Siri has been on the Apple Watch since day one, though I'm usually hard-pressed to find people who actually make good use of it. It's kind of just… been there - mostly as a way to set timers when my hands are full.
Source: [The Verge](https://www.theverge.com/tech/964800/watchos-27-preview-siri-ai-apple-watch-gestures-smartwatch)