diff --git a/packages/tailwindcss-language-server/src/config.ts b/packages/tailwindcss-language-server/src/config.ts
index 2e417fce..90fb3207 100644
--- a/packages/tailwindcss-language-server/src/config.ts
+++ b/packages/tailwindcss-language-server/src/config.ts
@@ -27,6 +27,7 @@ function getDefaultSettings(): Settings {
         invalidVariant: 'error',
         invalidConfigPath: 'error',
         invalidTailwindDirective: 'error',
+        invalidSourceDirective: 'error',
         recommendedVariantOrder: 'warning',
       },
       showPixelEquivalents: true,
diff --git a/packages/tailwindcss-language-server/src/language/cssServer.ts b/packages/tailwindcss-language-server/src/language/cssServer.ts
index 11caad45..c33e3ebd 100644
--- a/packages/tailwindcss-language-server/src/language/cssServer.ts
+++ b/packages/tailwindcss-language-server/src/language/cssServer.ts
@@ -336,11 +336,7 @@ function replace(delta = 0) {
 }
 
 function createVirtualCssDocument(textDocument: TextDocument): TextDocument {
-  return TextDocument.create(
-    textDocument.uri,
-    textDocument.languageId,
-    textDocument.version,
-    textDocument
+  let content = textDocument
       .getText()
       .replace(/@screen(\s+[^{]+){/g, replace(-2))
       .replace(/@variants(\s+[^{]+){/g, replace())
@@ -350,7 +346,19 @@ function createVirtualCssDocument(textDocument: TextDocument): TextDocument {
         /@media(\s+screen\s*\([^)]+\))/g,
         (_match, screen) => `@media (${MEDIA_MARKER})${' '.repeat(screen.length - 4)}`,
       )
-      .replace(/(?<=\b(?:theme|config)\([^)]*)[.[\]]/g, '_'),
+      // Remove`source(…)`, `theme(…)`, and `prefix(…)` from `@import`s
+      // otherwise we'll show syntax-error diagnostics which we don't want
+      .replace(
+        /@import\s*("(?:[^"]+)"|'(?:[^']+)')\s*((source|theme|prefix)\([^)]+\)\s*)+/g,
+        (_match, url) => `@import "${url.slice(1, -1)}"`,
+      )
+      .replace(/(?<=\b(?:theme|config)\([^)]*)[.[\]]/g, '_')
+
+  return TextDocument.create(
+    textDocument.uri,
+    textDocument.languageId,
+    textDocument.version,
+    content,
   )
 }
 
diff --git a/packages/tailwindcss-language-server/tests/completions/at-config.test.js b/packages/tailwindcss-language-server/tests/completions/at-config.test.js
index b97d1873..15d99ac6 100644
--- a/packages/tailwindcss-language-server/tests/completions/at-config.test.js
+++ b/packages/tailwindcss-language-server/tests/completions/at-config.test.js
@@ -296,4 +296,90 @@ withFixture('v4/dependencies', (c) => {
       ],
     })
   })
+
+  test.concurrent('@import "…" source(…)', async ({ expect }) => {
+    let result = await completion({
+      text: '@import "tailwindcss" source("',
+      lang: 'css',
+      position: {
+        line: 0,
+        character: 30,
+      },
+    })
+
+    expect(result).toEqual({
+      isIncomplete: false,
+      items: [
+        {
+          label: 'sub-dir/',
+          kind: 19,
+          command: { command: 'editor.action.triggerSuggest', title: '' },
+          data: expect.anything(),
+          textEdit: {
+            newText: 'sub-dir/',
+            range: { start: { line: 0, character: 30 }, end: { line: 0, character: 30 } },
+          },
+        },
+      ],
+    })
+  })
+
+  test.concurrent('@tailwind utilities source(…)', async ({ expect }) => {
+    let result = await completion({
+      text: '@tailwind utilities source("',
+      lang: 'css',
+      position: {
+        line: 0,
+        character: 28,
+      },
+    })
+
+    expect(result).toEqual({
+      isIncomplete: false,
+      items: [
+        {
+          label: 'sub-dir/',
+          kind: 19,
+          command: { command: 'editor.action.triggerSuggest', title: '' },
+          data: expect.anything(),
+          textEdit: {
+            newText: 'sub-dir/',
+            range: { start: { line: 0, character: 28 }, end: { line: 0, character: 28 } },
+          },
+        },
+      ],
+    })
+  })
+
+  test.concurrent('@import "…" source(…) directory', async ({ expect }) => {
+    let result = await completion({
+      text: '@import "tailwindcss" source("sub-dir/',
+      lang: 'css',
+      position: {
+        line: 0,
+        character: 38,
+      },
+    })
+
+    expect(result).toEqual({
+      isIncomplete: false,
+      items: [],
+    })
+  })
+
+  test.concurrent('@tailwind utilities source(…) directory', async ({ expect }) => {
+    let result = await completion({
+      text: '@tailwind utilities source("sub-dir/',
+      lang: 'css',
+      position: {
+        line: 0,
+        character: 36,
+      },
+    })
+
+    expect(result).toEqual({
+      isIncomplete: false,
+      items: [],
+    })
+  })
 })
diff --git a/packages/tailwindcss-language-server/tests/completions/completions.test.js b/packages/tailwindcss-language-server/tests/completions/completions.test.js
index 767a3102..cd678845 100644
--- a/packages/tailwindcss-language-server/tests/completions/completions.test.js
+++ b/packages/tailwindcss-language-server/tests/completions/completions.test.js
@@ -507,6 +507,40 @@ withFixture('v4/basic', (c) => {
     )
   })
 
