FlexCTC is a new open-source toolkit that provides fully GPU-based beam decoding for Connectionist Temporal Classification (CTC) models. It provides a fast, user-friendly, and highly scalable Python and PyTorch-based alternative to existing C++, CUDA, or WFST-based decoders. It features a high-performance, fully batched GPU implementation that eliminates CPU-GPU synchronization and minimizes kernel execution overhead via CUDA graphs. It also supports advanced contextualization techniques, such as GPU-based N-gram language model fusion and phrase-level boosting, enabling accurate and efficient decoding.