**The Piauí Senate race for the two seats on October 4 remains highly competitive, with recent polls showing Marcelo Castro (MDB) in first and a tight contest for second between Júlio César (PSD) and Ciro Nogueira (PP).** Multiple surveys from mid-to-late September, including Amostragem, Datamax, and Datafolha, place the three main candidates within a few points of each other in stimulated scenarios, often separated by margins inside the error range, amid elevated undecided and blank/null responses exceeding 30-50% in some samples. Júlio César has gained ground in later polls, benefiting from explicit backing by President Lula and Governor Rafael Fonteles, while Ciro Nogueira faces the highest rejection rates (around 17%). Lower-polling names such as Tiago Junqueira trail significantly. With voters selecting two senators and the campaign in its final week, shifts in turnout or late preference consolidation among the leading trio could determine second place.