diff --git a/driver/lib/sessions/ios.ts b/driver/lib/sessions/ios.ts
index feedb04c..3f638393 100644
--- a/driver/lib/sessions/ios.ts
+++ b/driver/lib/sessions/ios.ts
@@ -26,7 +26,7 @@ export async function startIOSSession(
   ...args: any[]
 ): Promise<[XCUITestDriver, IsolateSocket | null]> {
   this.log.info(`Starting an IOS proxy session`);
-  injectDartVmServicePortFlags(caps);
+  injectDartVmServicePortFlags(caps, args);
   const iosdriver = new XCUITestDriver({} as XCUITestDriverOpts);
   if (!caps.observatoryWsUri) {
     iosdriver.eventEmitter.once('syslogStarted', (syslog) => {
@@ -249,10 +249,17 @@ async function ensureDeviceLogCaptureStarted(
  * Other entries (including a user-supplied `--observatory-port=*`) are left
  * untouched.
  *
+ * `caps` is the driver's own processed copy, while XCUITest is started from the
+ * raw W3C capabilities in `w3cCapsList`, so the resulting `processArguments` are
+ * mirrored into each of their `alwaysMatch` (and dropped from `firstMatch` to
+ * avoid a duplicate-key validation error). Otherwise the flags never reach the
+ * app under test.
+ *
  * If `dartVmServicePort` is not set, the caps are left untouched.
- * @param caps The W3C capabilities passed to the driver session.
+ * @param caps The processed capabilities of the driver session.
+ * @param w3cCapsList The raw W3C capabilities forwarded to XCUITest.
  */
-function injectDartVmServicePortFlags(caps: Record<string, any>): void {
+function injectDartVmServicePortFlags(caps: Record<string, any>, w3cCapsList: any[] = []): void {
   const port = caps.dartVmServicePort;
   if (typeof port !== 'number') {
     return;
@@ -265,6 +272,16 @@ function injectDartVmServicePortFlags(caps: Record<string, any>): void {
     filtered.push(DISABLE_SERVICE_AUTH_CODES_FLAG);
   }
   caps.processArguments.args = filtered;
+
+  for (const w3cCaps of w3cCapsList) {
+    if (!w3cCaps?.alwaysMatch || typeof w3cCaps.alwaysMatch !== 'object') {
+      continue;
+    }
+    w3cCaps.alwaysMatch['appium:processArguments'] = caps.processArguments;
+    for (const firstMatch of Array.isArray(w3cCaps.firstMatch) ? w3cCaps.firstMatch : []) {
+      delete firstMatch?.['appium:processArguments'];
+    }
+  }
 }
 
 async function requireFreePort(this: FlutterDriver, port: number) {
diff --git a/driver/test/ios-dart-vm-service-port.test.mjs b/driver/test/ios-dart-vm-service-port.test.mjs
new file mode 100644
index 00000000..95a6ff7c
--- /dev/null
+++ b/driver/test/ios-dart-vm-service-port.test.mjs
@@ -0,0 +1,60 @@
+import assert from 'node:assert/strict';
+import {afterEach, beforeEach, it, mock} from 'node:test';
+
+import {XCUITestDriver} from 'appium-xcuitest-driver';
+
+import {startIOSSession} from '../build/lib/sessions/ios.js';
+
+const noopLog = {info() {}, debug() {}, warn() {}, error() {}};
+const w3cCaps = (alwaysMatch = {}, firstMatch = [{}]) => ({alwaysMatch, firstMatch});
+
+let forwardedArgs;
+
+beforeEach(() => {
+  forwardedArgs = undefined;
+  mock.method(XCUITestDriver.prototype, 'createSession', async (...args) => {
+    forwardedArgs = args;
+  });
+});
+
+afterEach(() => mock.restoreAll());
+
+// Without `app`/`bundleId`, startIOSSession returns right after creating the XCUITest session,
+// so these tests only exercise what gets forwarded to XCUITest.
+const start = (caps, ...args) => startIOSSession.call({log: noopLog}, caps, ...args);
+
+it('forwards the injected VM service flags to XCUITest', async () => {
+  const caps = {dartVmServicePort: 9123, processArguments: {args: ['--foo'], env: {A: '1'}}};
+  const forwarded = w3cCaps({'appium:dartVmServicePort': 9123}, [
+    {'appium:processArguments': {args: ['--foo'], env: {A: '1'}}},
+  ]);
+
+  await start(caps, forwarded, undefined, {});
+
+  assert.equal(forwardedArgs[0], forwarded);
+  assert.deepEqual(forwarded.alwaysMatch['appium:processArguments'], {
+    args: ['--foo', '--vm-service-port=9123', '--disable-service-auth-codes'],
+    env: {A: '1'},
+  });
+  assert.deepEqual(forwarded.firstMatch, [{}]);
+});
+
+it('replaces a user-supplied --vm-service-port with the capability value', async () => {
+  const caps = {dartVmServicePort: 9123, processArguments: {args: ['--vm-service-port=1']}};
+  const forwarded = w3cCaps();
+
+  await start(caps, forwarded);
+
+  assert.deepEqual(forwardedArgs[0].alwaysMatch['appium:processArguments'].args, [
+    '--vm-service-port=9123',
+    '--disable-service-auth-codes',
+  ]);
+});
+
+it('forwards the W3C caps unchanged when dartVmServicePort is not set', async () => {
+  const forwarded = w3cCaps({'appium:app': 'x'});
+
+  await start({}, forwarded);
+
+  assert.deepEqual(forwardedArgs[0], w3cCaps({'appium:app': 'x'}));
+});