The 4th Anniversary Campaign begins on February 5th (Thu)!
“You can obtain rewards from the 4th Anniversary Celebration by logging in!
-1000 gems in total (enough for 10 packs)
-Three 4th Anniversary Packs
-“Dark Magician” (alternative artwork) Icon
-“Dark Magician” (alternative artwork/Royal Finish/Cannot be Dismantled)”

The tweet mentions that the Anniversary Packs contain a guaranteed UR from the relevant Secret Packs, as with previous anniversaries.

Source.

The tweet notes that you can obtain more rewards by sharing your code with more people, once again, like previous anniversaries.

Source.