The Open Trace Format Version 2 (OTF2) is a highly scalable, memory efficient event trace data format plus support library. It is the standard trace format for Scalasca, Vampir, and Tau and is open for other tools. OTF2 is available under the 3-clause BSD Open Source license. OTF2 is the common successor format for the Open Trace Format (OTF) and the Epilog trace format. It preserves the essential features as well as most record types of both and introduces new features such as support for multiple read/write substrates, in-place time stamp manipulation, and on-the-fly token translation. In particular, it will avoid copying during unification of parallel event streams. For features/changes/improvements introduced in the latest version, please see the ChangeLog file.