diff --git a/packages/llm/src/schema/events.ts b/packages/llm/src/schema/events.ts
index 98fcc9a24d41..aaebd4280e8f 100644
--- a/packages/llm/src/schema/events.ts
+++ b/packages/llm/src/schema/events.ts
@@ -1,5 +1,5 @@
 import { Schema } from "effect"
-import { ContentBlockID, FinishReason, ProtocolID, ProviderMetadata, RouteID, ToolCallID } from "./ids"
+import { ContentBlockID, FinishReason, ModelID, ProtocolID, ProviderMetadata, RouteID, ToolCallID } from "./ids"
 import { ModelSchema } from "./options"
 import { Message, ToolCallPart, ToolOutput, ToolResultPart, ToolResultValue, type ContentPart } from "./messages"
 import { ProviderFailureClassification } from "./errors"
@@ -184,6 +184,7 @@ export const StepFinish = Schema.Struct({
   type: Schema.tag("step-finish"),
   index: Schema.Number,
   reason: FinishReason,
+  modelID: Schema.optional(ModelID),
   usage: Schema.optional(Usage),
   providerMetadata: Schema.optional(ProviderMetadata),
 }).annotate({ identifier: "LLM.Event.StepFinish" })
diff --git a/packages/opencode/src/session/llm/ai-sdk.ts b/packages/opencode/src/session/llm/ai-sdk.ts
index 13d427aab62c..ec6fb3538e1b 100644
--- a/packages/opencode/src/session/llm/ai-sdk.ts
+++ b/packages/opencode/src/session/llm/ai-sdk.ts
@@ -1,4 +1,4 @@
-import { FinishReason, LLMEvent, ProviderMetadata, ToolResultValue } from "@opencode-ai/llm"
+import { FinishReason, LLMEvent, ModelID, ProviderMetadata, ToolResultValue } from "@opencode-ai/llm"
 import { Effect, Schema } from "effect"
 import { type streamText } from "ai"
 import { errorMessage } from "@/util/error"
@@ -105,6 +105,7 @@ export function toLLMEvents(
           LLMEvent.stepFinish({
             index: state.step++,
             reason: finishReason(event.finishReason),
+            modelID: ModelID.make(event.response.modelId),
             usage: usage(event.usage),
             providerMetadata: metadata,
           }),
diff --git a/packages/opencode/src/session/processor.ts b/packages/opencode/src/session/processor.ts
index 9f8530929c15..bdb920fc40c9 100644
--- a/packages/opencode/src/session/processor.ts
+++ b/packages/opencode/src/session/processor.ts
@@ -25,6 +25,7 @@ import { isRecord } from "@/util/record"
 import { EventV2Bridge } from "@/event-v2-bridge"
 import { Database } from "@opencode-ai/core/database/database"
 import { Usage, type LLMEvent } from "@opencode-ai/llm"
+import { ModelV2 } from "@opencode-ai/core/model"
 
 const DOOM_LOOP_THRESHOLD = 3
 export type Result = "compact" | "stop" | "continue"
@@ -464,6 +465,7 @@ const layer = Layer.effect(
               messageID: ctx.assistantMessage.id,
               sessionID: ctx.assistantMessage.sessionID,
               type: "step-finish",
+              modelID: value.modelID ? ModelV2.ID.make(value.modelID) : undefined,
               tokens: usage.tokens,
               cost: usage.cost,
             })
diff --git a/packages/opencode/test/session/llm.test.ts b/packages/opencode/test/session/llm.test.ts
index fcb536f46d91..3e34c2905894 100644
--- a/packages/opencode/test/session/llm.test.ts
+++ b/packages/opencode/test/session/llm.test.ts
@@ -220,7 +220,12 @@ describe("session.llm.ai-sdk adapter", () => {
       },
       {
         type: "finish-step",
-        response: { id: "response-1", timestamp: new Date(0), modelId: "gpt-test" },
+        response: {
+          id: "response-1",
+          timestamp: new Date(0),
+          modelId: "gpt-test",
+          headers: { authorization: "must-not-be-persisted" },
+        },
         finishReason: "other",
         rawFinishReason: "other",
         usage: {
@@ -281,6 +286,7 @@ describe("session.llm.ai-sdk adapter", () => {
         type: "step-finish",
         index: 0,
         reason: "unknown",
+        modelID: "gpt-test",
         usage: {
           inputTokens: 10,
           outputTokens: 5,
@@ -303,6 +309,7 @@ describe("session.llm.ai-sdk adapter", () => {
         },
       },
     ])
+    expect(events.find((event) => event.type === "step-finish")).not.toHaveProperty("responseHeaders")
   })
 
   test("creates stable block ids when AI SDK omits them", async () => {
diff --git a/packages/opencode/test/session/processor-effect.test.ts b/packages/opencode/test/session/processor-effect.test.ts
index c67f82d9c71b..42fdde6df78f 100644
--- a/packages/opencode/test/session/processor-effect.test.ts
+++ b/packages/opencode/test/session/processor-effect.test.ts
@@ -299,6 +299,7 @@ it.live("session.processor effect tests preserve text start time", () =>
               {
                 id: "chatcmpl-test",
                 object: "chat.completion.chunk",
+                model: "actual-model",
                 choices: [{ delta: { role: "assistant" } }],
               },
               {
@@ -358,10 +359,13 @@ it.live("session.processor effect tests preserve text start time", () =>
         gate.resolve()
 
         const exit = yield* Fiber.await(run)
-        const text = (yield* MessageV2.parts(msg.id)).find((part): part is SessionV1.TextPart => part.type === "text")
+        const parts = yield* MessageV2.parts(msg.id)
+        const text = parts.find((part): part is SessionV1.TextPart => part.type === "text")
+        const finish = parts.find((part): part is SessionV1.StepFinishPart => part.type === "step-finish")
 
         expect(Exit.isSuccess(exit)).toBe(true)
         expect(text?.text).toBe("hello")
+        expect(finish?.modelID).toBe(ModelV2.ID.make("actual-model"))
         expect(text?.time?.start).toBeDefined()
         expect(text?.time?.end).toBeDefined()
         if (!text?.time?.start || !text.time.end) return
diff --git a/packages/schema/src/v1/session.ts b/packages/schema/src/v1/session.ts
index 75e9282f117c..5e3a8edc6f81 100644
--- a/packages/schema/src/v1/session.ts
+++ b/packages/schema/src/v1/session.ts
@@ -241,6 +241,7 @@ export const StepFinishPart = Schema.Struct({
   ...partBase,
   type: Schema.Literal("step-finish"),
   reason: Schema.String,
+  modelID: optional(Model.ID),
   snapshot: Schema.optional(Schema.String),
   cost: Schema.Finite,
   tokens: Schema.Struct({
diff --git a/packages/sdk/js/src/v2/gen/types.gen.ts b/packages/sdk/js/src/v2/gen/types.gen.ts
index f06c20cc413e..5dd25b8a58bc 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -558,6 +558,7 @@ export type StepFinishPart = {
   messageID: string
   type: "step-finish"
   reason: string
+  modelID?: string
   snapshot?: string
   cost: number
   tokens: {