diff --git a/packages/create-docusaurus/templates/shared/blog/2019-05-28-first-blog-post.md b/packages/create-docusaurus/templates/shared/blog/2019-05-28-first-blog-post.mdx
similarity index 94%
rename from packages/create-docusaurus/templates/shared/blog/2019-05-28-first-blog-post.md
rename to packages/create-docusaurus/templates/shared/blog/2019-05-28-first-blog-post.mdx
index d3032efb35cf..a62ee55e1860 100644
--- a/packages/create-docusaurus/templates/shared/blog/2019-05-28-first-blog-post.md
+++ b/packages/create-docusaurus/templates/shared/blog/2019-05-28-first-blog-post.mdx
@@ -7,6 +7,6 @@ tags: [hola, docusaurus]
 
 Lorem ipsum dolor sit amet...
 
-<!-- truncate -->
+{/* truncate */}
 
 ...consectetur adipiscing elit. Pellentesque elementum dignissim ultricies. Fusce rhoncus ipsum tempor eros aliquam consequat. Lorem ipsum dolor sit amet
diff --git a/packages/create-docusaurus/templates/shared/blog/2019-05-29-long-blog-post.md b/packages/create-docusaurus/templates/shared/blog/2019-05-29-long-blog-post.mdx
similarity index 96%
rename from packages/create-docusaurus/templates/shared/blog/2019-05-29-long-blog-post.md
rename to packages/create-docusaurus/templates/shared/blog/2019-05-29-long-blog-post.mdx
index eb4435de591c..681cf0ec358c 100644
--- a/packages/create-docusaurus/templates/shared/blog/2019-05-29-long-blog-post.md
+++ b/packages/create-docusaurus/templates/shared/blog/2019-05-29-long-blog-post.mdx
@@ -7,9 +7,9 @@ tags: [hello, docusaurus]
 
 This is the summary of a very long blog post,
 
-Use a `<!--` `truncate` `-->` comment to limit blog post size in the list view.
+Use a `{/*` `truncate` `*/}` comment to limit blog post size in the list view.
 
-<!-- truncate -->
+{/* truncate */}
 
 Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque elementum dignissim ultricies. Fusce rhoncus ipsum tempor eros aliquam consequat. Lorem ipsum dolor sit amet
 
diff --git a/packages/create-docusaurus/templates/shared/blog/2021-08-26-welcome/index.md b/packages/create-docusaurus/templates/shared/blog/2021-08-26-welcome/index.mdx
similarity index 97%
rename from packages/create-docusaurus/templates/shared/blog/2021-08-26-welcome/index.md
rename to packages/create-docusaurus/templates/shared/blog/2021-08-26-welcome/index.mdx
index 349ea075f5bb..a21bccd5f379 100644
--- a/packages/create-docusaurus/templates/shared/blog/2021-08-26-welcome/index.md
+++ b/packages/create-docusaurus/templates/shared/blog/2021-08-26-welcome/index.mdx
@@ -9,7 +9,7 @@ tags: [facebook, hello, docusaurus]
 
 Here are a few tips you might find useful.
 
-<!-- truncate -->
+{/* truncate */}
 
 Simply add Markdown files (or folders) to the `blog` directory.
 
diff --git a/packages/create-docusaurus/templates/shared/docs/intro.md b/packages/create-docusaurus/templates/shared/docs/intro.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/docs/intro.md
rename to packages/create-docusaurus/templates/shared/docs/intro.mdx
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/congratulations.md b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/congratulations.mdx
similarity index 90%
rename from packages/create-docusaurus/templates/shared/docs/tutorial-basics/congratulations.md
rename to packages/create-docusaurus/templates/shared/docs/tutorial-basics/congratulations.mdx
index 04771a00b72f..2917c3971f75 100644
--- a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/congratulations.md
+++ b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/congratulations.mdx
@@ -8,7 +8,7 @@ You have just learned the **basics of Docusaurus** and made some changes to the
 
 Docusaurus has **much more to offer**!
 
-Have **5 more minutes**? Take a look at **[versioning](../tutorial-extras/manage-docs-versions.md)** and **[i18n](../tutorial-extras/translate-your-site.md)**.
+Have **5 more minutes**? Take a look at **[versioning](../tutorial-extras/manage-docs-versions.mdx)** and **[i18n](../tutorial-extras/translate-your-site.mdx)**.
 
