The Euramet.PR-K2.a comparison on spectral responsivity for the wavelength range 900 nm to 1600 nm, as described in this report, was carried out to establish the degree of equivalence for the participating European laboratories with respect to the Key Comparison Reference Value (KCRV) of the CCPR-K2.a-2003 comparison. Seven laboratories, including pilot and link laboratory, participated. The comparison was piloted by VSL (Netherlands). Both VSL and NPL (UK) act as link laboratories to the CCPR-K2.a-2003 comparison. Most laboratories show a DoE within 1 % from the CCPR KCRV for almost the full wavelength range, with some slightly larger differences mostly above 1450 nm. One laboratory shows larger deviations, up to 3%. This report provides an overview of the comparison, a description of the characterization of the reference detectors, the data-analysis, participant results and their uncertainties and the degree of equivalence of participating laboratories with the CCPR KCRV. The full Technical Reports of the participants are included in the Appendix of the comparison report. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCPR, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).