diff --git a/.github/workflows/nodejs-sdk-tests.yml b/.github/workflows/nodejs-sdk-tests.yml
index 9e978a22f..9dec01667 100644
--- a/.github/workflows/nodejs-sdk-tests.yml
+++ b/.github/workflows/nodejs-sdk-tests.yml
@@ -62,6 +62,9 @@ jobs:
       - name: Typecheck SDK
         run: npm run typecheck
 
+      - name: Build SDK
+        run: npm run build
+
       - name: Install test harness dependencies
         working-directory: ./test/harness
         run: npm ci --ignore-scripts
diff --git a/nodejs/README.md b/nodejs/README.md
index e9d23c529..6a9059e20 100644
--- a/nodejs/README.md
+++ b/nodejs/README.md
@@ -850,6 +850,26 @@ try {
 - Node.js >= 18.0.0
 - GitHub Copilot CLI installed and in PATH (or provide custom `cliPath`)
 
+### CJS / CommonJS Support
+
+The SDK ships both ESM and CJS builds. Node.js and bundlers (esbuild, webpack, etc.) automatically select the correct format via the `exports` field in `package.json`:
+
+- `import` / `from` → ESM (`dist/index.js`)
+- `require()` → CJS (`dist/cjs/index.cjs`)
+
+This means the SDK works out of the box in CJS environments such as VS Code extensions bundled with `esbuild format:"cjs"`.
+
+### System-installed CLI (winget, brew, apt)
+
+If you installed the Copilot CLI separately rather than relying on the SDK's bundled copy, pass `cliPath` explicitly:
+
+```typescript
+const client = new CopilotClient({
+    cliPath: '/usr/local/bin/copilot',   // macOS/Linux
+    // cliPath: 'C:\\path\\to\\copilot.exe', // Windows (winget, etc.)
+});
+```
+
 ## License
 
 MIT
diff --git a/nodejs/esbuild-copilotsdk-nodejs.ts b/nodejs/esbuild-copilotsdk-nodejs.ts
index 059b8cfa6..f65a47236 100644
--- a/nodejs/esbuild-copilotsdk-nodejs.ts
+++ b/nodejs/esbuild-copilotsdk-nodejs.ts
@@ -4,6 +4,7 @@ import { execSync } from "child_process";
 
 const entryPoints = globSync("src/**/*.ts");
 
+// ESM build
 await esbuild.build({
     entryPoints,
     outbase: "src",
@@ -15,5 +16,22 @@ await esbuild.build({
     outExtension: { ".js": ".js" },
 });
 
+// CJS build — uses .js extension with a "type":"commonjs" package.json marker
+await esbuild.build({
+    entryPoints,
+    outbase: "src",
+    outdir: "dist/cjs",
+    format: "cjs",
+    platform: "node",
+    target: "es2022",
+    sourcemap: false,
+    outExtension: { ".js": ".js" },
+    logOverride: { "empty-import-meta": "silent" },
+});
+
+// Mark the CJS directory so Node treats .js files as CommonJS
+import { writeFileSync } from "fs";
+writeFileSync("dist/cjs/package.json", JSON.stringify({ type: "commonjs" }) + "\n");
+
 // Generate .d.ts files
 execSync("tsc", { stdio: "inherit" });
diff --git a/nodejs/package.json b/nodejs/package.json
index 214ef3466..6b0d30f2c 100644
--- a/nodejs/package.json
+++ b/nodejs/package.json
@@ -6,16 +6,28 @@
   },
   "version": "0.1.8",
   "description": "TypeScript SDK for programmatic control of GitHub Copilot CLI via JSON-RPC",
-  "main": "./dist/index.js",
+  "main": "./dist/cjs/index.js",
   "types": "./dist/index.d.ts",
   "exports": {
     ".": {
-      "import": "./dist/index.js",
-      "types": "./dist/index.d.ts"
+      "import": {
+        "types": "./dist/index.d.ts",
+        "default": "./dist/index.js"
+      },
+      "require": {
+        "types": "./dist/index.d.ts",
+        "default": "./dist/cjs/index.js"
+      }
     },
     "./extension": {
-      "import": "./dist/extension.js",
-      "types": "./dist/extension.d.ts"
+      "import": {
+        "types": "./dist/extension.d.ts",
+        "default": "./dist/extension.js"
+      },
+      "require": {
+        "types": "./dist/extension.d.ts",
+        "default": "./dist/cjs/extension.js"
+      }
     }
   },
   "type": "module",
diff --git a/nodejs/src/client.ts b/nodejs/src/client.ts
index b8e7b31dc..46d932242 100644
--- a/nodejs/src/client.ts
+++ b/nodejs/src/client.ts
@@ -14,6 +14,7 @@
 import { spawn, type ChildProcess } from "node:child_process";
 import { randomUUID } from "node:crypto";
 import { existsSync } from "node:fs";
+import { createRequire } from "node:module";
 import { Socket } from "node:net";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
@@ -91,14 +92,35 @@ function getNodeExecPath(): string {
 /**
  * Gets the path to the bundled CLI from the @github/copilot package.
  * Uses index.js directly rather than npm-loader.js (which spawns the native binary).
+ *
+ * In ESM, uses import.meta.resolve directly. In CJS (e.g., VS Code extensions
+ * bundled with esbuild format:"cjs"), import.meta is empty so we fall back to
+ * walking node_modules to find the package.
  */
 function getBundledCliPath(): string {
-    // Find the actual location of the @github/copilot package by resolving its sdk export
-    const sdkUrl = import.meta.resolve("@github/copilot/sdk");
-    const sdkPath = fileURLToPath(sdkUrl);
-    // sdkPath is like .../node_modules/@github/copilot/sdk/index.js
-    // Go up two levels to get the package root, then append index.js
-    return join(dirname(dirname(sdkPath)), "index.js");
+    if (typeof import.meta.resolve === "function") {
+        // ESM: resolve via import.meta.resolve
+        const sdkUrl = import.meta.resolve("@github/copilot/sdk");
+        const sdkPath = fileURLToPath(sdkUrl);
+        // sdkPath is like .../node_modules/@github/copilot/sdk/index.js
+        // Go up two levels to get the package root, then append index.js
+        return join(dirname(dirname(sdkPath)), "index.js");
+    }
+
+    // CJS fallback: the @github/copilot package has ESM-only exports so
+    // require.resolve cannot reach it. Walk the module search paths instead.
+    const req = createRequire(__filename);
+    const searchPaths = req.resolve.paths("@github/copilot") ?? [];
+    for (const base of searchPaths) {
+        const candidate = join(base, "@github", "copilot", "index.js");
+        if (existsSync(candidate)) {
+            return candidate;
+        }
+    }
+    throw new Error(
+        `Could not find @github/copilot package. Searched ${searchPaths.length} paths. ` +
+            `Ensure it is installed, or pass cliPath/cliUrl to CopilotClient.`
+    );
 }
 
