that is a very open question. Anaplan is very flexible so we do a lot of different thing and thus have a wide range of architecture. And even for the same use case, you can use two very different architecture depending on constraint such as number of users, volume of data, reporting level etc.
If you ask me what is the architecture of one of my work I'd answer you with:
- the list of models: data hub, model, reporting model etc
- the data flow between the sources, the data hub and the other models
- High level schema of the main parts of the models, with major structuring lists and important modules
- the number of users ans teams using these different models
I look at it from two different perspectives. One - Solution architecture, as what @nathan_rudman explained, which differs from solution to solution.
Another one is the software architecture which describes a database - application - middle tier - web client etc the technical components which makes up the software. Being a cloud product, it is not shared in public.