diff --git a/readme-dev.md b/readme-dev.md
index bc147807..9cd0ec48 100644
--- a/readme-dev.md
+++ b/readme-dev.md
@@ -13,6 +13,19 @@ Set `CODEX_PATH` to run a different Codex binary; versions other than the one sp
 - `NO_BROWSER` - hide browser-based ChatGPT auth when set.
 - `APP_SERVER_LOGS` - directory for adapter logs.
 
+`CODEX_CONFIG` can enable network access for the `agent` (workspace-write) mode:
+
+```json
+{
+  "sandbox_workspace_write": {
+    "network_access": true
+  }
+}
+```
+
+Only a boolean value overrides the workspace-write default of `false`. This setting
+does not change the `read-only` or `agent-full-access` policies.
+
 ### Quick start
 
 #### Develop on Windows?
diff --git a/src/CodexAcpClient.ts b/src/CodexAcpClient.ts
index 0c7af207..57e73764 100644
--- a/src/CodexAcpClient.ts
+++ b/src/CodexAcpClient.ts
@@ -704,7 +704,10 @@ export class CodexAcpClient {
             threadId: request.sessionId,
             input: input,
             approvalPolicy: agentMode.approvalPolicy,
-            sandboxPolicy: addAdditionalDirectoriesToSandboxPolicy(agentMode.sandboxPolicy, additionalDirectories),
+            sandboxPolicy: applySandboxWorkspaceWriteNetworkAccess(
+                addAdditionalDirectoriesToSandboxPolicy(agentMode.sandboxPolicy, additionalDirectories),
+                this.config,
+            ),
             summary: disableSummary ? "none" : "auto",
             effort: effort,
             model: modelId.model,
@@ -1062,6 +1065,25 @@ function addAdditionalDirectoriesToSandboxPolicy(
     };
 }
 
+function applySandboxWorkspaceWriteNetworkAccess(
+    sandboxPolicy: SandboxPolicy,
+    config: JsonObject,
+): SandboxPolicy {
+    if (sandboxPolicy.type !== "workspaceWrite") {
+        return sandboxPolicy;
+    }
+
+    const sandboxConfig = config["sandbox_workspace_write"];
+    if (!isJsonObject(sandboxConfig) || typeof sandboxConfig["network_access"] !== "boolean") {
+        return sandboxPolicy;
+    }
+
+    return {
+        ...sandboxPolicy,
+        networkAccess: sandboxConfig["network_access"],
+    };
+}
+
 function uniqueStrings(values: string[]): string[] {
     return Array.from(new Set(values));
 }
diff --git a/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts b/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts
index d58bd594..e682bc13 100644
--- a/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts
+++ b/src/__tests__/CodexACPAgent/CodexAcpClient.test.ts
@@ -848,6 +848,72 @@ describe('ACP server test', { timeout: 40_000 }, () => {
         });
     });
 