+  test.concurrent('@theme suggests options', async ({ expect }) => {
+    let result = await completion({
+      lang: 'css',
+      text: '@theme ',
+      position: { line: 0, character: 7 },
+    })
+
+    expect(result.items.length).toBe(3)
+    expect(result.items).toEqual(
+      expect.arrayContaining([
+        expect.objectContaining({ label: 'reference' }),
+        expect.objectContaining({ label: 'inline' }),
+        expect.objectContaining({ label: 'default' }),
+      ]),
+    )
+  })
+
+  test.concurrent('@import "…" theme(…) suggests options', async ({ expect }) => {
+    let result = await completion({
+      lang: 'css',
+      text: '@import "tailwindcss/theme" theme()',
+      position: { line: 0, character: 34 },
+    })
+
+    expect(result.items.length).toBe(3)
+    expect(result.items).toEqual(
+      expect.arrayContaining([
+        expect.objectContaining({ label: 'reference' }),
+        expect.objectContaining({ label: 'inline' }),
+        expect.objectContaining({ label: 'default' }),
+      ]),
+    )
+  })
+
   test.concurrent('resolve', async ({ expect }) => {
     let result = await completion({
       text: '<div class="">',
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js b/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js
index 48cdd4f7..56fe9f7f 100644
--- a/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js
+++ b/packages/tailwindcss-language-server/tests/diagnostics/diagnostics.test.js
@@ -314,4 +314,72 @@ withFixture('v4/basic', (c) => {
       },
     ],
   })
+
+  testMatch('Old Tailwind directives warn when used in a v4 project', {
+    language: 'css',
+    code: `
+      @tailwind base;
+      @tailwind preflight;
+      @tailwind components;
+      @tailwind screens;
+      @tailwind variants;
+    `,
+    expected: [
+      {
+        code: 'invalidTailwindDirective',
+        message:
+          "'@tailwind base' is no longer available in v4. Use '@import \"tailwindcss/preflight\"' instead.",
+        suggestions: [],
+        range: {
+          start: { line: 1, character: 16 },
+          end: { line: 1, character: 20 },
+        },
+        severity: 1,
+      },
+      {
+        code: 'invalidTailwindDirective',
+        message:
+          "'@tailwind preflight' is no longer available in v4. Use '@import \"tailwindcss/preflight\"' instead.",
+        suggestions: [],
+        range: {
+          start: { line: 2, character: 16 },
+          end: { line: 2, character: 25 },
+        },
+        severity: 1,
+      },
+      {
+        code: 'invalidTailwindDirective',
+        message:
+          "'@tailwind components' is no longer available in v4. Use '@tailwind utilities' instead.",
+        suggestions: ['utilities'],
+        range: {
+          start: { line: 3, character: 16 },
+          end: { line: 3, character: 26 },
+        },
+        severity: 1,
+      },
+      {
+        code: 'invalidTailwindDirective',
+        message:
+          "'@tailwind screens' is no longer available in v4. Use '@tailwind utilities' instead.",
+        suggestions: ['utilities'],
+        range: {
+          start: { line: 4, character: 16 },
+          end: { line: 4, character: 23 },
+        },
+        severity: 1,
+      },
+      {
+        code: 'invalidTailwindDirective',
+        message:
+          "'@tailwind variants' is no longer available in v4. Use '@tailwind utilities' instead.",
+        suggestions: ['utilities'],
+        range: {
+          start: { line: 5, character: 16 },
+          end: { line: 5, character: 24 },
+        },
+        severity: 1,
+      },
+    ],
+  })
 })
diff --git a/packages/tailwindcss-language-server/tests/diagnostics/source-diagnostics.test.js b/packages/tailwindcss-language-server/tests/diagnostics/source-diagnostics.test.js
new file mode 100644
index 00000000..f6287b63
--- /dev/null
+++ b/packages/tailwindcss-language-server/tests/diagnostics/source-diagnostics.test.js
@@ -0,0 +1,148 @@
+import { expect, test } from 'vitest'
+import { withFixture } from '../common'
+
+withFixture('v4/basic', (c) => {
+  function runTest(name, { code, expected, language }) {
+    test(name, async () => {
+      let promise = new Promise((resolve) => {
+        c.onNotification('textDocument/publishDiagnostics', ({ diagnostics }) => {
+          resolve(diagnostics)
+        })
+      })
+
+      let doc = await c.openDocument({ text: code, lang: language })
+      let diagnostics = await promise
+
+      expected = JSON.parse(JSON.stringify(expected).replaceAll('{{URI}}', doc.uri))
+
+      expect(diagnostics).toMatchObject(expected)
+    })
+  }
+
+  runTest('Source directives require paths', {
+    language: 'css',
+    code: `
+      @import 'tailwindcss' source();
+      @import 'tailwindcss' source('');
+      @import 'tailwindcss' source("");
+      @tailwind utilities source();
+      @tailwind utilities source('');
+      @tailwind utilities source("");
+    `,
+    expected: [
+      {
+        code: 'invalidSourceDirective',
+        message: 'The source directive requires a path to a directory.',
+        range: {
+          start: { line: 1, character: 35 },
+          end: { line: 1, character: 35 },
+        },
+      },
+      {
+        code: 'invalidSourceDirective',
+        message: 'The source directive requires a path to a directory.',
+        range: {
+          start: { line: 2, character: 35 },
+          end: { line: 2, character: 37 },
+        },
+      },
+      {
+        code: 'invalidSourceDirective',
+        message: 'The source directive requires a path to a directory.',
+        range: {
+          start: { line: 3, character: 35 },
+          end: { line: 3, character: 37 },
+        },
+      },
+      {
+        code: 'invalidSourceDirective',
+        message: 'The source directive requires a path to a directory.',
+        range: {
+          start: { line: 4, character: 33 },
+          end: { line: 4, character: 33 },
+        },
+      },
+      {
+        code: 'invalidSourceDirective',
+        message: 'The source directive requires a path to a directory.',
+        range: {
+          start: { line: 5, character: 33 },
+          end: { line: 5, character: 35 },
+        },
+      },
+      {
+        code: 'invalidSourceDirective',
+        message: 'The source directive requires a path to a directory.',
+        range: {
+          start: { line: 6, character: 33 },
+          end: { line: 6, character: 35 },
+        },
+      },
+    ],
+  })
+
+  runTest('source(none) must not be misspelled', {
+    language: 'css',
+    code: `
+      @import 'tailwindcss' source(no);
+      @tailwind utilities source(no);
+    `,
+    expected: [
+      {
+        code: 'invalidSourceDirective',
+        message: '`source(no)` is invalid. Did you mean `source(none)`?',
+        range: {
+          start: { line: 1, character: 35 },
+          end: { line: 1, character: 37 },
+        },
+      },
+      {
+        code: 'invalidSourceDirective',
+        message: '`source(no)` is invalid. Did you mean `source(none)`?',
+        range: {
+          start: { line: 2, character: 33 },
+          end: { line: 2, character: 35 },
+        },
+      },
+    ],
+  })
+
+  runTest('source("…") does not produce diagnostics', {
+    language: 'css',
+    code: `
+      @import 'tailwindcss' source('../app');
+      @tailwind utilities source('../app');
+      @import 'tailwindcss' source("../app");
+      @tailwind utilities source("../app");
+    `,
+    expected: [],
+  })
+
+  runTest('paths given to source("…") must error when not POSIX', {
+    language: 'css',
+    code: String.raw`
+      @import 'tailwindcss' source('C:\\absolute\\path');
+      @import 'tailwindcss' source('C:relative.txt');
+    `,
+    expected: [
+      {
+        code: 'invalidSourceDirective',
+        message:
+          'POSIX-style paths are required with `source(…)` but `C:\\absolute\\path` is a Windows-style path.',
+        range: {
+          start: { line: 1, character: 35 },
+          end: { line: 1, character: 55 },
+        },
+      },
+      {
+        code: 'invalidSourceDirective',
+        message:
+          'POSIX-style paths are required with `source(…)` but `C:relative.txt` is a Windows-style path.',
+        range: {
+          start: { line: 2, character: 35 },
+          end: { line: 2, character: 51 },
+        },
+      },
+    ],
+  })
+})
diff --git a/packages/tailwindcss-language-server/tests/document-links/document-links.test.js b/packages/tailwindcss-language-server/tests/document-links/document-links.test.js
index 595eeec2..861f74c9 100644
--- a/packages/tailwindcss-language-server/tests/document-links/document-links.test.js
+++ b/packages/tailwindcss-language-server/tests/document-links/document-links.test.js
@@ -130,4 +130,46 @@ withFixture('v4/basic', (c) => {
       },
     ],
   })
+
+  testDocumentLinks('Directories in source(…) show links', {
+    text: `
+      @import "tailwindcss" source("../../");
+      @tailwind utilities source("../../");
+    `,
+    lang: 'css',
+    expected: [
+      {
+        target: `file://${path.resolve('./tests/fixtures').replace(/@/g, '%40')}`,
+        range: { start: { line: 1, character: 35 }, end: { line: 1, character: 43 } },
+      },
+      {
+        target: `file://${path.resolve('./tests/fixtures').replace(/@/g, '%40')}`,
+        range: { start: { line: 2, character: 33 }, end: { line: 2, character: 41 } },
+      },
+    ],
+  })
+
+  testDocumentLinks('Globs in source(…) do not show links', {
+    text: `
+      @import "tailwindcss" source("../{a,b,c}");
+      @tailwind utilities source("../{a,b,c}");
+    `,
+    lang: 'css',
+    expected: [],
+  })
+
+  testDocumentLinks('Windows paths in source(…) do not show links', {
+    text: String.raw`
+      @import "tailwindcss" source("..\foo\bar");
+      @tailwind utilities source("..\foo\bar");
+
+      @import "tailwindcss" source("C:\foo\bar");
+      @tailwind utilities source("C:\foo\bar");
+
+      @import "tailwindcss" source("C:foo");
+      @tailwind utilities source("C:bar");
+    `,
+    lang: 'css',
+    expected: [],
+  })
 })
diff --git a/packages/tailwindcss-language-server/tests/fixtures/v4/dependencies/file.d.ts b/packages/tailwindcss-language-server/tests/fixtures/v4/dependencies/file.d.ts
new file mode 100644
index 00000000..39a995a9
--- /dev/null
+++ b/packages/tailwindcss-language-server/tests/fixtures/v4/dependencies/file.d.ts
@@ -0,0 +1 @@
+export type ColorSpace = 'srgb' | 'display-p3'
diff --git a/packages/tailwindcss-language-server/tests/hover/hover.test.js b/packages/tailwindcss-language-server/tests/hover/hover.test.js
index ce271963..878fed21 100644
--- a/packages/tailwindcss-language-server/tests/hover/hover.test.js
+++ b/packages/tailwindcss-language-server/tests/hover/hover.test.js
@@ -157,7 +157,10 @@ withFixture('basic', (c) => {
 })
 
 withFixture('v4/basic', (c) => {
-  async function testHover(name, { text, lang, position, expected, expectedRange, settings }) {
+  async function testHover(
+    name,
+    { text, exact = false, lang, position, expected, expectedRange, settings },
+  ) {
     test.concurrent(name, async ({ expect }) => {
       let textDocument = await c.openDocument({ text, lang, settings })
       let res = await c.sendRequest('textDocument/hover', {
@@ -165,17 +168,17 @@ withFixture('v4/basic', (c) => {
         position,
       })
 
