Four metagenome-assembled genomes (MAGs) from 40-kyr relic marine brines (cryopeg brines) trapped within the permafrost. Each of these genomes contained a full Calvin-Benson-Bassham pathway and was therefore considered autotrophic. The FASTA files for the MAGs are available, along with the gene annotations in gff format for the two Thiomicrorhabdus MAGs. Details on the methods are contained in the README.