New technological advancements and solutions should be investigated to overcome the stringent performance and societal requirements that 6G networks will pose in terms of capacity scaling, performance, efficiency, and sustainability. In this regard, the design and implementation of modular, scalable, cost-effective, and programmable transceiver architectures are key towards meeting future 6G network targets. In this paper, multiband (MB) sliceable bandwidth/bitrate variable transceivers with advanced capabilities are proposed and experimentally assessed, enabling full reconfigurability, sliceability, and scalability following a pay-as-you grow approach. Different transceiver building blocks will be enabled/disabled and will operate within different spectral bands beyond the C-band, according to the network condition. The proposed architecture enables point-to-point and point-to-multipoint operation maximizing the network’s resiliency, efficiency, and sustainability. 60 Gb/s MB transmission (C + S) is demonstrated over a metro-regional aggregation network path of 25.2 km. Scalability towards multi-Tb/s transmission is envisioned by exploiting the whole available spectral bands.