diff --git a/src/cli.ts b/src/cli.ts
index 337cbab1..c2bc0913 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -149,7 +149,7 @@ program
     console.log("  mex check --quiet      One-liner drift score");
     console.log("  mex check --json       Full drift report as JSON");
     console.log("  mex check --fix        Check and fix any errors found");
-    console.log("  mex sync               Fix drift — Claude updates only what's broken");
+    console.log("  mex sync               Fix drift — AI updates only what's broken");
     console.log("  mex sync --dry-run     Preview fix prompts without running them");
     console.log("  mex sync --warnings    Include warning-only files in sync");
     console.log("  mex init               Pre-scan codebase, build brief for AI");
diff --git a/src/config.ts b/src/config.ts
index 82147e73..c210f73a 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -1,6 +1,6 @@
-import { existsSync } from "node:fs";
+import { existsSync, readFileSync, writeFileSync, mkdirSync } from "node:fs";
 import { resolve, dirname } from "node:path";
-import type { MexConfig } from "./types.js";
+import type { MexConfig, AiTool } from "./types.js";
 
 /**
  * Walk up from startDir looking for .git to find project root,
@@ -35,7 +35,8 @@ export function findConfig(startDir?: string): MexConfig {
     );
   }
 
-  return { projectRoot, scaffoldRoot };
+  const aiTools = loadAiTools(scaffoldRoot);
+  return { projectRoot, scaffoldRoot, aiTools };
 }
 
 function findProjectRoot(dir: string): string | null {
@@ -50,6 +51,47 @@ function findProjectRoot(dir: string): string | null {
   }
 }
 
+// ── AI Tool persistence ──
+
+const CONFIG_FILE = "config.json";
+
+interface MexPersistedConfig {
+  aiTools?: unknown;
+  [key: string]: unknown;
+}
+
+const VALID_AI_TOOLS = new Set<string>(["claude", "cursor", "windsurf", "copilot", "opencode", "codex"]);
+
+function loadAiTools(scaffoldRoot: string): AiTool[] {
+  const configPath = resolve(scaffoldRoot, CONFIG_FILE);
+  if (!existsSync(configPath)) return [];
+  try {
+    const raw = JSON.parse(readFileSync(configPath, "utf-8"));
+    if (typeof raw !== "object" || raw === null || Array.isArray(raw)) return [];
+    const arr = (raw as MexPersistedConfig).aiTools;
+    if (!Array.isArray(arr)) return [];
+    return arr.filter((v): v is AiTool => typeof v === "string" && VALID_AI_TOOLS.has(v));
+  } catch {
+    return [];
+  }
+}
+
+export function saveAiTools(scaffoldRoot: string, tools: AiTool[]): void {
+  const configPath = resolve(scaffoldRoot, CONFIG_FILE);
+  let existing: Record<string, unknown> = {};
+  if (existsSync(configPath)) {
+    try {
+      const raw = JSON.parse(readFileSync(configPath, "utf-8"));
+      if (typeof raw === "object" && raw !== null && !Array.isArray(raw)) {
+        existing = raw as Record<string, unknown>;
+      }
+    } catch { /* start fresh */ }
+  }
+  existing.aiTools = [...new Set(tools)];
+  mkdirSync(dirname(configPath), { recursive: true });
+  writeFileSync(configPath, JSON.stringify(existing, null, 2) + "\n");
+}
+
 function findScaffoldRoot(projectRoot: string): string | null {
   // Prefer .mex/ directory
   const mexDir = resolve(projectRoot, ".mex");
diff --git a/src/setup/index.ts b/src/setup/index.ts
index 96ee9614..7a168381 100644
--- a/src/setup/index.ts
+++ b/src/setup/index.ts
@@ -11,6 +11,8 @@ import {
   buildExistingWithBriefPrompt,
   buildExistingNoBriefPrompt,
 } from "./prompts.js";
+import { saveAiTools } from "../config.js";
+import type { AiTool } from "../types.js";
 
