diff --git a/.changeset/hip-dancers-move.md b/.changeset/hip-dancers-move.md
new file mode 100644
index 000000000..bcebddf5c
--- /dev/null
+++ b/.changeset/hip-dancers-move.md
@@ -0,0 +1,6 @@
+---
+'astro': minor
+'@astrojs/markdown-remark': patch
+---
+
+Speed up internal markdown builds with new vite-plugin markdown
diff --git a/examples/docs/src/components/PageContent/PageContent.astro b/examples/docs/src/components/PageContent/PageContent.astro
index e0d96b57c..9af4056c9 100644
--- a/examples/docs/src/components/PageContent/PageContent.astro
+++ b/examples/docs/src/components/PageContent/PageContent.astro
@@ -2,9 +2,8 @@
 import MoreMenu from "../RightSidebar/MoreMenu.astro";
 import TableOfContents from "../RightSidebar/TableOfContents";
 
-const { content, githubEditUrl } = Astro.props;
+const { content, headings, githubEditUrl } = Astro.props;
 const title = content.title;
-const headings = content.astro.headings;
 ---
 
 <article id="article" class="content">
@@ -29,9 +28,11 @@ const headings = content.astro.headings;
 		display: flex;
 		flex-direction: column;
 	}
-	.content > section {
+
+	.content>section {
 		margin-bottom: 4rem;
 	}
+
 	.block {
 		display: block;
 	}
diff --git a/examples/docs/src/components/RightSidebar/RightSidebar.astro b/examples/docs/src/components/RightSidebar/RightSidebar.astro
index c009d2202..71ad5e1c2 100644
--- a/examples/docs/src/components/RightSidebar/RightSidebar.astro
+++ b/examples/docs/src/components/RightSidebar/RightSidebar.astro
@@ -1,8 +1,7 @@
 ---
 import TableOfContents from "./TableOfContents";
 import MoreMenu from "./MoreMenu.astro";
-const { content, githubEditUrl } = Astro.props;
-const headings = content.astro.headings;
+const { content, headings, githubEditUrl } = Astro.props;
 ---
 
 <nav class="sidebar-nav" aria-labelledby="grid-right">
@@ -18,6 +17,7 @@ const headings = content.astro.headings;
 		position: sticky;
 		top: 0;
 	}
+
 	.sidebar-nav-inner {
 		height: 100%;
 		padding: 0;
diff --git a/packages/astro/package.json b/packages/astro/package.json
index 9a47eebee..22321bf46 100644
--- a/packages/astro/package.json
+++ b/packages/astro/package.json
@@ -48,6 +48,8 @@
     "./vite-plugin-astro-postprocess/*": "./dist/vite-plugin-astro-postprocess/*",
     "./vite-plugin-jsx/*": "./dist/vite-plugin-jsx/*",
     "./vite-plugin-jsx": "./dist/vite-plugin-jsx/index.js",
+    "./vite-plugin-markdown-legacy": "./dist/vite-plugin-markdown-legacy/index.js",
+    "./vite-plugin-markdown-legacy/*": "./dist/vite-plugin-markdown-legacy/*",
     "./vite-plugin-markdown": "./dist/vite-plugin-markdown/index.js",
     "./vite-plugin-markdown/*": "./dist/vite-plugin-markdown/*",
     "./dist/jsx/*": "./dist/jsx/*"
diff --git a/packages/astro/src/core/config.ts b/packages/astro/src/core/config.ts
index 182b6b35a..3329dfb77 100644
--- a/packages/astro/src/core/config.ts
+++ b/packages/astro/src/core/config.ts
@@ -17,6 +17,7 @@ import { z } from 'zod';
 import { LogOptions } from './logger/core.js';
 import { appendForwardSlash, prependForwardSlash, trimSlashes } from './path.js';
 import { arraify, isObject } from './util.js';
+import jsxRenderer from '../jsx/renderer.js';
 
 load.use([loadTypeScript]);
 
@@ -343,16 +344,11 @@ export async function validateConfig(
 		_ctx: {
 			pageExtensions: ['.astro', '.md', '.html'],
 			scripts: [],
-			renderers: [],
+			renderers: [jsxRenderer],
 			injectedRoutes: [],
 			adapter: undefined,
 		},
 	};
-	if (result.integrations.find((integration) => integration.name === '@astrojs/mdx')) {
-		// Enable default JSX integration. It needs to come first, so unshift rather than push!
-		const { default: jsxRenderer } = await import('../jsx/renderer.js');
-		(result._ctx.renderers as any[]).unshift(jsxRenderer);
-	}
 
 	// If successful, return the result as a verified AstroConfig object.
 	return result;
diff --git a/packages/astro/src/core/create-vite.ts b/packages/astro/src/core/create-vite.ts
index d197fb409..37a31ed66 100644
--- a/packages/astro/src/core/create-vite.ts
+++ b/packages/astro/src/core/create-vite.ts
@@ -12,6 +12,7 @@ import envVitePlugin from '../vite-plugin-env/index.js';
 import htmlVitePlugin from '../vite-plugin-html/index.js';
 import astroIntegrationsContainerPlugin from '../vite-plugin-integrations-container/index.js';
 import jsxVitePlugin from '../vite-plugin-jsx/index.js';
+import legacyMarkdownVitePlugin from '../vite-plugin-markdown-legacy/index.js';
 import markdownVitePlugin from '../vite-plugin-markdown/index.js';
 import astroScriptsPlugin from '../vite-plugin-scripts/index.js';
 import astroScriptsPageSSRPlugin from '../vite-plugin-scripts/page-ssr.js';
@@ -76,7 +77,9 @@ export async function createVite(
 			// the build to run very slow as the filewatcher is triggered often.
 			mode !== 'build' && astroViteServerPlugin({ config: astroConfig, logging }),
 			envVitePlugin({ config: astroConfig }),
-			markdownVitePlugin({ config: astroConfig, logging }),
+			astroConfig.legacy.astroFlavoredMarkdown
+				? legacyMarkdownVitePlugin({ config: astroConfig, logging })
+				: markdownVitePlugin({ config: astroConfig, logging }),
 			htmlVitePlugin(),
 			jsxVitePlugin({ config: astroConfig, logging }),
 			astroPostprocessVitePlugin({ config: astroConfig }),
diff --git a/packages/astro/src/vite-plugin-jsx/index.ts b/packages/astro/src/vite-plugin-jsx/index.ts
index 56005413e..3a6f47e86 100644
--- a/packages/astro/src/vite-plugin-jsx/index.ts
+++ b/packages/astro/src/vite-plugin-jsx/index.ts
@@ -137,9 +137,31 @@ export default function jsx({ config, logging }: AstroPluginJSXOptions): Plugin
 				JSX_RENDERER_CACHE.set(config, jsxRenderers);
 			}
 
-			// Attempt: Single JSX renderer
+			const astroRenderer = jsxRenderers.get('astro');
+
+			// Shortcut: only use Astro renderer for MD and MDX files
+			if ((id.includes('.mdx') || id.includes('.md')) && astroRenderer) {
+				const { code: jsxCode } = await esbuild.transform(code, {
+					loader: getEsbuildLoader(path.extname(id)) as esbuild.Loader,
+					jsx: 'preserve',
+					sourcefile: id,
+					sourcemap: 'inline',
+				});
+				return transformJSX({
+					code: jsxCode,
+					id,
+					renderer: astroRenderer,
+					mode,
+					ssr,
+				});
+			}
+
+			// Attempt: Single JSX integration
 			// If we only have one renderer, we can skip a bunch of work!
-			if (jsxRenderers.size === 1) {
+			const nonAstroJsxRenderers = new Map(
+				[...jsxRenderers.entries()].filter(([key]) => key !== 'astro')
+			);
+			if (nonAstroJsxRenderers.size === 1) {
 				// downlevel any non-standard syntax, but preserve JSX
 				const { code: jsxCode } = await esbuild.transform(code, {
 					loader: getEsbuildLoader(path.extname(id)) as esbuild.Loader,
@@ -150,7 +172,7 @@ export default function jsx({ config, logging }: AstroPluginJSXOptions): Plugin
 				return transformJSX({
 					code: jsxCode,
 					id,
-					renderer: [...jsxRenderers.values()][0],
+					renderer: [...nonAstroJsxRenderers.values()][0],
 					mode,
 					ssr,
 				});
@@ -196,10 +218,6 @@ export default function jsx({ config, logging }: AstroPluginJSXOptions): Plugin
 				}
 			}
 