+    describe('workspace-write network access configuration', () => {
+        async function promptWithConfig(
+            networkAccess: boolean | string,
+            sessionOverrides: Partial<SessionState> = {},
+        ) {
+            const {mockFixture, turnStartSpy} = setupPromptFixture(
+                {additionalDirectories: ["/workspace/extra"], ...sessionOverrides},
+                {sandbox_workspace_write: {network_access: networkAccess}},
+            );
+
+            await mockFixture.getCodexAcpAgent().prompt({
+                sessionId: "session-id",
+                prompt: [{type: "text", text: "Hello"}],
+            });
+
+            return turnStartSpy.mock.calls[0]![0].sandboxPolicy;
+        }
+
+        it('enables network access when configured', async () => {
+            await expect(promptWithConfig(true)).resolves.toEqual({
+                type: "workspaceWrite",
+                writableRoots: ["/workspace/extra"],
+                networkAccess: true,
+                excludeTmpdirEnvVar: false,
+                excludeSlashTmp: false,
+            });
+        });
+
+        it('keeps the false default when the setting is absent', async () => {
+            const {mockFixture, turnStartSpy} = setupPromptFixture({additionalDirectories: ["/workspace/extra"]});
+
+            await mockFixture.getCodexAcpAgent().prompt({
+                sessionId: "session-id",
+                prompt: [{type: "text", text: "Hello"}],
+            });
+
+            expect(turnStartSpy.mock.calls[0]![0].sandboxPolicy).toEqual({
+                type: "workspaceWrite",
+                writableRoots: ["/workspace/extra"],
+                networkAccess: false,
+                excludeTmpdirEnvVar: false,
+                excludeSlashTmp: false,
+            });
+        });
+
+        it('ignores non-boolean network access values', async () => {
+            await expect(promptWithConfig("true")).resolves.toMatchObject({
+                type: "workspaceWrite",
+                networkAccess: false,
+            });
+        });
+
+        it('preserves an explicit false setting', async () => {
+            await expect(promptWithConfig(false)).resolves.toMatchObject({
+                type: "workspaceWrite",
+                networkAccess: false,
+            });
+        });
+
+        it('leaves Agent Full Access policy unchanged', async () => {
+            await expect(promptWithConfig(true, {agentMode: AgentMode.AgentFullAccess})).resolves.toEqual({
+                type: "dangerFullAccess",
+            });
+        });
+    });
+
     function loadNotifications(){
         //TODO collect logs form dev run and then load them from file to speedup
         const serverNotifications: ServerNotification[] = [
@@ -3114,8 +3180,8 @@ describe('ACP server test', { timeout: 40_000 }, () => {
      * Sets up a mock fixture with turnStart/awaitTurnCompleted spied on,
      * and a given session state. Returns the fixture and turnStart spy.
      */
-    function setupPromptFixture(sessionOverrides?: Partial<SessionState>) {
-        const mockFixture = createCodexMockTestFixture();
+    function setupPromptFixture(sessionOverrides?: Partial<SessionState>, codexConfig?: Parameters<typeof createCodexMockTestFixture>[0]) {
+        const mockFixture = createCodexMockTestFixture(codexConfig);
         const sessionState = createTestSessionState(sessionOverrides);
         const turnStartSpy = vi.spyOn(mockFixture.getCodexAppServerClient(), "turnStart").mockResolvedValue({
             turn: {
diff --git a/src/__tests__/acp-test-utils.ts b/src/__tests__/acp-test-utils.ts
index de4ad962..6b2d842c 100644
--- a/src/__tests__/acp-test-utils.ts
+++ b/src/__tests__/acp-test-utils.ts
@@ -1,6 +1,6 @@
 import * as acp from "@agentclientprotocol/sdk";
 import type {CreateElicitationResponse, McpServerStdio, RequestPermissionResponse} from "@agentclientprotocol/sdk";
-import {CodexAcpClient} from '../CodexAcpClient';
+import {CodexAcpClient, type JsonObject} from '../CodexAcpClient';
 import {CodexAppServerClient, type CodexConnectionEvent} from '../CodexAppServerClient';
 import {startCodexConnection} from "../CodexJsonRpcConnection";
 import {CodexAcpServer, type SessionState} from "../CodexAcpServer";
@@ -85,6 +85,7 @@ export interface ConnectionConfig {
     connection: MessageConnection;
     getExitCode: () => number | null;
     acpConnection?: AcpConnectionConfig;
+    codexConfig?: JsonObject;
 }
 
 export function createBaseTestFixture(config: ConnectionConfig): TestFixture {
@@ -97,7 +98,7 @@ export function createBaseTestFixture(config: ConnectionConfig): TestFixture {
     });
 
     const codexAppServerClient = new CodexAppServerClient(config.connection);
-    const codexAcpClient = new CodexAcpClient(codexAppServerClient);
+    const codexAcpClient = new CodexAcpClient(codexAppServerClient, config.codexConfig);
     const codexAcpAgent = new CodexAcpServer(acpConnection, codexAcpClient, undefined, config.getExitCode);
 
     const transportEvents: CodexConnectionEvent[] = [];
@@ -255,7 +256,7 @@ export interface CodexMockTestFixture extends TestFixture {
  * Provides `sendServerRequest()` to simulate server-initiated requests (e.g., approval requests).
  * Provides `setPermissionResponse()` to control ACP permission dialog responses.
  */
-export function createCodexMockTestFixture(): CodexMockTestFixture {
+export function createCodexMockTestFixture(codexConfig?: JsonObject): CodexMockTestFixture {
     let unhandledNotificationHandler: ((notification: any) => void) | null = null;
     const requestHandlers = new Map<string, (params: unknown) => Promise<unknown>>();
 
@@ -303,6 +304,7 @@ export function createCodexMockTestFixture(): CodexMockTestFixture {
     const baseFixture = createBaseTestFixture({
         connection: mockCodexConnection,
         getExitCode: () => null,
+        ...(codexConfig === undefined ? {} : {codexConfig}),
         acpConnection: {
             connection: acpConnection,
             events: acpConnectionEvents,