 Anything **unclear** or **buggy** in this tutorial? [Please report it!](https://github.com/facebook/docusaurus/discussions/4610)
 
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-blog-post.md b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-blog-post.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-blog-post.md
rename to packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-blog-post.mdx
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-document.md b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-document.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-document.md
rename to packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-document.mdx
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-page.md b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-page.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-page.md
rename to packages/create-docusaurus/templates/shared/docs/tutorial-basics/create-a-page.mdx
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/deploy-your-site.md b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/deploy-your-site.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/docs/tutorial-basics/deploy-your-site.md
rename to packages/create-docusaurus/templates/shared/docs/tutorial-basics/deploy-your-site.mdx
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/markdown-features.mdx b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/markdown-features.mdx
index 35e00825ed77..e739ec4cd13a 100644
--- a/packages/create-docusaurus/templates/shared/docs/tutorial-basics/markdown-features.mdx
+++ b/packages/create-docusaurus/templates/shared/docs/tutorial-basics/markdown-features.mdx
@@ -20,9 +20,25 @@ slug: /my-custom-url
 ---
 // highlight-end
 
-## Markdown heading
+Markdown content
+```
+
+## Headings {/* #my-heading-id */}
+
+Markdown headings are supported using the standard “#” syntax and are automatically added to the table of contents. The number of `#` corresponds to the heading level.
+
+```md
+## Headings
 
-Markdown text with [links](./hello.md)
+My text
+```
+
+### Heading Ids {/* #my-custom-id */}
+
+Add `{/* #my-custom-id */}` after the heading text to assign it an explicit anchor id, used for linking.
+
+```md
+### Heading Ids {/_ #my-custom-id _/}
 ```
 
 ## Links
@@ -34,10 +50,10 @@ Let's see how to [Create a page](/create-a-page).
 ```
 
 ```md
-Let's see how to [Create a page](./create-a-page.md).
+Let's see how to [Create a page](./create-a-page.mdx).
 ```
 
-**Result:** Let's see how to [Create a page](./create-a-page.md).
+**Result:** Let's see how to [Create a page](./create-a-page.mdx).
 
 ## Images
 
@@ -80,26 +96,26 @@ function HelloDocusaurus() {
 Docusaurus has a special syntax to create admonitions and callouts:
 
 ```md
-:::tip My tip
+:::tip[My tip]
 
 Use this awesome feature option
 
 :::
 
-:::danger Take care
+:::danger[Take care]
 
 This action is dangerous
 
 :::
 ```
 
-:::tip My tip
+:::tip[My tip]
 
 Use this awesome feature option
 
 :::
 
-:::danger Take care
+:::danger[Take care]
 
 This action is dangerous
 
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-extras/manage-docs-versions.md b/packages/create-docusaurus/templates/shared/docs/tutorial-extras/manage-docs-versions.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/docs/tutorial-extras/manage-docs-versions.md
rename to packages/create-docusaurus/templates/shared/docs/tutorial-extras/manage-docs-versions.mdx
diff --git a/packages/create-docusaurus/templates/shared/docs/tutorial-extras/translate-your-site.md b/packages/create-docusaurus/templates/shared/docs/tutorial-extras/translate-your-site.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/docs/tutorial-extras/translate-your-site.md
rename to packages/create-docusaurus/templates/shared/docs/tutorial-extras/translate-your-site.mdx
diff --git a/packages/create-docusaurus/templates/shared/src/pages/markdown-page.md b/packages/create-docusaurus/templates/shared/src/pages/markdown-page.mdx
similarity index 100%
rename from packages/create-docusaurus/templates/shared/src/pages/markdown-page.md
rename to packages/create-docusaurus/templates/shared/src/pages/markdown-page.mdx
diff --git a/packages/docusaurus-types/src/config.d.ts b/packages/docusaurus-types/src/config.d.ts
index b6d3d8a0a396..6f88b68dc6c6 100644
--- a/packages/docusaurus-types/src/config.d.ts
+++ b/packages/docusaurus-types/src/config.d.ts
@@ -41,6 +41,7 @@ export type FutureV4Config = {
   useCssCascadeLayers: boolean;
   siteStorageNamespacing: boolean;
   fasterByDefault: boolean;
+  mdx1CompatDisabledByDefault: boolean;
 };
 
