diff --git a/open-sse/services/combo/promptCacheAffinity.ts b/open-sse/services/combo/promptCacheAffinity.ts
index f7675f0675..0739b59af3 100644
--- a/open-sse/services/combo/promptCacheAffinity.ts
+++ b/open-sse/services/combo/promptCacheAffinity.ts
@@ -290,6 +290,7 @@ export function shouldProtectOriginalFirst(
   return (
     stickyStuck ||
     autoUsedExplicitRouter ||
+    strategy === "auto" ||
     strategy === "quota-share" ||
     strategy === "weighted" ||
     strategy === "priority" ||
diff --git a/tests/unit/8370-priority-affinity-reorder.test.ts b/tests/unit/8370-priority-affinity-reorder.test.ts
index ce967a13d8..ad9a4c59cd 100644
--- a/tests/unit/8370-priority-affinity-reorder.test.ts
+++ b/tests/unit/8370-priority-affinity-reorder.test.ts
@@ -139,8 +139,8 @@ test("BUG #8370: priority combo keeps its declared model-1-first order despite c
   );
 });
 
-test("shouldProtectOriginalFirst covers priority, fill-first, and lkgp", () => {
-  for (const strategy of ["priority", "fill-first", "lkgp"]) {
+test("shouldProtectOriginalFirst covers auto, priority, fill-first, and lkgp", () => {
+  for (const strategy of ["auto", "priority", "fill-first", "lkgp"]) {
     assert.equal(
       shouldProtectOriginalFirst(false, false, strategy),
       true,