modelcontextprotocol/go-sdk

This is an official reference implementation of the Model Context Protocol, co-maintained by Google. Its defensibility stems from its status as a category-defining standard. While the code itself is a protocol implementation, the network effects of the MCP ecosystem (integrating with Anthropic's Claude, Google's Gemini, etc.) create massive switching costs and community lock-in. Frontier labs are the primary drivers of this protocol, not competitors to it.