 // ── Constants ──
 
@@ -197,7 +199,7 @@ export async function runSetup(opts: { dryRun?: boolean } = {}): Promise<void> {
     try {
       info("Scanning codebase...");
       const { runScan } = await import("../scanner/index.js");
-      const config = { projectRoot, scaffoldRoot: mexDir };
+      const config = { projectRoot, scaffoldRoot: mexDir, aiTools: [] as AiTool[] };
       const result = await runScan(config, { jsonOnly: true });
       scannerBrief = JSON.stringify(result, null, 2);
       ok("Pre-analysis complete — AI will reason from brief instead of exploring");
@@ -302,6 +304,15 @@ function detectProjectState(projectRoot: string, mexDir: string): ProjectState {
   }
 }
 
+const TOOL_CHOICE_MAP: Record<string, AiTool> = {
+  "1": "claude",
+  "2": "cursor",
+  "3": "windsurf",
+  "4": "copilot",
+  "5": "opencode",
+  "6": "codex",
+};
+
 async function selectToolConfig(
   rl: ReturnType<typeof createInterface>,
   projectRoot: string,
@@ -322,12 +333,15 @@ async function selectToolConfig(
   const choice = (await rl.question("Choice [1-8] (default: 1): ")).trim() || "1";
 
   let selectedClaude = false;
+  const selectedTools: AiTool[] = [];
 
   const copyConfig = (key: string) => {
     const config = TOOL_CONFIGS[key];
     if (!config) return;
 
     if (key === "1") selectedClaude = true;
+    const tool = TOOL_CHOICE_MAP[key];
+    if (tool) selectedTools.push(tool);
 
     const src = resolve(TEMPLATES_DIR, config.src);
     const dest = resolve(projectRoot, config.dest);
@@ -377,6 +391,12 @@ async function selectToolConfig(
       break;
   }
 
+  // Persist tool selection
+  if (selectedTools.length > 0 && !dryRun) {
+    const mexDir = resolve(projectRoot, ".mex");
+    saveAiTools(mexDir, selectedTools);
+  }
+
   return selectedClaude;
 }
 
diff --git a/src/sync/index.ts b/src/sync/index.ts
index 276c187e..841cd9f8 100644
--- a/src/sync/index.ts
+++ b/src/sync/index.ts
@@ -1,7 +1,8 @@
 import chalk from "chalk";
-import { spawnSync } from "node:child_process";
+import { spawnSync, execSync } from "node:child_process";
 import { createInterface } from "node:readline";
-import type { MexConfig, SyncTarget, DriftIssue } from "../types.js";
+import type { MexConfig, SyncTarget, DriftIssue, AiTool } from "../types.js";
+import { AI_TOOLS } from "../types.js";
 import { runDriftCheck } from "../drift/index.js";
 import { buildSyncBrief, buildCombinedBrief } from "./brief-builder.js";
 
@@ -15,8 +16,21 @@ function askUser(question: string): Promise<string> {
   });
 }
 
-function runClaudeInteractive(brief: string, cwd: string): boolean {
-  const result = spawnSync("claude", [brief], {
+function hasCliTool(cmd: string): boolean {
+  try {
+    execSync(`which ${cmd}`, { stdio: "ignore" });
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+function runToolInteractive(tool: AiTool, brief: string, cwd: string): boolean {
+  const meta = AI_TOOLS[tool];
+  if (!meta.cli) return false;
+
+  const args = [...meta.promptFlag, brief];
+  const result = spawnSync(meta.cli, args, {
     cwd,
     stdio: "inherit",
     timeout: 300_000,
@@ -24,6 +38,30 @@ function runClaudeInteractive(brief: string, cwd: string): boolean {
   return result.status === 0 || result.status === null;
 }
 
