diff --git a/.changeset/add-model-to-start-run-event.md b/.changeset/add-model-to-start-run-event.md
new file mode 100644
index 00000000..e07e5e52
--- /dev/null
+++ b/.changeset/add-model-to-start-run-event.md
@@ -0,0 +1,7 @@
+---
+"@perstack/core": patch
+"@perstack/runtime": patch
+"perstack": patch
+---
+
+feat: add model field to startRun and resumeFromStop event payloads
diff --git a/packages/core/src/adapters/event-creators.test.ts b/packages/core/src/adapters/event-creators.test.ts
index 368e6351..00f40699 100644
--- a/packages/core/src/adapters/event-creators.test.ts
+++ b/packages/core/src/adapters/event-creators.test.ts
@@ -74,7 +74,13 @@ describe("@perstack/core: event-creators", () => {
         output: "",
       })
       const initCheckpoint = { ...checkpoint, status: "init" as const, stepNumber: 0 }
-      const event = createStartRunEvent("job-1", "run-1", "expert-key", initCheckpoint)
+      const event = createStartRunEvent(
+        "job-1",
+        "run-1",
+        "expert-key",
+        initCheckpoint,
+        "claude-sonnet-4-20250514",
+      )
       expect(event.type).toBe("startRun")
       expect(event.jobId).toBe("job-1")
       expect(event.runId).toBe("run-1")
diff --git a/packages/core/src/adapters/event-creators.ts b/packages/core/src/adapters/event-creators.ts
index a8341e55..fcbaf3f9 100644
--- a/packages/core/src/adapters/event-creators.ts
+++ b/packages/core/src/adapters/event-creators.ts
@@ -49,6 +49,7 @@ export function createStartRunEvent(
   runId: string,
   expertKey: string,
   checkpoint: Checkpoint,
+  model: string,
 ): RunEvent {
   return {
     type: "startRun",
@@ -60,6 +61,7 @@ export function createStartRunEvent(
     stepNumber: checkpoint.stepNumber,
     initialCheckpoint: checkpoint,
     inputMessages: [],
+    model,
   }
 }
 
diff --git a/packages/core/src/schemas/runtime.test.ts b/packages/core/src/schemas/runtime.test.ts
index 82963cee..c1926bb6 100644
--- a/packages/core/src/schemas/runtime.test.ts
+++ b/packages/core/src/schemas/runtime.test.ts
@@ -78,6 +78,7 @@ describe("@perstack/core: createEvent", () => {
     const event = startRun(mockSetting, mockCheckpoint, {
       initialCheckpoint: mockCheckpoint,
       inputMessages: [],
+      model: "test-model",
     })
     expect(event.type).toBe("startRun")
     expect(event.jobId).toBe("job-123")
diff --git a/packages/core/src/schemas/runtime.ts b/packages/core/src/schemas/runtime.ts
index 4009d391..3dfe2a59 100644
--- a/packages/core/src/schemas/runtime.ts
+++ b/packages/core/src/schemas/runtime.ts
@@ -235,10 +235,14 @@ type ExpertStatePayloads = {
   startRun: {
     initialCheckpoint: Checkpoint
     inputMessages: (InstructionMessage | UserMessage | ToolMessage)[]
+    /** Resolved model name used for this run */
+    model: string
   }
   /** Resume from stoppedByDelegate or stoppedByInteractiveTool */
   resumeFromStop: {
     checkpoint: Checkpoint
+    /** Resolved model name used for this run */
+    model: string
   }
   /** Proceed to CallingInteractiveTools from ResumingFromStop */
   proceedToInteractiveTools: {
diff --git a/packages/runtime/src/state-machine/states/init.test.ts b/packages/runtime/src/state-machine/states/init.test.ts
index 064e7e5d..f5d35a13 100644
--- a/packages/runtime/src/state-machine/states/init.test.ts
+++ b/packages/runtime/src/state-machine/states/init.test.ts
@@ -50,6 +50,7 @@ describe("@perstack/runtime: StateMachineLogic['Init']", () => {
           contents: [{ type: "textPart", id: expect.any(String), text: "How are you?" }],
         },
       ],
+      model: setting.model,
     })
   })
 
@@ -208,6 +209,7 @@ describe("@perstack/runtime: StateMachineLogic['Init']", () => {
           contents: [{ type: "textPart", id: expect.any(String), text: "test-text" }],
         },
       ],
+      model: setting.model,
     })
   })
 
@@ -264,6 +266,7 @@ describe("@perstack/runtime: StateMachineLogic['Init']", () => {
           contents: [{ type: "textPart", id: expect.any(String), text: "resume-text" }],
         },
       ],
+      model: setting.model,
     })
   })
 })
diff --git a/packages/runtime/src/state-machine/states/init.ts b/packages/runtime/src/state-machine/states/init.ts
index 8500bd5b..05022436 100644
--- a/packages/runtime/src/state-machine/states/init.ts
+++ b/packages/runtime/src/state-machine/states/init.ts
@@ -28,12 +28,16 @@ export async function initLogic({
       if (!setting.input.text) {
         throw new Error("Input message is undefined")
       }
+      if (!setting.model) {
+        throw new Error("Model is not resolved")
+      }
       return startRun(setting, checkpoint, {
         initialCheckpoint: checkpoint,
         inputMessages: [
           createInstructionMessage(expert, setting.startedAt),
           createUserMessage([{ type: "textPart", text: setting.input.text }]),
         ],
+        model: setting.model,
       })
     }
     case "stoppedByDelegate":
@@ -41,6 +45,9 @@ export async function initLogic({
       if (!setting.input.interactiveToolCallResult) {
         throw new Error("Interactive tool call result is undefined")
       }
+      if (!setting.model) {
+        throw new Error("Model is not resolved")
+      }
       const { toolCallId, toolName, skillName, text } = setting.input.interactiveToolCallResult
       const pendingToolCalls = checkpoint.pendingToolCalls ?? []
       const newToolResult: ToolResult = {
@@ -58,15 +65,20 @@ export async function initLogic({
       }
       return resumeFromStop(setting, checkpoint, {
         checkpoint: updatedCheckpoint,
+        model: setting.model,
       })
     }
     default:
       if (!setting.input.text) {
         throw new Error("Input message is undefined")
       }
+      if (!setting.model) {
+        throw new Error("Model is not resolved")
+      }
       return startRun(setting, checkpoint, {
         initialCheckpoint: checkpoint,
         inputMessages: [createUserMessage([{ type: "textPart", text: setting.input.text }])],
+        model: setting.model,
       })
   }
 }