In what sense is the 38mm f2.8 Sonnar on the Contax T or T2 a Sonnar lens?

I am just after a bit of history of the lens design of the contax T or T2. The classic sonnar design is 7 elements in 3 groups (https://en.wikipedia.org/wiki/Zeiss_Sonnar) but the contax is 5 elements in 4 groups. So what characteristics are inherited from the classic sonnar design? For example, is the famed bokeh and transition to OOF areas preserved?

Look further back into the history of the Sonnar and you'll find the Ernostar design. This is helpful in understanding the later derivatives that diverge from the classic 6/3 or 7/3 Sonnar formulae.

Ah thanks!

https://en.wikipedia.org/wiki/History_of_photographic_lens_design#Ernostar_and_Sonnar

Still, how close is the 38mm f2.8 to these old designs?

Pretty close from what I've seen. Search for Ernostar and Contax T lens block diagrams and you'll see considerable similarity. Same goes for the Nikon 35/2.8 in the L35AF - there's a good Nikon historical piece on the development of that lens floating around on the web somewhere.