-      expect(res).toEqual(
-        expected
-          ? {
-              contents: {
-                language: 'css',
-                value: expected,
-              },
-              range: expectedRange,
-            }
-          : expected,
-      )
+      if (!exact && expected) {
+        expected = {
+          contents: {
+            language: 'css',
+            value: expected,
+          },
+          range: expectedRange,
+        }
+      }
+
+      expect(res).toEqual(expected)
     })
   }
 
@@ -242,6 +245,33 @@ withFixture('v4/basic', (c) => {
       end: { line: 2, character: 18 },
     },
   })
+
+  testHover('css @source glob expansion', {
+    exact: true,
+    lang: 'css',
+    text: `@source "../{app,components}/**/*.jsx"`,
+    position: { line: 0, character: 23 },
+    expected: {
+      contents: {
+        kind: 'markdown',
+        value: [
+          '**Expansion**',
+          '```plaintext',
+          '- ../app/**/*.jsx',
+          '- ../components/**/*.jsx',
+          '```',
+        ].join('\n'),
+      },
+      range: {
+        start: { line: 0, character: 8 },
+        end: { line: 0, character: 38 },
+      },
+    },
+    expectedRange: {
+      start: { line: 2, character: 9 },
+      end: { line: 2, character: 18 },
+    },
+  })
 })
 
 withFixture('v4/css-loading-js', (c) => {
diff --git a/packages/tailwindcss-language-service/package.json b/packages/tailwindcss-language-service/package.json
index 3c66323d..29034fb0 100644
--- a/packages/tailwindcss-language-service/package.json
+++ b/packages/tailwindcss-language-service/package.json
@@ -19,6 +19,7 @@
     "@types/culori": "^2.1.0",
     "@types/moo": "0.5.3",
     "@types/semver": "7.3.10",
+    "braces": "3.0.3",
     "color-name": "1.1.4",
     "css.escape": "1.5.1",
     "culori": "^4.0.1",
diff --git a/packages/tailwindcss-language-service/src/completionProvider.ts b/packages/tailwindcss-language-service/src/completionProvider.ts
index a8f1f21a..157c4610 100644
--- a/packages/tailwindcss-language-service/src/completionProvider.ts
+++ b/packages/tailwindcss-language-service/src/completionProvider.ts
@@ -39,6 +39,7 @@ import {
 import { customClassesIn } from './util/classes'
 import { IS_SCRIPT_SOURCE, IS_TEMPLATE_SOURCE } from './metadata/extensions'
 import * as postcss from 'postcss'
+import { findFileDirective } from './completions/file-paths'
 
 let isUtil = (className) =>
   Array.isArray(className.__info)
@@ -1599,6 +1600,95 @@ function isInsideAtRule(name: string, document: TextDocument, position: Position
   return braceLevel(text.slice(block)) > 0
 }
 
+// Provide completions for directives that take file paths
+const PATTERN_AT_THEME = /@(?<directive>theme)\s+(?:(?<parts>[^{]+)\s$|$)/
+const PATTERN_IMPORT_THEME = /@(?<directive>import)\s*[^;]+?theme\((?:(?<parts>[^)]+)\s$|$)/
+
+async function provideThemeDirectiveCompletions(
+  state: State,
+  document: TextDocument,
+  position: Position,
+): Promise<CompletionList> {
+  if (!state.v4) return null
+
+  let text = document.getText({ start: { line: position.line, character: 0 }, end: position })
+
+  let match = text.match(PATTERN_AT_THEME) ?? text.match(PATTERN_IMPORT_THEME)
+
+  // Are we in a context where suggesting theme(…) stuff makes sense?
+  if (!match) return null
+
+  let directive = match.groups.directive
+  let parts = new Set(
+    (match.groups.parts ?? '')
+      .trim()
+      .split(/\s+/)
+      .map((part) => part.trim())
+      .filter((part) => part !== ''),
+  )
+
+  let items: CompletionItem[] = [
+    {
+      label: 'reference',
+      documentation: {
+        kind: 'markdown',
+        value:
+          directive === 'import'
+            ? `Don't emit CSS variables for imported theme values.`
+            : `Don't emit CSS variables for these theme values.`,
+      },
+      sortText: '-000000',
+    },
+    {
+      label: 'inline',
+      documentation: {
+        kind: 'markdown',
+        value:
+          directive === 'import'
+            ? `Inline imported theme values into generated utilities instead of using \`var(…)\`.`
+            : `Inline these theme values into generated utilities instead of using \`var(…)\`.`,
+      },
+      sortText: '-000001',
+    },
+    {
+      label: 'default',
+      documentation: {
+        kind: 'markdown',
+        value:
+          directive === 'import'
+            ? `Allow imported theme values to be overriden by JS configs and plugins.`
+            : `Allow these theme values to be overriden by JS configs and plugins.`,
+      },
+      sortText: '-000003',
+    },
+  ]
+
+  items = items.filter((item) => !parts.has(item.label))
+
+  if (items.length === 0) return null
+
+  return withDefaults(
+    {
+      isIncomplete: false,
+      items,
+    },
+    {
+      data: {
+        ...(state.completionItemData ?? {}),
+        _type: 'filesystem',
+      },
+      range: {
+        start: {
+          line: position.line,
+          character: position.character,
+        },
+        end: position,
+      },
+    },
+    state.editor.capabilities.itemDefaults,
+  )
+}
+
 // Provide completions for directives that take file paths
 async function provideFileDirectiveCompletions(
   state: State,
@@ -1613,39 +1703,43 @@ async function provideFileDirectiveCompletions(
     return null
   }
 
-  let pattern = state.v4
-    ? /@(?<directive>config|plugin|source)\s*(?<partial>'[^']*|"[^"]*)$/
-    : /@(?<directive>config)\s*(?<partial>'[^']*|"[^"]*)$/
-
   let text = document.getText({ start: { line: position.line, character: 0 }, end: position })
-  let match = text.match(pattern)
-  if (!match) {
-    return null
+
+  let fd = await findFileDirective(state, text)
+  if (!fd) return null
+
+  let { partial, suggest } = fd
+
+  function isAllowedFile(name: string) {
+    if (suggest === 'script') return IS_SCRIPT_SOURCE.test(name)
+
+    if (suggest === 'source') return IS_TEMPLATE_SOURCE.test(name)
+
+    // Files are not allowed but directories are
+    if (suggest === 'directory') return false
+
+    return false
   }
-  let directive = match.groups.directive
-  let partial = match.groups.partial.slice(1) // remove quote
+
   let valueBeforeLastSlash = partial.substring(0, partial.lastIndexOf('/'))
   let valueAfterLastSlash = partial.substring(partial.lastIndexOf('/') + 1)
 
   let entries = await state.editor.readDirectory(document, valueBeforeLastSlash || '.')
 
