This is Conn 84319, a soprano saxophone in C, concert key!
One could argue that this is the only saxophone type that requires no transposition of any kind. There exists a YouTube video somewhere, where Brandsma demonstrates it. Good luck finding it!
During 2 concerts, on May 13 & 14. 2017, with the wonderfull stride-pianist Jan-Hendrik Ehlers, the C-soprano could be heard in a short solo.