Google will unveil an Amazon Echo competitor called Google Home tomorrow, according to The New York Times. It's not stated exactly what form the device will take — a speaker seems like a reasonable guess, but it's only ever referred to as a "voice-activated home device." Like the Echo, it'll be able to answer questions and take commands by voice.
Though it'll be demonstrated tomorrow, according to the report, Google Home won't ship until this fall. The early demonstration is somewhat unusual for Google, but there's good reason it may want to unveil it at I/O. Announcing Google Home now would let third party developers begin building out integrations with it, which could then be ready at launch.
Amazon's Alexa assistant is well known for the huge number of integrations it has. But it's taken well over a year for those to come together into a coherent whole. By starting early, Google could have a more compelling product at launch. Of course, that's assuming third-party integrations are supported — but I/O is a developer conference, after all, so it's hard to imagine otherwise.