diff --git a/plugins/multi/scripts/lib/adapters/qwen.mjs b/plugins/multi/scripts/lib/adapters/qwen.mjs
index 96a95c2..ddeb9eb 100644
--- a/plugins/multi/scripts/lib/adapters/qwen.mjs
+++ b/plugins/multi/scripts/lib/adapters/qwen.mjs
@@ -7,7 +7,7 @@
  * fork, optimized for Qwen3-Coder, and speaks the standard JSON-RPC
  * Agent Client Protocol over stdio (using @agentclientprotocol/sdk).
  *
- * The `--acp` flag graduated from `--experimental-acp` in Qwen Code v0.x
+ * The `--acp` flag graduated from `--experimental-acp` in Qwen Code v0.15.6
  * (PR #1355). The deprecated alias is still accepted but emits a warning,
  * so we always pass the stable flag.
  *
diff --git a/plugins/multi/scripts/test/qwen-acp-flag.mjs b/plugins/multi/scripts/test/qwen-acp-flag.mjs
new file mode 100644
index 0000000..51a947b
--- /dev/null
+++ b/plugins/multi/scripts/test/qwen-acp-flag.mjs
@@ -0,0 +1,120 @@
+#!/usr/bin/env node
+/**
+ * Qwen adapter ACP flag test
+ *
+ * Verifies that the Qwen adapter constructs its launch command with the
+ * stable `--acp` flag and does NOT use the deprecated `--experimental-acp`.
+ *
+ * Qwen Code v0.15.6 graduated `--acp` from `--experimental-acp` (PR #1355).
+ * The deprecated alias still works but emits a warning; the adapter should
+ * always pass the stable flag.
+ */
+
+import { execSync } from "node:child_process";
+import path from "node:path";
+import process from "node:process";
+import { fileURLToPath } from "node:url";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+// ─── Import the Qwen adapter ──────────────────────────────────────────────────
+
+const adapterPath = path.resolve(__dirname, "..", "lib", "adapters", "qwen.mjs");
+const { getQwenAvailability, adapter } = await import(adapterPath);
+
+let failures = 0;
+
+function assert(condition, message) {
+  if (condition) {
+    process.stdout.write(`  PASS: ${message}\n`);
+  } else {
+    process.stderr.write(`  FAIL: ${message}\n`);
+    failures++;
+  }
+}
+
+// ─── Test 1: adapter name ─────────────────────────────────────────────────────
+
+process.stdout.write("Test 1: adapter metadata\n");
+assert(adapter.name === "qwen", `adapter.name is "qwen" (got: ${adapter.name})`);
+assert(typeof adapter.isAvailable === "function", "isAvailable is a function");
+assert(typeof adapter.isAuthenticated === "function", "isAuthenticated is a function");
+assert(typeof adapter.invoke === "function", "invoke is a function");
+assert(typeof adapter.cancel === "function", "cancel is a function");
+
+// ─── Test 2: source-code inspection ────────────────────────────────────────────
+//
+// Read the adapter source and verify it uses --acp, not --experimental-acp.
+// This is a static-analysis guard: if someone reverts the flag, the test
+// catches it before any runtime failure.
+
+process.stdout.write("\nTest 2: source-code flag inspection\n");
+
+const fs = await import("node:fs");
+const source = fs.readFileSync(adapterPath, "utf8");
+
+// The args array in runAcpPromptQwen must contain "--acp".
+assert(source.includes('"--acp"'), 'adapter source contains "--acp"');
+
+// The adapter must NOT pass "--experimental-acp" in any args array.
+assert(
+  !source.includes('"--experimental-acp"'),
+  'adapter source does NOT contain "--experimental-acp" in args'
+);
+
+// The comment documenting the migration should mention v0.15.6
+assert(
+  source.includes("v0.15.6"),
+  "adapter comment references Qwen Code v0.15.6"
+);
+
+// ─── Test 3: binary resolution (non-fatal if Qwen is not installed) ───────────
+
+process.stdout.write("\nTest 3: binary resolution\n");
+const avail = getQwenAvailability();
+if (avail.available) {
+  process.stdout.write(`  INFO: Qwen Code CLI found — ${avail.detail}\n`);
+  assert(avail.version !== null, `version string is non-null (got: ${avail.version})`);
+} else {
+  process.stdout.write(`  SKIP: Qwen Code CLI not installed — ${avail.detail}\n`);
+  process.stdout.write("  (binary resolution logic was still exercised; no crash = pass)\n");
+}
+
+// ─── Test 4: verify --acp is accepted by the installed Qwen binary ─────────────
+//
+// If Qwen is installed, run `qwen --help` and confirm --acp is listed
+// and --experimental-acp is either absent or marked deprecated.
+
+if (avail.available) {
+  process.stdout.write("\nTest 4: Qwen --help flag verification\n");
+  try {
+    const helpOutput = execSync(`"${avail.detail.split(" ")[0]}" --help`, {
+      encoding: "utf8",
+      shell: true,
+      stdio: ["pipe", "pipe", "pipe"],
+      timeout: 8000
+    });
+
+    assert(helpOutput.includes("--acp"), "qwen --help lists --acp");
+
+    // --experimental-acp may still appear (deprecated alias) — that's OK.
+    // We just verify --acp is the primary/stable flag.
+    if (helpOutput.includes("--experimental-acp")) {
+      process.stdout.write("  INFO: --experimental-acp still present (deprecated alias) — OK\n");
+    }
+  } catch (err) {
+    process.stdout.write(`  SKIP: qwen --help failed — ${err.message ?? err}\n`);
+  }
+} else {
+  process.stdout.write("\nTest 4: SKIP (Qwen not installed)\n");
+}
+
+// ─── Summary ───────────────────────────────────────────────────────────────────
+
+process.stdout.write("\n");
+if (failures > 0) {
+  process.stderr.write(`${failures} test(s) FAILED\n`);
+  process.exitCode = 1;
+} else {
+  process.stdout.write("All tests passed.\n");
+}