Which type of contract is most appropriate when you have not finalized the statement of work for additional software developers and testers?

The most suitable choice in this situation is a Time and Materials contract. This type of contract is designed to be flexible, accommodating situations where the scope of work is not fully defined. Since the statement of work for the additional software developers and testers has not been finalized, a Time and Materials contract allows for adjustments in hours worked and materials used as the project evolves.

This contract type facilitates paying for actual work performed (time) and materials consumed, which is essential when the specifics of the work are uncertain. It provides the client with the flexibility to adapt the project as more information becomes available, ensuring that developers and testers can be engaged immediately without waiting for detailed specifications.

In projects where requirements may change or are not fully established at the outset, this contract type can effectively manage the risks associated with scope creep and evolving project needs. Thus, this approach aligns well with the requirements of your scenario.