ai4j is a multi-module Java SDK designed to accelerate AI application development on the JVM. It provides a unified interface for accessing diverse LLM providers including OpenAI, ChatGLM, DeepSeek, Moonshot, Tencent Hunyuan, and others, normalizing inputs and outputs to OpenAI compatibility. The SDK offers built-in support for tool calling, Model Context Protocol (MCP), and retrieval-augmented generation with VectorStore abstraction. It includes agent runtime capabilities, a coding agent module, and integrations with platforms like Dify, Coze, and n8n.