diff --git a/apps/daemon/src/runtimes/defs/grok-build.ts b/apps/daemon/src/runtimes/defs/grok-build.ts
new file mode 100644
index 0000000000..404cbf7f90
--- /dev/null
+++ b/apps/daemon/src/runtimes/defs/grok-build.ts
@@ -0,0 +1,76 @@
+import { parseLineSeparatedModels, DEFAULT_MODEL_OPTION } from './shared.js';
+import type { RuntimeAgentDef } from '../types.js';
+
+// xAI's first-party CLI agent — https://x.ai/cli — distributed as the
+// `grok` binary. Installed via `curl -fsSL https://x.ai/cli/install.sh | bash`,
+// which symlinks `~/.grok/bin/grok` into PATH.
+//
+// `grok` ships its own SuperGrok OAuth dance (same `auth.x.ai` issuer +
+// loopback-redirect shape Open Design's xAI Settings panel uses), so it's
+// already authenticated by the time OD detects the binary; OD does not
+// need to inject credentials. Users authenticate once with `grok login
+// --oauth` and the resulting `~/.grok/auth.json` is what every spawned
+// invocation reads.
+//
+// Headless mode follows Claude Code's pattern (`-p <PROMPT>` for single-
+// turn, `--output-format streaming-json` for structured streaming), but
+// the streaming-json schema is xAI-specific and we do not yet have a
+// daemon-side parser for it. To ship the runtime now and let users at
+// least chat with grok inside OD, this defaults to `plain` streamFormat
+// (single-turn text reply, no tool_use streaming). Upgrading to a
+// `grok-stream-json` event parser is follow-up work once the format is
+// stable enough to lock in.
+export const grokBuildAgentDef = {
+  id: 'grok-build',
+  name: 'Grok Build',
+  bin: 'grok',
+  versionArgs: ['--version'],
+  helpArgs: ['-p', '--help'],
+  // `grok models` prints one model id per line, plus a `Default model:`
+  // header line that parseLineSeparatedModels strips because it isn't
+  // an id token. Falls back to the static list below when probing fails
+  // (no SuperGrok Heavy entitlement on this machine, network blip, etc.).
+  listModels: {
+    args: ['models'],
+    timeoutMs: 10_000,
+    parse: parseLineSeparatedModels,
+  },
+  fallbackModels: [
+    DEFAULT_MODEL_OPTION,
+    { id: 'grok-build', label: 'grok-build (xAI · default)' },
+    { id: 'grok-4.3', label: 'grok-4.3 (xAI)' },
+    { id: 'grok-4.20-reasoning', label: 'grok-4.20-reasoning (xAI · deep)' },
+    {
+      id: 'grok-4.20-non-reasoning',
+      label: 'grok-4.20-non-reasoning (xAI · fast)',
+    },
+    {
+      id: 'grok-4.20-multi-agent',
+      label: 'grok-4.20-multi-agent (xAI · orchestration)',
+    },
+  ],
+  // Prompt delivered via stdin so Windows `spawn ENAMETOOLONG` and Linux
+  // `spawn E2BIG` can't truncate large composed prompts. `grok -p` with
+  // no positional argument reads from piped stdin.
+  buildArgs: (_prompt, _imagePaths, _extra = [], options = {}) => {
+    const args = ['-p'];
+    if (options.model && options.model !== DEFAULT_MODEL_OPTION.id) {
+      args.push('--model', options.model);
+    }
+    if (options.reasoning) {
+      args.push('--effort', options.reasoning);
+    }
+    return args;
+  },
+  reasoningOptions: [
+    { id: 'low', label: 'low' },
+    { id: 'medium', label: 'medium' },
+    { id: 'high', label: 'high' },
+    { id: 'xhigh', label: 'xhigh' },
+    { id: 'max', label: 'max' },
+  ],
+  promptViaStdin: true,
+  streamFormat: 'plain',
+  installUrl: 'https://x.ai/cli',
+  docsUrl: 'https://x.ai/cli',
+} satisfies RuntimeAgentDef;
diff --git a/apps/daemon/src/runtimes/registry.ts b/apps/daemon/src/runtimes/registry.ts
index 200e80e3cb..72483c3fb8 100644
--- a/apps/daemon/src/runtimes/registry.ts
+++ b/apps/daemon/src/runtimes/registry.ts
@@ -4,6 +4,7 @@ import { devinAgentDef } from './defs/devin.js';
 import { geminiAgentDef } from './defs/gemini.js';
 import { opencodeAgentDef } from './defs/opencode.js';
 import { hermesAgentDef } from './defs/hermes.js';
+import { grokBuildAgentDef } from './defs/grok-build.js';
 import { kimiAgentDef } from './defs/kimi.js';
 import { cursorAgentDef } from './defs/cursor-agent.js';
 import { qwenAgentDef } from './defs/qwen.js';
@@ -24,6 +25,7 @@ const BASE_AGENT_DEFS: RuntimeAgentDef[] = [
   geminiAgentDef,
   opencodeAgentDef,
   hermesAgentDef,
+  grokBuildAgentDef,
   kimiAgentDef,
   cursorAgentDef,
   qwenAgentDef,
diff --git a/apps/web/public/agent-icons/grok-build.svg b/apps/web/public/agent-icons/grok-build.svg
new file mode 100644
index 0000000000..f26b8d81bc
--- /dev/null
+++ b/apps/web/public/agent-icons/grok-build.svg
@@ -0,0 +1,15 @@
+<!--
+  Geometric "X" silhouette evoking xAI's mathematical-double-struck X
+  brand mark (Unicode U+1D54F 𝕏). Drawn as simple straight strokes so
+  AgentIcon's mono mask path can paint it in the active theme color
+  alongside hermes / mimo / pi / kilo / cursor-agent. The fill is set
+  to a baked dark color so any non-masked render path still produces
+  a legible mark instead of black-on-black.
+-->
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024" fill="#1c1b1a">
+  <path d="M 158 158 L 432 432 L 158 432 L 158 158 Z" />
+  <path d="M 866 158 L 866 432 L 592 432 L 866 158 Z" />
+  <path d="M 432 592 L 158 592 L 158 866 L 432 592 Z" />
+  <path d="M 592 592 L 866 592 L 866 866 L 592 592 Z" />
+  <path d="M 432 432 L 592 432 L 592 592 L 432 592 L 432 432 Z" />
+</svg>
diff --git a/apps/web/src/components/AgentIcon.tsx b/apps/web/src/components/AgentIcon.tsx
index bdc1f9c05e..b2e8328df6 100644
--- a/apps/web/src/components/AgentIcon.tsx
+++ b/apps/web/src/components/AgentIcon.tsx
@@ -23,6 +23,7 @@ const ICON_EXT: Record<string, 'svg' | 'png'> = {
   deepseek: 'svg',
   mimo: 'svg',
   hermes: 'svg',
+  'grok-build': 'svg',
   kimi: 'svg',
   pi: 'svg',
   kiro: 'svg',
@@ -46,6 +47,7 @@ const MONO_ICONS = new Set([
   'mimo',
   'pi',
   'kilo',
+  'grok-build',
 ]);
 
 export function AgentIcon({ id, size = 36, className }: Props) {