-  let isAllowedFile = directive === 'source' ? IS_TEMPLATE_SOURCE : IS_SCRIPT_SOURCE
-
-  // Only show directories and JavaScript/TypeScript files
   entries = entries.filter(([name, type]) => {
-    return type.isDirectory || isAllowedFile.test(name)
+    return type.isDirectory || isAllowedFile(name)
   })
 
+  let items: CompletionItem[] = entries.map(([name, type]) => ({
+    label: type.isDirectory ? name + '/' : name,
+    kind: type.isDirectory ? 19 : 17,
+    command: type.isDirectory ? { command: 'editor.action.triggerSuggest', title: '' } : undefined,
+  }))
+
   return withDefaults(
     {
       isIncomplete: false,
-      items: entries.map(([name, type]) => ({
-        label: type.isDirectory ? name + '/' : name,
-        kind: type.isDirectory ? 19 : 17,
-        command: type.isDirectory
-          ? { command: 'editor.action.triggerSuggest', title: '' }
-          : undefined,
-      })),
+      items,
     },
     {
       data: {
@@ -1751,6 +1845,7 @@ export async function doComplete(
 
   const result =
     (await provideClassNameCompletions(state, document, position, context)) ||
+    (await provideThemeDirectiveCompletions(state, document, position)) ||
     provideCssHelperCompletions(state, document, position) ||
     provideCssDirectiveCompletions(state, document, position) ||
     provideScreenDirectiveCompletions(state, document, position) ||
diff --git a/packages/tailwindcss-language-service/src/completions/file-paths.test.ts b/packages/tailwindcss-language-service/src/completions/file-paths.test.ts
new file mode 100644
index 00000000..c79fcbdd
--- /dev/null
+++ b/packages/tailwindcss-language-service/src/completions/file-paths.test.ts
@@ -0,0 +1,56 @@
+import { expect, test } from 'vitest'
+import { findFileDirective } from './file-paths'
+
+test('Detecting v3 directives that point to files', async () => {
+  function find(text: string) {
+    return findFileDirective({ enabled: true, v4: false }, text)
+  }
+
+  await expect(find('@config "./')).resolves.toEqual({
+    directive: 'config',
+    partial: './',
+    suggest: 'script',
+  })
+
+  // The following are not supported in v3
+  await expect(find('@plugin "./')).resolves.toEqual(null)
+  await expect(find('@source "./')).resolves.toEqual(null)
+  await expect(find('@import "tailwindcss" source("./')).resolves.toEqual(null)
+  await expect(find('@tailwind utilities source("./')).resolves.toEqual(null)
+})
+
+test('Detecting v4 directives that point to files', async () => {
+  function find(text: string) {
+    return findFileDirective({ enabled: true, v4: true }, text)
+  }
+
+  await expect(find('@config "./')).resolves.toEqual({
+    directive: 'config',
+    partial: './',
+    suggest: 'script',
+  })
+
+  await expect(find('@plugin "./')).resolves.toEqual({
+    directive: 'plugin',
+    partial: './',
+    suggest: 'script',
+  })
+
+  await expect(find('@source "./')).resolves.toEqual({
+    directive: 'source',
+    partial: './',
+    suggest: 'source',
+  })
+
+  await expect(find('@import "tailwindcss" source("./')).resolves.toEqual({
+    directive: 'import',
+    partial: './',
+    suggest: 'directory',
+  })
+
+  await expect(find('@tailwind utilities source("./')).resolves.toEqual({
+    directive: 'tailwind',
+    partial: './',
+    suggest: 'directory',
+  })
+})
diff --git a/packages/tailwindcss-language-service/src/completions/file-paths.ts b/packages/tailwindcss-language-service/src/completions/file-paths.ts
new file mode 100644
index 00000000..f9b1898d
--- /dev/null
+++ b/packages/tailwindcss-language-service/src/completions/file-paths.ts
@@ -0,0 +1,53 @@
+import type { State } from '../util/state'
+
+// @config, @plugin, @source
+const PATTERN_CUSTOM_V4 = /@(?<directive>config|plugin|source)\s*(?<partial>'[^']*|"[^"]*)$/
+const PATTERN_CUSTOM_V3 = /@(?<directive>config)\s*(?<partial>'[^']*|"[^"]*)$/
+
+// @import … source('…')
+// @tailwind utilities source('…')
+const PATTERN_IMPORT_SOURCE = /@(?<directive>import)\s*(?<path>'[^']*'|"[^"]*")\s*source\((?<partial>'[^']*|"[^"]*)$/
+const PATTERN_UTIL_SOURCE = /@(?<directive>tailwind)\s+utilities\s+source\((?<partial>'[^']*|"[^"]*)?$/
+
+export type FileDirective = {
+  directive: string
+  partial: string
+  suggest: 'script' | 'source' | 'directory'
+}
+
+export async function findFileDirective(state: State, text: string): Promise<FileDirective | null> {
+  if (state.v4) {
+    let match = text.match(PATTERN_CUSTOM_V4)
+      ?? text.match(PATTERN_IMPORT_SOURCE)
+      ?? text.match(PATTERN_UTIL_SOURCE)
+
+    if (!match) return null
+
+    let directive = match.groups.directive
+    let partial = match.groups.partial?.slice(1) ?? "" // remove leading quote
+
+    // Most suggestions are for JS files so we'll default to that
+    let suggest: FileDirective['suggest'] = 'script'
+
+    // If we're looking at @source then it's for a template file
+    if (directive === 'source') {
+      suggest = 'source'
+    }
+
+    // If we're looking at @import … source('…') or @tailwind … source('…') then
+    // we want to list directories instead of files
+    else if (directive === 'import' || directive === 'tailwind') {
+      suggest = 'directory'
+    }
+
+    return { directive, partial, suggest }
+  }
+
+  let match = text.match(PATTERN_CUSTOM_V3)
+  if (!match) return null
+
+  let directive = match.groups.directive
+  let partial = match.groups.partial.slice(1) // remove leading quote
+
+  return { directive, partial, suggest: 'script' }
+}
diff --git a/packages/tailwindcss-language-service/src/diagnostics/diagnosticsProvider.ts b/packages/tailwindcss-language-service/src/diagnostics/diagnosticsProvider.ts
index 34c03b22..18994526 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/diagnosticsProvider.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/diagnosticsProvider.ts
@@ -8,6 +8,7 @@ import { getInvalidVariantDiagnostics } from './getInvalidVariantDiagnostics'
 import { getInvalidConfigPathDiagnostics } from './getInvalidConfigPathDiagnostics'
 import { getInvalidTailwindDirectiveDiagnostics } from './getInvalidTailwindDirectiveDiagnostics'
 import { getRecommendedVariantOrderDiagnostics } from './getRecommendedVariantOrderDiagnostics'
+import { getInvalidSourceDiagnostics } from './getInvalidSourceDiagnostics'
 
