We investigate the morphological evolution of two linear ABC triblock terpolymers, poly(1,1-dimethylsilacyclobutane-block-styrene-block-methyl methacrylate) (PDMSB-b-PS-b-PMMA or DSM) and poly(1,1-dimethylsilacyclobutane-block-styrene-block-lactide) (PDMSB-b-PS-bPLA or DSL), in situ during solvent vapor annealing using grazing-incidence small-angle X-ray scattering. The morphology, orientation, and period of the microdomains are characterized under a continuous solvent vapor flow of CHCl3 as a function of swelling ratio and deswelling rate. The 90 nm thick films of DSM form in-plane core-shell cylinders, while DSL films of 150 nm thickness predominantly form out-of plane core-shell cylinders within perforated lamellae oriented parallel to the substrate. A reversible order-order phase transformation between spheres and cylinders and a reorientation from in-plane to out-of-plane cylinders occur during the annealing process.