-			if (!importSource && jsxRenderers.has('astro') && id.includes('.mdx')) {
-				importSource = 'astro';
-			}
-
 			// if JSX renderer found, then use that
 			if (importSource) {
 				const jsxRenderer = jsxRenderers.get(importSource);
diff --git a/packages/astro/src/vite-plugin-markdown-legacy/README.md b/packages/astro/src/vite-plugin-markdown-legacy/README.md
new file mode 100644
index 000000000..ee7fd0e54
--- /dev/null
+++ b/packages/astro/src/vite-plugin-markdown-legacy/README.md
@@ -0,0 +1,3 @@
+# vite-plugin-markdown-legacy
+
+Adds Markdown support to Vite, both at the top level as well as within `.astro` files.
diff --git a/packages/astro/src/vite-plugin-markdown-legacy/index.ts b/packages/astro/src/vite-plugin-markdown-legacy/index.ts
new file mode 100644
index 000000000..5cb66caa5
--- /dev/null
+++ b/packages/astro/src/vite-plugin-markdown-legacy/index.ts
@@ -0,0 +1,260 @@
+import { renderMarkdown } from '@astrojs/markdown-remark';
+import ancestor from 'common-ancestor-path';
+import esbuild from 'esbuild';
+import fs from 'fs';
+import matter from 'gray-matter';
+import { fileURLToPath } from 'url';
+import type { Plugin } from 'vite';
+import type { AstroConfig } from '../@types/astro';
+import { pagesVirtualModuleId } from '../core/app/index.js';
+import { collectErrorMetadata } from '../core/errors.js';
+import type { LogOptions } from '../core/logger/core.js';
+import { cachedCompilation, CompileProps } from '../vite-plugin-astro/compile.js';
+import { getViteTransform, TransformHook } from '../vite-plugin-astro/styles.js';
+import type { PluginMetadata as AstroPluginMetadata } from '../vite-plugin-astro/types';
+import { getFileInfo } from '../vite-plugin-utils/index.js';
+
+interface AstroPluginOptions {
+	config: AstroConfig;
+	logging: LogOptions;
+}
+
+const MARKDOWN_IMPORT_FLAG = '?mdImport';
+const MARKDOWN_CONTENT_FLAG = '?content';
+
+function safeMatter(source: string, id: string) {
+	try {
+		return matter(source);
+	} catch (e) {
+		(e as any).id = id;
+		throw collectErrorMetadata(e);
+	}
+}
+
+// TODO: Clean up some of the shared logic between this Markdown plugin and the Astro plugin.
+// Both end up connecting a `load()` hook to the Astro compiler, and share some copy-paste
+// logic in how that is done.
+export default function markdown({ config, logging }: AstroPluginOptions): Plugin {
+	function normalizeFilename(filename: string) {
+		if (filename.startsWith('/@fs')) {
+			filename = filename.slice('/@fs'.length);
+		} else if (filename.startsWith('/') && !ancestor(filename, config.root.pathname)) {
+			filename = new URL('.' + filename, config.root).pathname;
+		}
+		return filename;
+	}
+
+	// Weird Vite behavior: Vite seems to use a fake "index.html" importer when you
+	// have `enforce: pre`. This can probably be removed once the vite issue is fixed.
+	// see: https://github.com/vitejs/vite/issues/5981
+	const fakeRootImporter = fileURLToPath(new URL('index.html', config.root));
+	function isRootImport(importer: string | undefined) {
+		if (!importer) {
+			return true;
+		}
+		if (importer === fakeRootImporter) {
+			return true;
+		}
+		if (importer === '\0' + pagesVirtualModuleId) {
+			return true;
+		}
+		return false;
+	}
+
+	let viteTransform: TransformHook;
+
+	return {
+		name: 'astro:markdown',
+		enforce: 'pre',
+		configResolved(_resolvedConfig) {
+			viteTransform = getViteTransform(_resolvedConfig);
+		},
+		async resolveId(id, importer, options) {
+			// Resolve any .md files with the `?content` cache buster. This should only come from
+			// an already-resolved JS module wrapper. Needed to prevent infinite loops in Vite.
+			// Unclear if this is expected or if cache busting is just working around a Vite bug.
+			if (id.endsWith(`.md${MARKDOWN_CONTENT_FLAG}`)) {
+				const resolvedId = await this.resolve(id, importer, { skipSelf: true, ...options });
+				return resolvedId?.id.replace(MARKDOWN_CONTENT_FLAG, '');
+			}
+			// If the markdown file is imported from another file via ESM, resolve a JS representation
+			// that defers the markdown -> HTML rendering until it is needed. This is especially useful
+			// when fetching and then filtering many markdown files, like with import.meta.glob() or Astro.glob().
+			// Otherwise, resolve directly to the actual component.
+			if (id.endsWith('.md') && !isRootImport(importer)) {
+				const resolvedId = await this.resolve(id, importer, { skipSelf: true, ...options });
+				if (resolvedId) {
+					return resolvedId.id + MARKDOWN_IMPORT_FLAG;
+				}
+			}
+			// In all other cases, we do nothing and rely on normal Vite resolution.
+			return undefined;
+		},
+		async load(id, opts) {
+			// A markdown file has been imported via ESM!
+			// Return the file's JS representation, including all Markdown
+			// frontmatter and a deferred `import() of the compiled markdown content.
+			if (id.endsWith(`.md${MARKDOWN_IMPORT_FLAG}`)) {
+				const { fileId, fileUrl } = getFileInfo(id, config);
+
+				const source = await fs.promises.readFile(fileId, 'utf8');
+				const { data: frontmatter, content: rawContent } = safeMatter(source, fileId);
+				return {
+					code: `
+						// Static
+						export const frontmatter = ${escapeViteEnvReferences(JSON.stringify(frontmatter))};
+						export const file = ${JSON.stringify(fileId)};
+						export const url = ${JSON.stringify(fileUrl)};
+						export function rawContent() {
+							return ${escapeViteEnvReferences(JSON.stringify(rawContent))};
+						}
+						export async function compiledContent() {
+							return load().then((m) => m.compiledContent());
+						}
+						export function $$loadMetadata() {
+							return load().then((m) => m.$$metadata);
+						}
+
+						// Deferred
+						export default async function load() {
+							return (await import(${JSON.stringify(fileId + MARKDOWN_CONTENT_FLAG)}));
+						}
+						export function Content(...args) {
+							return load().then((m) => m.default(...args));
+						}
+						Content.isAstroComponentFactory = true;
+						export function getHeadings() {
+							return load().then((m) => m.metadata.headings);
+						}
+						export function getHeaders() {
+							console.warn('getHeaders() have been deprecated. Use getHeadings() function instead.');
+							return load().then((m) => m.metadata.headings);
+						};`,
+					map: null,
+				};
+			}
+
+			// A markdown file is being rendered! This markdown file was either imported
+			// directly as a page in Vite, or it was a deferred render from a JS module.
+			// This returns the compiled markdown -> astro component that renders to HTML.
+			if (id.endsWith('.md')) {
+				const filename = normalizeFilename(id);
+				const source = await fs.promises.readFile(filename, 'utf8');
+				const renderOpts = config.markdown;
+
+				const fileUrl = new URL(`file://${filename}`);
+
+				// Extract special frontmatter keys
+				let { data: frontmatter, content: markdownContent } = safeMatter(source, filename);
+
+				// Turn HTML comments into JS comments while preventing nested `*/` sequences
+				// from ending the JS comment by injecting a zero-width space
+				// Inside code blocks, this is removed during renderMarkdown by the remark-escape plugin.
+				markdownContent = markdownContent.replace(
+					/<\s*!--([^-->]*)(.*?)-->/gs,
+					(whole) => `{/*${whole.replace(/\*\//g, '*\u200b/')}*/}`
+				);
+
+				let renderResult = await renderMarkdown(markdownContent, {
+					...renderOpts,
+					fileURL: fileUrl,
+					isAstroFlavoredMd: true,
+				} as any);
+				let { code: astroResult, metadata } = renderResult;
+				const { layout = '', components = '', setup = '', ...content } = frontmatter;
+				content.astro = metadata;
+				content.url = getFileInfo(id, config).fileUrl;
+				content.file = filename;
+
+				const prelude = `---
+import Slugger from 'github-slugger';
+${layout ? `import Layout from '${layout}';` : ''}
+${components ? `import * from '${components}';` : ''}
+${setup}
+
+const slugger = new Slugger();
+function $$slug(value) {
+	return slugger.slug(value);
+}
+
+const $$content = ${JSON.stringify(content)};
+
+Object.defineProperty($$content.astro, 'headers', {
+	get() {
+		console.warn('[${JSON.stringify(id)}] content.astro.headers is now content.astro.headings.');
+		return this.headings;
+	}
+});
+---`;
+
+				const imports = `${layout ? `import Layout from '${layout}';` : ''}
+${setup}`.trim();
+
+				// If the user imported "Layout", wrap the content in a Layout
+				if (/\bLayout\b/.test(imports)) {
+					astroResult = `${prelude}\n<Layout content={$$content}>\n\n${astroResult}\n\n</Layout>`;
+				} else {
+					// Note: without a Layout, we need to inject `head` manually so `maybeRenderHead` runs
+					astroResult = `${prelude}\n<head></head>${astroResult}`;
+				}
+
+				// Transform from `.astro` to valid `.ts`
+				const compileProps: CompileProps = {
+					config,
+					filename,
+					moduleId: id,
+					source: astroResult,
+					ssr: Boolean(opts?.ssr),
+					viteTransform,
+					pluginContext: this,
+				};
+
+				let transformResult = await cachedCompilation(compileProps);
+				let { code: tsResult } = transformResult;
+
+				tsResult = `\nexport const metadata = ${JSON.stringify(metadata)};
+export const frontmatter = ${JSON.stringify(content)};
+export function rawContent() {
+	return ${JSON.stringify(markdownContent)};
+}
+export function compiledContent() {
+		return ${JSON.stringify(renderResult.metadata.html)};
+}
+${tsResult}`;
+
+				// Compile from `.ts` to `.js`
+				const { code } = await esbuild.transform(tsResult, {
+					loader: 'ts',
+					sourcemap: false,
+					sourcefile: id,
+				});
+
+				const astroMetadata: AstroPluginMetadata['astro'] = {
+					clientOnlyComponents: transformResult.clientOnlyComponents,
+					hydratedComponents: transformResult.hydratedComponents,
+					scripts: transformResult.scripts,
+				};
+
+				return {
+					code: escapeViteEnvReferences(code),
+					map: null,
+					meta: {
+						astro: astroMetadata,
+						vite: {
+							lang: 'ts',
+						},
+					},
+				};
+			}
+
+			return null;
+		},
+	};
+}
+
+// Converts the first dot in `import.meta.env` to its Unicode escape sequence,
+// which prevents Vite from replacing strings like `import.meta.env.SITE`
+// in our JS representation of loaded Markdown files
+function escapeViteEnvReferences(code: string) {
+	return code.replace(/import\.meta\.env/g, 'import\\u002Emeta.env');
+}
diff --git a/packages/astro/src/vite-plugin-markdown/README.md b/packages/astro/src/vite-plugin-markdown/README.md
index 217d21904..ee7fd0e54 100644
--- a/packages/astro/src/vite-plugin-markdown/README.md
+++ b/packages/astro/src/vite-plugin-markdown/README.md
@@ -1,3 +1,3 @@
-# vite-plugin-markdown
+# vite-plugin-markdown-legacy
 