 // VCS (Version Control System) info about a given change, e.g., a git commit.
diff --git a/packages/docusaurus-types/src/index.d.ts b/packages/docusaurus-types/src/index.d.ts
index 6d153c387a71..6dfca63d1f70 100644
--- a/packages/docusaurus-types/src/index.d.ts
+++ b/packages/docusaurus-types/src/index.d.ts
@@ -21,6 +21,7 @@ export {
 } from './config';
 
 export {
+  MDX1CompatOptions,
   MarkdownConfig,
   MarkdownHooks,
   DefaultParseFrontMatter,
diff --git a/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap b/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap
index c0437a9e133a..35701f702613 100644
--- a/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap
+++ b/packages/docusaurus/src/server/__tests__/__snapshots__/config.test.ts.snap
@@ -27,6 +27,7 @@ exports[`loadSiteConfig website with .cjs siteConfig 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -114,6 +115,7 @@ exports[`loadSiteConfig website with ts + js config 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -201,6 +203,7 @@ exports[`loadSiteConfig website with valid JS CJS config 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -288,6 +291,7 @@ exports[`loadSiteConfig website with valid JS ESM config 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -375,6 +379,7 @@ exports[`loadSiteConfig website with valid TypeScript CJS config 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -462,6 +467,7 @@ exports[`loadSiteConfig website with valid TypeScript ESM config 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -549,6 +555,7 @@ exports[`loadSiteConfig website with valid async config 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -638,6 +645,7 @@ exports[`loadSiteConfig website with valid async config creator function 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -727,6 +735,7 @@ exports[`loadSiteConfig website with valid config creator function 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -819,6 +828,7 @@ exports[`loadSiteConfig website with valid siteConfig 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
diff --git a/packages/docusaurus/src/server/__tests__/__snapshots__/site.test.ts.snap b/packages/docusaurus/src/server/__tests__/__snapshots__/site.test.ts.snap
index a6999ad02ad6..d10c593e052c 100644
--- a/packages/docusaurus/src/server/__tests__/__snapshots__/site.test.ts.snap
+++ b/packages/docusaurus/src/server/__tests__/__snapshots__/site.test.ts.snap
@@ -107,6 +107,7 @@ exports[`loadSite custom-i18n-site loads site 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -282,6 +283,7 @@ exports[`loadSite simple-site-with-baseUrl loads site - custom config 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -449,6 +451,7 @@ exports[`loadSite simple-site-with-baseUrl loads site - custom outDir 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -616,6 +619,7 @@ exports[`loadSite simple-site-with-baseUrl loads site 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -827,6 +831,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site -  locale fr + custom
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -1060,6 +1065,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site - custom outDir 1`] =
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -1293,6 +1299,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site - locale de 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -1526,6 +1533,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site - locale en 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -1759,6 +1767,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site - locale es 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -1992,6 +2001,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site - locale fr 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -2225,6 +2235,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site - locale it 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
@@ -2458,6 +2469,7 @@ exports[`loadSite simple-site-with-baseUrl-i18n loads site 1`] = `
       },
