anomalyco/opencode (formerly sst/opencode, 210k stars, MIT) splits the coding agent into a client layer and a server layer: the server exposes OpenAPI 3.1 plus an SDK generated from the spec, and the TUI is just one remote frontend of it, so a single session can be driven from a terminal, an IDE, GitHub Actions and ACP clients such as Zed. More than 75 providers plug in through the AI SDK and Models.dev, OpenCode Zen offers a curated gateway of models tested before listing, the 35+ built-in LSPs ship disabled with docs stating they are not always a net win, skills resolve from .opencode, .claude and .agents roots, and permissions are a three-state allow/ask/deny. It is the most engineering-first branch of open-source coding agents: interface before UI.