Unlike Alexa and Google Assistant, Siri has been limited to only Apple devices since it was introduced nearly a decade ago. That's changing this year, though — Apple just announced that third-party devices would be able to take advantage of Siri as part of an update to the company's HomeKid system. Apple showed someone summoning Siri on an Ecobee thermostat. But based on the brief demo, it sounds like these third-party devices won't be full-fledged devices running Siri themselves. Instead, it'll relay the command to a HomePod mini which will then send the request. Apple specifically said that third-party companies won't be able to see those Siri commands.
It's unclear whether other devices, like the Apple TV, will also be able to serve as a Siri hub. We'd have to imagine that the original, now-discontinued HomePod will also be able to link to third-party Siri devices, but we'll have to wait until Apple's event is over and dig into the fine print here.