 Adds Markdown support to Vite, both at the top level as well as within `.astro` files.
diff --git a/packages/astro/src/vite-plugin-markdown/index.ts b/packages/astro/src/vite-plugin-markdown/index.ts
index 6794b499a..d1f04f32d 100644
--- a/packages/astro/src/vite-plugin-markdown/index.ts
+++ b/packages/astro/src/vite-plugin-markdown/index.ts
@@ -1,28 +1,19 @@
 import { renderMarkdown } from '@astrojs/markdown-remark';
-import ancestor from 'common-ancestor-path';
-import esbuild from 'esbuild';
-import fs from 'fs';
 import matter from 'gray-matter';
-import { fileURLToPath } from 'url';
+import fs from 'fs';
 import type { Plugin } from 'vite';
 import type { AstroConfig } from '../@types/astro';
-import { pagesVirtualModuleId } from '../core/app/index.js';
 import { collectErrorMetadata } from '../core/errors.js';
 import type { LogOptions } from '../core/logger/core.js';
-import { warn } from '../core/logger/core.js';
-import { cachedCompilation, CompileProps } from '../vite-plugin-astro/compile.js';
-import { getViteTransform, TransformHook } from '../vite-plugin-astro/styles.js';
-import type { PluginMetadata as AstroPluginMetadata } from '../vite-plugin-astro/types';
+import type { PluginMetadata } from '../vite-plugin-astro/types.js';
 import { getFileInfo } from '../vite-plugin-utils/index.js';
+import { warn } from '../core/logger/core.js';
 
 interface AstroPluginOptions {
 	config: AstroConfig;
 	logging: LogOptions;
 }
 
-const MARKDOWN_IMPORT_FLAG = '?mdImport';
-const MARKDOWN_CONTENT_FLAG = '?content';
-
 function safeMatter(source: string, id: string) {
 	try {
 		return matter(source);
@@ -32,146 +23,31 @@ function safeMatter(source: string, id: string) {
 	}
 }
 
-// TODO: Clean up some of the shared logic between this Markdown plugin and the Astro plugin.
-// Both end up connecting a `load()` hook to the Astro compiler, and share some copy-paste
-// logic in how that is done.
 export default function markdown({ config, logging }: AstroPluginOptions): Plugin {
-	function normalizeFilename(filename: string) {
-		if (filename.startsWith('/@fs')) {
-			filename = filename.slice('/@fs'.length);
-		} else if (filename.startsWith('/') && !ancestor(filename, config.root.pathname)) {
-			filename = new URL('.' + filename, config.root).pathname;
-		}
-		return filename;
-	}
-
-	// Weird Vite behavior: Vite seems to use a fake "index.html" importer when you
-	// have `enforce: pre`. This can probably be removed once the vite issue is fixed.
-	// see: https://github.com/vitejs/vite/issues/5981
-	const fakeRootImporter = fileURLToPath(new URL('index.html', config.root));
-	function isRootImport(importer: string | undefined) {
-		if (!importer) {
-			return true;
-		}
-		if (importer === fakeRootImporter) {
-			return true;
-		}
-		if (importer === '\0' + pagesVirtualModuleId) {
-			return true;
-		}
-		return false;
-	}
-
-	let viteTransform: TransformHook;
-
 	return {
-		name: 'astro:markdown',
 		enforce: 'pre',
-		configResolved(_resolvedConfig) {
-			viteTransform = getViteTransform(_resolvedConfig);
-		},
-		async resolveId(id, importer, options) {
-			// Resolve any .md files with the `?content` cache buster. This should only come from
-			// an already-resolved JS module wrapper. Needed to prevent infinite loops in Vite.
-			// Unclear if this is expected or if cache busting is just working around a Vite bug.
-			if (id.endsWith(`.md${MARKDOWN_CONTENT_FLAG}`)) {
-				const resolvedId = await this.resolve(id, importer, { skipSelf: true, ...options });
-				return resolvedId?.id.replace(MARKDOWN_CONTENT_FLAG, '');
-			}
-			// If the markdown file is imported from another file via ESM, resolve a JS representation
-			// that defers the markdown -> HTML rendering until it is needed. This is especially useful
-			// when fetching and then filtering many markdown files, like with import.meta.glob() or Astro.glob().
-			// Otherwise, resolve directly to the actual component.
-			if (id.endsWith('.md') && !isRootImport(importer)) {
-				const resolvedId = await this.resolve(id, importer, { skipSelf: true, ...options });
-				if (resolvedId) {
-					return resolvedId.id + MARKDOWN_IMPORT_FLAG;
-				}
-			}
-			// In all other cases, we do nothing and rely on normal Vite resolution.
-			return undefined;
-		},
-		async load(id, opts) {
-			// A markdown file has been imported via ESM!
-			// Return the file's JS representation, including all Markdown
-			// frontmatter and a deferred `import() of the compiled markdown content.
-			if (id.endsWith(`.md${MARKDOWN_IMPORT_FLAG}`)) {
-				const { fileId, fileUrl } = getFileInfo(id, config);
-
-				const source = await fs.promises.readFile(fileId, 'utf8');
-				const { data: frontmatter, content: rawContent } = safeMatter(source, fileId);
-				return {
-					code: `
-						// Static
-						export const frontmatter = ${escapeViteEnvReferences(JSON.stringify(frontmatter))};
-						export const file = ${JSON.stringify(fileId)};
-						export const url = ${JSON.stringify(fileUrl)};
-						export function rawContent() {
-							return ${escapeViteEnvReferences(JSON.stringify(rawContent))};
-						}
-						export async function compiledContent() {
-							return load().then((m) => m.compiledContent());
-						}
-						export function $$loadMetadata() {
-							return load().then((m) => m.$$metadata);
-						}
-
-						// Deferred
-						export default async function load() {
-							return (await import(${JSON.stringify(fileId + MARKDOWN_CONTENT_FLAG)}));
-						}
-						export function Content(...args) {
-							return load().then((m) => m.default(...args));
-						}
-						Content.isAstroComponentFactory = true;
-						export function getHeadings() {
-							return load().then((m) => m.metadata.headings);
-						}
-						export function getHeaders() {
-							console.warn('getHeaders() have been deprecated. Use getHeadings() function instead.');
-							return load().then((m) => m.metadata.headings);
-						};`,
-					map: null,
-				};
-			}
-
-			// A markdown file is being rendered! This markdown file was either imported
-			// directly as a page in Vite, or it was a deferred render from a JS module.
-			// This returns the compiled markdown -> astro component that renders to HTML.
+		name: 'astro:markdown',
+		// Why not the "transform" hook instead of "load" + readFile?
+		// A: Vite transforms all "import.meta.env" references to their values before
+		// passing to the transform hook. This lets us get the truly raw value
+		// to escape "import.meta.env" ourselves.
+		async load(id) {
 			if (id.endsWith('.md')) {
-				const filename = normalizeFilename(id);
-				const source = await fs.promises.readFile(filename, 'utf8');
-				const renderOpts = config.markdown;
-				const isAstroFlavoredMd = config.legacy.astroFlavoredMarkdown;
-
-				const fileUrl = new URL(`file://${filename}`);
-
-				// Extract special frontmatter keys
-				let { data: frontmatter, content: markdownContent } = safeMatter(source, filename);
-
-				// Turn HTML comments into JS comments while preventing nested `*/` sequences
-				// from ending the JS comment by injecting a zero-width space
-				// Inside code blocks, this is removed during renderMarkdown by the remark-escape plugin.
-				if (isAstroFlavoredMd) {
-					markdownContent = markdownContent.replace(
-						/<\s*!--([^-->]*)(.*?)-->/gs,
-						(whole) => `{/*${whole.replace(/\*\//g, '*\u200b/')}*/}`
-					);
-				}
-
-				let renderResult = await renderMarkdown(markdownContent, {
-					...renderOpts,
-					fileURL: fileUrl,
-					isAstroFlavoredMd,
+				const { fileId, fileUrl } = getFileInfo(id, config);
+				const rawFile = await fs.promises.readFile(fileId, 'utf-8');
+				const raw = safeMatter(rawFile, id);
+				const renderResult = await renderMarkdown(raw.content, {
+					...config.markdown,
+					fileURL: new URL(`file://${fileId}`),
+					isAstroFlavoredMd: false,
 				} as any);
-				let { code: astroResult, metadata } = renderResult;
-				const { layout = '', components = '', setup = '', ...content } = frontmatter;
-				content.astro = metadata;
-				content.url = getFileInfo(id, config).fileUrl;
-				content.file = filename;
 
