xAI open-sources Grok Build, its 844K-line coding agent

xAI open-sourced Grok Build on July 15, publishing all 844,530 lines of its production coding agent's Rust code on GitHub under Apache 2.0. This is the harness xAI runs in production. That matters for anyone building a competing coding agent: the architecture decisions xAI already made are now free to study or copy.

Grok Build splits big jobs across subagents that run in parallel. Each one gets its own git worktree, so it can edit files without stepping on another subagent's unsaved work. That's the same isolation trick a lot of people building multi-agent setups end up needing. Now there's a production-grade version to copy instead of inventing it from scratch.

It also runs local-first. Point config.toml at your own inference setup after building from source, and none of it touches xAI's servers. The catch: Apache 2.0 is permissive, but this is still production code from a frontier lab. Read the license closely before anyone bolts it into a commercial product.

Reading the actual scheduler and worktree isolation code beats guessing at the pattern from a blog post. It's a rare look at how a frontier lab actually solved a problem most agent builders are still hacking around on their own. Grok Build isn't the only open release worth reading. trycua/cua adds the other half, agents that evaluate and operate on a real machine instead of a chat window.