diff --git a/open-sse/translator/response/openai-responses.ts b/open-sse/translator/response/openai-responses.ts
index 768cc8b609..cdc981cf92 100644
--- a/open-sse/translator/response/openai-responses.ts
+++ b/open-sse/translator/response/openai-responses.ts
@@ -412,6 +412,9 @@ function closeMessage(state, emit, idx) {
 
 function emitToolCall(state, emit, tc) {
   const tcIdx = tc.index ?? 0;
+  const outputIndex = state.reasoningId
+    ? normalizeOutputIndex(state.reasoningIndex) + 1 + normalizeOutputIndex(tcIdx)
+    : normalizeOutputIndex(tcIdx);
   const newCallId = tc.id;
   const funcName = tc.function?.name;
 
@@ -440,7 +443,7 @@ function emitToolCall(state, emit, tc) {
 
     emit("response.output_item.added", {
       type: "response.output_item.added",
-      output_index: tcIdx,
+      output_index: outputIndex,
       item: isCustomTool
         ? {
             id: `fc_${newCallId}`,
@@ -448,6 +451,7 @@ function emitToolCall(state, emit, tc) {
             input: "",
             call_id: newCallId,
             name: state.funcNames[tcIdx] || "",
+            status: "in_progress",
           }
         : {
             id: `fc_${newCallId}`,
@@ -455,6 +459,7 @@ function emitToolCall(state, emit, tc) {
             arguments: "",
             call_id: newCallId,
             name: state.funcNames[tcIdx] || "",
+            status: "in_progress",
           },
     });
   }
@@ -476,7 +481,7 @@ function emitToolCall(state, emit, tc) {
       emit(deltaEvent, {
         type: deltaEvent,
         item_id: `fc_${refCallId}`,
-        output_index: tcIdx,
+        output_index: outputIndex,
         delta: emittedDelta,
       });
     }
@@ -486,7 +491,9 @@ function emitToolCall(state, emit, tc) {
 function closeToolCall(state, emit, idx, recordAsCompleted = true) {
   const callId = state.funcCallIds[idx];
   if (callId && !state.funcItemDone[idx]) {
-    const normalizedIndex = normalizeOutputIndex(idx);
+    const normalizedIndex = state.reasoningId
+      ? normalizeOutputIndex(state.reasoningIndex) + 1 + normalizeOutputIndex(idx)
+      : normalizeOutputIndex(idx);
     const args = state.funcArgsBuf[idx] || "{}";
     const isCustomTool = (state.funcNames[idx] || "") === "apply_patch";
 
@@ -515,6 +522,7 @@ function closeToolCall(state, emit, idx, recordAsCompleted = true) {
         input: rawInput,
         call_id: callId,
         name: state.funcNames[idx] || "",
+        status: "completed",
       };
 
       emit("response.output_item.done", {
@@ -536,6 +544,7 @@ function closeToolCall(state, emit, idx, recordAsCompleted = true) {
         arguments: args,
         call_id: callId,
         name: state.funcNames[idx] || "",
+        status: "completed",
       };
 
       emit("response.output_item.done", {
diff --git a/tests/unit/responses-translation-fixes.test.ts b/tests/unit/responses-translation-fixes.test.ts
index 2cffb53ff2..1d8c478de1 100644
--- a/tests/unit/responses-translation-fixes.test.ts
+++ b/tests/unit/responses-translation-fixes.test.ts
@@ -673,3 +673,48 @@ test("Responses→Chat streaming: flush finalizes stop when no tool call was emi
   assert.ok(result, "flush should emit a final chunk");
   assert.equal(result.choices[0].finish_reason, "stop");
 });
+
+test("Chat→Responses streaming: reasoning and a following tool call use distinct output indexes", () => {
+  const state = initState(FORMATS.OPENAI_RESPONSES);
+
+  const reasoningEvents = openaiToOpenAIResponsesResponse(
+    {
+      id: "chatcmpl-grok",
+      choices: [{ index: 0, delta: { reasoning_content: "I should call the tool." } }],
+    },
+    state
+  );
+  const toolEvents = openaiToOpenAIResponsesResponse(
+    {
+      choices: [
+        {
+          index: 0,
+          delta: {
+            tool_calls: [
+              {
+                index: 0,
+                id: "call_grok",
+                type: "function",
+                function: { name: "lookup", arguments: '{"query":"status"}' },
+              },
+            ],
+          },
+        },
+      ],
+    },
+    state
+  );
+
+  const reasoningItem = reasoningEvents.find(
+    (event) => event.event === "response.output_item.added" && event.data.item.type === "reasoning"
+  );
+  const toolItem = toolEvents.find(
+    (event) =>
+      event.event === "response.output_item.added" && event.data.item.type === "function_call"
+  );
+
+  assert.ok(reasoningItem, "should announce the reasoning item");
+  assert.ok(toolItem, "should announce the function call item");
+  assert.equal(reasoningItem.data.output_index, 0);
+  assert.equal(toolItem.data.output_index, 1);
+});