       "v4": {
         "fasterByDefault": false,
+        "mdx1CompatDisabledByDefault": false,
         "removeLegacyPostBuildHeadAttribute": false,
         "siteStorageNamespacing": false,
         "useCssCascadeLayers": false,
diff --git a/packages/docusaurus/src/server/__tests__/configValidation.test.ts b/packages/docusaurus/src/server/__tests__/configValidation.test.ts
index 63c58e82da1e..6ed937c2a31d 100644
--- a/packages/docusaurus/src/server/__tests__/configValidation.test.ts
+++ b/packages/docusaurus/src/server/__tests__/configValidation.test.ts
@@ -67,6 +67,7 @@ describe('normalizeConfig', () => {
           useCssCascadeLayers: true,
           siteStorageNamespacing: true,
           fasterByDefault: true,
+          mdx1CompatDisabledByDefault: true,
         },
         faster: {
           swcJsLoader: true,
@@ -513,6 +514,7 @@ describe('markdown', () => {
   ): MarkdownConfig {
     return normalizeConfig({markdown}).markdown;
   }
+
   it('accepts undefined object', () => {
     expect(normalizeMarkdown(undefined)).toEqual(DEFAULT_CONFIG.markdown);
   });
@@ -1348,6 +1350,7 @@ describe('future', () => {
         useCssCascadeLayers: true,
         siteStorageNamespacing: true,
         fasterByDefault: true,
+        mdx1CompatDisabledByDefault: true,
       },
       faster: {
         swcJsLoader: true,
@@ -2566,6 +2569,7 @@ describe('future', () => {
         useCssCascadeLayers: true,
         siteStorageNamespacing: true,
         fasterByDefault: true,
+        mdx1CompatDisabledByDefault: true,
       };
       expect(
         normalizeConfig({
@@ -2906,5 +2910,64 @@ describe('future', () => {
         `);
       });
     });
+
+    describe('mdx1CompatDisabledByDefault', () => {
+      function mdx1CompatContaining(mdx1Compat: object) {
+        return expect.objectContaining({
+          markdown: expect.objectContaining({mdx1Compat}),
+        });
+      }
+
+      const MDX1_COMPAT_ALL_TRUE = {
+        comments: true,
+        admonitions: true,
+        headingIds: true,
+      };
+
+      const MDX1_COMPAT_ALL_FALSE = {
+        comments: false,
+        admonitions: false,
+        headingIds: false,
+      };
+
+      it('defaults mdx1Compat to all true when flag is off', () => {
+        expect(normalizeConfig({})).toEqual(
+          mdx1CompatContaining(MDX1_COMPAT_ALL_TRUE),
+        );
+      });
+
+      it('defaults mdx1Compat to all false when flag is on', () => {
+        expect(
+          normalizeConfig({
+            future: {v4: {mdx1CompatDisabledByDefault: true}},
+          }),
+        ).toEqual(mdx1CompatContaining(MDX1_COMPAT_ALL_FALSE));
+      });
+
+      it('defaults mdx1Compat to all false when v4: true', () => {
+        expect(
+          normalizeConfig({
+            future: {v4: true},
+          }),
+        ).toEqual(mdx1CompatContaining(MDX1_COMPAT_ALL_FALSE));
+      });
+
+      it('keeps explicit mdx1Compat overrides when flag is on', () => {
+        expect(
+          normalizeConfig({
+            future: {v4: {mdx1CompatDisabledByDefault: true}},
+            markdown: {
+              mdx1Compat: {admonitions: true},
+            },
+          }),
+        ).toEqual(
+          mdx1CompatContaining({
+            comments: false,
+            admonitions: true,
+            headingIds: false,
+          }),
+        );
+      });
+    });
   });
 });
diff --git a/packages/docusaurus/src/server/configValidation.ts b/packages/docusaurus/src/server/configValidation.ts
index 5558b509ca75..724f4ea70cf2 100644
--- a/packages/docusaurus/src/server/configValidation.ts
+++ b/packages/docusaurus/src/server/configValidation.ts
@@ -26,6 +26,7 @@ import type {
   FutureV4Config,
   I18nConfig,
   I18nLocaleConfig,
+  MDX1CompatOptions,
   MarkdownConfig,
   MarkdownHooks,
   StorageConfig,
@@ -102,6 +103,7 @@ export const DEFAULT_FUTURE_V4_CONFIG: FutureV4Config = {
   useCssCascadeLayers: false,
   siteStorageNamespacing: false,
   fasterByDefault: false,
+  mdx1CompatDisabledByDefault: false,
 };
 
