Though the majority of companies have policies pertaining to responding to speculation, sometimes it just gets to a point they have to. For instance, say a rumor makes the rounds (with at least some supporting evidence) that Google has something up its sleeve that might possibly have to do with an operating system. Google can keep mum for a while, but it obviously has to be formally addressed, sooner or later.
It's unclear whether Google originally intended on announcing its Native Code Project last night, or if it hoped it could squeak out some more prep time before anyone noticed something was afoot. Either way, Google has unveiled Native Client, a technology that Google says will give web developers the full power of the client's CPU while maintaining browser safety, complete portability, and safety. And yes, it is open source.