All trains in Moscow metro have access to Free Wi-Fi internet. General information is given on Metro page. It’s an important notice that access to Wi-Fi have exactly trains, on stations and transfer tunnels Wi-Fi is not available. On stations and transfer tunnels regular mobile connection in accessible.
Signs showing that Wi-Fi is available usually look like on the picture below. But for now they are not so actual because Wi-Fi is available in every train, they were actual on the period when Wi-Fi was implemented widely in Metro.
The Wi-FI network is called: MosMetro_Free
Ones you connected to Wi-Fi network, open a browser and you will be redirected to access page.
First of all you have to register on network. This action is done only once. To register you have to choose a Green Button and enter your mobile number.
Then you will receive an activation code via sms. You can follow the link provided in sms or manually input code on welcome page of Wi-Fi network under register tab.
After registration you will see Welcome page only with one button that says you about ability to connect to internet.