Sandia National Laboratories recently released an open source code for design and analysis of axial‐flow and cross‐flow marine and hydrokinetic (MHK) turbines, CACTUS (Code for Axial and Cross‐flow TUrbine Simulation), and has initiated an outreach effort to promote its use among MHK researchers and developers. Our aim in this paper is to summarize the recent developments in CACTUS, and present model performance evaluation results that demonstrate CACTUS's potential use as a design and optimization tool for marine hydrokinetic turbines. We present several model validation tests to evaluate the model's ability to predict MHK turbine performance. The results show both the potential use of CACTUS as a design tool and its current limitations. At least two more model validation tests are planned for 2014 as part of this effort: scaled model tests of DOE's Reference Model 1(RM1) and Reference Model 2 (RM2) turbines in 2014 at the University of Minnesota's St. Anthony Falls Laboratory (SAFL).