 export async function doValidate(
   state: State,
@@ -19,6 +20,7 @@ export async function doValidate(
     DiagnosticKind.InvalidVariant,
     DiagnosticKind.InvalidConfigPath,
     DiagnosticKind.InvalidTailwindDirective,
+    DiagnosticKind.InvalidSourceDirective,
     DiagnosticKind.RecommendedVariantOrder,
   ],
 ): Promise<AugmentedDiagnostic[]> {
@@ -44,6 +46,9 @@ export async function doValidate(
         ...(only.includes(DiagnosticKind.InvalidTailwindDirective)
           ? getInvalidTailwindDirectiveDiagnostics(state, document, settings)
           : []),
+        ...(only.includes(DiagnosticKind.InvalidSourceDirective)
+          ? getInvalidSourceDiagnostics(state, document, settings)
+          : []),
         ...(only.includes(DiagnosticKind.RecommendedVariantOrder)
           ? await getRecommendedVariantOrderDiagnostics(state, document, settings)
           : []),
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidSourceDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidSourceDiagnostics.ts
new file mode 100644
index 00000000..e8b4ba56
--- /dev/null
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidSourceDiagnostics.ts
@@ -0,0 +1,155 @@
+import type { State, Settings } from '../util/state'
+import { DiagnosticKind, InvalidSourceDirectiveDiagnostic } from './types'
+import { findAll, indexToPosition } from '../util/find'
+import type { TextDocument } from 'vscode-languageserver-textdocument'
+import { getCssBlocks } from '../util/language-blocks'
+import { absoluteRange } from '../util/absoluteRange'
+
+// @import … source('…')
+// @tailwind utilities source('…')
+const PATTERN_IMPORT_SOURCE =
+  /(?:\s|^)@(?<directive>import)\s*(?<path>'[^']*'|"[^"]*")\s*source\((?<source>'[^']*'?|"[^"]*"?|[a-z]*|\)|;)/dg
+const PATTERN_UTIL_SOURCE =
+  /(?:\s|^)@(?<directive>tailwind)\s+(?<layer>\S+)\s+source\((?<source>'[^']*'?|"[^"]*"?|[a-z]*|\)|;)/dg
+
+// @source …
+const PATTERN_AT_SOURCE =
+  /(?:\s|^)@(?<directive>source)\s*(?<source>'[^']*'?|"[^"]*"?|[a-z]*|\)|;)/dg
+
+const HAS_DRIVE_LETTER = /^[A-Z]:/
+
+export function getInvalidSourceDiagnostics(
+  state: State,
+  document: TextDocument,
+  settings: Settings,
+): InvalidSourceDirectiveDiagnostic[] {
+  let severity = settings.tailwindCSS.lint.invalidSourceDirective
+  if (severity === 'ignore') return []
+
+  let diagnostics: InvalidSourceDirectiveDiagnostic[] = []
+
+  function add(diag: Omit<InvalidSourceDirectiveDiagnostic, 'code' | 'severity'>) {
+    diagnostics.push({
+      code: DiagnosticKind.InvalidSourceDirective,
+      severity:
+        severity === 'error'
+          ? 1 /* DiagnosticSeverity.Error */
+          : 2 /* DiagnosticSeverity.Warning */,
+      ...diag,
+    })
+  }
+
+  for (let block of getCssBlocks(state, document)) {
+    let text = block.text
+
+    let matches = [
+      ...findAll(PATTERN_IMPORT_SOURCE, text),
+      ...findAll(PATTERN_UTIL_SOURCE, text),
+      ...findAll(PATTERN_AT_SOURCE, text),
+    ]
+
+    for (let match of matches) {
+      let directive = match.groups.directive
+      let source = match.groups.source?.trim() ?? ''
+      let rawSource = source
+      let sourceRange = match.indices.groups.source
+      let isQuoted = false
+
+      if (source.startsWith("'")) {
+        source = source.slice(1)
+        isQuoted = true
+      } else if (source.startsWith('"')) {
+        source = source.slice(1)
+        isQuoted = true
+      }
+
+      if (source.endsWith("'")) {
+        source = source.slice(0, -1)
+        isQuoted = true
+      } else if (source.endsWith('"')) {
+        source = source.slice(0, -1)
+        isQuoted = true
+      }
+
+      source = source.trim()
+
+      // - `@import "tailwindcss" source()`
+      // - `@import "tailwindcss" source('')`
+      // - `@import "tailwindcss" source("")`
+
+      // - `@source ;`
+      // - `@source '';`
+      // - `@source "";`
+      if (source === '' || source === ')' || source === ';') {
+        let range = {
+          start: indexToPosition(text, sourceRange[0]),
+          end: indexToPosition(text, sourceRange[1]),
+        }
+
+        add({
+          message: 'The source directive requires a path to a directory.',
+          range: absoluteRange(range, block.range),
+        })
+      }
+
+      // - `@import "tailwindcss" source(no)`
+      // - `@tailwind utilities source('')`
+      else if (directive !== 'source' && source !== 'none' && !isQuoted) {
+        let range = {
+          start: indexToPosition(text, sourceRange[0]),
+          end: indexToPosition(text, sourceRange[1]),
+        }
+
+        add({
+          message: `\`source(${source})\` is invalid. Did you mean \`source(none)\`?`,
+          range: absoluteRange(range, block.range),
+        })
+      }
+
+      // Detection of Windows-style paths
+      else if (source.includes('\\') || HAS_DRIVE_LETTER.test(source)) {
+        source = source.replaceAll('\\\\', '\\')
+
+        let range = {
+          start: indexToPosition(text, sourceRange[0]),
+          end: indexToPosition(text, sourceRange[1]),
+        }
+
+        add({
+          message: `POSIX-style paths are required with \`source(…)\` but \`${source}\` is a Windows-style path.`,
+          range: absoluteRange(range, block.range),
+        })
+      }
+
+      // `@source none` is invalid
+      else if (directive === 'source' && source === 'none') {
+        let range = {
+          start: indexToPosition(text, sourceRange[0]),
+          end: indexToPosition(text, sourceRange[1]),
+        }
+
+        add({
+          message:
+            '`@source none;` is not valid. Did you mean to use `source(none)` on an `@import`?',
+          range: absoluteRange(range, block.range),
+        })
+      }
+
+      // - `@import "tailwindcss" source(no)`
+      // - `@tailwind utilities source('')`
+      else if (directive === 'source' && source !== 'none' && !isQuoted) {
+        let range = {
+          start: indexToPosition(text, sourceRange[0]),
+          end: indexToPosition(text, sourceRange[1]),
+        }
+
+        add({
+          message: `\`@source ${rawSource};\` is invalid.`,
+          range: absoluteRange(range, block.range),
+        })
+      }
+    }
+  }
+
+  return diagnostics
+}
diff --git a/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts b/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts
index 7325d49e..480bb8cd 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/getInvalidTailwindDirectiveDiagnostics.ts
@@ -37,51 +37,23 @@ export function getInvalidTailwindDirectiveDiagnostics(
     regex = /(?:\s|^)@tailwind\s+(?<value>[^;]+)/g
   }
 
-  let hasVariantsDirective = state.jit && semver.gte(state.version, '2.1.99')
-
   ranges.forEach((range) => {
     let text = getTextWithoutComments(document, 'css', range)
     let matches = findAll(regex, text)
 
-    let valid = [
-      'utilities',
-      'components',
-      'screens',
-      semver.gte(state.version, '1.0.0-beta.1') ? 'base' : 'preflight',
-      hasVariantsDirective && 'variants',
-    ].filter(Boolean)
-
-    let suggestable = valid
-
-    if (hasVariantsDirective) {
-      // Don't suggest `screens`, because it's deprecated
-      suggestable = suggestable.filter((value) => value !== 'screens')
-    }
-
     matches.forEach((match) => {
-      if (valid.includes(match.groups.value)) {
-        return null
-      }
+      let layerName = match.groups.value
 
-      let message = `'${match.groups.value}' is not a valid value.`
-      let suggestions: string[] = []
-
-      if (match.groups.value === 'preflight') {
-        suggestions.push('base')
-        message += ` Did you mean 'base'?`
-      } else {
-        let suggestion = closest(match.groups.value, suggestable)
-        if (suggestion) {
-          suggestions.push(suggestion)
-          message += ` Did you mean '${suggestion}'?`
-        }
-      }
+      let result = validateLayerName(state, layerName)
+      if (!result) return
+
+      let { message, suggestions } = result
 
       diagnostics.push({
         code: DiagnosticKind.InvalidTailwindDirective,
         range: absoluteRange(
           {
-            start: indexToPosition(text, match.index + match[0].length - match.groups.value.length),
+            start: indexToPosition(text, match.index + match[0].length - layerName.length),
             end: indexToPosition(text, match.index + match[0].length),
           },
           range,
@@ -98,3 +70,87 @@ export function getInvalidTailwindDirectiveDiagnostics(
 
