CytonMT: an Efficient Neural Machine Translation Open-source Toolkit Implemented in C++. This paper presents an open-source neural machine translation toolkit named CytonMT ( The toolkit is built from scratch only using C++ and NVIDIA’s GPU-accelerated libraries. The toolkit features training efficiency, code simplicity and translation quality. Benchmarks show that CytonMT accelerates the training speed by 64.5% to 110.8% on neural networks of various sizes, and achieves competitive translation quality.