-				// Warn when attempting to use setup without the legacy flag
-				if (setup && !isAstroFlavoredMd) {
+				const html = renderResult.code;
+				const { headings } = renderResult.metadata;
+				const frontmatter = { ...raw.data, url: fileUrl, file: fileId } as any;
+				const { layout } = frontmatter;
+
+				if (frontmatter.setup) {
 					warn(
 						logging,
 						'markdown',
@@ -179,100 +55,59 @@ export default function markdown({ config, logging }: AstroPluginOptions): Plugi
 					);
 				}
 
-				const prelude = `---
-import Slugger from 'github-slugger';
-${layout ? `import Layout from '${layout}';` : ''}
-${isAstroFlavoredMd && components ? `import * from '${components}';` : ''}
-${isAstroFlavoredMd ? setup : ''}
+				const code = escapeViteEnvReferences(`
+				import { Fragment, jsx as h } from 'astro/jsx-runtime';
+				${layout ? `import Layout from ${JSON.stringify(layout)};` : ''}
 
-const slugger = new Slugger();
-function $$slug(value) {
-	return slugger.slug(value);
-}
+				const html = ${JSON.stringify(html)};
 
-const $$content = ${JSON.stringify(
-					isAstroFlavoredMd
-						? content
-						: // Avoid stripping "setup" and "components"
-						  // in plain MD mode
-						  { ...content, setup, components }
-				)};
-
-Object.defineProperty($$content.astro, 'headers', {
-	get() {
-		console.warn('[${JSON.stringify(id)}] content.astro.headers is now content.astro.headings.');
-		return this.headings;
-	}
-});
----`;
-
-				const imports = `${layout ? `import Layout from '${layout}';` : ''}
-${isAstroFlavoredMd ? setup : ''}`.trim();
-
-				// Wrap with set:html fragment to skip
-				// JSX expressions and components in "plain" md mode
-				if (!isAstroFlavoredMd) {
-					astroResult = `<Fragment set:html={${JSON.stringify(astroResult)}} />`;
+				export const frontmatter = ${JSON.stringify(frontmatter)};
+				export const file = ${JSON.stringify(fileId)};
+				export const url = ${JSON.stringify(fileUrl)};
+				export function rawContent() {
+					return ${JSON.stringify(raw.content)};
 				}
-
-				// If the user imported "Layout", wrap the content in a Layout
-				if (/\bLayout\b/.test(imports)) {
-					astroResult = `${prelude}\n<Layout content={$$content}>\n\n${astroResult}\n\n</Layout>`;
-				} else {
-					// Note: without a Layout, we need to inject `head` manually so `maybeRenderHead` runs
-					astroResult = `${prelude}\n<head></head>${astroResult}`;
+				export function compiledContent() {
+					return html;
 				}
-
-				// Transform from `.astro` to valid `.ts`
-				const compileProps: CompileProps = {
-					config,
-					filename,
-					moduleId: id,
-					source: astroResult,
-					ssr: Boolean(opts?.ssr),
-					viteTransform,
-					pluginContext: this,
+				export function getHeadings() {
+					return ${JSON.stringify(headings)};
+				}
+				export function getHeaders() {
+					console.warn('getHeaders() have been deprecated. Use getHeadings() function instead.');
+					return getHeadings();
 				};
-
-				let transformResult = await cachedCompilation(compileProps);
-				let { code: tsResult } = transformResult;
-
-				tsResult = `\nexport const metadata = ${JSON.stringify(metadata)};
-export const frontmatter = ${JSON.stringify(content)};
-export function rawContent() {
-	return ${JSON.stringify(markdownContent)};
-}
-export function compiledContent() {
-		return ${JSON.stringify(renderResult.metadata.html)};
-}
-${tsResult}`;
-
-				// Compile from `.ts` to `.js`
-				const { code } = await esbuild.transform(tsResult, {
-					loader: 'ts',
-					sourcemap: false,
-					sourcefile: id,
-				});
-
-				const astroMetadata: AstroPluginMetadata['astro'] = {
-					clientOnlyComponents: transformResult.clientOnlyComponents,
-					hydratedComponents: transformResult.hydratedComponents,
-					scripts: transformResult.scripts,
-				};
-
+				export async function Content() {
+					const { layout, ...content } = frontmatter;
+					content.astro = {};
+					Object.defineProperty(content.astro, 'headings', {
+						get() {
+							throw new Error('The "astro" property is no longer supported! To access "headings" from your layout, try using "Astro.props.headings."')
+						}
+					});
+					const contentFragment = h(Fragment, { 'set:html': html });
+					return ${
+						layout
+							? `h(Layout, { content, frontmatter: content, headings: getHeadings(), 'server:root': true, children: contentFragment })`
+							: `contentFragment`
+					};
+				}
+				export default Content;
+				`);
 				return {
-					code: escapeViteEnvReferences(code),
-					map: null,
+					code,
 					meta: {
-						astro: astroMetadata,
+						astro: {
+							hydratedComponents: [],
+							clientOnlyComponents: [],
+							scripts: [],
+						} as PluginMetadata['astro'],
 						vite: {
 							lang: 'ts',
 						},
 					},
 				};
 			}
-
-			return null;
 		},
 	};
 }
diff --git a/packages/astro/test/astro-markdown-md-mode.test.js b/packages/astro/test/astro-markdown-md-mode.test.js
deleted file mode 100644
index 89f2a26ab..000000000
--- a/packages/astro/test/astro-markdown-md-mode.test.js
+++ /dev/null
@@ -1,51 +0,0 @@
-import { expect } from 'chai';
-import * as cheerio from 'cheerio';
-import { loadFixture } from './test-utils.js';
-
-describe('Astro Markdown - plain MD mode', () => {
-	let fixture;
-
-	before(async () => {
-		fixture = await loadFixture({
-			root: './fixtures/astro-markdown-md-mode/',
-		});
-		await fixture.build();
-	});
-
-	it('Leaves JSX expressions unprocessed', async () => {
-		const html = await fixture.readFile('/jsx-expressions/index.html');
-		const $ = cheerio.load(html);
-
-		expect($('h2').html()).to.equal('{frontmatter.title}');
-	});
-
-	it('Leaves JSX components un-transformed', async () => {
-		const html = await fixture.readFile('/components/index.html');
-
-		expect(html).to.include('<counter client:load="" count="{0}">');
-	});
-
-	describe('syntax highlighting', async () => {
-		it('handles Shiki', async () => {
-			const html = await fixture.readFile('/code-in-md/index.html');
-			const $ = cheerio.load(html);
-
-			expect($('pre.astro-code').length).to.not.equal(0);
-		});
-
-		it('handles Prism', async () => {
-			fixture = await loadFixture({
-				root: './fixtures/astro-markdown-md-mode/',
-				markdown: {
-					syntaxHighlight: 'prism',
-				},
-			});
-			await fixture.build();
-
-			const html = await fixture.readFile('/code-in-md/index.html');
-			const $ = cheerio.load(html);
-
-			expect($('pre.language-html').length).to.not.equal(0);
-		});
-	});
-});
diff --git a/packages/astro/test/astro-markdown.test.js b/packages/astro/test/astro-markdown.test.js
index 92b78121a..eb1b43bcc 100644
--- a/packages/astro/test/astro-markdown.test.js
+++ b/packages/astro/test/astro-markdown.test.js
@@ -2,199 +2,130 @@ import { expect } from 'chai';
 import * as cheerio from 'cheerio';
 import { loadFixture, fixLineEndings } from './test-utils.js';
 
+const FIXTURE_ROOT = './fixtures/astro-markdown/';
+
 describe('Astro Markdown', () => {
 	let fixture;
 
 	before(async () => {
 		fixture = await loadFixture({
-			root: './fixtures/astro-markdown/',
+			root: FIXTURE_ROOT,
 		});
 		await fixture.build();
 	});
 
-	it('Can parse JSX expressions in markdown pages', async () => {
+	it('Leaves JSX expressions unprocessed', async () => {
 		const html = await fixture.readFile('/jsx-expressions/index.html');
 		const $ = cheerio.load(html);
 
-		expect($('h2').html()).to.equal('Blog Post with JSX expressions');
-
-		expect(html).to.contain('JSX at the start of the line!');
-		for (let listItem of ['test-1', 'test-2', 'test-3']) {
-			expect($(`#${listItem}`).html()).to.equal(`${listItem}`);
-		}
+		expect($('h2').html()).to.equal('{frontmatter.title}');
 	});
 
-	it('Can handle slugs with JSX expressions in markdown pages', async () => {
-		const html = await fixture.readFile('/slug/index.html');
-		const $ = cheerio.load(html);
+	it('Leaves JSX components un-transformed', async () => {
+		const html = await fixture.readFile('/components/index.html');
 
