diff --git a/nodejs/src/protocols/acp/acp-adapter.ts b/nodejs/src/protocols/acp/acp-adapter.ts
index 6a28eff59..1bf7057fe 100644
--- a/nodejs/src/protocols/acp/acp-adapter.ts
+++ b/nodejs/src/protocols/acp/acp-adapter.ts
@@ -313,9 +313,10 @@ class AcpConnection implements ProtocolConnection {
 
         if (config.model) {
             const id = ++this.requestId;
-            await this.transport.sendRequest(id, "session/set_model", {
+            await this.transport.sendRequest(id, "session/set_config_option", {
                 sessionId,
-                modelId: config.model,
+                configId: "model",
+                value: config.model,
             });
         }
     }
diff --git a/nodejs/src/protocols/acp/acp-types.ts b/nodejs/src/protocols/acp/acp-types.ts
index 9c62ac29f..acc5aaa11 100644
--- a/nodejs/src/protocols/acp/acp-types.ts
+++ b/nodejs/src/protocols/acp/acp-types.ts
@@ -87,31 +87,23 @@ export interface AcpServerCapabilities {
 // ============================================================================
 
 /**
- * ACP session/set_model request params
+ * ACP session/set_config_option request params
+ * @see https://agentclientprotocol.com/protocol/session-config-options
  */
-export interface AcpSetModelParams {
+export interface AcpSetConfigOptionParams {
     sessionId: string;
-    modelId: string;
+    configId: string;
+    value: string;
 }
 
 /**
- * ACP session/set_model response
+ * ACP session/set_config_option response
+ * Returns the complete configuration state after the change.
  */
-export interface AcpSetModelResult {}
-
-/**
- * ACP session/set_mode request params
- */
-export interface AcpSetModeParams {
-    sessionId: string;
-    modeId: string;
+export interface AcpSetConfigOptionResult {
+    [configId: string]: string;
 }
 
-/**
- * ACP session/set_mode response
- */
-export interface AcpSetModeResult {}
-
 // ============================================================================
 // ACP Session Types
 // ============================================================================
diff --git a/nodejs/test/protocols/acp/acp-adapter.test.ts b/nodejs/test/protocols/acp/acp-adapter.test.ts
index fba2f224d..fe27ab58e 100644
--- a/nodejs/test/protocols/acp/acp-adapter.test.ts
+++ b/nodejs/test/protocols/acp/acp-adapter.test.ts
@@ -158,11 +158,16 @@ describe("AcpProtocolAdapter", () => {
             };
             mockProcess.stdout.write(JSON.stringify(response) + "\n");
 
-            // session.create with model triggers session/set_model
+            // session.create with model triggers session/set_config_option
             await new Promise((resolve) => setImmediate(resolve));
             const sentData2 = mockProcess.stdin.read();
             const sentMessage2 = JSON.parse(sentData2.toString().trim());
-            expect(sentMessage2.method).toBe("session/set_model");
+            expect(sentMessage2.method).toBe("session/set_config_option");
+            expect(sentMessage2.params).toEqual({
+                sessionId: "acp-session-123",
+                configId: "model",
+                value: "gemini-pro",
+            });
 
             const response2 = {
                 jsonrpc: "2.0",
@@ -175,7 +180,7 @@ describe("AcpProtocolAdapter", () => {
             expect(result).toEqual({ sessionId: "acp-session-123" });
         });
 
-        it("should call session/set_model after session.create when model is provided", async () => {
+        it("should call session/set_config_option after session.create when model is provided", async () => {
             adapter.start();
             await new Promise((resolve) => setImmediate(resolve));
 
@@ -203,16 +208,17 @@ describe("AcpProtocolAdapter", () => {
             // Wait for the set_model request to be sent
             await new Promise((resolve) => setImmediate(resolve));
 
-            // Read the session/set_model request
+            // Read the session/set_config_option request
             const sentData2 = mockProcess.stdin.read();
             const sentMessage2 = JSON.parse(sentData2.toString().trim());
-            expect(sentMessage2.method).toBe("session/set_model");
+            expect(sentMessage2.method).toBe("session/set_config_option");
             expect(sentMessage2.params).toEqual({
                 sessionId: "acp-session-456",
-                modelId: "claude-sonnet-4-5-20250929",
+                configId: "model",
+                value: "claude-sonnet-4-5-20250929",
             });
 
-            // Respond to session/set_model
+            // Respond to session/set_config_option
             const response2 = {
                 jsonrpc: "2.0",
                 id: sentMessage2.id,
@@ -224,7 +230,7 @@ describe("AcpProtocolAdapter", () => {
             expect(result).toEqual({ sessionId: "acp-session-456" });
         });
 
-        it("should not call session/set_model when model is not provided", async () => {
+        it("should not call session/set_config_option when model is not provided", async () => {
             adapter.start();
             await new Promise((resolve) => setImmediate(resolve));
 
@@ -251,7 +257,7 @@ describe("AcpProtocolAdapter", () => {
             const result = await createPromise;
             expect(result).toEqual({ sessionId: "acp-session-789" });
 
-            // Verify no additional request was sent (no session/set_model)
+            // Verify no additional request was sent (no session/set_config_option)
             await new Promise((resolve) => setImmediate(resolve));
             const extraData = mockProcess.stdin.read();
             expect(extraData).toBeNull();