Arteta joined the Gunners on a four-year deal just before the 23:00 BST deadline. The deal had looked dead after talks between the two clubs broke down. However, Arteta handed in a transfer request an hour before the deadline.
Reports claim the transfer fee for the 29-year-old is somewhere in the £10 million region.
Speaking on Twitter, Benayoun informed fans about the move:
I sign with Arsenal, very happy and excited about it, but now my head is only in the game against Greece on Friday, thanks for the support.
I had a great time at Werder, and owe them a lot, but the move to London is a wish come true. The English Premier League has for me always represented an interesting challenge.
While the ferocity of the changes at Arsenal may be surprising, Arsene Wenger's proactiveness is not. These signings were desperately needed, it now just remains to be seen if they are the right ones.