Introduction: Autoclaved Aerated Concrete (AAC) is a lightweight and energy‐efficient material which makes it one of the most convenient materials to be used in infill walls. Accordingly, AAC walls are becoming more and more favored infill systems in earthquake‐prone regions. Although the infills are not considered primary components in seismic design, they are highly susceptible to be damaged under seismic actions in in‐plane (IP) and out‐of‐plane (OOP) directions. Objective: Past post‐earthquake site surveys indicated that the failure of infill walls may result in severe casualties, injuries, and economic losses. In addition, damage to infills may hinder the functionality of critical buildings, which are expected to be in service after earthquakes. The application of horizontal bed‐joint reinforcement between infill courses is one of the promising solutions to increase the seismic resilience of infill walls. Methodology: This paper presents the experimental performance investigation of AAC infill walls with flat‐truss bed‐joint reinforcement being subjected to lateral loading in IP and OOP directions. The specimens represent relatively thin infills with a thickness of 150 mm, which are generally used in indoor environments. To consider the seismic actions in the IP direction, two full‐scale infill wall specimens (one unreinforced reference and one with flat‐truss reinforcement) built in reinforced concrete frames were first tested under reversed cyclic IP displacement reversals and then tested under the cyclic OOP displacements. Conclusions: The results revealed that the use of flat‐truss reinforcement enhanced the OOP strength, ultimate displacement, and energy dissipation capacity of infill walls that have been subjected to cyclic IP displacements previously. [ABSTRACT FROM AUTHOR]