+/** Pick which AI tool to use for interactive sync */
+async function pickSyncTool(configuredTools: AiTool[]): Promise<AiTool | null> {
+  // Filter to tools that have a CLI and are installed
+  const available = configuredTools.filter((t) => {
+    const meta = AI_TOOLS[t];
+    return meta.cli && hasCliTool(meta.cli);
+  });
+
+  if (available.length === 0) return null;
+  if (available.length === 1) return available[0];
+
+  // Multiple CLI tools available — ask user
+  console.log(chalk.bold("\nWhich tool should fix these?"));
+  console.log();
+  available.forEach((t, i) => {
+    console.log(`  ${i + 1}) ${AI_TOOLS[t].name}`);
+  });
+  console.log();
+
+  const choice = await askUser(`Choice [1-${available.length}] (default: 1): `);
+  const idx = parseInt(choice || "1", 10) - 1;
+  return available[idx] ?? available[0];
+}
+
 type SyncMode = "interactive" | "prompts";
 
 /** Run targeted sync: detect → brief → AI → verify → ask → loop */
@@ -33,6 +71,7 @@ export async function runSync(
 ): Promise<void> {
   let cycle = 0;
   let mode: SyncMode | null = null;
+  let activeTool: AiTool | null = null;
 
   while (true) {
     cycle++;
@@ -107,9 +146,17 @@ export async function runSync(
 
     // Ask user for mode (only on first cycle)
     if (mode === null) {
+      // Determine if any configured tool has a usable CLI
+      const syncTool = await pickSyncTool(config.aiTools);
+      const toolName = syncTool ? AI_TOOLS[syncTool].name : null;
+
       console.log(chalk.bold("\nHow should we fix these?"));
       console.log();
-      console.log("  1) Interactive — Claude fixes with you watching (default)");
+      if (toolName) {
+        console.log(`  1) Interactive — ${toolName} fixes with you watching (default)`);
+      } else {
+        console.log("  1) Interactive — AI fixes with you watching (default)");
+      }
       console.log("  2) Show prompts — I'll paste manually");
       console.log("  3) Exit");
       console.log();
@@ -119,7 +166,15 @@ export async function runSync(
 
       switch (picked) {
         case "1":
-          mode = "interactive";
+          if (!syncTool) {
+            console.log(chalk.yellow("No supported AI CLI detected. Falling back to prompts mode."));
+            console.log(chalk.dim("Supported CLIs: claude, opencode, codex"));
+            console.log();
+            mode = "prompts";
+          } else {
+            activeTool = syncTool;
+            mode = "interactive";
+          }
           break;
         case "2":
           mode = "prompts";
@@ -143,13 +198,14 @@ export async function runSync(
 
     // Step 3: Fix all files in one interactive session
     console.log();
-    console.log(chalk.bold(`\nSending all ${targets.length} file(s) to Claude in one session...\n`));
+    const toolLabel = activeTool ? AI_TOOLS[activeTool].name : "AI";
+    console.log(chalk.bold(`\nSending all ${targets.length} file(s) to ${toolLabel} in one session...\n`));
 
     const brief = await buildCombinedBrief(targets, config.projectRoot);
-    const ok = runClaudeInteractive(brief, config.projectRoot);
+    const ok = runToolInteractive(activeTool!, brief, config.projectRoot);
 
     if (!ok) {
-      console.log(chalk.red("  ✗ Claude session failed"));
+      console.log(chalk.red(`  ✗ ${toolLabel} session failed`));
     }
 
     // Step 4: Verify
diff --git a/src/types.ts b/src/types.ts
index 9efbc517..ac100c3a 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1,5 +1,25 @@
 // ── Shared Types ──
 
+// ── AI Tool ──
+
+export type AiTool = "claude" | "cursor" | "windsurf" | "copilot" | "opencode" | "codex";
+
+export interface AiToolMeta {
+  name: string;
+  cli: string | null;
+  /** CLI flag to pass a prompt string directly */
+  promptFlag: string[];
+}
+
+export const AI_TOOLS: Record<AiTool, AiToolMeta> = {
+  claude:   { name: "Claude Code", cli: "claude",   promptFlag: [] },
+  cursor:   { name: "Cursor",      cli: null,       promptFlag: [] },
+  windsurf: { name: "Windsurf",    cli: null,       promptFlag: [] },
+  copilot:  { name: "Copilot",     cli: null,       promptFlag: [] },
+  opencode: { name: "OpenCode",    cli: "opencode", promptFlag: ["run"] },
+  codex:    { name: "Codex",       cli: "codex",    promptFlag: [] },
+};
+
 // ── Config ──
 