-		expect($('h1').attr('id')).to.equal('my-blog-post');
-	});
-
-	it('Can handle code elements without extra spacing', async () => {
-		const html = await fixture.readFile('/code-element/index.html');
-		const $ = cheerio.load(html);
-
-		$('code').each((_, el) => {
-			expect($(el).html()).to.equal($(el).html().trim());
-		});
-	});
-
-	it('Can handle namespaced components in markdown', async () => {
-		const html = await fixture.readFile('/namespace/index.html');
-		const $ = cheerio.load(html);
-
-		expect($('h1').text()).to.equal('Hello Namespace!');
-		expect($('button').length).to.equal(1);
-	});
-
-	it('Correctly handles component children in markdown pages (#3319)', async () => {
-		const html = await fixture.readFile('/children/index.html');
-
-		expect(html).not.to.contain('<p></p>');
-	});
-
-	it('Can handle HTML comments in markdown pages', async () => {
-		const html = await fixture.readFile('/comment/index.html');
-		const $ = cheerio.load(html);
-
-		expect($('h1').text()).to.equal('It works!');
-	});
-
-	it('Prevents `*/` sequences from breaking HTML comments (#3476)', async () => {
-		const html = await fixture.readFile('/comment-with-js/index.html');
-		const $ = cheerio.load(html);
-
-		expect($('h1').text()).to.equal('It still works!');
-	});
-
-	it('Can handle HTML comments in inline code', async () => {
-		const html = await fixture.readFile('/comment-with-js/index.html');
-		const $ = cheerio.load(html);
-
-		expect($('p code').text()).to.equal('<!-- HTML comments in code -->');
-	});
-
-	it('Can handle HTML comments in code fences', async () => {
-		const html = await fixture.readFile('/comment-with-js/index.html');
-		const $ = cheerio.load(html);
-
-		expect($('pre > code').text()).to.equal('<!-- HTML comments in code fence -->');
-	});
-
-	// https://github.com/withastro/astro/issues/3254
-	it('Can handle scripts in markdown pages', async () => {
-		const html = await fixture.readFile('/script/index.html');
-		expect(html).not.to.match(new RegExp('/src/scripts/test.js'));
-	});
-
-	it('Empty code blocks do not fail', async () => {
-		const html = await fixture.readFile('/empty-code/index.html');
-		const $ = cheerio.load(html);
-
-		// test 1: There is not a `<code>` in the codeblock
-		expect($('pre')[0].children).to.have.lengthOf(1);
-
-		// test 2: The empty `<pre>` failed to render
-		expect($('pre')[1].children).to.have.lengthOf(0);
-	});
-
-	it('Can render markdown with --- for horizontal rule', async () => {
-		const html = await fixture.readFile('/dash/index.html');
-		expect(!!html).to.equal(true);
+		expect(html).to.include('<counter client:load="" count="{0}">');
 	});
 
+	
 	it('Exposes raw markdown content', async () => {
 		const { raw } = JSON.parse(await fixture.readFile('/raw-content.json'));
 
-		expect(fixLineEndings(raw)).to.equal(
-			`\n## With components\n\n### Non-hydrated\n\n<Hello name="Astro Naut" />\n\n### Hydrated\n\n<Counter client:load />\n<SvelteButton client:load />\n`
+		expect(fixLineEndings(raw).trim()).to.equal(
+			`# Basic page\n\nLets make sure raw and compiled content look right!`
 		);
 	});
 
-	it('Exposes HTML parser for raw markdown content', async () => {
+	it('Exposes compiled HTML content', async () => {
 		const { compiled } = JSON.parse(await fixture.readFile('/raw-content.json'));
 
-		expect(fixLineEndings(compiled)).to.equal(
-			`<h2 id="with-components">With components</h2>\n<h3 id="non-hydrated">Non-hydrated</h3>\n<Hello name="Astro Naut" />\n<h3 id="hydrated">Hydrated</h3>\n<Counter client:load />\n<SvelteButton client:load />`
+		expect(fixLineEndings(compiled).trim()).to.equal(
+			`<h1 id="basic-page">Basic page</h1>\n<p>Lets make sure raw and compiled content look right!</p>`
 		);
 	});
 
-	it('Allows referencing Vite env var names in markdown (#3412)', async () => {
-		const html = await fixture.readFile('/vite-env-vars/index.html');
-		const $ = cheerio.load(html);
+	describe('syntax highlighting', async () => {
+		it('handles Shiki', async () => {
+			const html = await fixture.readFile('/code-in-md/index.html');
+			const $ = cheerio.load(html);
 
-		// test 1: referencing an existing var name
-		expect($('code').eq(0).text()).to.equal('import.meta.env.SITE');
-		expect($('li').eq(0).text()).to.equal('import.meta.env.SITE');
-		expect($('code').eq(3).text()).to.contain('site: import.meta.env.SITE');
-		expect($('blockquote').text()).to.contain('import.meta.env.SITE');
+			expect($('pre.astro-code').length).to.not.equal(0);
+		});
 
-		// test 2: referencing a non-existing var name
-		expect($('code').eq(1).text()).to.equal('import.meta.env.TITLE');
-		expect($('li').eq(1).text()).to.equal('import.meta.env.TITLE');
-		expect($('code').eq(3).text()).to.contain('title: import.meta.env.TITLE');
-		expect($('blockquote').text()).to.contain('import.meta.env.TITLE');
+		it('handles Prism', async () => {
+			const prismFixture = await loadFixture({
+				root: FIXTURE_ROOT,
+				markdown: {
+					syntaxHighlight: 'prism',
+				},
+			});
+			await prismFixture.build();
 
-		// test 3: referencing `import.meta.env` itself (without any var name)
-		expect($('code').eq(2).text()).to.equal('import.meta.env');
-		expect($('li').eq(2).text()).to.equal('import.meta.env');
-		expect($('code').eq(3).text()).to.contain('// Use Vite env vars with import.meta.env');
-		expect($('blockquote').text()).to.match(/import\.meta\.env\s*$/);
+			const html = await prismFixture.readFile('/code-in-md/index.html');
+			const $ = cheerio.load(html);
+
+			expect($('pre.language-html').length).to.not.equal(0);
+		});
 	});
 
-	it('Escapes HTML tags in code blocks', async () => {
-		const html = await fixture.readFile('/code-in-md/index.html');
+
+	it('Passes frontmatter to layout via "content" and "frontmatter" props', async () => {
+		const html = await fixture.readFile('/with-layout/index.html');
 		const $ = cheerio.load(html);
 
-		expect($('code').eq(0).html()).to.equal('&lt;script&gt;');
-		expect($('blockquote').length).to.equal(1);
-		expect($('code').eq(1).html()).to.equal('&lt;/script&gt;');
-		expect($('pre').html()).to.contain('&gt;This should also work without any problems.&lt;');
+		const contentTitle = $('[data-content-title]');
+		const frontmatterTitle = $('[data-frontmatter-title]');
+
+		expect(contentTitle.text()).to.equal('With layout');
+		expect(frontmatterTitle.text()).to.equal('With layout');
 	});
 
-	it('Allows defining slot contents in component children', async () => {
-		const html = await fixture.readFile('/slots/index.html');
+	it('Passes headings to layout via "headings" prop', async () => {
+		const html = await fixture.readFile('/with-layout/index.html');
 		const $ = cheerio.load(html);
 
-		const slots = $('article').eq(0);
-		expect(slots.find('> .fragmentSlot > div').text()).to.contain('1:');
-		expect(slots.find('> .fragmentSlot > div + p').text()).to.contain('2:');
-		expect(slots.find('> .pSlot > p[title="hello"]').text()).to.contain('3:');
-		expect(slots.find('> .defaultSlot').html()).to.match(
-			new RegExp(
-				`<div>4: Div in default slot</div>` +
-					// Optional extra paragraph due to the line breaks between components
-					`(<p></p>)?` +
-					`<p>5: Paragraph in fragment in default slot</p>` +
-					// Optional whitespace due to the line breaks between components
-					`[\s\n]*` +
-					`6: Regular text in default slot`
-			)
+		const headingSlugs = [...$('body').find('[data-headings] > li')].map(
+			(el) => $(el).text()
 		);
 
-		const nestedSlots = $('article').eq(1);
-		expect(nestedSlots.find('> .fragmentSlot').html()).to.contain('1:');
-		expect(nestedSlots.find('> .pSlot > p').text()).to.contain('2:');
-		expect(nestedSlots.find('> .defaultSlot > article').text().replace(/\s+/g, ' ')).to.equal(
-			`
-			3: nested fragmentSlot
-			4: nested pSlot
-			5: nested text in default slot
-		`.replace(/\s+/g, ' ')
-		);
-
-		expect($('article').eq(3).text().replace(/[^❌]/g, '')).to.equal('❌❌❌');
-
-		expect($('article').eq(4).text().replace(/[^❌]/g, '')).to.equal('❌❌❌');
+		expect(headingSlugs.length).to.be.greaterThan(0);
+		expect(headingSlugs).to.contain('section-1');
+		expect(headingSlugs).to.contain('section-2');
 	});
 
-	it('Generate the right props for the layout', async () => {
-		const html = await fixture.readFile('/layout-props/index.html');
-		const $ = cheerio.load(html);
+	it('Exposes getHeadings() on glob imports', async () => {
+		const { headings } = JSON.parse(await fixture.readFile('/headings-glob.json'));
 
