It was March 13, 1997 when the general public would learn, via a report on Next Generation Online, some of the first real details Sega's last console.
http://web.archive.org/web/19970417001506/www.next-generation.com/news/031397a.chtml
at the time, the project was only known to the world outside SEGA, as Black Belt.
but NGO nailed three critical details
*PowerVR graphics chip
*Microsoft OS
*late 1998 release (Japan)
most of the stuff put out on websites and in magazines regarding Sega's next console before this report came out was merely rumor & speculation. This article was no rumor, but the first actual public report about what would be a real Sega console.
Yes, I know, the "Black Belt" machine was actually the Sega of America project using 3Dfx, which was eventually canceled. However although the article mentions Black Belt, what NGO was actually unknowingly talking about, which they and everyone discovered a few weeks or months later, were early details of the Sega of Japan project; Dural, later named Katana.
Later articles by Next Generation Online, Next Generation Magazine and the rest of the media would tell us that Sega had two consoles in development, in parallel, for a final shootout to see which one would get to replace the Saturn. ....it was pretty much fixed that the SoJ Dural/Katana would win, for various reasons.... that's another story.
The report describes an early version of the Dural/Katana which would later have a customized PowerVR2 instead of PCX2 (re: PowerVR1 "version 2"), the machine that would
indeed eventually become known to us all as,
Dreamcast. 
