diff --git a/docs/supported-tools.md b/docs/supported-tools.md
index 389cfc77..2f9b6152 100644
--- a/docs/supported-tools.md
+++ b/docs/supported-tools.md
@@ -19,7 +19,7 @@ For each tool you select, OpenSpec installs:
 | Claude Code | `.claude/skills/` | `.claude/commands/opsx/` |
 | Cline | `.cline/skills/` | `.clinerules/workflows/` |
 | CodeBuddy | `.codebuddy/skills/` | `.codebuddy/commands/opsx/` |
-| Codex | `.codex/skills/` | `.codex/prompts/` |
+| Codex | `.codex/skills/` | `~/.codex/prompts/`* |
 | Continue | `.continue/skills/` | `.continue/prompts/` |
 | CoStrict | `.cospec/skills/` | `.cospec/openspec/commands/` |
 | Crush | `.crush/skills/` | `.crush/commands/opsx/` |
@@ -36,6 +36,8 @@ For each tool you select, OpenSpec installs:
 | Trae | `.trae/skills/` | `.trae/skills/` (via `/openspec-*`) |
 | Windsurf | `.windsurf/skills/` | `.windsurf/workflows/` |
 
+\* Codex commands are installed to the global home directory (`~/.codex/prompts/` or `$CODEX_HOME/prompts/`), not the project directory.
+
 ## Non-Interactive Setup
 
 For CI/CD or scripted setup, use the `--tools` flag:
diff --git a/openspec/changes/multi-provider-skill-generation/design.md b/openspec/changes/multi-provider-skill-generation/design.md
index bdf87183..c870aeae 100644
--- a/openspec/changes/multi-provider-skill-generation/design.md
+++ b/openspec/changes/multi-provider-skill-generation/design.md
@@ -18,7 +18,7 @@ Each AI tool has:
 - Create a generic, extensible command generation system
 
 **Non-Goals:**
-- Global path installation (deferred to future work)
+- Global path installation for tools other than Codex (Codex uses absolute adapter paths today)
 - Multi-tool generation in single command (future enhancement)
 - Unifying with existing SlashCommandConfigurator (separate systems for now)
 
@@ -41,7 +41,7 @@ interface AIToolOption {
 **Rationale**:
 - Skills follow Agent Skills spec: `<toolDir>/skills/` - suffix is standard
 - Commands need per-tool formatting, handled by adapters (not a simple path)
-- Global paths deferred - can extend interface later
+- Global paths supported — Codex adapter returns absolute paths via os.homedir()
 
 ### 2. Strategy/Adapter pattern for command generation
 
diff --git a/openspec/changes/multi-provider-skill-generation/specs/command-generation/spec.md b/openspec/changes/multi-provider-skill-generation/specs/command-generation/spec.md
index ce538282..26e8602c 100644
--- a/openspec/changes/multi-provider-skill-generation/specs/command-generation/spec.md
+++ b/openspec/changes/multi-provider-skill-generation/specs/command-generation/spec.md
@@ -30,7 +30,7 @@ The system SHALL define a `ToolCommandAdapter` interface for per-tool formatting
 - **WHEN** implementing a tool adapter
 - **THEN** `ToolCommandAdapter` SHALL require:
   - `toolId`: string identifier matching `AIToolOption.value`
-  - `getFilePath(commandId: string)`: returns relative file path for command
+  - `getFilePath(commandId: string)`: returns file path for command (relative from project root, or absolute for global-scoped tools like Codex)
   - `formatFile(content: CommandContent)`: returns complete file content with frontmatter
 
 #### Scenario: Claude adapter formatting
diff --git a/src/core/command-generation/adapters/codex.ts b/src/core/command-generation/adapters/codex.ts
index 1593dff2..64e73550 100644
--- a/src/core/command-generation/adapters/codex.ts
+++ b/src/core/command-generation/adapters/codex.ts
@@ -2,21 +2,34 @@
  * Codex Command Adapter
  *
  * Formats commands for Codex following its frontmatter specification.
+ * Codex custom prompts live in the global home directory (~/.codex/prompts/)
+ * and are not shared through the repository. The CODEX_HOME env var can
+ * override the default ~/.codex location.
  */
 
+import os from 'os';
 import path from 'path';
 import type { CommandContent, ToolCommandAdapter } from '../types.js';
 
+/**
+ * Returns the Codex home directory.
+ * Respects the CODEX_HOME env var, defaulting to ~/.codex.
+ */
+function getCodexHome(): string {
+  const envHome = process.env.CODEX_HOME?.trim();
+  return path.resolve(envHome ? envHome : path.join(os.homedir(), '.codex'));
+}
+
 /**
  * Codex adapter for command generation.
- * File path: .codex/prompts/opsx-<id>.md
+ * File path: <CODEX_HOME>/prompts/opsx-<id>.md (absolute, global)
  * Frontmatter: description, argument-hint
  */
 export const codexAdapter: ToolCommandAdapter = {
   toolId: 'codex',
 
   getFilePath(commandId: string): string {
-    return path.join('.codex', 'prompts', `opsx-${commandId}.md`);
+    return path.join(getCodexHome(), 'prompts', `opsx-${commandId}.md`);
   },
 
