It looks like Sonos is nearing the release of a speaker that has a built-in voice control assistant. According to an FCC filing found by Dave Zatz, the company is seeking to get approval from the U.S. Government to sell a speaker that sports "integrated voice control functionality with far field microphones" and "multiple voice platforms."
It's impossible to say if Sonos is building in Alexa, but the company has been making moves as of late to play friendly with Amazon's voice platform and in the past expressed plans to build the voice control platform into its speakers.
Back in January the new CEO sent a memo to his staff challenging them to boldly innovate, and to partner with global leaders, which he named as Amazon, Google and "(likely) Apple." Since then the company started rolling out services that links Sonos speakers with Alexa devices, allowing for voice control. This function is a start and great for current speakers, but the speaker shown in this FCC filing would take the integration to the logical conclusion.
According to the FCC filing, the unreleased Sonos will have far-field microphones much like Amazon Echo devices. The speaker would also support multiple voice platforms and music services. Most of this report is redacted so the details mostly stop there.
For Sonos the best move would be to let users pick between Amazon, Google, and maybe, eventually, Apple's home voice control assistant. That could be what is mentioned here, though since the speaker is still in testing, it's unclear what function will eventually launch with the speaker.
The company could reveal more details at the upcoming CEDIA tradeshow in early September, which features home control, and audio and video companies.