The Acinetobacter baumannii bacteriophage Aci01-1 that belongs to the genus Saclayvirus of the Caudoviricetes order has an icosahedral head and a contractile rigid tail. We report that Aci01-1 has, attached to the tail conical tip, a remarkable 146 nm-long flexible fiber with seven beads and a terminal knot. Its putative gene coding for a 241.36 kDa tail fiber protein is homologous to genes in Aci01-1-related and unrelated phages. We also identified a putative receptor of the phage on the bacteria capsule that is hypothesized to interact with the Aci01-1 long fiber.