diff --git a/core/config/types.ts b/core/config/types.ts
index d9f58aca6e2..9e72ec1ce01 100644
--- a/core/config/types.ts
+++ b/core/config/types.ts
@@ -302,6 +302,7 @@ declare global {
       name: string;
       arguments: string;
     };
+    responsesOutputItemId?: string;
   }
   
   export interface ToolCallDelta {
@@ -311,6 +312,7 @@ declare global {
       name?: string;
       arguments?: string;
     };
+    responsesOutputItemId?: string;
   }
   
   export interface ToolResultChatMessage {
diff --git a/core/index.d.ts b/core/index.d.ts
index f31b62ed7d6..02577388f65 100644
--- a/core/index.d.ts
+++ b/core/index.d.ts
@@ -348,6 +348,7 @@ export interface ToolCall {
     name: string;
     arguments: string;
   };
+  responsesOutputItemId?: string;
 }
 
 export interface ToolCallDelta {
@@ -357,6 +358,7 @@ export interface ToolCallDelta {
     name?: string;
     arguments?: string;
   };
+  responsesOutputItemId?: string;
 }
 
 export interface ToolResultChatMessage {
diff --git a/core/llm/openaiTypeConverters.ts b/core/llm/openaiTypeConverters.ts
index a7e3d6bacd8..48119a64051 100644
--- a/core/llm/openaiTypeConverters.ts
+++ b/core/llm/openaiTypeConverters.ts
@@ -774,6 +774,7 @@ function toResponseInputContentList(
   return list;
 }
 
+// eslint-disable-next-line complexity
 export function toResponsesInput(messages: ChatMessage[]): ResponseInput {
   const input: ResponseInput = [];
 
@@ -816,22 +817,34 @@ export function toResponsesInput(messages: ChatMessage[]): ResponseInput {
         const respId = msg.metadata?.responsesOutputItemId as
           | string
           | undefined;
+
         const toolCalls = msg.toolCalls as ToolCallDelta[] | undefined;
 
-        if (respId && Array.isArray(toolCalls) && toolCalls.length > 0) {
-          // Emit full function_call output item
-          const tc = toolCalls[0];
-          const name = tc?.function?.name as string | undefined;
-          const args = tc?.function?.arguments as string | undefined;
-          const call_id = tc?.id as string | undefined;
-          const functionCallItem: ResponseFunctionToolCall = {
-            id: respId,
-            type: "function_call",
-            name: name || "",
-            arguments: typeof args === "string" ? args : "{}",
-            call_id: call_id || respId,
-          };
-          input.push(functionCallItem);
+        if (Array.isArray(toolCalls) && toolCalls.length > 0) {
+          // Emit one function_call item per recorded tool call,
+          // prefer per-tool responsesOutputItemId when available
+          for (const tc of toolCalls) {
+            const name = tc?.function?.name as string | undefined;
+            const args = tc?.function?.arguments as string | undefined;
+            const tcRespId = (tc as any).responsesOutputItemId as
+              | string
+              | undefined;
+            const callId = tc?.id as string | undefined;
+            const rawItemId = tcRespId || respId || callId;
+            const itemId = rawItemId
+              ? rawItemId.startsWith("fc")
+                ? rawItemId
+                : `fc_${rawItemId}`
+              : undefined;
+            const functionCallItem: ResponseFunctionToolCall = {
+              id: itemId,
+              type: "function_call",
+              name: name || "",
+              arguments: typeof args === "string" ? args : "{}",
+              call_id: callId || tcRespId || respId || "",
+            };
+            input.push(functionCallItem);
+          }
         } else if (respId) {
           // Emit full assistant output message item
           const outputMessageItem: ResponseOutputMessage = {
diff --git a/gui/src/redux/slices/sessionSlice.ts b/gui/src/redux/slices/sessionSlice.ts
index 3656af0c185..f7697e60dfc 100644
--- a/gui/src/redux/slices/sessionSlice.ts
+++ b/gui/src/redux/slices/sessionSlice.ts
@@ -87,9 +87,12 @@ export function handleToolCallsInMessage(
 
     // Initialize tool call states for each filtered tool call in the message
     // Each tool call gets its own state to track generation/execution progress
-    lastItem.toolCallStates = filteredToolCalls.map((toolCallDelta) =>
-      addToolCallDeltaToState(toolCallDelta, undefined),
-    );
+    lastItem.toolCallStates = filteredToolCalls.map((toolCallDelta) => {
+      const state = addToolCallDeltaToState(toolCallDelta, undefined);
+      state.toolCall.responsesOutputItemId =
+        (message.metadata?.responsesOutputItemId as string) ?? undefined;
+      return state;
+    });
 
     // Update the message's toolCalls array to reflect the processed tool calls
     // We can safely cast because we verified the role above
@@ -116,6 +119,7 @@ export function handleToolCallsInMessage(
 function applyToolCallDelta(
   toolCallDelta: ToolCallDelta,
   toolCallStates: ToolCallState[],
+  responsesOutputItemId: string,
 ): void {
   // Find existing state by matching toolCallId - this ensures we update
   // the correct tool call even when multiple tool calls are being streamed
@@ -150,6 +154,7 @@ function applyToolCallDelta(
     toolCallStates[existingStateIndex] = updatedState;
   } else {
     // Add new tool call state for a newly discovered tool call
+    updatedState.toolCall.responsesOutputItemId = responsesOutputItemId;
     toolCallStates.push(updatedState);
   }
 }
@@ -181,7 +186,11 @@ export function handleStreamingToolCallUpdates(
 
     // Process each filtered tool call delta, matching by ID to update the correct state
     filteredToolCalls.forEach((toolCallDelta) => {
-      applyToolCallDelta(toolCallDelta, updatedToolCallStates);
+      applyToolCallDelta(
+        toolCallDelta,
+        updatedToolCallStates,
+        message.metadata?.responsesOutputItemId as string,
+      );
     });
 
     // Replace the entire tool call states array with the updated version
diff --git a/gui/src/util/toolCallState.ts b/gui/src/util/toolCallState.ts
index c7b9bcbd7df..5c990f20fd5 100644
--- a/gui/src/util/toolCallState.ts
+++ b/gui/src/util/toolCallState.ts
@@ -63,6 +63,7 @@ export function addToolCallDeltaToState(
         name: mergedName,
         arguments: mergedArgs,
       },
+      responsesOutputItemId: currentCall?.responsesOutputItemId,
     },
     toolCallId: callId,
     parsedArgs,