These instances were used in The Third Parameterized Algorithms and Computational Experiments Challenge (PACE 2018) for the Steiner Tree problem.
Half of the instances were made public before the challenge (the odd instances) and the other half remained hidden until the conclusion of the challenge (the even instances). Details can be found in the official PACE 2018 report.
Track1 contains instances for the exact with low number of terminals track.
Track2 contains instances for the exact with low treewidth track.
Track3 contrains instances with larger instances for the heuristic track (note : there was a problem with instance58 and was therefore removed from the set).
More informations are on the PACE official website.
The instances are released under the CC0 license.
Format can be seen in the Appendix A of this page
Optimal values of solutions are given in the csv files. Lower/upper bounds are given for the heuristic track (if the optimum is known, they are equal).
See the PACE 2018 report for a list of known solvers with public repository as well as the ranking.