The Multi Device options are available with the blue Mobile S/M/L, inOne premium/basic and Swiss mobile light mobile subscriptions, as well as all SME and older subscriptions (Swiss mobile flat, inOne XS-XL, young).
With blue Mobile L and inOne mobile premium, the Connect Pack and thus the Multi Device Option is included, and you can use your subscription on up to 3 additional devices free of charge.  Additional options can be purchased flexibly.