In the eastern Islamicate lands of the fifth/eleventh century, New Persian was accruing political, cultural, and epistemic power even as the centuries-old imprimatur of Arabic remained strong. Composing poetry in Arabic, Persian, or indeed both became viable and meaningful options. Beyond translations between the Arabic and Persian, however, what has attracted less attention is the remarkable translation of poetic forms, which implies a more complex connection between the Arabic and Persian literary traditions than previously understood. On the one hand, Persian poetry’s debt to the Arabic tradition is well known: themes, motifs, and formal characteristics like quantitative metre and monorhyme were adapted into the Persian qaṣīda. On the other, as the old Arabocentric hegemony was challenged by a nascent Persianate prestige, Arabic poems began experimentally to take on distinctly Persian forms too. Dumyat al-qaṣr, a poetry anthology compiled by al-Bākharzī (d. 467/1075), includes several quatrains (rubāʿī) originally composed in Arabic. The rubāʿī being a quintessential Persian poetic form with its own non-Arabic metre, these poems are possibly the first attested instances of such a combination of form and language. Another instance is the qaṣīda composed by al-Ṭanṭarānī (fl. ca. 480/1087), significant for its use of the tarkīb-band form, which has a stanzaic rhyme scheme alien to the traditional monorhyme of Arabic poetry. Such experimental forms, fleeting as they may have been in the broader swathe of literary history, illustrate medieval Islamicate cosmopolitanisms in flux, when the boundaries between languages and traditions were unsettled and individuals could inhabit, benefit from, and reshape their multiple affiliations. I take the disciplinary boundary between classical Arabic and Persian literary studies as an invitation to theorise their contact zones and approach their texts from the multilingual, multiracial perspectives of their medieval producers.