Dirk lets Mavericks know he's opting out

The official letter stating that Dirk Nowitzki is opting out
of the final year of his contract has arrived in the Mavericks’ offices,
an NBA source says.
 
That letter had to arrive before 11:01 p.m. Wednesday.
 
That means Nowitzki officially is no longer the Mavericks’
property, or at least, he won’t be as of Wednesday night.
 
Negotiations can then begin on a new contract – one that
could run four seasons and include a no-trade clause, which is rare in the NBA.