Sumbel is attested in some of the oldest surviving Germanic literature, including scenes in Beowulf where warriors in the hall drink and speak in formal turns, and it is these literary and historical sources, rather than any unbroken line of practice, that modern Heathenry has worked from in reviving the rite. Old sources describe rounds with distinct purposes: an opening round toasting the gods, a round remembering ancestors and the dead, and a boasting or oath round in which a speaker might publicly commit to some future deed, a pledge the assembled company then witnessed and effectively held the speaker to. That last function gave sumbel real social weight in the world the sagas describe, since a boast made over the horn in front of one's peers was a serious, witnessed undertaking rather than a private resolution.
Because organized Germanic religious practice lapsed for centuries before its modern revival, scholars and practitioners alike are candid that the reconstructed rite fills gaps in the sources with reasoned inference rather than continuous transmission, and Heathen communities differ over how closely a modern sumbel should mirror the saga accounts versus function more informally as a structured round of toasts and memories among friends, with the binding, oath sworn quality of the old sources present in spirit rather than in legal force.