The PDF4LHC21 combination of global PDF fits for the LHC Run III: an updated combination of the CT18, MSHT20 and NNPDF3.1 parton sets, PDF4LHC21, is presented in arXiv:2203.05506. The variant of the NNPDF3.1 determination that enters the combination, called NNPDF3.1.1, is documented in Sect. 2.3 of arXiv:2203.05506. The corresponding LHAPDF grid, made of 300 Monte Carlo replicas, is available as NNPDF311_nnlo_as_0118.tar.gz