If it's like every single web browser for it, an insanely long amalgam of the user agent strings of every competing browser, every browser that came before it, and the word Spartan.
Or even worse, the UA of another browser verbatim, for "compability purposes".
Probably the same as IE Edge mode, which has disavowed its heritage completely: Mozilla/5.0 (Windows NT 6.4; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1985.143 Safari/537.36 Edge/12.0