diff --git a/src/CodexAcpClient.ts b/src/CodexAcpClient.ts
index 2ea875b5..01ed13c0 100644
--- a/src/CodexAcpClient.ts
+++ b/src/CodexAcpClient.ts
@@ -13,6 +13,7 @@ import type {Disposable} from "vscode-jsonrpc";
 import type {
     ClientInfo,
     ReasoningEffort,
+    ReasoningSummary,
     ServiceTier,
     ServerNotification
 } from "./app-server";
@@ -672,7 +673,8 @@ export class CodexAcpClient {
             input: input,
             approvalPolicy: agentMode.approvalPolicy,
             sandboxPolicy: addAdditionalDirectoriesToSandboxPolicy(agentMode.sandboxPolicy, additionalDirectories),
-            summary: disableSummary ? "none" : "auto",
+            // Preserve safety overrides while honoring CODEX_CONFIG.
+            summary: resolveReasoningSummary(this.config, disableSummary),
             effort: effort,
             model: modelId.model,
             serviceTier: serviceTier,
@@ -841,6 +843,22 @@ export class CodexAcpClient {
 
 export type JsonObject = { [key in string]?: JsonValue }
 
+function resolveReasoningSummary(config: JsonObject, disableSummary: boolean): ReasoningSummary {
+    if (disableSummary) {
+        return "none";
+    }
+
+    switch (config["model_reasoning_summary"]) {
+        case "auto":
+        case "concise":
+        case "detailed":
+        case "none":
+            return config["model_reasoning_summary"];
+        default:
+            return "auto";
+    }
+}
+
 export type SessionMetadata = {
     sessionId: string,
     currentModelId: string,
diff --git a/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts b/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts
index 255d4ab2..87e832e1 100644
--- a/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts
+++ b/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts
@@ -16,6 +16,7 @@ import {AgentMode} from "../../AgentMode";
 import type {Model, ReviewStartResponse, ThreadGoal, TurnCompletedNotification, TurnStartParams} from "../../app-server/v2";
 import type {RateLimitsMap} from "../../RateLimitsMap";
 import {ModelId} from "../../ModelId";
+import {CodexAcpClient} from "../../CodexAcpClient";
 
 describe('ACP server test', { timeout: 40_000 }, () => {
 
@@ -3057,14 +3058,25 @@ describe('ACP server test', { timeout: 40_000 }, () => {
         expect(turnStartSpy).toHaveBeenCalledWith(expect.objectContaining({ summary: "none" }));
     });
 
-    it ('should enable reasoning.summary by default', async () => {
-        const { mockFixture, turnStartSpy } = setupPromptFixture({
-            account: { type: "chatgpt", email: "test@example.com", planType: "pro" },
-        });
+    // Explicit adapter config must override the default summary mode.
+    it ('should prefer CODEX_CONFIG reasoning.summary', async () => {
+        const { mockFixture, turnStartSpy } = setupPromptFixture();
+        const configuredClient = new CodexAcpClient(
+            mockFixture.getCodexAppServerClient(),
+            {model_reasoning_summary: "detailed"},
+        );
 
-        await mockFixture.getCodexAcpAgent().prompt({ sessionId: "id", prompt: [{ type: "text", text: "test" }] });
+        await configuredClient.sendPrompt(
+            {sessionId: "id", prompt: [{type: "text", text: "test"}]},
+            AgentMode.DEFAULT_AGENT_MODE,
+            ModelId.create("model-id", "medium"),
+            null,
+            false,
+            "/test/cwd",
+            [],
+        );
 
-        expect(turnStartSpy).toHaveBeenCalledWith(expect.objectContaining({ summary: "auto" }));
+        expect(turnStartSpy).toHaveBeenCalledWith(expect.objectContaining({summary: "detailed"}));
     });
 
     it ('should disable reasoning.summary when model lacks reasoning', async () => {
@@ -3078,7 +3090,7 @@ describe('ACP server test', { timeout: 40_000 }, () => {
         expect(turnStartSpy).toHaveBeenCalledWith(expect.objectContaining({ summary: "none" }));
     });
 
-    it ('should enable reasoning.summary when model supports reasoning', async () => {
+    it ('should use auto reasoning.summary by default when model supports reasoning', async () => {
         const { mockFixture, turnStartSpy } = setupPromptFixture({
             account: { type: "chatgpt", email: "test@example.com", planType: "pro" },
             supportedReasoningEfforts: [
@@ -3089,7 +3101,7 @@ describe('ACP server test', { timeout: 40_000 }, () => {
 
         await mockFixture.getCodexAcpAgent().prompt({ sessionId: "id", prompt: [{ type: "text", text: "test" }] });
 
-        expect(turnStartSpy).toHaveBeenCalledWith(expect.objectContaining({ summary: "auto" }));
+        expect(turnStartSpy).toHaveBeenCalledWith(expect.objectContaining({summary: "auto"}));
     });
 
     it ('should reject prompt with images when model does not support image input', async () => {