Given that Hattusa was to the south and Nerik likely further north, both of which had initially been Hattic speaking; that the Hattic language is found in the Sapinuwa archive alongside an apparent paucity of the Palaic language; and that the name of the city makes sense in Hattic as a theophoric (sapi "god", Sapinuwa "[land] of the god"), it is likely that Hattians founded Sapinuwa as well.
ɡˈɪvən ðæt hˈæɾuːsə wʌz tə ðə sˈaʊθ ænd nˈɛɹɪk lˈaɪkli fˈɜːðɚ nˈɔːɹθ, bˈoʊθ ʌvwˈɪtʃ hæd ɪnˈɪʃəli bˌɪn hˈæɾɪk spˈiːkɪŋ; ðætðə hˈæɾɪk lˈæŋɡwɪdʒ ɪz fˈaʊnd ɪnðə sˈæpɪnˌuːwə ˈɑːɹkaɪv ɐlˈɔŋsaɪd ɐn ɐpˈæɹənt pˈɔːsᵻɾi ʌvðə pælˈeɪɪk lˈæŋɡwɪdʒ; ænd ðætðə nˈeɪm ʌvðə sˈɪɾi mˌeɪks sˈɛns ɪn hˈæɾɪk æz ɐ θiːəfˈɔːɹɪk sˈæpi "ɡˈɑːd", sˈæpɪnˌuːwə "lˈænd ʌvðə ɡˈɑːd", ɪɾ ɪz lˈaɪkli ðæt hˈætiənz fˈaʊndᵻd sˈæpɪnˌuːwə æz wˈɛl.