diff --git a/open-sse/translator/request/openai-responses.ts b/open-sse/translator/request/openai-responses.ts
index bc2a36c8c7..822229b984 100644
--- a/open-sse/translator/request/openai-responses.ts
+++ b/open-sse/translator/request/openai-responses.ts
@@ -445,11 +445,14 @@ export function openaiResponsesToOpenAIRequest(
   }
   delete result.store;
 
-  // Copilot-only: promote Responses `reasoning.{effort,summary}` to Chat fields
-  // so the downstream openai-to-claude translator can enable extended thinking.
-  // Gated by the UA marker from translateRequest; other clients see `reasoning` dropped.
+  // Promote Responses `reasoning.effort` to the Chat-Completions-native
+  // `reasoning_effort` field so OpenAI-family upstreams (and the downstream
+  // openai-to-claude translator's extended-thinking path) keep the hint when a
+  // Responses client is routed across formats. The Copilot-only `summary` ->
+  // Claude summarized-thinking marker stays behind the UA gate from
+  // translateRequest because it is Copilot-specific glue, not an OpenAI-native
+  // field. Ported from upstream PR decolua/9router#1817 (ryanngit).
   if (
-    credentialRecord._copilotClient === true &&
     root.reasoning &&
     typeof root.reasoning === "object" &&
     !Array.isArray(root.reasoning)
@@ -459,7 +462,10 @@ export function openaiResponsesToOpenAIRequest(
     if (effort && result.reasoning_effort === undefined) {
       result.reasoning_effort = normalizeResponsesReasoningEffort(effort);
     }
-    if (shouldRequestClaudeSummarizedThinking(reasoningRec.summary)) {
+    if (
+      credentialRecord._copilotClient === true &&
+      shouldRequestClaudeSummarizedThinking(reasoningRec.summary)
+    ) {
       result[COPILOT_REASONING_SUMMARY_MARKER] = "summarized";
     }
   }
diff --git a/tests/unit/openai-responses-reasoning-effort.test.ts b/tests/unit/openai-responses-reasoning-effort.test.ts
new file mode 100644
index 0000000000..9b8151bf15
--- /dev/null
+++ b/tests/unit/openai-responses-reasoning-effort.test.ts
@@ -0,0 +1,72 @@
+/**
+ * Reasoning-effort mapping across the OpenAI Chat <-> Responses request translators.
+ *
+ * Chat Completions carries the reasoning hint as top-level `reasoning_effort`; the
+ * Responses API nests it as `reasoning.effort`. These tests pin both directions so
+ * the hint survives when a request crosses formats (e.g. a Responses client routed
+ * to an OpenAI-native Chat Completions upstream).
+ *
+ * Ported from upstream PR https://github.com/decolua/9router/pull/1817 (ryanngit).
+ * Adapted: OmniRoute previously promoted `reasoning.effort` only behind the
+ * Copilot-client gate (commit 75d9a83c25), which silently dropped the field for
+ * every other Responses client (OpenCode, Cursor, raw OpenAI Responses, ...).
+ * This test pins the unconditional promotion of effort while keeping the
+ * Copilot-only `summary` -> Claude thinking marker behind its existing gate.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+import {
+  openaiToOpenAIResponsesRequest,
+  openaiResponsesToOpenAIRequest,
+} from "../../open-sse/translator/request/openai-responses.ts";
+import { convertResponsesApiFormat } from "../../open-sse/translator/helpers/responsesApiHelper.ts";
+
+function asRecord(value: unknown): Record<string, unknown> {
+  return value as Record<string, unknown>;
+}
+
+test("Responses -> Chat promotes reasoning.effort for non-Copilot clients", () => {
+  const out = asRecord(
+    openaiResponsesToOpenAIRequest(
+      "gpt-test",
+      { input: "hello", reasoning: { effort: "high" } },
+      true,
+      {} // no _copilotClient marker
+    )
+  );
+  assert.equal(out.reasoning_effort, "high");
+  assert.equal(out.reasoning, undefined);
+});
+
+test("Responses -> Chat preserves reasoning.effort via the helper wrapper", () => {
+  const out = asRecord(
+    convertResponsesApiFormat({ input: "hello", reasoning: { effort: "medium" } })
+  );
+  assert.equal(out.reasoning_effort, "medium");
+  assert.equal(out.reasoning, undefined);
+});
+
+test("Responses -> Chat does not overwrite an explicit reasoning_effort", () => {
+  const out = asRecord(
+    openaiResponsesToOpenAIRequest(
+      "gpt-test",
+      { input: "hello", reasoning_effort: "low", reasoning: { effort: "high" } },
+      true,
+      {}
+    )
+  );
+  // Explicit Chat-level field wins over the Responses nesting.
+  assert.equal(out.reasoning_effort, "low");
+});
+
+test("Chat -> Responses already wraps reasoning_effort into reasoning.effort", () => {
+  const out = asRecord(
+    openaiToOpenAIResponsesRequest(
+      "gpt-test",
+      { messages: [{ role: "user", content: "hi" }], reasoning_effort: "high" },
+      true,
+      {}
+    )
+  );
+  assert.deepEqual(out.reasoning, { effort: "high" });
+});
diff --git a/tests/unit/translator-openai-responses-req.test.ts b/tests/unit/translator-openai-responses-req.test.ts
index b20ac64bb0..4ce567f8e1 100644
--- a/tests/unit/translator-openai-responses-req.test.ts
+++ b/tests/unit/translator-openai-responses-req.test.ts
@@ -623,7 +623,10 @@ test("Chat -> Responses prefers max_completion_tokens over max_tokens when both
   assert.equal((result as any).max_completion_tokens, undefined);
 });
 
-test("Responses -> Chat drops `reasoning` and does not synthesize reasoning_effort without Copilot marker", () => {
+test("Responses -> Chat drops `reasoning` and promotes effort to reasoning_effort even without Copilot marker", () => {
+  // Updated per upstream PR decolua/9router#1817 (ryanngit): the OpenAI-native
+  // `reasoning_effort` hint is always preserved across the Responses -> Chat
+  // hop; only the Copilot-specific `summary` -> Claude marker stays gated.
   const result = openaiResponsesToOpenAIRequest(
     "claude-opus-4-7",
     {
@@ -635,7 +638,7 @@ test("Responses -> Chat drops `reasoning` and does not synthesize reasoning_effo
   ) as Record<string, unknown>;
 
   assert.equal(result.reasoning, undefined);
-  assert.equal(result.reasoning_effort, undefined);
+  assert.equal(result.reasoning_effort, "high");
 });
 
 test("Responses -> Chat promotes reasoning.effort to reasoning_effort when _copilotClient is set", () => {