 export interface MexConfig {
@@ -7,6 +27,8 @@ export interface MexConfig {
   projectRoot: string;
   /** Absolute path to scaffold root (.mex/ directory) */
   scaffoldRoot: string;
+  /** Which AI tool(s) the user selected during setup */
+  aiTools: AiTool[];
 }
 
 // ── Claims (extracted from markdown) ──
diff --git a/test/config.test.ts b/test/config.test.ts
index 422a5cc9..d36b1176 100644
--- a/test/config.test.ts
+++ b/test/config.test.ts
@@ -1,8 +1,8 @@
 import { describe, it, expect, beforeEach, afterEach } from "vitest";
-import { mkdtempSync, mkdirSync, rmSync, writeFileSync } from "node:fs";
+import { mkdtempSync, mkdirSync, rmSync, writeFileSync, readFileSync, existsSync } from "node:fs";
 import { join } from "node:path";
 import { tmpdir } from "node:os";
-import { findConfig } from "../src/config.js";
+import { findConfig, saveAiTools } from "../src/config.js";
 
 let tmpDir: string;
 
@@ -63,4 +63,52 @@ describe("findConfig", () => {
     const config = findConfig(tmpDir);
     expect(config.scaffoldRoot).toBe(mexPath);
   });
+
+  it("returns empty aiTools when no config.json exists", () => {
+    mkdirSync(join(tmpDir, ".git"));
+    const mexPath = join(tmpDir, ".mex");
+    mkdirSync(mexPath);
+    writeFileSync(join(mexPath, "ROUTER.md"), "");
+    const config = findConfig(tmpDir);
+    expect(config.aiTools).toEqual([]);
+  });
+
+  it("loads aiTools from config.json when present", () => {
+    mkdirSync(join(tmpDir, ".git"));
+    const mexPath = join(tmpDir, ".mex");
+    mkdirSync(mexPath);
+    writeFileSync(join(mexPath, "ROUTER.md"), "");
+    writeFileSync(join(mexPath, "config.json"), JSON.stringify({ aiTools: ["opencode", "claude"] }));
+    const config = findConfig(tmpDir);
+    expect(config.aiTools).toEqual(["opencode", "claude"]);
+  });
+});
+
+describe("saveAiTools", () => {
+  it("creates config.json with aiTools", () => {
+    const mexPath = join(tmpDir, ".mex");
+    mkdirSync(mexPath, { recursive: true });
+    saveAiTools(mexPath, ["opencode"]);
+    const raw = JSON.parse(readFileSync(join(mexPath, "config.json"), "utf-8"));
+    expect(raw.aiTools).toEqual(["opencode"]);
+  });
+
+  it("preserves existing config keys when saving", () => {
+    const mexPath = join(tmpDir, ".mex");
+    mkdirSync(mexPath, { recursive: true });
+    writeFileSync(join(mexPath, "config.json"), JSON.stringify({ someOther: true }));
+    saveAiTools(mexPath, ["codex"]);
+    const raw = JSON.parse(readFileSync(join(mexPath, "config.json"), "utf-8"));
+    expect(raw.aiTools).toEqual(["codex"]);
+    expect(raw.someOther).toBe(true);
+  });
+
+  it("overwrites previous aiTools value", () => {
+    const mexPath = join(tmpDir, ".mex");
+    mkdirSync(mexPath, { recursive: true });
+    saveAiTools(mexPath, ["claude"]);
+    saveAiTools(mexPath, ["opencode", "codex"]);
+    const raw = JSON.parse(readFileSync(join(mexPath, "config.json"), "utf-8"));
+    expect(raw.aiTools).toEqual(["opencode", "codex"]);
+  });
 });