Stimulates transcription elongation. Heterodimer composed of Spt4 and Spt5. Interacts with RNA polymerase (RNAP). Forms a homodimer in solution. Composed of only a NusG N-terminal (NGN) domain and a KOW domain, similar to bacterial NusG. The NGN domain is the effector domain of the complex that mediates the interaction with RNAP and is essential for elongation activity. Belongs to the archaeal Spt5 family.