   return diagnostics
 }
+
+function validateLayerName(
+  state: State,
+  layerName: string,
+): { message: string; suggestions: string[] } | null {
+  if (state.v4) {
+    // `@tailwind utilities` is valid
+    if (layerName === 'utilities') {
+      return null
+    }
+
+    // `@tailwind base | preflight` do not exist in v4
+    if (layerName === 'base' || layerName === 'preflight') {
+      return {
+        message: `'@tailwind ${layerName}' is no longer available in v4. Use '@import "tailwindcss/preflight"' instead.`,
+        suggestions: [],
+      }
+    }
+
+    // `@tailwind components | screens | variants` do not exist in v4
+    if (layerName === 'components' || layerName === 'screens' || layerName === 'variants') {
+      return {
+        message: `'@tailwind ${layerName}' is no longer available in v4. Use '@tailwind utilities' instead.`,
+        suggestions: ['utilities'],
+      }
+    }
+
+    let parts = layerName.split(/\s+/)
+
+    // `@tailwind utilities source(…)` is valid
+    if (parts[0] === 'utilities' && parts[1]?.startsWith('source(')) {
+      return null
+    }
+
+    return {
+      message: `'${layerName}' is not a valid value.`,
+      suggestions: [],
+    }
+  }
+
+  let valid = ['utilities', 'components', 'screens']
+
+  if (semver.gte(state.version, '1.0.0-beta.1')) {
+    valid.push('base')
+  } else {
+    valid.push('preflight')
+  }
+
+  let hasVariantsDirective = state.jit && semver.gte(state.version, '2.1.99')
+
+  if (hasVariantsDirective) {
+    valid.push('variants')
+  }
+
+  if (valid.includes(layerName)) {
+    return null
+  }
+
+  let suggestable = valid
+
+  if (hasVariantsDirective) {
+    // Don't suggest `screens`, because it's deprecated
+    suggestable = suggestable.filter((value) => value !== 'screens')
+  }
+
+  let message = `'${layerName}' is not a valid value.`
+  let suggestions: string[] = []
+
+  if (layerName === 'preflight') {
+    suggestions.push('base')
+    message += ` Did you mean 'base'?`
+  } else {
+    let suggestion = closest(layerName, suggestable)
+    if (suggestion) {
+      suggestions.push(suggestion)
+      message += ` Did you mean '${suggestion}'?`
+    }
+  }
+
+  return {
+    message,
+    suggestions,
+  }
+}
diff --git a/packages/tailwindcss-language-service/src/diagnostics/types.ts b/packages/tailwindcss-language-service/src/diagnostics/types.ts
index 115079a2..7cb68a7e 100644
--- a/packages/tailwindcss-language-service/src/diagnostics/types.ts
+++ b/packages/tailwindcss-language-service/src/diagnostics/types.ts
@@ -8,6 +8,7 @@ export enum DiagnosticKind {
   InvalidVariant = 'invalidVariant',
   InvalidConfigPath = 'invalidConfigPath',
   InvalidTailwindDirective = 'invalidTailwindDirective',
+  InvalidSourceDirective = 'invalidSourceDirective',
   RecommendedVariantOrder = 'recommendedVariantOrder',
 }
 
@@ -78,6 +79,16 @@ export function isInvalidTailwindDirectiveDiagnostic(
   return diagnostic.code === DiagnosticKind.InvalidTailwindDirective
 }
 
+export type InvalidSourceDirectiveDiagnostic = Diagnostic & {
+  code: DiagnosticKind.InvalidSourceDirective
+}
+
+export function isInvalidSourceDirectiveDiagnostic(
+  diagnostic: AugmentedDiagnostic,
+): diagnostic is InvalidSourceDirectiveDiagnostic {
+  return diagnostic.code === DiagnosticKind.InvalidSourceDirective
+}
+
 export type RecommendedVariantOrderDiagnostic = Diagnostic & {
   code: DiagnosticKind.RecommendedVariantOrder
   suggestions: string[]
@@ -96,4 +107,5 @@ export type AugmentedDiagnostic =
   | InvalidVariantDiagnostic
   | InvalidConfigPathDiagnostic
   | InvalidTailwindDirectiveDiagnostic
+  | InvalidSourceDirectiveDiagnostic
   | RecommendedVariantOrderDiagnostic
diff --git a/packages/tailwindcss-language-service/src/documentLinksProvider.ts b/packages/tailwindcss-language-service/src/documentLinksProvider.ts
index 3dcc15bb..b18a4711 100644
--- a/packages/tailwindcss-language-service/src/documentLinksProvider.ts
+++ b/packages/tailwindcss-language-service/src/documentLinksProvider.ts
@@ -1,26 +1,26 @@
 import type { TextDocument } from 'vscode-languageserver-textdocument'
 import type { State } from './util/state'
 import type { DocumentLink, Range } from 'vscode-languageserver'
-import { isCssDoc } from './util/css'
-import { getLanguageBoundaries } from './util/getLanguageBoundaries'
 import { findAll, indexToPosition } from './util/find'
-import { getTextWithoutComments } from './util/doc'
 import { absoluteRange } from './util/absoluteRange'
 import * as semver from './util/semver'
+import { getCssBlocks } from './util/language-blocks'
+
+const HAS_DRIVE_LETTER = /^[A-Z]:/
 
 export function getDocumentLinks(
   state: State,
   document: TextDocument,
   resolveTarget: (linkPath: string) => string,
 ): DocumentLink[] {
-  let patterns = [
-    /@config\s*(?<path>'[^']+'|"[^"]+")/g,
-  ]
+  let patterns = [/@config\s*(?<path>'[^']+'|"[^"]+")/g]
 
   if (state.v4) {
     patterns.push(
       /@plugin\s*(?<path>'[^']+'|"[^"]+")/g,
       /@source\s*(?<path>'[^']+'|"[^"]+")/g,
+      /@import\s*('[^']*'|"[^"]*")\s*source\((?<path>'[^']*'?|"[^"]*"?)/g,
+      /@tailwind\s*utilities\s*source\((?<path>'[^']*'?|"[^"]*"?)/g,
     )
   }
 
@@ -38,18 +38,10 @@ function getDirectiveLinks(
   }
 
   let links: DocumentLink[] = []
-  let ranges: Range[] = []
 
-  if (isCssDoc(state, document)) {
-    ranges.push(undefined)
-  } else {
-    let boundaries = getLanguageBoundaries(state, document)
-    if (!boundaries) return []
-    ranges.push(...boundaries.filter((b) => b.type === 'css').map(({ range }) => range))
-  }
+  for (let block of getCssBlocks(state, document)) {
+    let text = block.text
 
-  for (let range of ranges) {
-    let text = getTextWithoutComments(document, 'css', range)
     let matches: RegExpMatchArray[] = []
 
     for (let pattern of patterns) {
@@ -57,15 +49,26 @@ function getDirectiveLinks(
     }
 
     for (let match of matches) {
+      let path = match.groups.path.slice(1, -1)
+
+      // Ignore glob-like paths
+      if (path.includes('*') || path.includes('{') || path.includes('}')) {
+        continue
+      }
+
+      // Ignore Windows-style paths
+      if (path.includes('\\') || HAS_DRIVE_LETTER.test(path)) {
+        continue
+      }
+
+      let range = {
+        start: indexToPosition(text, match.index + match[0].length - match.groups.path.length),
+        end: indexToPosition(text, match.index + match[0].length),
+      }
+
       links.push({
-        target: resolveTarget(match.groups.path.slice(1, -1)),
-        range: absoluteRange(
-          {
-            start: indexToPosition(text, match.index + match[0].length - match.groups.path.length),
-            end: indexToPosition(text, match.index + match[0].length),
-          },
-          range,
-        ),
+        target: resolveTarget(path),
+        range: absoluteRange(range, block.range),
       })
     }
   }
diff --git a/packages/tailwindcss-language-service/src/hoverProvider.ts b/packages/tailwindcss-language-service/src/hoverProvider.ts
index 1ef981a0..51ef67e3 100644
--- a/packages/tailwindcss-language-service/src/hoverProvider.ts
+++ b/packages/tailwindcss-language-service/src/hoverProvider.ts
@@ -1,9 +1,14 @@
 import type { State } from './util/state'
-import type { Hover, Position } from 'vscode-languageserver'
+import type { Hover, MarkupContent, Position, Range } from 'vscode-languageserver'
 import { stringifyCss, stringifyConfigValue } from './util/stringify'
 import dlv from 'dlv'
 import { isCssContext } from './util/css'
-import { findClassNameAtPosition, findHelperFunctionsInRange } from './util/find'
+import {
+  findAll,
+  findClassNameAtPosition,
+  findHelperFunctionsInRange,
+  indexToPosition,
+} from './util/find'
 import { validateApply } from './util/validateApply'
 import { getClassNameParts } from './util/getClassNameAtPosition'
 import * as jit from './util/jit'
@@ -11,6 +16,9 @@ import { validateConfigPath } from './diagnostics/getInvalidConfigPathDiagnostic
 import { isWithinRange } from './util/isWithinRange'
 import type { TextDocument } from 'vscode-languageserver-textdocument'
 import { addPixelEquivalentsToValue } from './util/pixelEquivalents'
+import { getTextWithoutComments } from './util/doc'
+import braces from 'braces'
+import { absoluteRange } from './util/absoluteRange'
 
