xAI Open-Sources Grok Build: Rust Agent Harness, TUI, and Tool Layer for Coding CLI

xAI has open-sourced Grok Build, the underlying infrastructure behind its Grok coding CLI, including the Rust-based agent harness, terminal UI (TUI), and tool integration layer. This release exposes the architectural skeleton of a production coding agent — specifically how xAI structures tool calls, manages agent state, and surfaces outputs in a terminal environment. For developers building their own CLI agents or coding assistants, this is a rare look at a real-world, production-grade agentic architecture written in Rust, which carries significant implications for performance and safety guarantees. The tool layer design in particular is worth studying for teams wrestling with how to structure function-calling and tool orchestration in long-running agent loops. This is a meaningful open-source drop for the agent tooling ecosystem, and Rust-native AI infrastructure is an underexplored area relative to the Python-dominant landscape.