diff --git a/src/execCmd.ts b/src/execCmd.ts
index 497eb4dc..dc0f1859 100644
--- a/src/execCmd.ts
+++ b/src/execCmd.ts
@@ -114,18 +114,21 @@ const getExitCodeError = (cmd: string, expectedCode: number, output: ShellString
  *
  * If the cli is 'inherit', the executable preference order is:
  *    1. TESTKIT_EXECUTABLE_PATH env var
- *    2. `bin/dev` (default)
+ *    2. `bin/dev.js` (default)
  *
  * @returns The command string with CLI executable. E.g., `"node_modules/bin/sf org:create:user -a testuser1"`
  */
 const determineExecutable = (cli: CLI = 'inherit'): string => {
   const debug = Debug('testkit:determineExecutable');
 
-  const bin =
+  let bin =
     cli === 'inherit'
       ? env.getString('TESTKIT_EXECUTABLE_PATH') ??
-        pathJoin(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev')
+        pathJoin(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev.js')
       : cli;
+
+  // Support plugins who still use bin/dev instead of bin/dev.js
+  if (bin.endsWith('dev.js') && !fs.existsSync(bin)) bin = bin.replace('.js', '');
   const which = shelljs.which(bin);
   let resolvedPath = pathResolve(bin);
 
diff --git a/test/unit/execCmd.test.ts b/test/unit/execCmd.test.ts
index e7748ce9..010b7f88 100644
--- a/test/unit/execCmd.test.ts
+++ b/test/unit/execCmd.test.ts
@@ -37,8 +37,8 @@ describe('execCmd (sync)', () => {
     sandbox.restore();
   });
 
-  it('should default to bin/dev executable', () => {
-    const binPath = join(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev');
+  it('should default to bin/dev.js executable', () => {
+    const binPath = join(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev.js');
     sandbox.stub(fs, 'existsSync').returns(true);
     sandbox.stub(shelljs, 'which').callsFake((x) => new ShellString(x));
     const shellString = new ShellString(JSON.stringify(output));
@@ -49,8 +49,20 @@ describe('execCmd (sync)', () => {
     expect(execStub.args[0][0]).to.include('2> stderr');
   });
 
-  it('should default to bin/dev executable when cli = inherit', () => {
+  it('should default to bin/dev executable if bin/dev.js does not exist', async () => {
     const binPath = join(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev');
+    sandbox.stub(fs, 'existsSync').withArgs(binPath).returns(false).withArgs(binPath.replace('.js', '')).returns(true);
+    sandbox.stub(shelljs, 'which').callsFake((x) => new ShellString(x));
+    const shellString = new ShellString(JSON.stringify(output));
+    const execStub = stubMethod(sandbox, shelljs, 'exec').returns(shellString);
+    execCmd(cmd);
+    expect(execStub.args[0][0]).to.include(`${binPath} ${cmd}`);
+    expect(execStub.args[0][0]).to.include('1> stdout');
+    expect(execStub.args[0][0]).to.include('2> stderr');
+  });
+
+  it('should default to bin/dev.js executable when cli = inherit', () => {
+    const binPath = join(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev.js');
     sandbox.stub(fs, 'existsSync').returns(true);
     sandbox.stub(shelljs, 'which').callsFake((x) => new ShellString(x));
     const shellString = new ShellString(JSON.stringify(output));
@@ -228,8 +240,8 @@ describe('execCmd (async)', () => {
     sandbox.restore();
   });
 
-  it('should default to bin/dev executable', async () => {
-    const binPath = join(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev');
+  it('should default to bin/dev.js executable', async () => {
+    const binPath = join(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev.js');
     sandbox.stub(fs, 'existsSync').returns(true);
     sandbox.stub(shelljs, 'which').callsFake((x) => new ShellString(x));
     const shellString = new ShellString(JSON.stringify(output));
@@ -240,6 +252,18 @@ describe('execCmd (async)', () => {
     expect(execStub.args[0][0]).to.match(/2> .*stderr.*txt/);
   });
 
+  it('should default to bin/dev executable if bin/dev.js does not exist', async () => {
+    const binPath = join(process.cwd(), 'bin', process.platform === 'win32' ? 'dev.cmd' : 'dev');
+    sandbox.stub(fs, 'existsSync').withArgs(binPath).returns(false).withArgs(binPath.replace('.js', '')).returns(true);
+    sandbox.stub(shelljs, 'which').callsFake((x) => new ShellString(x));
+    const shellString = new ShellString(JSON.stringify(output));
+    const execStub = stubMethod(sandbox, shelljs, 'exec').yields(0, shellString, '');
+    await execCmd(cmd, { async: true });
+    expect(execStub.args[0][0]).to.include(`${binPath} ${cmd}`);
+    expect(execStub.args[0][0]).to.match(/1> .*stdout.*txt/);
+    expect(execStub.args[0][0]).to.match(/2> .*stderr.*txt/);
+  });
+
   it('should accept valid sfdx path in env var', async () => {
     const binPath = join('@salesforce', 'cli', 'bin', 'sfdx');
     sandbox.stub(fs, 'existsSync').returns(true);