Anthropic open-sources MCP, a standard for connecting AI assistants to data and tools. Within a year it was adopted by OpenAI, Google, Microsoft and most of the agent ecosystem — becoming the de-facto tool-connect layer of agent harnesses.
DeepSeek releases a macOS and Windows Desktop app for DeepSeek Harness, its open-source agent harness where everything — tools, sub-agents, even the loop — is a plugin. The repo passed 240k stars within three months of its August launch, making it the fastest-growing harness in the field's history.
The Best of Agent Harnesses list ranks 167 agent harnesses weekly by capability, autonomy and recovery, ships an MCP server so agents can pick their own harness, and maintains a graveyard that flagged a 268k-star repo for suspected star manipulation. Curation itself becomes harness infrastructure.
xAI open-sources Grok Build — a Rust coding agent harness and fullscreen TUI around Grok models — unusually early for a first-party tool. It joins Claude Code, Codex and Gemini CLI as the fourth major first-party harness, now with a fourth open one.
Anthropic began enforcing its terms against third-party clients using Claude Code subscriptions, forcing alternative harnesses like opencode to rework authentication (its issue thread became the debate's ground zero). A defining platform-risk moment for the open-harness ecosystem: the model provider owns the login, the harness does not.