 // When using the "v4: true" shortcut
@@ -110,6 +112,7 @@ export const DEFAULT_FUTURE_V4_CONFIG_TRUE: FutureV4Config = {
   useCssCascadeLayers: true,
   siteStorageNamespacing: true,
   fasterByDefault: true,
+  mdx1CompatDisabledByDefault: true,
 };
 
 export const DEFAULT_FUTURE_CONFIG: FutureConfig = {
@@ -124,17 +127,22 @@ export const DEFAULT_MARKDOWN_HOOKS: MarkdownHooks = {
   onBrokenMarkdownImages: 'throw',
 };
 
+export const DEFAULT_MARKDOWN_MDX1COMPAT: MDX1CompatOptions = {
+  comments: true,
+  admonitions: true,
+  headingIds: true,
+};
+
 export const DEFAULT_MARKDOWN_CONFIG: MarkdownConfig = {
-  format: 'mdx', // TODO change this to "detect" in Docusaurus v4?
+  // TODO Docusaurus v5: change this to "detect"?
+  //  we probably need stable CommonMark support first
+  //  see https://github.com/facebook/docusaurus/issues/9092
+  format: 'mdx',
   mermaid: false,
   emoji: true,
   preprocessor: undefined,
   parseFrontMatter: DEFAULT_PARSE_FRONT_MATTER,
-  mdx1Compat: {
-    comments: true,
-    admonitions: true,
-    headingIds: true,
-  },
+  mdx1Compat: DEFAULT_MARKDOWN_MDX1COMPAT,
   anchors: {
     maintainCase: false,
   },
@@ -319,6 +327,9 @@ const FUTURE_V4_SCHEMA = Joi.alternatives()
       fasterByDefault: Joi.boolean().default(
         DEFAULT_FUTURE_V4_CONFIG.fasterByDefault,
       ),
+      mdx1CompatDisabledByDefault: Joi.boolean().default(
+        DEFAULT_FUTURE_V4_CONFIG.mdx1CompatDisabledByDefault,
+      ),
     }),
     Joi.boolean()
       .required()
@@ -511,17 +522,14 @@ export const ConfigSchema = Joi.object<DocusaurusConfig>({
       .arity(1)
       .optional()
       .default(() => DEFAULT_CONFIG.markdown.preprocessor),
+    // Individual boolean defaults are not set here on purpose
+    // They are resolved in postProcessDocusaurusConfig based on
+    // the future.v4.mdx1CompatDisabledByDefault flag
     mdx1Compat: Joi.object({
-      comments: Joi.boolean().default(
-        DEFAULT_CONFIG.markdown.mdx1Compat.comments,
-      ),
-      admonitions: Joi.boolean().default(
-        DEFAULT_CONFIG.markdown.mdx1Compat.admonitions,
-      ),
-      headingIds: Joi.boolean().default(
-        DEFAULT_CONFIG.markdown.mdx1Compat.headingIds,
-      ),
-    }).default(DEFAULT_CONFIG.markdown.mdx1Compat),
+      comments: Joi.boolean(),
+      admonitions: Joi.boolean(),
+      headingIds: Joi.boolean(),
+    }).default({}),
     remarkRehypeOptions:
       // add proper external options validation?
       // Not sure if it's a good idea, validation is likely to become stale
@@ -546,7 +554,12 @@ export const ConfigSchema = Joi.object<DocusaurusConfig>({
         )
         .default(DEFAULT_CONFIG.markdown.hooks.onBrokenMarkdownImages),
     }).default(DEFAULT_CONFIG.markdown.hooks),
-  }).default(DEFAULT_CONFIG.markdown),
+  }).default({
+    ...DEFAULT_CONFIG.markdown,
+    mdx1Compat: {
+      // erased on purpose, filled using postprocessing
+    },
+  }),
 }).messages({
   'docusaurus.configValidationWarning':
     'Docusaurus config validation warning. Field {#label}: {#warningMessage}',
@@ -576,6 +589,16 @@ function postProcessDocusaurusConfig(config: DocusaurusConfig) {
     }
   }
 
+  // Resolve mdx1Compat config based on the v4.mdx1CompatDisabledByDefault flag
+  // undefined means "not explicitly set by user"
+  const mdx1CompatDefault = !config.future.v4.mdx1CompatDisabledByDefault;
+  const mdx1CompatKeys = Object.keys(
+    DEFAULT_MARKDOWN_MDX1COMPAT,
+  ) as (keyof MDX1CompatOptions)[];
+  for (const key of mdx1CompatKeys) {
+    config.markdown.mdx1Compat[key] ??= mdx1CompatDefault;
+  }
+
   if (config.onBrokenMarkdownLinks) {
     logger.warn`The code=${'siteConfig.onBrokenMarkdownLinks'} config option is deprecated and will be removed in Docusaurus v4.
 Please migrate and move this option to code=${'siteConfig.markdown.hooks.onBrokenMarkdownLinks'} instead.`;
diff --git a/website/_dogfooding/_pages tests/markdown-tests-mdx.mdx b/website/_dogfooding/_pages tests/markdown-tests-mdx.mdx
index 1adab642b270..3c982b5300a7 100644
--- a/website/_dogfooding/_pages tests/markdown-tests-mdx.mdx	
+++ b/website/_dogfooding/_pages tests/markdown-tests-mdx.mdx	
@@ -56,11 +56,11 @@ MDX comment in JSX:
 
 <>
   {/* comment */}
-  <span>
+  <div>
     {/* comment */}
     TEST
     {/* comment */}
-  </span>
+  </div>
 </>
 
