No, and that's the point. You can generate an OBI from AWS's or GCP's existing OpenAPI specs today with the ob CLI. An OBI is a unified primitive that tools can build on. You can generate OBIs ad hoc for your own consumption without the vendor knowing or caring. Vendor buy-in makes the ecosystem stronger, but it's not required to get value.

The longer game is vendor-published OBIs and shared interface roles (e.g. a neutral object-storage interface that S3 and GCS both satisfy), but one OBI, generated from specs that already exist, is still useful on day one.