In 2016 the SKA Organisation decided that, due to the complexity of the software and the uncertainty of the implementation details, the software development would be managed as an agile development programme. This led to a strategic decision to retain control of the primary risks of software construction and, by implication, some degree of central management. In the years before construction began we selected the Scaled Agile Framework (R) as the basis for agile development and the NEC4 (R) framework as the contract structure to hire the developers needed. The latter is complemented by the Vested (R) methodology for creating highly collaborative business relationships. All of these are unusual in our environment, but reflect world best practice in other areas. We report on the progress of the contracts after about three years of construction. Overall, we believe it has been a success, with: the competitive rates offered allowing the engagement of more resources than what was estimated at the time of the SKA System CDR due to the low risk structure; positive results from a regular "happiness" survey of the developers; high levels of trust; a strong engagement with suppliers actively contributing to the governance; and the development being largely on time and budget with no expected impact on the critical path. Finally, we will report on the lessons we have learned and what we feel others should take away to consider for use in future large scale scientific software programmes.