-		expect($('#title').text()).to.equal('Hello world!');
-		expect($('#url').text()).to.equal('/layout-props');
-		expect($('#file').text()).to.match(/.*\/layout-props.md$/);
+		const headingSlugs = headings.map(heading => heading?.slug);
+
+		expect(headingSlugs).to.contain('section-1');
+		expect(headingSlugs).to.contain('section-2');
+	});
+
+	describe('Vite env vars (#3412)', () => {
+		it('Allows referencing import.meta.env in content', async () => {
+			const html = await fixture.readFile('/vite-env-vars/index.html');
+			const $ = cheerio.load(html);
+	
+			// test 1: referencing an existing var name
+			expect($('code').eq(0).text()).to.equal('import.meta.env.SITE');
+			expect($('li').eq(0).text()).to.equal('import.meta.env.SITE');
+			expect($('code').eq(3).text()).to.contain('site: import.meta.env.SITE');
+	
+			// // test 2: referencing a non-existing var name
+			expect($('code').eq(1).text()).to.equal('import.meta.env.TITLE');
+			expect($('li').eq(1).text()).to.equal('import.meta.env.TITLE');
+			expect($('code').eq(3).text()).to.contain('title: import.meta.env.TITLE');
+	
+			// // test 3: referencing `import.meta.env` itself (without any var name)
+			expect($('code').eq(2).text()).to.equal('import.meta.env');
+			expect($('li').eq(2).text()).to.equal('import.meta.env');
+			expect($('code').eq(3).text()).to.contain('// Use Vite env vars with import.meta.env');
+		});
+		it('Allows referencing import.meta.env in frontmatter', async () => {
+			const { title = '' } = JSON.parse(await fixture.readFile('/vite-env-vars-glob.json'));
+			expect(title).to.contain('import.meta.env.SITE');
+			expect(title).to.contain('import.meta.env.TITLE');
+		});
 	});
 });
diff --git a/packages/astro/test/fixtures/astro-head/package.json b/packages/astro/test/fixtures/astro-head/package.json
new file mode 100644
index 000000000..bc4b5a2c2
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-head/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "@test/astro-head",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}
diff --git a/packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/code-in-md.md b/packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/code-in-md.md
deleted file mode 100644
index 72206a868..000000000
--- a/packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/code-in-md.md
+++ /dev/null
@@ -1,7 +0,0 @@
-# Fenced code blocks
-
-```html
-<body>
-	<div>This should also work without any problems.</div>
-</body>
-```
diff --git a/packages/astro/test/fixtures/astro-markdown/astro.config.mjs b/packages/astro/test/fixtures/astro-markdown/astro.config.mjs
index baefed8cc..908e3442f 100644
--- a/packages/astro/test/fixtures/astro-markdown/astro.config.mjs
+++ b/packages/astro/test/fixtures/astro-markdown/astro.config.mjs
@@ -1,12 +1,8 @@
 import { defineConfig } from 'astro/config';
-import preact from '@astrojs/preact';
 import svelte from "@astrojs/svelte";
 
 // https://astro.build/config
 export default defineConfig({
-  integrations: [preact(), svelte()],
+  integrations: [svelte()],
   site: 'https://astro.build/',
-	legacy: {
-		astroFlavoredMarkdown: true,
-	}
 });
diff --git a/packages/astro/test/fixtures/astro-markdown/package.json b/packages/astro/test/fixtures/astro-markdown/package.json
index e5a54cf7c..48a6c6816 100644
--- a/packages/astro/test/fixtures/astro-markdown/package.json
+++ b/packages/astro/test/fixtures/astro-markdown/package.json
@@ -1,9 +1,8 @@
 {
-  "name": "@test/astro-markdown",
+  "name": "@test/astro-markdown-md-mode",
   "version": "0.0.0",
   "private": true,
   "dependencies": {
-    "@astrojs/preact": "workspace:*",
     "@astrojs/svelte": "workspace:*",
     "astro": "workspace:*"
   }
diff --git a/packages/astro/test/fixtures/astro-markdown-md-mode/src/components/Counter.svelte b/packages/astro/test/fixtures/astro-markdown/src/components/Counter.svelte
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown-md-mode/src/components/Counter.svelte
rename to packages/astro/test/fixtures/astro-markdown/src/components/Counter.svelte
diff --git a/packages/astro/test/fixtures/astro-markdown/src/layouts/Base.astro b/packages/astro/test/fixtures/astro-markdown/src/layouts/Base.astro
new file mode 100644
index 000000000..e4fa7560a
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-markdown/src/layouts/Base.astro
@@ -0,0 +1,28 @@
+---
+const {
+	content = { title: "content didn't work" },
+	frontmatter = { title: "frontmatter didn't work" },
+	headings = [],
+} = Astro.props;
+---
+
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+	<meta charset="UTF-8">
+	<meta http-equiv="X-UA-Compatible" content="IE=edge">
+	<meta name="viewport" content="width=device-width, initial-scale=1.0">
+</head>
+
+<body>
+	<p data-content-title>{content.title}</p>
+	<p data-frontmatter-title>{frontmatter.title}</p>
+	<p data-layout-rendered>Layout rendered!</p>
+	<ul data-headings>
+		{headings.map(heading => <li>{heading.slug}</li>)}
+	</ul>
+	<slot />
+</body>
+
+</html>
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/basic.md b/packages/astro/test/fixtures/astro-markdown/src/pages/basic.md
new file mode 100644
index 000000000..224c48f65
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-markdown/src/pages/basic.md
@@ -0,0 +1,3 @@
+# Basic page
+
+Lets make sure raw and compiled content look right!
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/code-in-md.md b/packages/astro/test/fixtures/astro-markdown/src/pages/code-in-md.md
index 52a799ab1..72206a868 100644
--- a/packages/astro/test/fixtures/astro-markdown/src/pages/code-in-md.md
+++ b/packages/astro/test/fixtures/astro-markdown/src/pages/code-in-md.md
@@ -1,12 +1,3 @@
-# Inline code blocks
-
-`<script>` tags in **Astro** components are now built,
-bundled and optimized by default.
-
-> Markdown formatting still works between tags in inline code blocks.
-
-We can also use closing `</script>` tags without any problems.
-
 # Fenced code blocks
 
 ```html
diff --git a/packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/components.md b/packages/astro/test/fixtures/astro-markdown/src/pages/components.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/components.md
rename to packages/astro/test/fixtures/astro-markdown/src/pages/components.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/headings-glob.json.js b/packages/astro/test/fixtures/astro-markdown/src/pages/headings-glob.json.js
new file mode 100644
index 000000000..631250c33
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-markdown/src/pages/headings-glob.json.js
@@ -0,0 +1,9 @@
+import { getHeadings } from './with-layout.md';
+
+export async function get() {
+	return {
+		body: JSON.stringify({
+			headings: getHeadings(),
+		}),
+	}
+}
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/raw-content.json.js b/packages/astro/test/fixtures/astro-markdown/src/pages/raw-content.json.js
index 21be533e1..ef933a373 100644
--- a/packages/astro/test/fixtures/astro-markdown/src/pages/raw-content.json.js
+++ b/packages/astro/test/fixtures/astro-markdown/src/pages/raw-content.json.js
@@ -1,4 +1,4 @@
-import { rawContent, compiledContent } from '../imported-md/with-components.md';
+import { rawContent, compiledContent } from './basic.md';
 
 export async function get() {
 	return {
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/vite-env-vars-glob.json.js b/packages/astro/test/fixtures/astro-markdown/src/pages/vite-env-vars-glob.json.js
new file mode 100644
index 000000000..4a7e4dd78
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-markdown/src/pages/vite-env-vars-glob.json.js
@@ -0,0 +1,7 @@
+import { frontmatter } from './vite-env-vars.md';
+
+export async function get() {
+	return {
+		body: JSON.stringify(frontmatter),
+	}
+}
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/vite-env-vars.md b/packages/astro/test/fixtures/astro-markdown/src/pages/vite-env-vars.md
index 30a9ab177..f4983af2c 100644
--- a/packages/astro/test/fixtures/astro-markdown/src/pages/vite-env-vars.md
+++ b/packages/astro/test/fixtures/astro-markdown/src/pages/vite-env-vars.md
@@ -1,6 +1,5 @@
 ---
 title: Referencing Vite Env Vars like import.meta.env.SITE, import.meta.env.TITLE and import.meta.env
-layout: ../layouts/content.astro
 ---
 
 ## Referencing the full name of Vite env vars
@@ -29,7 +28,3 @@ export const get = () => rss({
 	items: import.meta.glob('./**/*.md'),
 });
 ```
-
-## Usage in frontmatter
-
-> frontmatter.title: {frontmatter.title}
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/with-layout.md b/packages/astro/test/fixtures/astro-markdown/src/pages/with-layout.md
new file mode 100644
index 000000000..37985beb8
--- /dev/null
+++ b/packages/astro/test/fixtures/astro-markdown/src/pages/with-layout.md
@@ -0,0 +1,8 @@
+---
+title: 'With layout'
+layout: '../layouts/Base.astro'
+---
+
+## Section 1
+
+## Section 2
\ No newline at end of file
diff --git a/packages/astro/test/fixtures/client-address/package.json b/packages/astro/test/fixtures/client-address/package.json
new file mode 100644
index 000000000..e0bd7e3ed
--- /dev/null
+++ b/packages/astro/test/fixtures/client-address/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "@test/client-address",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}
diff --git a/packages/astro/test/fixtures/glob-pages-css/package.json b/packages/astro/test/fixtures/glob-pages-css/package.json
new file mode 100644
index 000000000..bc8412754
--- /dev/null
+++ b/packages/astro/test/fixtures/glob-pages-css/package.json
@@ -0,0 +1,8 @@
+{
+  "name": "@test/glob-pages-css",
+  "version": "0.0.0",
+  "private": true,
+  "dependencies": {
+    "astro": "workspace:*"
+  }
+}
diff --git a/packages/astro/test/fixtures/astro-markdown-md-mode/astro.config.mjs b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/astro.config.mjs
similarity index 59%
rename from packages/astro/test/fixtures/astro-markdown-md-mode/astro.config.mjs
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/astro.config.mjs
index 908e3442f..baefed8cc 100644
--- a/packages/astro/test/fixtures/astro-markdown-md-mode/astro.config.mjs
+++ b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/astro.config.mjs
@@ -1,8 +1,12 @@
 import { defineConfig } from 'astro/config';
+import preact from '@astrojs/preact';
 import svelte from "@astrojs/svelte";
 
