You have to take a leap of faith on this one, but according to PhoneArena, a Portuguese source entrenched in HTC's production facility in Brazil provided some "hot tips" about the Nexus 9, one of which is that it's expected to be announced on October 8th. What's interesting about that date is it marks an HTC press event, the implication being that HTC will announce the Nexus 9, not Google. HTC is also expected to announce a camera product that will compete against the GoPro series.
Google's Nexus 9 built by HTC will feature NVIDIA's Tegra K1 chip
While we understand the desire to release the Nexus 9 in time for the holiday shopping season, it seems odd that Google would hand the unveiling over to HTC, especially since Google took care of the chore itself for the past two Nexus tablets. That said, it's possible that a Google executive could show up to the press event and share the stage with HTC.
An October 8th unveiling would also fall nearly in line with information obtained from NVIDIA's legal documents. NVIDIA is suing Samsung and Qualcomm for allegedly infringing on its GPU patents, and in the accompanying legal papers, NVIDIA writes that the "HTC Nexus 9, expected in the third quarter of 2014, is also expected to use the Tegra K1."