According to this notice the expected publication date of the contract documents (note that this could change) is 2020-10-23
Production, testing and delivery of up to 10 SML klystron modulators rated 115kV/100A (respectively, pulse voltage and current amplitudes) and 3.5ms/14Hz (respectively pulse width and repetition rate). These modulators are intended to be used within the High Beta section of the ESS linear accelerator. The foreseen production contract is intended to be based on a “built-to-print” specification, based on ESS design. The bill of materials, detailed mechanical drawings, electrical schematics, testing procedures will be provided by ESS as part of the technical specifications.