 Swarm V2 is a novel and open source Amplicon clustering program that produces fine scale molecular operational taxonomic units, OTUs. It works with an initial phase that uses iterative single linkage with a local clustering threshold, D, followed by a phase that uses the internal abundant structures of clusters to break chained OTUs. Additionally, it has two important novel features. One, a new algorithm for D equals one that allows the computation time of the program to scale linearly with increasing amounts of data. And, two, the new fastidious option that reduces under grouping by grafting low abundant OTUs, singletons and doubletons, onto larger ones. The program also directly integrates the clustering and breaking phases, D-replicate sequencing reads with D equals zero, outputs OTU representatives in faster format, and plots individual OTUs as two-dimensional networks. This article was authored by Frederic Mahe, Torbjorn Rohns, Christopher Quince, and others. We are article.tv, links in the description below.