Assistant in certain areas, which has to be a sore spot for Apple, since Siri predates these other personal assistants by several years.
If you've used Google Assistant and then gone back to Siri, you've probably noticed Siri sounds pretty robotic. That's because Siri's voice was really just a bunch of spliced audio clips, so sometimes the cadence of a word didn't quite fit a sentence. Right now, Siri will play music only from Apple services like Apple Music and iTunes -- and nothing else. It's a bad look, since Amazon Alexa and Google Assistant let you play music from any other service.
Spotify has not announced support for it yet, but the tool is open to any app developer, so it would make sense for Spotify to add it in order to be more integrated with Apple's platforms.