In the last two decades, the automotive software industry has undergone an enormous transformation from assembler hand-coding to model-based simulation with source code generation. With model-based development, the huge community of engineers gained the ability to create automotive software without knowledge of any programming language such as C or C++. On the other hand, from the perspective of Automotive SPICE, functional safety, and security, there are stringent requirements for specification of software detailed design regardless of whether the implementation is model based or not. The presentation shows how the software detailed design for model-based development can be structured to fulfill the requirements of ASPICE and ISO 26262 and bring sustainable benefits to the development organization and quality of the software product.