diff --git a/src/agents/openai-ws-stream.ts b/src/agents/openai-ws-stream.ts
index dd82ced9e95..9591143d880 100644
--- a/src/agents/openai-ws-stream.ts
+++ b/src/agents/openai-ws-stream.ts
@@ -605,10 +605,9 @@ export function createOpenAIWebSocketStreamFn(
         ...extraParams,
       };
       const nextPayload = await options?.onPayload?.(payload, model);
-      const requestPayload =
-        nextPayload && typeof nextPayload === "object"
-          ? (nextPayload as Parameters<OpenAIWebSocketManager["send"]>[0])
-          : (payload as Parameters<OpenAIWebSocketManager["send"]>[0]);
+      const requestPayload = (nextPayload ?? payload) as Parameters<
+        OpenAIWebSocketManager["send"]
+      >[0];
 
       try {
         session.manager.send(requestPayload);
diff --git a/src/agents/pi-embedded-runner-extraparams.test.ts b/src/agents/pi-embedded-runner-extraparams.test.ts
index 500df72cced..79113484a16 100644
--- a/src/agents/pi-embedded-runner-extraparams.test.ts
+++ b/src/agents/pi-embedded-runner-extraparams.test.ts
@@ -276,7 +276,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = { model: "deepseek/deepseek-r1" };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -308,7 +308,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = {};
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -332,7 +332,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = { reasoning_effort: "high" };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -357,7 +357,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = { reasoning: { max_tokens: 256 } };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -381,7 +381,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = { reasoning_effort: "medium" };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -588,7 +588,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = { thinking: "off" };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -619,7 +619,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = { thinking: "off" };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -650,7 +650,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = {};
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -674,7 +674,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = { tool_choice: "required" };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -699,7 +699,7 @@ describe("applyExtraParamsToAgent", () => {
     const payloads: Record<string, unknown>[] = [];
     const baseStreamFn: StreamFn = (_model, _context, options) => {
       const payload: Record<string, unknown> = {};
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -749,7 +749,7 @@ describe("applyExtraParamsToAgent", () => {
         ],
         tool_choice: { type: "tool", name: "read" },
       };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -793,7 +793,7 @@ describe("applyExtraParamsToAgent", () => {
           },
         ],
       };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -832,7 +832,7 @@ describe("applyExtraParamsToAgent", () => {
           },
         ],
       };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -896,7 +896,7 @@ describe("applyExtraParamsToAgent", () => {
           },
         },
       };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };
@@ -943,7 +943,7 @@ describe("applyExtraParamsToAgent", () => {
           },
         },
       };
-      options?.onPayload?.(payload, _model);
+      options?.onPayload?.(payload, model);
       payloads.push(payload);
       return {} as ReturnType<StreamFn>;
     };