A method and apparatus are provided for implementing modal selection of a bimodal coherent accelerator in a computer system. Implementing modal selection of a bimodal coherent accelerator using a PCI-Express standard Vendor Specific Extended Capability (VSEC) structure or CAPI VSEC data in the configuration space of a CAPI-capable PCIE adapter and procedures defined in the Coherent Accelerator Interface Architecture (CAIA) to enable and control a coherent coprocessor adapter over PCIE. A CAPI-capable PCIE adapter is enabled to be bimodal and operate in conventional PCI-Express (PCIE) transaction modes or CAPI modes that utilize CAIA coherence and programming interface capabilities.