Open-Agent is an open-source agentic AI framework designed as an alternative to Claude Agent SDK and ChatGPT Agents. It enables multi-agent collaboration where multiple frontier models work together to complete tasks. The system integrates OpenAI, Claude, Gemini, and open-source models through a spec and context engineering approach that gives agents structure to plan, score, and surface options for decision-making. It is self-hostable and designed to be customized or extended as a foundation for dedicated agents.