To manage scope creep in a fixed-budget project under Agile methodologies, prioritize frequent communication and collaboration with stakeholders to maintain alignment on project goals and priorities. Employ iterative planning and delivery cycles, breaking down requirements into manageable chunks to facilitate flexibility and adaptability. Implement robust change management processes, requiring thorough evaluation of proposed changes against project objectives and budget constraints before incorporation. Continuously monitor project progress and scope against the budget, identifying and addressing any deviations promptly. Finally, empower the Product Owner to make informed decisions on scope adjustments, ensuring that changes add significant value within the fixed budget constraints.