The Siri Remote was released in 2015 along with the Apple TV Generation 4. This remote had a glass trackpad, two microphones, and five buttons. The buttons included Menu, Home, Siri, Play/Pause, and a combined Volume up/down button. This remote used both IR and Bluetooth to connect to the Apple TV. The remote also included two sensors for gaming, an accelerometer and a gyroscope.
The finishes of the remote included a matte finish on the trackpad and a smooth, glossy finish at the bottom. The textured finishes helped differentiate the orientation of the remote when using it in the dark or by touch.
The trackpad on the Siri Remote supported limited gestures, including swipe, click, and tap.
Unlike earlier Apple Remotes, the Siri Remote used a built-in rechargeable Lithium Polymer Battery that charged using a Lightning port at the bottom.
The design of this remote was slightly revised after initial production. The original design had a solid black Menu button. The revised design added a white raised ring around the the Menu button.
References: Wikipedia.com, Apple Developer