diff --git a/addons/xterm-addon-serialize/src/SerializeAddon.test.ts b/addons/xterm-addon-serialize/src/SerializeAddon.test.ts
index 67b83884..05f2c61c 100644
--- a/addons/xterm-addon-serialize/src/SerializeAddon.test.ts
+++ b/addons/xterm-addon-serialize/src/SerializeAddon.test.ts
@@ -74,7 +74,7 @@ describe('xterm-addon-serialize', () => {
       }
     });
 
-    terminal = new Terminal({ cols: 10, rows: 2 });
+    terminal = new Terminal({ cols: 10, rows: 2, allowProposedApi: true });
     terminal.loadAddon(serializeAddon);
 
     selectionService = new TestSelectionService((terminal as any)._core._bufferService);
diff --git a/demo/client.ts b/demo/client.ts
index 66ba7bd7..adbbd85a 100644
--- a/demo/client.ts
+++ b/demo/client.ts
@@ -194,6 +194,7 @@ function createTerminal(): void {
 
   const isWindows = ['Windows', 'Win16', 'Win32', 'WinCE'].indexOf(navigator.platform) >= 0;
   term = new Terminal({
+    allowProposedApi: true,
     allowTransparency: true,
     windowsMode: isWindows,
     fontFamily: 'Fira Code, courier-new, courier, monospace',
diff --git a/src/common/services/OptionsService.ts b/src/common/services/OptionsService.ts
index a8c4ff75..4889f120 100644
--- a/src/common/services/OptionsService.ts
+++ b/src/common/services/OptionsService.ts
@@ -33,7 +33,7 @@ export const DEFAULT_OPTIONS: Readonly<ITerminalOptions> = {
   macOptionClickForcesSelection: false,
   minimumContrastRatio: 1,
   disableStdin: false,
-  allowProposedApi: true,
+  allowProposedApi: false,
   allowTransparency: false,
   tabStopWidth: 8,
   theme: {},
diff --git a/src/headless/public/Terminal.test.ts b/src/headless/public/Terminal.test.ts
index a65d8775..403cf35a 100644
--- a/src/headless/public/Terminal.test.ts
+++ b/src/headless/public/Terminal.test.ts
@@ -12,7 +12,7 @@ let term: Terminal;
 describe('Headless API Tests', function (): void {
   beforeEach(() => {
     // Create default terminal to be used by most tests
-    term = new Terminal();
+    term = new Terminal({ allowProposedApi: true });
   });
 
   it('Default options', async () => {
@@ -102,7 +102,7 @@ describe('Headless API Tests', function (): void {
   });
 
   it('clear', async () => {
-    term = new Terminal({ rows: 5 });
+    term = new Terminal({ rows: 5, allowProposedApi: true });
     for (let i = 0; i < 10; i++) {
       await writeSync('\n\rtest' + i);
     }
@@ -254,7 +254,7 @@ describe('Headless API Tests', function (): void {
 
   describe('buffer', () => {
     it('cursorX, cursorY', async () => {
-      term = new Terminal({ rows: 5, cols: 5 });
+      term = new Terminal({ rows: 5, cols: 5, allowProposedApi: true });
       strictEqual(term.buffer.active.cursorX, 0);
       strictEqual(term.buffer.active.cursorY, 0);
       await writeSync('foo');
@@ -275,7 +275,7 @@ describe('Headless API Tests', function (): void {
     });
 
     it('viewportY', async () => {
-      term = new Terminal({ rows: 5 });
+      term = new Terminal({ rows: 5, allowProposedApi: true });
       strictEqual(term.buffer.active.viewportY, 0);
       await writeSync('\n\n\n\n');
       strictEqual(term.buffer.active.viewportY, 0);
@@ -290,7 +290,7 @@ describe('Headless API Tests', function (): void {
     });
 
     it('baseY', async () => {
-      term = new Terminal({ rows: 5 });
+      term = new Terminal({ rows: 5, allowProposedApi: true });
       strictEqual(term.buffer.active.baseY, 0);
       await writeSync('\n\n\n\n');
       strictEqual(term.buffer.active.baseY, 0);
@@ -305,7 +305,7 @@ describe('Headless API Tests', function (): void {
     });
 
     it('length', async () => {
-      term = new Terminal({ rows: 5 });
+      term = new Terminal({ rows: 5, allowProposedApi: true });
       strictEqual(term.buffer.active.length, 5);
       await writeSync('\n\n\n\n');
       strictEqual(term.buffer.active.length, 5);
@@ -317,13 +317,13 @@ describe('Headless API Tests', function (): void {
 
     describe('getLine', () => {
       it('invalid index', async () => {
-        term = new Terminal({ rows: 5 });
+        term = new Terminal({ rows: 5, allowProposedApi: true });
         strictEqual(term.buffer.active.getLine(-1), undefined);
         strictEqual(term.buffer.active.getLine(5), undefined);
       });
 