 ## Import code block from source code file
diff --git a/website/docs/api/docusaurus.config.js.mdx b/website/docs/api/docusaurus.config.js.mdx
index 8e0019f461aa..f1547f79aef0 100644
--- a/website/docs/api/docusaurus.config.js.mdx
+++ b/website/docs/api/docusaurus.config.js.mdx
@@ -254,6 +254,7 @@ export default {
       useCssCascadeLayers: true,
       siteStorageNamespacing: true,
       fasterByDefault: true,
+      mdx1CompatDisabledByDefault: true,
     },
     faster: {
       swcJsLoader: true,
@@ -275,6 +276,7 @@ export default {
   - [`useCssCascadeLayers`](https://github.com/facebook/docusaurus/pull/11142): This enables the [Docusaurus CSS Cascade Layers plugin](./plugins/plugin-css-cascade-layers.mdx) with pre-configured layers that we plan to apply by default for Docusaurus v4.
   - `siteStorageNamespacing`: Defaults the [`storage.namespace`](#storage) config to `true` instead of `false`. This enables automatic browser storage key namespacing, which avoids storage key conflicts when multiple Docusaurus sites are hosted under the same domain, or on localhost.
   - `fasterByDefault`: Defaults all `future.faster` flags to `true` instead of `false`. This enables [Docusaurus Faster](https://github.com/facebook/docusaurus/issues/10556) features by default. Requires having `@docusaurus/faster` in your dependencies. If you explicitly set individual `faster` flags, those explicit values take precedence.
+  - `mdx1CompatDisabledByDefault`: Defaults all [`markdown.mdx1Compat`](#markdown) flags to `false` instead of `true`. This prepares your site for Docusaurus v4, which will not enable MDX v1 compatibility by default. If you explicitly set individual `mdx1Compat` flags, those explicit values take precedence.
 - `faster`: An object containing feature flags to make the Docusaurus build faster. This requires adding the `@docusaurus/faster` package to your site's dependencies. Use `true` as a shorthand to enable all flags. Read more on the [Docusaurus Faster](https://github.com/facebook/docusaurus/issues/10556) issue. Available feature flags:
   - [`swcJsLoader`](https://github.com/facebook/docusaurus/pull/10435): Use [SWC](https://swc.rs/) to transpile JS (instead of [Babel](https://babeljs.io/)).
   - [`swcJsMinimizer`](https://github.com/facebook/docusaurus/pull/10441): Use [SWC](https://swc.rs/) to minify JS (instead of [Terser](https://github.com/terser/terser)).
@@ -734,7 +736,7 @@ export default {
 | `emoji` | `boolean` | `true` | When `true`, allows Docusaurus to render emoji shortcodes (e.g., `:+1:`) as Unicode emoji (👍). When `false`, emoji shortcodes are left as-is. |
 | `preprocessor` | `MarkdownPreprocessor` | `undefined` | Gives you the ability to alter the Markdown content string before parsing. Use it as a last-resort escape hatch or workaround: it is almost always better to implement a Remark/Rehype plugin. |
 | `parseFrontMatter` | `ParseFrontMatter` | `undefined` | Gives you the ability to provide your own front matter parser, or to enhance the default parser. Read our [front matter guide](../guides/markdown-features/markdown-features-intro.mdx#front-matter) for details. |
-| `mdx1Compat` | `MDX1CompatOptions` | `{comments: true, admonitions: true, headingIds: true}` | Compatibility options to make it easier to upgrade to Docusaurus v3+. |
+| `mdx1Compat` | `MDX1CompatOptions` | `{comments: true, admonitions: true, headingIds: true}` | Compatibility options to make it easier to upgrade to Docusaurus v3+. Defaults to all `false` when [`future.v4.mdx1CompatDisabledByDefault`](#future) is enabled. |
 | `anchors` | `MarkdownAnchorsConfig` | `{maintainCase: false}` | Options to control the behavior of anchors generated from Markdown headings |
 | `remarkRehypeOptions` | `object` | `undefined` | Makes it possible to pass custom [`remark-rehype` options](https://github.com/remarkjs/remark-rehype#options). |
 | `hooks` | `MarkdownHooks` | `object` | Make it possible to customize the MDX loader behavior with callbacks or built-in options. |
diff --git a/website/docusaurus.config.ts b/website/docusaurus.config.ts
index e0477b74bc17..7246fcc3266e 100644
--- a/website/docusaurus.config.ts
+++ b/website/docusaurus.config.ts
@@ -234,8 +234,9 @@ export default async function createConfigAsync() {
         onBrokenMarkdownLinks: 'warn',
       },
       mdx1Compat: {
-        headingIds: false,
-        comments: false,
+        // Needed for us until Crowdin improves support
+        // See https://github.com/facebook/docusaurus/pull/11847#issuecomment-4183213345
+        admonitions: true,
       },
       remarkRehypeOptions: {
         footnoteLabel: getLocalizedConfigValue('remarkRehypeOptions_footnotes'),
diff --git a/yarn.lock b/yarn.lock
index 4185826e1bee..a9a7ff263b88 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -12325,9 +12325,9 @@ lodash.uniq@^4.5.0:
   integrity sha512-xfBaXQd9ryd9dlSDvnvI0lvxfLJlYAZzXomUYzLKtUeOQvOP5piqAWuGtrhWeqaXK9hhoM/iyJc5AV+XfsX3HQ==
 