 // https://astro.build/config
 export default defineConfig({
-  integrations: [svelte()],
+  integrations: [preact(), svelte()],
   site: 'https://astro.build/',
+	legacy: {
+		astroFlavoredMarkdown: true,
+	}
 });
diff --git a/packages/astro/test/fixtures/astro-markdown-md-mode/package.json b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/package.json
similarity index 65%
rename from packages/astro/test/fixtures/astro-markdown-md-mode/package.json
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/package.json
index 48a6c6816..e5a54cf7c 100644
--- a/packages/astro/test/fixtures/astro-markdown-md-mode/package.json
+++ b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/package.json
@@ -1,8 +1,9 @@
 {
-  "name": "@test/astro-markdown-md-mode",
+  "name": "@test/astro-markdown",
   "version": "0.0.0",
   "private": true,
   "dependencies": {
+    "@astrojs/preact": "workspace:*",
     "@astrojs/svelte": "workspace:*",
     "astro": "workspace:*"
   }
diff --git a/packages/astro/test/fixtures/astro-markdown/src/components/Counter.jsx b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/Counter.jsx
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/components/Counter.jsx
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/Counter.jsx
diff --git a/packages/astro/test/fixtures/astro-markdown/src/components/Example.jsx b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/Example.jsx
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/components/Example.jsx
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/Example.jsx
diff --git a/packages/astro/test/fixtures/astro-markdown/src/components/Hello.jsx b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/Hello.jsx
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/components/Hello.jsx
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/Hello.jsx
diff --git a/packages/astro/test/fixtures/astro-markdown/src/components/SlotComponent.astro b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/SlotComponent.astro
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/components/SlotComponent.astro
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/SlotComponent.astro
diff --git a/packages/astro/test/fixtures/astro-markdown/src/components/SvelteButton.svelte b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/SvelteButton.svelte
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/components/SvelteButton.svelte
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/SvelteButton.svelte
diff --git a/packages/astro/test/fixtures/astro-markdown/src/components/TextBlock.jsx b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/TextBlock.jsx
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/components/TextBlock.jsx
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/TextBlock.jsx
diff --git a/packages/astro/test/fixtures/astro-markdown/src/components/index.js b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/index.js
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/components/index.js
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/components/index.js
diff --git a/packages/astro/test/fixtures/astro-markdown/src/content/code-element.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/content/code-element.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/content/code-element.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/content/code-element.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/imported-md/plain.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/imported-md/plain.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/imported-md/plain.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/imported-md/plain.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/imported-md/with-components.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/imported-md/with-components.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/imported-md/with-components.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/imported-md/with-components.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/layouts/content.astro b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/layouts/content.astro
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/layouts/content.astro
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/layouts/content.astro
diff --git a/packages/astro/test/fixtures/astro-markdown/src/layouts/layout-props.astro b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/layouts/layout-props.astro
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/layouts/layout-props.astro
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/layouts/layout-props.astro
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/children.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/children.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/children.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/children.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/code-element.astro b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/code-element.astro
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/code-element.astro
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/code-element.astro
diff --git a/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/code-in-md.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/code-in-md.md
new file mode 100644
index 000000000..52a799ab1
--- /dev/null
+++ b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/code-in-md.md
@@ -0,0 +1,16 @@
+# Inline code blocks
+
+`<script>` tags in **Astro** components are now built,
+bundled and optimized by default.
+
+> Markdown formatting still works between tags in inline code blocks.
+
+We can also use closing `</script>` tags without any problems.
+
+# Fenced code blocks
+
+```html
+<body>
+	<div>This should also work without any problems.</div>
+</body>
+```
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/comment-with-js.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/comment-with-js.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/comment-with-js.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/comment-with-js.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/comment.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/comment.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/comment.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/comment.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/dash.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/dash.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/dash.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/dash.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/empty-code.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/empty-code.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/empty-code.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/empty-code.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/imported-md/with-components.astro b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/imported-md/with-components.astro
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/imported-md/with-components.astro
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/imported-md/with-components.astro
diff --git a/packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/jsx-expressions.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/jsx-expressions.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown-md-mode/src/pages/jsx-expressions.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/jsx-expressions.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/layout-props.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/layout-props.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/layout-props.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/layout-props.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/namespace.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/namespace.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/namespace.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/namespace.md
diff --git a/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/raw-content.json.js b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/raw-content.json.js
new file mode 100644
index 000000000..21be533e1
--- /dev/null
+++ b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/raw-content.json.js
@@ -0,0 +1,10 @@
+import { rawContent, compiledContent } from '../imported-md/with-components.md';
+
+export async function get() {
+	return {
+		body: JSON.stringify({
+			raw: rawContent(),
+			compiled: await compiledContent(),
+		}),
+	}
+}
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/script.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/script.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/script.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/script.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/slots.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/slots.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/slots.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/slots.md
diff --git a/packages/astro/test/fixtures/astro-markdown/src/pages/slug.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/slug.md
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/pages/slug.md
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/slug.md
diff --git a/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/vite-env-vars.md b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/vite-env-vars.md
new file mode 100644
index 000000000..30a9ab177
--- /dev/null
+++ b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/pages/vite-env-vars.md
@@ -0,0 +1,35 @@
+---
+title: Referencing Vite Env Vars like import.meta.env.SITE, import.meta.env.TITLE and import.meta.env
+layout: ../layouts/content.astro
+---
+
+## Referencing the full name of Vite env vars
+
+You can get the configured site URL with `import.meta.env.SITE`.
+
+The variable `import.meta.env.TITLE` is not configured.
+
+You can reference all env vars through `import.meta.env`.
+
+This should also work outside of code blocks:
+- import.meta.env.SITE
+- import.meta.env.TITLE
+- import.meta.env
+
+## Usage in fenced code blocks with syntax highlighting
+
+```js
+// src/pages/rss.xml.js
+import rss from '@astrojs/rss';
+
+export const get = () => rss({
+	// Use Vite env vars with import.meta.env
+	site: import.meta.env.SITE,
+	title: import.meta.env.TITLE,
+	items: import.meta.glob('./**/*.md'),
+});
+```
+
+## Usage in frontmatter
+
+> frontmatter.title: {frontmatter.title}
diff --git a/packages/astro/test/fixtures/astro-markdown/src/scripts/test.js b/packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/scripts/test.js
similarity index 100%
rename from packages/astro/test/fixtures/astro-markdown/src/scripts/test.js
rename to packages/astro/test/fixtures/legacy-astro-flavored-markdown/src/scripts/test.js
diff --git a/packages/astro/test/legacy-astro-flavored-markdown.test.js b/packages/astro/test/legacy-astro-flavored-markdown.test.js
new file mode 100644
index 000000000..e9199d1a2
--- /dev/null
+++ b/packages/astro/test/legacy-astro-flavored-markdown.test.js
@@ -0,0 +1,200 @@
+import { expect } from 'chai';
+import * as cheerio from 'cheerio';
+import { loadFixture, fixLineEndings } from './test-utils.js';
+
+describe('Legacy Astro-flavored Markdown', () => {
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: './fixtures/legacy-astro-flavored-markdown/',
+		});
+		await fixture.build();
+	});
+
+	it('Can parse JSX expressions in markdown pages', async () => {
+		const html = await fixture.readFile('/jsx-expressions/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('h2').html()).to.equal('Blog Post with JSX expressions');
+
+		expect(html).to.contain('JSX at the start of the line!');
+		for (let listItem of ['test-1', 'test-2', 'test-3']) {
+			expect($(`#${listItem}`).html()).to.equal(`${listItem}`);
+		}
+	});
+
+	it('Can handle slugs with JSX expressions in markdown pages', async () => {
+		const html = await fixture.readFile('/slug/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('h1').attr('id')).to.equal('my-blog-post');
+	});
+
+	it('Can handle code elements without extra spacing', async () => {
+		const html = await fixture.readFile('/code-element/index.html');
+		const $ = cheerio.load(html);
+
+		$('code').each((_, el) => {
+			expect($(el).html()).to.equal($(el).html().trim());
+		});
+	});
+
+	it('Can handle namespaced components in markdown', async () => {
+		const html = await fixture.readFile('/namespace/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('h1').text()).to.equal('Hello Namespace!');
+		expect($('button').length).to.equal(1);
+	});
+
+	it('Correctly handles component children in markdown pages (#3319)', async () => {
+		const html = await fixture.readFile('/children/index.html');
+
+		expect(html).not.to.contain('<p></p>');
+	});
+
+	it('Can handle HTML comments in markdown pages', async () => {
+		const html = await fixture.readFile('/comment/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('h1').text()).to.equal('It works!');
+	});
+
+	it('Prevents `*/` sequences from breaking HTML comments (#3476)', async () => {
+		const html = await fixture.readFile('/comment-with-js/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('h1').text()).to.equal('It still works!');
+	});
+
+	it('Can handle HTML comments in inline code', async () => {
+		const html = await fixture.readFile('/comment-with-js/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('p code').text()).to.equal('<!-- HTML comments in code -->');
+	});
+
+	it('Can handle HTML comments in code fences', async () => {
+		const html = await fixture.readFile('/comment-with-js/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('pre > code').text()).to.equal('<!-- HTML comments in code fence -->');
+	});
+
+	// https://github.com/withastro/astro/issues/3254
+	it('Can handle scripts in markdown pages', async () => {
+		const html = await fixture.readFile('/script/index.html');
+		expect(html).not.to.match(new RegExp('/src/scripts/test.js'));
+	});
+
+	it('Empty code blocks do not fail', async () => {
+		const html = await fixture.readFile('/empty-code/index.html');
+		const $ = cheerio.load(html);
+
+		// test 1: There is not a `<code>` in the codeblock
+		expect($('pre')[0].children).to.have.lengthOf(1);
+
+		// test 2: The empty `<pre>` failed to render
+		expect($('pre')[1].children).to.have.lengthOf(0);
+	});
+
+	it('Can render markdown with --- for horizontal rule', async () => {
+		const html = await fixture.readFile('/dash/index.html');
+		expect(!!html).to.equal(true);
+	});
+
+	it('Exposes raw markdown content', async () => {
+		const { raw } = JSON.parse(await fixture.readFile('/raw-content.json'));
+
+		expect(fixLineEndings(raw)).to.equal(
+			`\n## With components\n\n### Non-hydrated\n\n<Hello name="Astro Naut" />\n\n### Hydrated\n\n<Counter client:load />\n<SvelteButton client:load />\n`
+		);
+	});
+
+	it('Exposes compiled HTML content', async () => {
+		const { compiled } = JSON.parse(await fixture.readFile('/raw-content.json'));
+
+		expect(fixLineEndings(compiled)).to.equal(
+			`<h2 id="with-components">With components</h2>\n<h3 id="non-hydrated">Non-hydrated</h3>\n<Hello name="Astro Naut" />\n<h3 id="hydrated">Hydrated</h3>\n<Counter client:load />\n<SvelteButton client:load />`
+		);
+	});
+
+	it('Allows referencing Vite env var names in markdown (#3412)', async () => {
+		const html = await fixture.readFile('/vite-env-vars/index.html');
+		const $ = cheerio.load(html);
+
+		// test 1: referencing an existing var name
+		expect($('code').eq(0).text()).to.equal('import.meta.env.SITE');
+		expect($('li').eq(0).text()).to.equal('import.meta.env.SITE');
+		expect($('code').eq(3).text()).to.contain('site: import.meta.env.SITE');
+		expect($('blockquote').text()).to.contain('import.meta.env.SITE');
+
+		// test 2: referencing a non-existing var name
+		expect($('code').eq(1).text()).to.equal('import.meta.env.TITLE');
+		expect($('li').eq(1).text()).to.equal('import.meta.env.TITLE');
+		expect($('code').eq(3).text()).to.contain('title: import.meta.env.TITLE');
+		expect($('blockquote').text()).to.contain('import.meta.env.TITLE');
+
+		// test 3: referencing `import.meta.env` itself (without any var name)
+		expect($('code').eq(2).text()).to.equal('import.meta.env');
+		expect($('li').eq(2).text()).to.equal('import.meta.env');
+		expect($('code').eq(3).text()).to.contain('// Use Vite env vars with import.meta.env');
+		expect($('blockquote').text()).to.match(/import\.meta\.env\s*$/);
+	});
+
+	it('Escapes HTML tags in code blocks', async () => {
+		const html = await fixture.readFile('/code-in-md/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('code').eq(0).html()).to.equal('&lt;script&gt;');
+		expect($('blockquote').length).to.equal(1);
+		expect($('code').eq(1).html()).to.equal('&lt;/script&gt;');
+		expect($('pre').html()).to.contain('&gt;This should also work without any problems.&lt;');
+	});
+
+	it('Allows defining slot contents in component children', async () => {
+		const html = await fixture.readFile('/slots/index.html');
+		const $ = cheerio.load(html);
+
+		const slots = $('article').eq(0);
+		expect(slots.find('> .fragmentSlot > div').text()).to.contain('1:');
+		expect(slots.find('> .fragmentSlot > div + p').text()).to.contain('2:');
+		expect(slots.find('> .pSlot > p[title="hello"]').text()).to.contain('3:');
+		expect(slots.find('> .defaultSlot').html()).to.match(
+			new RegExp(
+				`<div>4: Div in default slot</div>` +
+					// Optional extra paragraph due to the line breaks between components
+					`(<p></p>)?` +
+					`<p>5: Paragraph in fragment in default slot</p>` +
+					// Optional whitespace due to the line breaks between components
+					`[\s\n]*` +
+					`6: Regular text in default slot`
+			)
+		);
+
+		const nestedSlots = $('article').eq(1);
+		expect(nestedSlots.find('> .fragmentSlot').html()).to.contain('1:');
+		expect(nestedSlots.find('> .pSlot > p').text()).to.contain('2:');
+		expect(nestedSlots.find('> .defaultSlot > article').text().replace(/\s+/g, ' ')).to.equal(
+			`
+			3: nested fragmentSlot
+			4: nested pSlot
+			5: nested text in default slot
+		`.replace(/\s+/g, ' ')
+		);
+
+		expect($('article').eq(3).text().replace(/[^❌]/g, '')).to.equal('❌❌❌');
+
+		expect($('article').eq(4).text().replace(/[^❌]/g, '')).to.equal('❌❌❌');
+	});
+
+	it('Generate the right props for the layout', async () => {
+		const html = await fixture.readFile('/layout-props/index.html');
+		const $ = cheerio.load(html);
+
+		expect($('#title').text()).to.equal('Hello world!');
+		expect($('#url').text()).to.equal('/layout-props');
+		expect($('#file').text()).to.match(/.*\/layout-props.md$/);
+	});
+});
diff --git a/packages/markdown/remark/src/remark-escape.ts b/packages/markdown/remark/src/remark-escape.ts
index dd8a921ff..84cdf2efa 100644
--- a/packages/markdown/remark/src/remark-escape.ts
+++ b/packages/markdown/remark/src/remark-escape.ts
@@ -2,7 +2,7 @@ import type { Literal } from 'unist';
 import { visit } from 'unist-util-visit';
 
