SQL Server 2012 autoupdate statistics default behaviour
I was just about to create a table, insert a bunch of data, create some statistics and do a test. But then I remembered this excellent blog post Erin Stellato wrote over on her blog. She's done that already.

Her tests show 20% in action. You can take what she's done her and the scripts provided, test it on your environment and witness the behavior yourself.

I've not experienced, seen or read anything that indicates this traceflag, or its behavior, is on by default in SQL Server 2012. I can't point you to official articles or documentations to prove a negative, though.

You can see for yourself which traceflags are enabled, however, by running

DBCC TRACESTATUS(-1)


Biggest advice here is - Empirical evidence rules the day. Not only will you know for sure, but you'll learn a lot in the process of figuring it out.