Six AI leaders—OpenAI, Microsoft, GitHub, AWS, Vercel, and Anysphere—jointly released the Agent Plugins 1.0.0 open specification on August 6, standardizing the packaging of AI agent plugins. Developers can package plugins once and deploy them across multiple clients, including Cursor, GitHub Copilot, and Codex. The specification defines structures such as plugin.json manifests, skills, and mcp.json, but only standardizes the packaging layer, leaving core differentiators like hooks and custom agents untouched. Anthropic, the pioneer of the Claude Code plugin system, did not participate in its development, yet its format has been widely adopted. Google was added as a core maintainer on the day of the release. The specification aims to eliminate repetitive work by standardizing the directory structure, manifest file, and MCP configuration format, allowing any compatible client to recognize the package. This shift indicates that competition at the foundational level has moved to the battle for plugin ecosystem dominance—where the real contest lies in attracting the most developers.