 // In code blocks, this removes the JS comment wrapper added to
-// HTML comments by vite-plugin-markdown.
+// HTML comments by vite-plugin-markdown-legacy.
 export default function remarkEscape() {
 	return (tree: any) => {
 		visit(tree, 'code', removeCommentWrapper);
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index ff53ebbca..85a6b95ed 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1199,6 +1199,12 @@ importers:
     dependencies:
       astro: link:../../..
 
+  packages/astro/test/fixtures/astro-head:
+    specifiers:
+      astro: workspace:*
+    dependencies:
+      astro: link:../../..
+
   packages/astro/test/fixtures/astro-jsx:
     specifiers:
       astro: workspace:*
@@ -1207,11 +1213,9 @@ importers:
 
   packages/astro/test/fixtures/astro-markdown:
     specifiers:
-      '@astrojs/preact': workspace:*
       '@astrojs/svelte': workspace:*
       astro: workspace:*
     dependencies:
-      '@astrojs/preact': link:../../../../integrations/preact
       '@astrojs/svelte': link:../../../../integrations/svelte
       astro: link:../../..
 
@@ -1227,14 +1231,6 @@ importers:
     dependencies:
       astro: link:../../..
 
-  packages/astro/test/fixtures/astro-markdown-md-mode:
-    specifiers:
-      '@astrojs/svelte': workspace:*
-      astro: workspace:*
-    dependencies:
-      '@astrojs/svelte': link:../../../../integrations/svelte
-      astro: link:../../..
-
   packages/astro/test/fixtures/astro-markdown-plugins:
     specifiers:
       '@astrojs/preact': workspace:*
@@ -1349,6 +1345,12 @@ importers:
     dependencies:
       astro: link:../../..
 
+  packages/astro/test/fixtures/client-address:
+    specifiers:
+      astro: workspace:*
+    dependencies:
+      astro: link:../../..
+
   packages/astro/test/fixtures/code-component:
     specifiers:
       astro: workspace:*
@@ -1479,6 +1481,12 @@ importers:
       '@fontsource/montserrat': 4.5.11
       astro: link:../../..
 
+  packages/astro/test/fixtures/glob-pages-css:
+    specifiers:
+      astro: workspace:*
+    dependencies:
+      astro: link:../../..
+
   packages/astro/test/fixtures/hmr-css:
     specifiers:
       astro: workspace:*
@@ -1566,6 +1574,16 @@ importers:
       '@astrojs/solid-js': link:../../../../integrations/solid
       astro: link:../../..
 
+  packages/astro/test/fixtures/legacy-astro-flavored-markdown:
+    specifiers:
+      '@astrojs/preact': workspace:*
+      '@astrojs/svelte': workspace:*
+      astro: workspace:*
+    dependencies:
+      '@astrojs/preact': link:../../../../integrations/preact
+      '@astrojs/svelte': link:../../../../integrations/svelte
+      astro: link:../../..
+
   packages/astro/test/fixtures/legacy-build:
     specifiers:
       '@astrojs/vue': workspace:*