       it('isWrapped', async () => {
-        term = new Terminal({ cols: 5 });
+        term = new Terminal({ cols: 5, allowProposedApi: true });
         strictEqual(term.buffer.active.getLine(0)!.isWrapped, false);
         strictEqual(term.buffer.active.getLine(1)!.isWrapped, false);
         await writeSync('abcde');
@@ -335,7 +335,7 @@ describe('Headless API Tests', function (): void {
       });
 
       it('translateToString', async () => {
-        term = new Terminal({ cols: 5 });
+        term = new Terminal({ cols: 5, allowProposedApi: true });
         strictEqual(term.buffer.active.getLine(0)!.translateToString(), '     ');
         strictEqual(term.buffer.active.getLine(0)!.translateToString(true), '');
         await writeSync('foo');
@@ -350,7 +350,7 @@ describe('Headless API Tests', function (): void {
       });
 
       it('getCell', async () => {
-        term = new Terminal({ cols: 5 });
+        term = new Terminal({ cols: 5, allowProposedApi: true });
         strictEqual(term.buffer.active.getLine(0)!.getCell(-1), undefined);
         strictEqual(term.buffer.active.getLine(0)!.getCell(5), undefined);
         strictEqual(term.buffer.active.getLine(0)!.getCell(0)!.getChars(), '');
@@ -366,7 +366,7 @@ describe('Headless API Tests', function (): void {
     });
 
     it('active, normal, alternate', async () => {
-      term = new Terminal({ cols: 5 });
+      term = new Terminal({ cols: 5, allowProposedApi: true });
       strictEqual(term.buffer.active.type, 'normal');
       strictEqual(term.buffer.normal.type, 'normal');
       strictEqual(term.buffer.alternate.type, 'alternate');
diff --git a/test/api/Terminal.api.ts b/test/api/Terminal.api.ts
index 3a023d4a..0e1f7764 100644
--- a/test/api/Terminal.api.ts
+++ b/test/api/Terminal.api.ts
@@ -734,7 +734,7 @@ describe('API Integration Tests', function(): void {
   describe('registerDecoration', () => {
     describe('bufferDecorations', () => {
       it('should register decorations and render them when terminal open is called', async () => {
-        await page.evaluate(`window.term = new Terminal({})`);
+        await page.evaluate(`window.term = new Terminal({ allowProposedApi: true })`);
         await page.evaluate(`window.term.open(document.querySelector('#terminal-container'))`);
         await page.waitForSelector('.xterm-text-layer');
         await page.evaluate(`window.marker1 = window.term.addMarker(1)`);
@@ -765,7 +765,7 @@ describe('API Integration Tests', function(): void {
     });
     describe('overviewRulerDecorations', () => {
       it('should not add an overview ruler when width is not set', async () => {
-        await page.evaluate(`window.term = new Terminal({})`);
+        await page.evaluate(`window.term = new Terminal({ allowProposedApi: true })`);
         await page.evaluate(`window.term.open(document.querySelector('#terminal-container'))`);
         await page.waitForSelector('.xterm-text-layer');
         await page.evaluate(`window.marker1 = window.term.addMarker(1)`);
@@ -776,7 +776,7 @@ describe('API Integration Tests', function(): void {
         await pollFor(page, `document.querySelectorAll('.xterm-decoration-overview-ruler').length`, 0);
       });
       it('should add an overview ruler when width is set', async () => {
-        await page.evaluate(`window.term = new Terminal({ overviewRulerWidth: 15 })`);
+        await page.evaluate(`window.term = new Terminal({ allowProposedApi: true, overviewRulerWidth: 15 })`);
         await page.evaluate(`window.term.open(document.querySelector('#terminal-container'))`);
         await page.waitForSelector('.xterm-text-layer');
         await page.evaluate(`window.marker1 = window.term.addMarker(1)`);
diff --git a/test/api/TestUtils.ts b/test/api/TestUtils.ts
index 2acc4d09..e059c92c 100644
--- a/test/api/TestUtils.ts
+++ b/test/api/TestUtils.ts
@@ -44,7 +44,7 @@ export async function timeout(ms: number): Promise<void> {
 }
 
 export async function openTerminal(page: playwright.Page, options: ITerminalOptions = {}): Promise<void> {
-  await page.evaluate(`window.term = new Terminal(${JSON.stringify(options)})`);
+  await page.evaluate(`window.term = new Terminal(${JSON.stringify({ allowProposedApi: true, ...options })})`);
   await page.evaluate(`window.term.open(document.querySelector('#terminal-container'))`);
   if (options.rendererType === 'dom') {
     await page.waitForSelector('.xterm-rows');