The inner 10-20 au of protoplanetary disks are the most interesting for studying (giant) planet formation. Whereas ALMA has revealed countless substructures in gas and dust at larger radii, the warm inner region has so far remained a mystery. Rovibrational line emission of CO at high spectral resolution provides information on the gas dynamics in this region, such as demonstrated by various surveys with e.g. CRIRES, NIRSPEC and iSHELL. The resulting CO line spectra reveal a diversity of line profiles, with kinematic evidence for gas gaps pointing towards the presence of protoplanets and disk winds which are related to evolutionary processes in the inner part of the disk. However, a clear picture of these physical processes is still missing, primarily because of the lack of spatially resolved information on the emission. In this talk I will present the latest insights on the interpretation of rovibrational CO spectra using our latest disk models and physical-chemical modeling, and the prospects for observations with METIS.