diff --git a/open-sse/services/modelDeprecation.ts b/open-sse/services/modelDeprecation.ts
index 4f38d68854..90ac077b1d 100644
--- a/open-sse/services/modelDeprecation.ts
+++ b/open-sse/services/modelDeprecation.ts
@@ -40,6 +40,13 @@ const BUILT_IN_ALIASES: Record<string, string> = {
   "fireworks/accounts/fireworks/models/kimi-k2": "moonshotai/Kimi-K2",
   "kimi-k2": "moonshotai/Kimi-K2",
 
+  // Qwen — the model ships only under the `-preview` id (bailian-coding-plan, qoder,
+  // qwen-cloud-token-plan, qwen-web). Without this, the bare id missed MODEL_SPECS and
+  // the context preflight fell back to contextManager's `default: 128000`, rejecting
+  // prompts the model's real 1M window accepts. Drop this line if Alibaba ever ships a
+  // distinct GA `qwen3.8-max` — it would no longer be the same model.
+  "qwen3.8-max": "qwen3.8-max-preview",
+
   // Mistral short aliases
   "mistral-large": "mistral-large-latest",
   "mistral-small": "mistral-small-latest",
diff --git a/tests/unit/qwen38-max-bare-id-alias.test.ts b/tests/unit/qwen38-max-bare-id-alias.test.ts
new file mode 100644
index 0000000000..e29d587b32
--- /dev/null
+++ b/tests/unit/qwen38-max-bare-id-alias.test.ts
@@ -0,0 +1,54 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { MODEL_SPECS } from "../../src/shared/constants/modelSpecs.ts";
+import { resolveModelAlias } from "../../open-sse/services/modelDeprecation.ts";
+import { resolveLifecycle } from "../../open-sse/handlers/chatCore/modelLifecyclePolicy.ts";
+
+/**
+ * Bare `qwen3.8-max` was an unroutable id: the model ships everywhere as
+ * `qwen3.8-max-preview` (bailian-coding-plan, qoder, qwen-cloud-token-plan, qwen-web),
+ * and nothing in the repo declared the short form. A client sending it therefore
+ *
+ *   1. missed MODEL_SPECS, so `getModelContextLimit()` fell through to the
+ *      `default: 128000` in open-sse/services/contextManager.ts, and the chatCore
+ *      preflight rejected any prompt above 128k with `context_length_exceeded`
+ *      ("Input exceeds context window ... limit 128000") even though the real
+ *      window is 1M; and
+ *   2. would have been dispatched verbatim to the upstream, which only knows the
+ *      `-preview` id.
+ *
+ * Both symptoms have one cause — the missing id — so the fix belongs in the
+ * deprecation/rename alias map (`BUILT_IN_ALIASES`), which `resolveLifecycle()`
+ * applies at open-sse/handlers/chatCore.ts:755, well before both the context
+ * preflight and the upstream dispatch. A MODEL_SPECS `aliases` entry would have
+ * fixed only (1): spec aliases resolve capabilities, never the dispatched id.
+ */
+
+const BARE = "qwen3.8-max";
+const CANONICAL = "qwen3.8-max-preview";
+
+test("bare qwen3.8-max resolves to the canonical -preview id", () => {
+  assert.equal(resolveModelAlias(BARE), CANONICAL);
+});
+
+test("the canonical id is a no-op through the alias map (no double rewrite)", () => {
+  assert.equal(resolveModelAlias(CANONICAL), CANONICAL);
+});
+
+test("the alias target carries the real 1M window, not the 128k fallback", () => {
+  const spec = MODEL_SPECS[CANONICAL];
+  assert.ok(spec, `MODEL_SPECS is missing ${CANONICAL}`);
+  assert.equal(spec.contextWindow, 1_000_000);
+  // The bare id must NOT gain its own spec entry — a second source of truth for the
+  // same model is what lets the two ids drift apart again.
+  assert.equal(MODEL_SPECS[BARE], undefined);
+});
+
+test("chatCore lifecycle resolution rewrites the model before dispatch", () => {
+  for (const provider of ["qwen-cloud-token-plan", "qoder", "bailian-coding-plan", "qwen-web"]) {
+    const [resolvedModel, effectiveModel, lifecycleError] = resolveLifecycle(provider, BARE);
+    assert.equal(resolvedModel, CANONICAL, `resolvedModel for ${provider}`);
+    assert.equal(effectiveModel, CANONICAL, `effectiveModel for ${provider}`);
+    assert.equal(lifecycleError, null, `unexpected lifecycle rejection for ${provider}`);
+  }
+});