Another source has referenced the “announcement” that the Sonic SXSW panel. However, this time it’s straight from SXSW itself:

Sonic the Hedgehog: 25 Year Anniversary
Yuji Naka (Sonic Original Creator), Takashi Iizuka (Head of Sonic Team), Roger Smith (Voice of Sonic the Hedgehog), Mike Pollock (Voice of Dr. Eggman), Austin Keys (Sega), Aaron Webber (Sega)
25 years had to go fast, and here we are today wondering where it all went. Join the original creator of Sonic the Hedgehog, along with the amazing production heads responsible for bringing the franchise to life, for an in-depth analysis of where Sonic came from and where he’s heading going forward. A special reveal will be made as part of the celebration for this anniversary milestone.
It isn’t a game, but to see this mentioned every time the panel is promoted is striking. There’s no telling what it could be, but that will change on the 19th. We are going all hands on deck for this panel, with people at the panel and even some live streaming coverage, so stay tuned.



source : http://www.tssznews.com/2016/03/08/sxsw-teases-special-reveal-that-will-be-made-at-sonic-panel/