 lodash@^4.17.20, lodash@^4.17.21:
-  version "4.17.23"
-  resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.23.tgz#f113b0378386103be4f6893388c73d0bde7f2c5a"
-  integrity sha512-LgVTMpQtIopCi79SJeDiP0TfWi5CNEc/L/aRdTh3yIvmZXTnheWpKjSZhnvMl8iXbC1tFg9gdHHDMLoV7CnG+w==
+  version "4.18.1"
+  resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.18.1.tgz#ff2b66c1f6326d59513de2407bf881439812771c"
+  integrity sha512-dMInicTPVE8d1e5otfwmmjlxkZoUpiVLwyeTdUsi/Caj/gfzzblBcCE5sRHV/AsjuCmxWrte2TNGSYuCeCq+0Q==
 
 log-symbols@^4.1.0:
   version "4.1.0"
@@ -15337,9 +15337,9 @@ postcss-zindex@^6.0.2:
   integrity sha512-5BxW9l1evPB/4ZIc+2GobEBoKC+h8gPGCMi+jxsYvd2x0mjq7wazk6DrP71pStqxE9Foxh5TVnonbWpFZzXaYg==
 
 postcss@^8.2.x, postcss@^8.4.19, postcss@^8.4.21, postcss@^8.4.24, postcss@^8.4.33, postcss@^8.5.4:
-  version "8.5.4"
-  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.5.4.tgz#d61014ac00e11d5f58458ed7247d899bd65f99c0"
-  integrity sha512-QSa9EBe+uwlGTFmHsPKokv3B/oEMQZxfqW0QqNCyhpa6mB1afzulwn8hihglqAb2pOw+BJgNlmXQ8la2VeHB7w==
+  version "8.5.8"
+  resolved "https://registry.yarnpkg.com/postcss/-/postcss-8.5.8.tgz#6230ecc8fb02e7a0f6982e53990937857e13f399"
+  integrity sha512-OW/rX8O/jXnm82Ey1k44pObPtdblfiuWnrd8X7GJ7emImCOstunGbXUpp7HdBrFQX6rJzn3sPT397Wp5aCwCHg==
   dependencies:
     nanoid "^3.3.11"
     picocolors "^1.1.1"
@@ -15693,9 +15693,9 @@ react-is@^17.0.1, react-is@^18.0.0, react-is@^18.3.1, react-is@^19.2.4:
   integrity sha512-W+EWGn2v0ApPKgKKCy/7s7WHXkboGcsrXE+2joLyVxkbyVQfO3MUEaUQDHoSmb8TFFrSKYa9mw64WZHNHSDzYA==
 
 react-json-view-lite@^2.3.0:
-  version "2.3.0"
-  resolved "https://registry.yarnpkg.com/react-json-view-lite/-/react-json-view-lite-2.3.0.tgz#872e36202c00711bf3f8582e0ae6c5cf63bbaac0"
-  integrity sha512-btGE+nynBIPRPLWMkE7ASOeF7QzzG6S3bTOTL0FLFNvprMsODmv8eUMFCUK9SOJqV8GCOW/avCpDJnMSchTafQ==
+  version "2.5.0"
+  resolved "https://registry.yarnpkg.com/react-json-view-lite/-/react-json-view-lite-2.5.0.tgz#c7ff011c7cc80e9900abc7aa4916c6a5c6d6c1c6"
+  integrity sha512-tk7o7QG9oYyELWHL8xiMQ8x4WzjCzbWNyig3uexmkLb54r8jO0yH3WCWx8UZS0c49eSA4QUmG5caiRJ8fAn58g==
 
 react-lite-youtube-embed@^2.3.52:
   version "2.4.0"