 export async function doHover(
   state: State,
@@ -19,7 +27,8 @@ export async function doHover(
 ): Promise<Hover> {
   return (
     (await provideClassNameHover(state, document, position)) ||
-    (await provideCssHelperHover(state, document, position))
+    (await provideCssHelperHover(state, document, position)) ||
+    (await provideSourceGlobHover(state, document, position))
   )
 }
 
@@ -48,7 +57,7 @@ async function provideCssHelperHover(
       helperFn.helper === 'theme' ? ['theme'] : [],
     )
 
-    // This property may not exist in the state object because of compatability with Tailwind Play
+    // This property may not exist in the state object because of compatibility with Tailwind Play
     let value = validated.isValid ? stringifyConfigValue(validated.value) : null
     if (value === null) return null
 
@@ -133,3 +142,64 @@ async function provideClassNameHover(
     range: className.range,
   }
 }
+
+function markdown(lines: string[]): MarkupContent {
+  return {
+    kind: 'markdown',
+    value: lines.join('\n'),
+  }
+}
+
+async function provideSourceGlobHover(
+  state: State,
+  document: TextDocument,
+  position: Position,
+): Promise<Hover> {
+  if (!isCssContext(state, document, position)) {
+    return null
+  }
+
+  let range = {
+    start: { line: position.line, character: 0 },
+    end: { line: position.line + 1, character: 0 },
+  }
+
+  let text = getTextWithoutComments(document, 'css', range)
+
+  let pattern = /@source\s*(?<path>'[^']+'|"[^"]+")/dg
+
+  for (let match of findAll(pattern, text)) {
+    let path = match.groups.path.slice(1, -1)
+
+    // Ignore paths that don't need brace expansion
+    if (!path.includes('{') || !path.includes('}')) continue
+
+    // Ignore paths that don't contain the current position
+    let slice: Range = absoluteRange(
+      {
+        start: indexToPosition(text, match.indices.groups.path[0]),
+        end: indexToPosition(text, match.indices.groups.path[1]),
+      },
+      range,
+    )
+
+    if (!isWithinRange(position, slice)) continue
+
+    // Perform brace expansion
+    let paths = new Set(braces.expand(path))
+    if (paths.size < 2) continue
+
+    return {
+      range: slice,
+      contents: markdown([
+        //
+        '**Expansion**',
+        '```plaintext',
+        ...Array.from(paths, (path) => `- ${path}`),
+        '```',
+      ]),
+    }
+  }
+
+  return null
+}
diff --git a/packages/tailwindcss-language-service/src/metadata/extensions.ts b/packages/tailwindcss-language-service/src/metadata/extensions.ts
index dab890d5..15babe94 100644
--- a/packages/tailwindcss-language-service/src/metadata/extensions.ts
+++ b/packages/tailwindcss-language-service/src/metadata/extensions.ts
@@ -3,9 +3,9 @@ let scriptExtensions = [
   'js',
   'cjs',
   'mjs',
-  'ts',
-  'mts',
-  'cts',
+  '(?<!d.)ts', // matches .ts but not .d.ts
+  '(?<!d.)mts', // matches .mts but not .d.mts
+  '(?<!d.)cts', // matches .cts but not .d.cts
 ]
 
 let templateExtensions = [
@@ -20,14 +20,14 @@ let templateExtensions = [
   // JS
   'astro',
   'cjs',
-  'cts',
+  '(?<!d.)cts', // matches .cts but not .d.cts
   'jade',
   'js',
   'jsx',
   'mjs',
-  'mts',
+  '(?<!d.)mts', // matches .mts but not .d.mts
   'svelte',
-  'ts',
+  '(?<!d.)ts', // matches .ts but not .d.ts
   'tsx',
   'vue',
 
diff --git a/packages/tailwindcss-language-service/src/util/find.ts b/packages/tailwindcss-language-service/src/util/find.ts
index 31de45c5..de1d6203 100644
--- a/packages/tailwindcss-language-service/src/util/find.ts
+++ b/packages/tailwindcss-language-service/src/util/find.ts
@@ -354,6 +354,24 @@ export function findHelperFunctionsInRange(
     text,
   )
 
+  // Eliminate matches that are on an `@import`
+  matches = matches.filter((match) => {
+    // Scan backwards to see if we're in an `@import` statement
+    for (let i = match.index - 1; i >= 0; i--) {
+      let char = text[i]
+      if (char === '\n') break
+      if (char === ';') break
+      // Detecting theme(…) inside the media query list of `@import` is okay
+      if (char === '(') break
+      if (char === ')') break
+      if (text.startsWith('@import', i)) {
+        return false
+      }
+    }
+
+    return true
+  })
+
   return matches.map((match) => {
     let quotesBefore = ''
     let path = match.groups.path
diff --git a/packages/tailwindcss-language-service/src/util/language-blocks.ts b/packages/tailwindcss-language-service/src/util/language-blocks.ts
new file mode 100644
index 00000000..10a3fe14
--- /dev/null
+++ b/packages/tailwindcss-language-service/src/util/language-blocks.ts
@@ -0,0 +1,45 @@
+import type { State } from '../util/state'
+import { type Range } from 'vscode-languageserver'
+import type { TextDocument } from 'vscode-languageserver-textdocument'
+import { getLanguageBoundaries } from '../util/getLanguageBoundaries'
+import { isCssDoc } from '../util/css'
+import { getTextWithoutComments } from './doc'
+
+export interface LanguageBlock {
+  document: TextDocument
+  range: Range | undefined
+  lang: string
+  readonly text: string
+}
+
+export function* getCssBlocks(
+  state: State,
+  document: TextDocument,
+): Iterable<LanguageBlock | undefined> {
+  if (isCssDoc(state, document)) {
+    yield {
+      document,
+      range: undefined,
+      lang: document.languageId,
+      get text() {
+        return getTextWithoutComments(document, 'css')
+      },
+    }
+  } else {
+    let boundaries = getLanguageBoundaries(state, document)
+    if (!boundaries) return []
+
+    for (let boundary of boundaries) {
+      if (boundary.type !== 'css') continue
+
+      yield {
+        document,
+        range: boundary.range,
+        lang: boundary.lang ?? document.languageId,
+        get text() {
+          return getTextWithoutComments(document, 'css', boundary.range)
+        },
+      }
+    }
+  }
+}
diff --git a/packages/tailwindcss-language-service/src/util/state.ts b/packages/tailwindcss-language-service/src/util/state.ts
index abe8863c..dd1966ce 100644
--- a/packages/tailwindcss-language-service/src/util/state.ts
+++ b/packages/tailwindcss-language-service/src/util/state.ts
@@ -59,6 +59,7 @@ export type TailwindCssSettings = {
     invalidVariant: DiagnosticSeveritySetting
     invalidConfigPath: DiagnosticSeveritySetting
     invalidTailwindDirective: DiagnosticSeveritySetting
+    invalidSourceDirective: DiagnosticSeveritySetting
     recommendedVariantOrder: DiagnosticSeveritySetting
   }
   experimental: {
diff --git a/packages/tailwindcss-language-service/src/util/v4/design-system.ts b/packages/tailwindcss-language-service/src/util/v4/design-system.ts
index ca2f9ad2..ee9396a8 100644
--- a/packages/tailwindcss-language-service/src/util/v4/design-system.ts
+++ b/packages/tailwindcss-language-service/src/util/v4/design-system.ts
@@ -3,7 +3,7 @@ import type { Rule } from './ast'
 import type { NamedVariant } from './candidate'
 
 export interface Theme {
-  // Prefix didn't exist on
+  // Prefix didn't exist for earlier Tailwind versions
   prefix?: string
   entries(): [string, any][]
 }
diff --git a/packages/vscode-tailwindcss/CHANGELOG.md b/packages/vscode-tailwindcss/CHANGELOG.md
index 665d847e..69321177 100644
--- a/packages/vscode-tailwindcss/CHANGELOG.md
+++ b/packages/vscode-tailwindcss/CHANGELOG.md
@@ -2,7 +2,21 @@
 
