Artificial-intelligence systems face a growing data-movement bottleneck and require higher interconnect bandwidth without a proportional increase in electrical power consumption or the number of laser sources and fibre connections. Moving optical interfaces closer to computing chips reduces electrical transmission loss, while demanding optical engines that combine high channel capacity, broadband modulation and simple packaging. Although wavelength multiplexing relieves pressure on the fibre budget, integrating shared multi-wavelength sources with dense wavelength routing and broadband modulation in a compact format remains challenging. Here we demonstrate a monolithic transmitter that brings these functions together on a single material platform, enabled by the low birefringence and native Pockels response of thin-film lithium tantalate. The device separates, independently modulates and recombines eight wavelength channels between one optical input and output. This architecture retains a two-fibre interface as the channel count grows, directly addressing the packaging burden of parallel optical links. Measurements across the eight channels establish an aggregate line rate of 1.6 Tbit s⁻¹. Operation with a shared optical frequency comb achieves an estimated net data rate of 0.58 Tbit s⁻¹ across four channels, demonstrating compatibility with a common multi-wavelength source. Scaling this architecture into multiple wavelength-multiplexed engines offers a path towards 10 Tbit s⁻¹ optical interfaces with high bandwidth per unit package edge, positioning thin-film lithium tantalate for the next generation of co-packaged optical interconnects.