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. 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:

PathContents

crates/codegen/xai-grok-pager-binComposition-root package; builds the xai-grok-pager binary

crates/codegen/xai-grok-pagerThe TUI: scrollback, prompt, modals, rendering

crates/codegen/xai-grok-shellAgent runtime plus leader/stdio/headless entry points

crates/codegen/xai-grok-toolsTool implementations (terminal, file edit, search)

crates/codegen/xai-grok-workspaceHost 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.

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~/.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?

AgentFirst-party licenseFork and modifyModel choiceExternal PRs

Grok Build (xai-org/grok-build)Apache 2.0PermittedAny, via config.tomlNot accepted

Codex CLI (openai/codex)Apache 2.0PermittedOpenAI modelsOpen PR queue

OpenCode (anomalyco/opencode)MITPermitted75+ providersCommunity project

Claude CodeProprietaryNot grantedAnthropic modelsn/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.

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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, the announcement, and the documentation.

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