 ## Prerelease
 
-- Nothing yet!
+- Add suggestions for theme options ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Add suggestions when using `@source "…"` and `source(…)` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Show brace expansion when hovering `@source` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Highlight `source(…)`, `theme(…)`, and `prefix(…)` when used with `@import "…"` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Highlight `@tailwind utilities source(…)` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Show document links when using `source(…)` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+
+- Ensure language server starts as needed ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Don't show syntax errors when using `source(…)`, `theme(…)`, or `prefix(…)` with `@import "…"` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Don't show warning when using `@tailwind utilities source(…)` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Don't suggest TypeScript declaration files for `@config`, `@plugin`, and `@source` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Don't link Windows-style paths in `@source`, `@config`, and `@plugin` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+
+- Warn on invalid uses of `source(…)`, `@source`, `@config`, and `@plugin` ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
+- Warn when a v4 project uses an old `@tailwind` directive ([#1083](https://github.com/tailwindlabs/tailwindcss-intellisense/pull/1083))
 
 ## 0.12.13
 
diff --git a/packages/vscode-tailwindcss/src/extension.ts b/packages/vscode-tailwindcss/src/extension.ts
index 3df1c216..d717d5a5 100755
--- a/packages/vscode-tailwindcss/src/extension.ts
+++ b/packages/vscode-tailwindcss/src/extension.ts
@@ -609,7 +609,7 @@ export async function activate(context: ExtensionContext) {
       return
     }
 
-    if (!anyFolderNeedsLanguageServer(Workspace.workspaceFolders ?? [])) {
+    if (!await anyFolderNeedsLanguageServer(Workspace.workspaceFolders ?? [])) {
       return
     }
 
diff --git a/packages/vscode-tailwindcss/syntaxes/at-rules.tmLanguage.json b/packages/vscode-tailwindcss/syntaxes/at-rules.tmLanguage.json
index d50b1007..92d02bd3 100644
--- a/packages/vscode-tailwindcss/syntaxes/at-rules.tmLanguage.json
+++ b/packages/vscode-tailwindcss/syntaxes/at-rules.tmLanguage.json
@@ -4,6 +4,53 @@
   "injectionSelector": "L:source.css -comment -source.css.scss",
   "name": "TailwindCSS",
   "patterns": [
+    {
+      "begin": "(?i)((@)import)(?:\\s+|$|(?=['\"]|/\\*))",
+      "beginCaptures": {
+        "1": {
+          "name": "keyword.control.at-rule.import.css"
+        },
+        "2": {
+          "name": "punctuation.definition.keyword.css"
+        }
+      },
+      "end": ";",
+      "endCaptures": {
+        "0": {
+          "name": "punctuation.terminator.rule.css"
+        }
+      },
+      "name": "meta.at-rule.import.css",
+      "patterns": [
+        {
+          "begin": "\\G\\s*(?=/\\*)",
+          "end": "(?<=\\*/)\\s*",
+          "patterns": [
+            {
+              "include": "source.css#comment-block"
+            }
+          ]
+        },
+        {
+          "include": "source.css#string"
+        },
+        {
+          "include": "source.css#url"
+        },
+        {
+          "include": "#source-fn"
+        },
+        {
+          "include": "#theme-meta-fn"
+        },
+        {
+          "include": "#prefix-meta-fn"
+        },
+        {
+          "include": "source.css#media-query-list"
+        }
+      ]
+    },
     {
       "begin": "(?i)((@)tailwind)(?=\\s|/\\*|$)",
       "beginCaptures": {
@@ -28,6 +75,9 @@
         {
           "include": "source.css#escapes"
         },
+        {
+          "include": "#source-fn"
+        },
         {
           "match": "[^\\s;]+?",
           "name": "variable.parameter.tailwind.tailwind"
@@ -200,6 +250,10 @@
         }
       },
       "patterns": [
+        {
+          "match": "none(?=;)",
+          "name": "invalid.illegal.invalid-source.css"
+        },
         {
           "include": "source.css#string"
         }
@@ -446,6 +500,114 @@
           "name": "punctuation.terminator.rule.css"
         }
       ]
+    },
+    "source-fn": {
+      "patterns": [
+        {
+          "begin": "(?i)(?:\\s*)(?<![\\w@-])(source)([(])",
+          "beginCaptures": {
+            "1": {
+              "name": "support.function.source.css"
+            },
+            "2": {
+              "name": "punctuation.section.function.begin.bracket.round.css"
+            }
+          },
+          "end": "[)]",
+          "endCaptures": {
+            "0": {
+              "name": "punctuation.section.function.end.bracket.round.css"
+            }
+          },
+          "patterns": [
+            {
+              "match": "none(?=[)])",
+              "name": "variable.other.css"
+            },
+            {
+              "include": "source.css#string"
+            }
+          ]
+        }
+      ]
+    },
+    "theme-meta-fn": {
+      "patterns": [
+        {
+          "begin": "(?i)(?:\\s*)(?<![\\w@-])(theme)([(])",
+          "beginCaptures": {
+            "1": {
+              "name": "support.function.theme.css"
+            },
+            "2": {
+              "name": "punctuation.section.function.begin.bracket.round.css"
+            }
+          },
+          "end": "[)]",
+          "endCaptures": {
+            "0": {
+              "name": "punctuation.section.function.end.bracket.round.css"
+            }
+          },
+          "patterns": [
+            {
+              "match": "\\s+",
+              "name": "variable.other.css"
+            },
+            {
+              "match": "reference",
+              "name": "variable.other.css"
+            },
+            {
+              "match": "inline",
+              "name": "variable.other.css"
+            },
+            {
+              "match": "default",
+              "name": "variable.other.css"
+            },
+            {
+              "match": "deprecated",
+              "name": "variable.other.css"
+            },
+            {
+              "match": "[^)]+",
+              "name": "invalid.illegal.invalid-source.css"
+            }
+          ]
+        }
+      ]
+    },
+    "prefix-meta-fn": {
+      "patterns": [
+        {
+          "begin": "(?i)(?:\\s*)(?<![\\w@-])(prefix)([(])",
+          "beginCaptures": {
+            "1": {
+              "name": "support.function.prefix.css"
+            },
+            "2": {
+              "name": "punctuation.section.function.begin.bracket.round.css"
+            }
+          },
+          "end": "[)]",
+          "endCaptures": {
+            "0": {
+              "name": "punctuation.section.function.end.bracket.round.css"
+            }
+          },
+          "patterns": [
+            {
+              "match": "[a-z]+",
+              "name": "variable.other.css"
+            },
+            {
+              "match": "[^a-z]+",
+              "name": "invalid.illegal.invalid-source.css"
+            }
+          ]
+        }
+      ]
     }
   }
 }
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 64c07a3b..f0ca5d41 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -227,6 +227,9 @@ importers:
       '@types/semver':
         specifier: 7.3.10
         version: 7.3.10
+      braces:
+        specifier: 3.0.3
+        version: 3.0.3
       color-name:
         specifier: 1.1.4
         version: 1.1.4