 /**
diff --git a/nodejs/test/cjs-compat.test.ts b/nodejs/test/cjs-compat.test.ts
new file mode 100644
index 000000000..f57403725
--- /dev/null
+++ b/nodejs/test/cjs-compat.test.ts
@@ -0,0 +1,72 @@
+/**
+ * Dual ESM/CJS build compatibility tests
+ *
+ * Verifies that both the ESM and CJS builds exist and work correctly,
+ * so consumers using either module system get a working package.
+ *
+ * See: https://github.com/github/copilot-sdk/issues/528
+ */
+
+import { describe, expect, it } from "vitest";
+import { existsSync } from "node:fs";
+import { execFileSync } from "node:child_process";
+import { join } from "node:path";
+
+const distDir = join(import.meta.dirname, "../dist");
+
+describe("Dual ESM/CJS build (#528)", () => {
+    it("ESM dist file should exist", () => {
+        expect(existsSync(join(distDir, "index.js"))).toBe(true);
+    });
+
+    it("CJS dist file should exist", () => {
+        expect(existsSync(join(distDir, "cjs/index.js"))).toBe(true);
+    });
+
+    it("CJS build is requireable and exports CopilotClient", () => {
+        const script = `
+            const sdk = require(${JSON.stringify(join(distDir, "cjs/index.js"))});
+            if (typeof sdk.CopilotClient !== 'function') {
+                console.error('CopilotClient is not a function');
+                process.exit(1);
+            }
+            console.log('CJS require: OK');
+        `;
+        const output = execFileSync(process.execPath, ["--eval", script], {
+            encoding: "utf-8",
+            timeout: 10000,
+            cwd: join(import.meta.dirname, ".."),
+        });
+        expect(output).toContain("CJS require: OK");
+    });
+
+    it("CJS build resolves bundled CLI path", () => {
+        const script = `
+            const sdk = require(${JSON.stringify(join(distDir, "cjs/index.js"))});
+            const client = new sdk.CopilotClient({ autoStart: false });
+            console.log('CJS CLI resolved: OK');
+        `;
+        const output = execFileSync(process.execPath, ["--eval", script], {
+            encoding: "utf-8",
+            timeout: 10000,
+            cwd: join(import.meta.dirname, ".."),
+        });
+        expect(output).toContain("CJS CLI resolved: OK");
+    });
+
+    it("ESM build resolves bundled CLI path", () => {
+        const esmPath = join(distDir, "index.js");
+        const script = `
+            import { pathToFileURL } from 'node:url';
+            const sdk = await import(pathToFileURL(${JSON.stringify(esmPath)}).href);
+            const client = new sdk.CopilotClient({ autoStart: false });
+            console.log('ESM CLI resolved: OK');
+        `;
+        const output = execFileSync(process.execPath, ["--input-type=module", "--eval", script], {
+            encoding: "utf-8",
+            timeout: 10000,
+            cwd: join(import.meta.dirname, ".."),
+        });
+        expect(output).toContain("ESM CLI resolved: OK");
+    });
+});