Hy4 vs. Composer 2.5

Hy4 preview is an innovative open-source Mixture-of-Experts model designed for numerous practical productivity applications, such as software development, office tasks, game creation, and scientific research. With an astounding 770 billion parameters and 49 billion activated per token, it features a remarkable 1 million-token context window, enabling it to adeptly handle extensive codebases, large sets of documents, and intricate multi-step operations. The model's architecture incorporates 78 layers that utilize Gated DeepSeek Sparse Attention and IndexCache for efficient sparse index reuse across layers, while identity Hyper-Connections are implemented to improve information flow within the model. Furthermore, a specialized Multi-Token Prediction layer supports speculative decoding, significantly boosting its performance. Hy4 preview is engineered to understand, strategize, troubleshoot, and verify complex engineering initiatives, all while delivering substantial advancements in the quality of front-end visuals and interaction design, ultimately serving as an essential tool for experts in a wide range of fields. This versatility makes it an outstanding choice for professionals seeking to enhance their productivity and efficiency in various projects.

Composer 2.5 is Cursor’s newest AI-powered coding model, designed to significantly improve software development productivity through stronger reasoning, enhanced collaboration, and better handling of complex engineering tasks. Compared to Composer 2, the new release delivers major gains in sustained coding performance, allowing developers to work on larger and more complicated projects with improved reliability. The model was trained using expanded compute resources, more advanced reinforcement learning environments, and additional optimization techniques focused on both intelligence and usability. Cursor also refined behavioral aspects of the AI, including communication style and effort calibration, to make interactions feel more natural and productive during real-world coding sessions. A major feature of Composer 2.5 is its targeted reinforcement learning system with textual feedback, which provides localized corrections during training when the model makes mistakes such as invalid tool calls or style violations. This approach helps the AI understand exactly where errors occur and improves its decision-making more effectively than broad reward signals alone. The company further strengthened the model by training it on 25 times more synthetic coding tasks than Composer 2, exposing it to a wider range of difficult engineering challenges and edge cases. These synthetic tasks included feature deletion exercises where the model had to reconstruct missing functionality in real codebases using automated tests as validation signals. During large-scale training, Composer 2.5 demonstrated advanced problem-solving capabilities by reverse-engineering cached data and decompiling Java bytecode to recover deleted APIs in synthetic environments. Cursor also implemented sophisticated distributed training systems such as Sharded Muon and dual mesh HSDP, allowing efficient optimization across extremely large AI models and infrastructure clusters.