens and I am very eager to be part of it."
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Hide AdStevens, 27, resigned from Bath last March following the drugs revelations. He had a four-year deal with the club believed to be worth around 1million.