Due to a non-compete clause, ARCO (yes, ARCO!) can't host concerts, sporting events or conventions that could otherwise be hosted at G1C.
The last commercial event was September 2016.
The last event of any kind was Sac State's winter commencement ceremonies December 16th and 17th 2016.
However, there has been talk of ARCO being used as a temporary convention center during the 2 year expansion of the downtown convention center scheduled to begin in 2019. There are hurdles to overcome for that to happen, though, as the Kings would have to give their OK (they still own the property and building) and the city would have to vote to override the non-compete clause (which may have happened already).