This paper investigates how Finsler geometry influences the thermodynamic features of Kiselev-type black holes surrounded by various cosmic fluids, including dust, radiation, quintessence-like, and the cosmological constant. Using the Finslerian Ricci scalar ( \(\varvec{\eta }\) ) as a deformation parameter, we analyze how this geometric modification affects quantities such as mass, temperature, free energy, and heat capacity. The results show that \(\varvec{\eta }\) alters the stability conditions and phase transition points of the system while preserving key thermodynamic identities. In all considered cases, the Finslerian correction strengthens the black hole’s thermodynamic stability. It shifts its critical parameters, suggesting that such geometric extensions can make the system more robust without violating established universal relations. These findings highlight Finsler geometry as a proper framework for examining anisotropic effects in black hole thermodynamics and possible deviations from standard general relativity.