   formatFile(content: CommandContent): string {
diff --git a/src/core/command-generation/types.ts b/src/core/command-generation/types.ts
index 96a74d3b..582d8c78 100644
--- a/src/core/command-generation/types.ts
+++ b/src/core/command-generation/types.ts
@@ -33,9 +33,10 @@ export interface ToolCommandAdapter {
   /** Tool identifier matching AIToolOption.value (e.g., 'claude', 'cursor') */
   toolId: string;
   /**
-   * Returns the relative file path for a command.
+   * Returns the file path for a command.
    * @param commandId - The command identifier (e.g., 'explore')
-   * @returns Relative path from project root (e.g., '.claude/commands/opsx/explore.md')
+   * @returns Path from project root (e.g., '.claude/commands/opsx/explore.md').
+   *          May be absolute for tools with global-scoped prompts (e.g., Codex).
    */
   getFilePath(commandId: string): string;
   /**
@@ -50,7 +51,7 @@ export interface ToolCommandAdapter {
  * Result of generating a command file.
  */
 export interface GeneratedCommand {
-  /** Relative file path from project root */
+  /** File path from project root, or absolute for global-scoped tools */
   path: string;
   /** Complete file content (frontmatter + body) */
   fileContent: string;
diff --git a/src/core/init.ts b/src/core/init.ts
index a1f9f3cc..e4df6df3 100644
--- a/src/core/init.ts
+++ b/src/core/init.ts
@@ -452,7 +452,7 @@ export class InitCommand {
           const generatedCommands = generateCommands(commandContents, adapter);
 
           for (const cmd of generatedCommands) {
-            const commandFile = path.join(projectPath, cmd.path);
+            const commandFile = path.isAbsolute(cmd.path) ? cmd.path : path.join(projectPath, cmd.path);
             await FileSystemUtils.writeFile(commandFile, cmd.fileContent);
           }
         } else {
diff --git a/src/core/update.ts b/src/core/update.ts
index b395409c..6538bc0a 100644
--- a/src/core/update.ts
+++ b/src/core/update.ts
@@ -127,7 +127,7 @@ export class UpdateCommand {
           const generatedCommands = generateCommands(commandContents, adapter);
 
           for (const cmd of generatedCommands) {
-            const commandFile = path.join(resolvedProjectPath, cmd.path);
+            const commandFile = path.isAbsolute(cmd.path) ? cmd.path : path.join(resolvedProjectPath, cmd.path);
             await FileSystemUtils.writeFile(commandFile, cmd.fileContent);
           }
         }
@@ -376,7 +376,7 @@ export class UpdateCommand {
           const generatedCommands = generateCommands(commandContents, adapter);
 
           for (const cmd of generatedCommands) {
-            const commandFile = path.join(projectPath, cmd.path);
+            const commandFile = path.isAbsolute(cmd.path) ? cmd.path : path.join(projectPath, cmd.path);
             await FileSystemUtils.writeFile(commandFile, cmd.fileContent);
           }
         }
diff --git a/test/core/command-generation/adapters.test.ts b/test/core/command-generation/adapters.test.ts
index 1360f61c..1b0c94d3 100644
--- a/test/core/command-generation/adapters.test.ts
+++ b/test/core/command-generation/adapters.test.ts
@@ -1,4 +1,5 @@
 import { describe, it, expect } from 'vitest';
+import os from 'os';
 import path from 'path';
 import { amazonQAdapter } from '../../../src/core/command-generation/adapters/amazon-q.js';
 import { antigravityAdapter } from '../../../src/core/command-generation/adapters/antigravity.js';
@@ -205,9 +206,43 @@ describe('command-generation/adapters', () => {
       expect(codexAdapter.toolId).toBe('codex');
     });
 
-    it('should generate correct file path', () => {
+    it('should return an absolute path', () => {
+      const filePath = codexAdapter.getFilePath('explore');
+      expect(path.isAbsolute(filePath)).toBe(true);
+    });
+
+    it('should generate path ending with correct structure', () => {
       const filePath = codexAdapter.getFilePath('explore');
-      expect(filePath).toBe(path.join('.codex', 'prompts', 'opsx-explore.md'));
+      expect(filePath).toMatch(/prompts[/\\]opsx-explore\.md$/);
+    });
+
+    it('should default to homedir/.codex', () => {
+      const original = process.env.CODEX_HOME;
+      delete process.env.CODEX_HOME;
+      try {
+        const filePath = codexAdapter.getFilePath('explore');
+        const expected = path.join(os.homedir(), '.codex', 'prompts', 'opsx-explore.md');
+        expect(filePath).toBe(expected);
+      } finally {
+        if (original !== undefined) {
+          process.env.CODEX_HOME = original;
+        }
+      }
+    });
+
+    it('should respect CODEX_HOME env var', () => {
+      const original = process.env.CODEX_HOME;
+      process.env.CODEX_HOME = '/custom/codex-home';
+      try {
+        const filePath = codexAdapter.getFilePath('explore');
+        expect(filePath).toBe(path.join('/custom/codex-home', 'prompts', 'opsx-explore.md'));
+      } finally {
+        if (original !== undefined) {
+          process.env.CODEX_HOME = original;
+        } else {
+          delete process.env.CODEX_HOME;
+        }
+      }
     });
 
     it('should format file with description and argument-hint', () => {