The optimization of post-buckling behavior remains a major challenge in the design of slender composite structures when pronounced nonlinear responses and imperfection sensitivity are present [1]. Accurate prediction of post-buckling performance therefore requires efficient computational strategies capable of capturing multiple equilibrium paths associated with imperfection effects . In this context, reduced-order models based on Koiter’s asymptotic analysis provide an effective framework for describing the post-buckling regime with limited computational cost [2]. However, their integration into gradient-based optimization procedures necessitates the accurate and consistent evaluation of derivatives of the objective function with respect to design variables, which is not straightforward for asymptotic formulations [3]. This work proposes an exact implicit algorithmic differentiation approach tailored to Koiter’s asymptotic analysis. The developed formulation enables the efficient and robust computation of analytical derivatives and is employed within a gradient-based optimization framework for the design of variable-angle tow composite slender structures. The proposed approach is evaluated in terms of both accuracy and computational efficiency, and its performance is benchmarked against conventional numerical differentiation techniques. REFERENCES [1] F.S. Liguori, A. Madeo, D. Magisano, L. Leonetti, G. Garcea, Post-buckling optimisation strategy of imperfection sensitive composite shells using Koiter method and Monte Carlo simulation, Composite Structures, Vol.192, pp.654-670, 2018. [2] G. Garcea, F.S. Liguori, L. Leonetti , D. Magisano, A. Madeo , Accurate and efficient a-posteriori account of geometrical imperfections in Koiter finite element analysis, International Journal for Numerical Methods in Engineering, Vol.112, pp.1154-1174, 2017. [3] F.S. Liguori, G. Zucco, A. Madeo, G. Garcea, L. Leonetti, P.M. Weaver, An isogeometric framework for the optimal design of variable stiffness shells undergoing large deformations, International Journal of Solids and Structures, Vol.210, pp.18-34, 2021.