tl;dr: OpenCode 2.0 overhauls the AI coding agent with a persistent background client/server process that unifies TUI, web, and desktop clients, plus a rewritten API and new `@opencode/sdk` for embedding OpenCode as a library. It introduces "Code Mode," a minimal JS interpreter that converts MCP servers and OpenAPI endpoints into callable functions, letting agents compose tool calls in single scripts rather than sequential round trips. Other additions include background subagents and shell commands, hot-reloadable plugins (now powering 80+ internal features), and a stable TUI plugin API—though upgrading breaks 1.0 plugins and the old server API.