diff --git a/changelog.d/fixes/9580-standalone-ws-multipart-uploads.md b/changelog.d/fixes/9580-standalone-ws-multipart-uploads.md
new file mode 100644
index 0000000000..b22b6f7fc2
--- /dev/null
+++ b/changelog.d/fixes/9580-standalone-ws-multipart-uploads.md
@@ -0,0 +1 @@
+- **fix(standalone):** multipart uploads (`POST /v1/audio/transcriptions`) no longer hang — the WebDAV wrapper hands non-WebDAV requests to Next synchronously instead of losing the start of a streaming body ([#9580](https://github.com/diegosouzapw/OmniRoute/pull/9580))
diff --git a/scripts/dev/standalone-server-ws.mjs b/scripts/dev/standalone-server-ws.mjs
index 439a9c5171..ee5f0a1bec 100644
--- a/scripts/dev/standalone-server-ws.mjs
+++ b/scripts/dev/standalone-server-ws.mjs
@@ -3,7 +3,7 @@ import net from "node:net";
 import { randomUUID } from "node:crypto";
 import { createResponsesWsProxy } from "./responses-ws-proxy.mjs";
 import { ensurePeerStampToken, wrapRequestListenerWithPeerStamp } from "./peer-stamp.mjs";
-import { maybeHandleWebdav } from "./webdav-handler.mjs";
+import { maybeHandleWebdav, WEBDAV_PREFIX } from "./webdav-handler.mjs";
 import methodGuard from "./http-method-guard.cjs";
 import headResponseGuard from "./head-response-guard.cjs";
 import { resolveTlsOptions, createServerListener } from "./tls-options.mjs";
@@ -122,14 +122,20 @@ function wrapUpgradeListener(server, listener) {
  * Returns true if the request was handled; the wrapped listener is never called.
  */
 function wrapRequestListenerWithWebdav(listener) {
-  return async function webdavAwareRequestHandler(req, res) {
-    try {
-      const handled = await maybeHandleWebdav(req, res);
-      if (handled) return;
-    } catch {
-      // Never block a request on WebDAV errors — fall through to Next
+  return function webdavAwareRequestHandler(req, res) {
+    if (!(req.url || "").startsWith(WEBDAV_PREFIX)) {
+      return listener.call(this, req, res);
     }
-    return listener.call(this, req, res);
+    const self = this;
+    (async () => {
+      try {
+        const handled = await maybeHandleWebdav(req, res);
+        if (handled) return;
+      } catch {
+        // Never block a request on WebDAV errors — fall through to Next
+      }
+      return listener.call(self, req, res);
+    })();
   };
 }
 
diff --git a/tests/unit/standalone-server-ws-webdav-sync-listener.test.ts b/tests/unit/standalone-server-ws-webdav-sync-listener.test.ts
new file mode 100644
index 0000000000..40b7e490d6
--- /dev/null
+++ b/tests/unit/standalone-server-ws-webdav-sync-listener.test.ts
@@ -0,0 +1,60 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+
+// The WebDAV wrapper used to be `async` and awaited maybeHandleWebdav() for every
+// request. Even when it returned false, that await deferred listener.call() by a
+// microtask, so Next attached its 'data'/'end' handlers one tick late and lost the
+// beginning of a streaming request body — multipart uploads (POST
+// /v1/audio/transcriptions) then hung forever in request.formData().
+//
+// standalone-server-ws.mjs has top-level side effects (it monkeypatches
+// http.createServer and awaits ./server.js, which only exists in the assembled
+// standalone output), so it cannot be imported in-process. Guard the fix by
+// inspecting the source, mirroring standalone-server-ws-keepalive-timeout-7003.test.ts.
+const here = path.dirname(fileURLToPath(import.meta.url));
+const source = fs.readFileSync(
+  path.resolve(here, "../../scripts/dev/standalone-server-ws.mjs"),
+  "utf8"
+);
+
+const wrapper = source.slice(
+  source.indexOf("function wrapRequestListenerWithWebdav"),
+  source.indexOf("http.createServer = function createServerWithResponsesWs")
+);
+
+test("standalone-server-ws.mjs imports WEBDAV_PREFIX to gate the async branch", () => {
+  assert.match(
+    source,
+    /import\s*\{[^}]*WEBDAV_PREFIX[^}]*\}\s*from\s*["']\.\/webdav-handler\.mjs["']/,
+    "expected WEBDAV_PREFIX to come from the shipped sibling ./webdav-handler.mjs"
+  );
+});
+
+test("the WebDAV request wrapper is not async", () => {
+  assert.ok(wrapper.length > 0, "expected to find wrapRequestListenerWithWebdav");
+  assert.doesNotMatch(
+    wrapper,
+    /return\s+async\s+function\s+webdavAwareRequestHandler/,
+    "an async handler defers listener.call() by a microtask and truncates streaming bodies"
+  );
+});
+
+test("non-WebDAV requests reach the wrapped listener before any await", () => {
+  const prefixGuard = wrapper.indexOf("WEBDAV_PREFIX");
+  const firstListenerCall = wrapper.indexOf("listener.call");
+  const firstAwait = wrapper.indexOf("await ");
+
+  assert.ok(prefixGuard >= 0, "expected the handler to test req.url against WEBDAV_PREFIX");
+  assert.ok(firstListenerCall >= 0, "expected the handler to call the wrapped listener");
+  assert.ok(
+    prefixGuard < firstListenerCall,
+    "expected the URL guard to run before the listener is invoked"
+  );
+  assert.ok(
+    firstListenerCall < firstAwait,
+    "expected the synchronous listener.call() to precede any await"
+  );
+});