As far as official announcements go, they don't get much more official than this. Aldon Smith has posted a picture to his Instagram account of himself with Reggie McKenzie having signed his new contract with the team.
UPDATE: The Raiders have made the signing official.
It is said to be a 2-year deal according to NFL Network's Ian Rapoport.
Aldon Smith and the #Raiders have reached an agreement on a contract, as @AdamSchefter said. It's a 2-year deal, I'm told, through 2017.— Ian Rapoport (@RapSheet) April 4, 2016
A 2-year deal makes sense for both sides as Smith will miss most of this season completing his one-year suspension. Then he can have all of the following season to try and stay clean and prove he can be the dominant pass rusher he once was. That would mean he would be 28 years old when he hits free agency again with the chance to sign one more good nfl contract and salvage his career.