This is the part of the migration you will hardly notice happening. It is the work behind the scenes utilizing the fruit harvested in the previous steps.
The code base is being amended in a fully automated way, using the migration rules formulated in previous steps. In this phase modules will be developed and interfaced with the source code base to accommodate the requirements for system specific code and services (if any).
Your business goes on as usual in the production environment. You are still able to maintain (thus change and expand) the application software in the production environment. And you will be able to do so until the start of the implementation phase.
The automated part of this stage is repeatable and interacts with the next stage, Testing, which is the final step before implementing.