An extravascular neural interface is disclosed containing electrodes for neurostimulation of the vessel. The devices are housed in flexible substrates, each substrate having a spinal portion for routing leads/conductors into the device for connection to the electrodes. Extending from opposite sides of the spinal portion is a self-sizing inner flap that supports and positions the electrodes to be inward facing, i.e., extravascular designs, and one more rigid outer flap. The electrodes may be flexible multifilar coil electrodes.