Catalyzes the conversion of cobalt-precorrin-8 to cobyrinate. Co-precorrin-8X = cob(II)yrinate Cofactor biosynthesis; adenosylcobalamin biosynthesis; cob(II)yrinate a,c-diamide from sirohydrochlorin (anaerobic route): step 9/10. Homodimer. Belongs to the CobH/CbiC family.