Cassotis IME（言泉输入法） is a Chinese input method for Windows 10/11. Licensed under GPL-3.0, it has a very clear positioning: open source and auditable, local-first, and restrained in behavior. It emphasizes no bundling, no overreach, and no unauthorized changes to system settings. Candidate learning, user dictionaries, and configuration are kept on the local machine by default, making it suitable for users who are sensitive to input method privacy and system boundaries.
Cassotis IME is built on Windows TSF (Text Services Framework) and supports both Win64 and Win32 architectures. This makes it a relatively native Windows input method implementation rather than a wrapped or shell-based solution. Feature-wise, it includes the basics such as a status floating window, candidate list, input modes, Simplified/Traditional Chinese switching, and punctuation settings. For dictionaries, it builds separate base dictionaries for Simplified and Traditional Chinese, maintains the user dictionary separately, and supports full-sentence decoding. Candidate ranking uses bigram/trigram language-model learning to adapt to typing habits, while emphasizing that the data can be inspected, cleaned, and reset.
The project is licensed under GPL-3.0, with its code, dictionaries, and build scripts all publicly available for inspection, building, and modification. The main text does not mention any paid or commercial version. Given that installers are available via GitHub and the official website, it can be considered a free and open-source project. In terms of ecosystem, it currently focuses mainly on the Windows desktop input experience, offering a one-click x64 installer that includes TSF service registration, dictionary initialization, and a tray utility. The project also plans to improve its compatibility matrix for editors, browsers, and IDEs.
Its main strength is a clear privacy boundary: typed content is not uploaded to servers, there is no telemetry or log reporting, and learning data stays on the local machine. Being open source also reduces black-box risk. The downside is that the project is still iterating quickly, and benchmark results show that its Top-1 hit rate for long sentences still has room for improvement. The main text also does not indicate support for macOS, Linux, or mobile platforms, and there is no information on commercial support, APIs/SDKs, or enterprise services.
Cassotis IME is suitable for Windows users who type Chinese and care about privacy, dislike bundled promotions, and want transparent input method behavior. It is also useful for developers interested in studying open-source input method implementations. Access conditions from China are not specified in the main text. If GitHub downloads are unstable, trying the official website installer first may be preferable. Alternatives include RIME/小狼毫, Microsoft Pinyin, and Sogou Input Method.
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