SpaceXAI Open-Sources Grok Build: The Rust Agent Harness, TUI, and Tool Layer Behind Its Coding CLI

SpaceXAI has open-sourced Grok Build, the terminal-based AI coding agent behind its grok CLI, under the Apache 2.0 license. The release includes the agent harness, TUI, CLI shell, and developer tooling, enabling fully local-first operation with any model via config.toml. The move positions Grok Build as a competitive open-source alternative to Codex CLI and Claude Code for AI-assisted coding.

SpaceXAI has open-sourced Grok Build , the terminal-based AI coding agent behind its grok CLI. The source landed on GitHub today. The release covers the agent harness, TUI, CLI shell, and developer tooling under the Apache 2.0 license What is Grok Build? A harness is the scaffolding around a model. It assembles context, calls the model, parses the reply, and dispatches tool calls. Grok Build was launched as an early beta on May 25, 2026. It is an agent that understands your codebase, edits files, executes shell commands, and searches the web. It also manages long-running tasks. It runs as a full-screen, mouse-interactive TUI. Three surfaces exist. There is the interactive TUI, headless mode for scripting and CI. Editors embed it through the Agent Client Protocol ACP . What does the published area contain? Building on that framing, SpaceXAI lists four published areas. The agent loop covers context assembly, response parsing, and tool-call dispatch. The tools cover how the agent reads, edits, and searches code. The terminal UI covers rendering, input handling, plan review, and the inline diff viewer. The extension system covers skills, plugins, hooks, MCP servers, and subagents. Those areas map onto named crates: | Path | Contents | |---|---| crates/codegen/xai-grok-pager-bin | Composition-root package; builds the xai-grok-pager binary | crates/codegen/xai-grok-pager | The TUI: scrollback, prompt, modals, rendering | crates/codegen/xai-grok-shell | Agent runtime plus leader/stdio/headless entry points | crates/codegen/xai-grok-tools | Tool implementations terminal, file edit, search | crates/codegen/xai-grok-workspace | Host filesystem, VCS, execution, checkpoints | third party/ | Vendored upstream source Mermaid diagram stack | Read that table as a reading order. Start at xai-grok-shell for the loop, then xai-grok-tools . One build note is easy to miss. The root Cargo.toml is generated, and the README says to treat it as read-only. How does the local-first path work? Beyond inspection, SpaceXAI frames one practical outcome. Grok Build can now run fully local-first. Compile it yourself, point it at local inference, and drive everything from config.toml . ~/.grok/config.toml Windows: %USERPROFILE%\.grok\config.toml model.my-model model = "model-id" base url = "https://api.example.com/v1" name = "Display Name" env key = "API KEY" models default = "my-model" grok inspect then prints what the harness discovered in the current directory. That covers config sources, instructions, skills, plugins, hooks, and MCP servers. How does Grok Build compare? | Agent | First-party license | Fork and modify | Model choice | External PRs | |---|---|---|---|---| Grok Build xai-org/grok-build | Apache 2.0 | Permitted | Any, via config.toml | Not accepted | Codex CLI openai/codex | Apache 2.0 | Permitted | OpenAI models | Open PR queue | OpenCode anomalyco/opencode | MIT | Permitted | 75+ providers | Community project | | Claude Code | Proprietary | Not granted | Anthropic models | n/a | Use cases and examples Given all of that, four uses hold up today. Audit before adoption : Read xai-grok-tools before letting an agent run shell commands in a regulated repo. Fork for an internal harness : Apache 2.0 permits it; upstream merge is not on offer. Air-gapped runs : Compile locally, set base url to an internal endpoint, and skip api.x.ai . CI automation : Headless mode feeds structured output into a pipeline step. Prebuilt binary macOS, Linux, Windows curl -fsSL https://x.ai/cli/install.sh | bash grok --version Or build from source needs protoc and the pinned Rust toolchain cargo build -p xai-grok-pager-bin --release - target/release/xai-grok-pager Audit path: per-crate commands, because full-workspace builds are slow cargo check -p xai-grok-tools cargo test -p xai-grok-config cargo clippy -p xai-grok-shell Headless run with machine-readable output grok -p "Explain the architecture" --output-format streaming-json Route one run through a model declared in ~/.grok/config.toml grok inspect grok -p "Hello" -m my-model Check out the GitHub Repo https://github.com/xai-org/grok-build , the announcement https://x.ai/news/grok-build-open-source , and the documentation https://docs.x.ai/build/overview . Michal Sutter is a data science professional with a Master of Science in Data Science from the University of Padova. With a solid foundation in statistical analysis, machine learning, and data engineering, Michal excels at transforming complex datasets into actionable insights.