diff --git a/.nx/version-plans/version-plan-1784663569372.md b/.nx/version-plans/version-plan-1784663569372.md
new file mode 100644
index 00000000000..2667e08834d
--- /dev/null
+++ b/.nx/version-plans/version-plan-1784663569372.md
@@ -0,0 +1,8 @@
+---
+eslint-plugin-gamut: minor
+gamut-styles: major
+variance: minor
+gamut: major
+---
+
+Adding new zIndex scale to Gamut. Inclues a new eslint rule for avoiding raw z-index values. Allows variance scales to include raw values if need be.
diff --git a/packages/eslint-plugin-gamut/src/index.tsx b/packages/eslint-plugin-gamut/src/index.tsx
index 9459f37a2a0..f4346fbc28d 100644
--- a/packages/eslint-plugin-gamut/src/index.tsx
+++ b/packages/eslint-plugin-gamut/src/index.tsx
@@ -2,6 +2,7 @@ import gamutImportPaths from './gamut-import-paths';
 import noCssStandalone from './no-css-standalone';
 import noInlineStyle from './no-inline-style';
 import noKbdElement from './no-kbd-element';
+import noRawZIndex from './no-raw-z-index';
 import preferThemed from './prefer-themed';
 import recommended from './recommended';
 
@@ -10,6 +11,7 @@ const rules = {
   'no-css-standalone': noCssStandalone,
   'no-inline-style': noInlineStyle,
   'no-kbd-element': noKbdElement,
+  'no-raw-z-index': noRawZIndex,
   'prefer-themed': preferThemed,
 };
 
diff --git a/packages/eslint-plugin-gamut/src/no-raw-z-index.test.ts b/packages/eslint-plugin-gamut/src/no-raw-z-index.test.ts
new file mode 100644
index 00000000000..4a0180cf5fb
--- /dev/null
+++ b/packages/eslint-plugin-gamut/src/no-raw-z-index.test.ts
@@ -0,0 +1,55 @@
+import { ESLintUtils } from '@typescript-eslint/utils';
+
+import rule from './no-raw-z-index';
+
+const ruleTester = new ESLintUtils.RuleTester({
+  parser: '@typescript-eslint/parser',
+  parserOptions: {
+    ecmaFeatures: {
+      jsx: true,
+    },
+  },
+});
+
+ruleTester.run('no-raw-z-index', rule, {
+  valid: [
+    // Semantic tokens are the expected usage.
+    `const styles = { zIndex: zIndexes.modal };`,
+    `<Box zIndex={zIndexes.stickyHeader} />;`,
+    // Arithmetic on a token is allowed (e.g. Tip's shadow).
+    `const styles = { zIndex: zIndexes.foreground - 2 };`,
+    `<Box zIndex={zIndexes.modal + 5} />;`,
+    // Variables / non-literal expressions are not flagged.
+    `<Box zIndex={zIndex} />;`,
+    `const styles = { zIndex };`,
+    // Unrelated properties.
+    `const styles = { padding: 0 };`,
+    `<Box top={0} />;`,
+  ],
+  invalid: [
+    {
+      code: `const styles = { zIndex: 1 };`,
+      errors: [{ messageId: 'noRawZIndex' }],
+    },
+    {
+      code: `const styles = { zIndex: 0 };`,
+      errors: [{ messageId: 'noRawZIndex' }],
+    },
+    {
+      code: `const styles = { zIndex: -1 };`,
+      errors: [{ messageId: 'noRawZIndex' }],
+    },
+    {
+      code: `const styles = { 'z-index': 100 };`,
+      errors: [{ messageId: 'noRawZIndex' }],
+    },
+    {
+      code: `<Box zIndex={2} />;`,
+      errors: [{ messageId: 'noRawZIndex' }],
+    },
+    {
+      code: `<Box zIndex={-1} />;`,
+      errors: [{ messageId: 'noRawZIndex' }],
+    },
+  ],
+});
diff --git a/packages/eslint-plugin-gamut/src/no-raw-z-index.ts b/packages/eslint-plugin-gamut/src/no-raw-z-index.ts
new file mode 100644
index 00000000000..77da92ae299
--- /dev/null
+++ b/packages/eslint-plugin-gamut/src/no-raw-z-index.ts
@@ -0,0 +1,62 @@
+import { AST_NODE_TYPES, TSESTree } from '@typescript-eslint/utils';
+
+import { createRule } from './createRule';
+
+/**
+ * True for a numeric literal, including a negated one like `-1`.
+ */
+const isNumericLiteral = (node: TSESTree.Node | null | undefined): boolean => {
+  if (!node) return false;
+  if (node.type === AST_NODE_TYPES.Literal && typeof node.value === 'number') {
+    return true;
+  }
+  return (
+    node.type === AST_NODE_TYPES.UnaryExpression &&
+    (node.operator === '-' || node.operator === '+') &&
+    isNumericLiteral(node.argument)
+  );
+};
+
+const isZIndexKey = (key: TSESTree.Node): boolean =>
+  (key.type === AST_NODE_TYPES.Identifier && key.name === 'zIndex') ||
+  (key.type === AST_NODE_TYPES.Literal && key.value === 'zIndex') ||
+  (key.type === AST_NODE_TYPES.Literal && key.value === 'z-index');
+
+export default createRule({
+  create(context) {
+    return {
+      // Style objects: `{ zIndex: 1 }` / `{ 'z-index': 1 }`
+      Property(node) {
+        if (isZIndexKey(node.key) && isNumericLiteral(node.value)) {
+          context.report({ messageId: 'noRawZIndex', node: node.value });
+        }
+      },
+      // JSX props: `<Box zIndex={1} />`
+      JSXAttribute(node) {
+        if (
+          node.name.type === AST_NODE_TYPES.JSXIdentifier &&
+          node.name.name === 'zIndex' &&
+          node.value?.type === AST_NODE_TYPES.JSXExpressionContainer &&
+          isNumericLiteral(node.value.expression as TSESTree.Node)
+        ) {
+          context.report({ messageId: 'noRawZIndex', node: node.value });
+        }
+      },
+    };
+  },
+  defaultOptions: [],
+  meta: {
+    docs: {
+      description:
+        'Discourage raw numeric z-index values which can lead to z-index stacking issues and encourage usage of semantic tokens from the `zIndexes` scale.',
+      recommended: 'error',
+    },
+    messages: {
+      noRawZIndex:
+        'Semantic tokens from the `zIndexes` scale (e.g. `zIndexes.modal`) are recommendedinstead of a raw z-index number. For a deliberate in-between value, disable this rule inline with a justifying comment.',
+    },
+    type: 'suggestion',
+    schema: [],
+  },
+  name: 'no-raw-z-index',
+});
diff --git a/packages/eslint-plugin-gamut/src/recommended.ts b/packages/eslint-plugin-gamut/src/recommended.ts
index 970bb7700ff..a1d71b635c9 100644
--- a/packages/eslint-plugin-gamut/src/recommended.ts
+++ b/packages/eslint-plugin-gamut/src/recommended.ts
@@ -2,6 +2,7 @@ export default {
   rules: {
     'gamut/no-css-standalone': 'error',
     'gamut/no-inline-style': 'error',
+    'gamut/no-raw-z-index': 'error',
     'gamut/prefer-themed': 'off',
     'gamut/gamut-import-paths': 'error',
   },
diff --git a/packages/gamut-styles/src/themes/__tests__/__snapshots__/theme.test.ts.snap b/packages/gamut-styles/src/themes/__tests__/__snapshots__/theme.test.ts.snap
index 2be2c419212..66fe5e546ad 100644
--- a/packages/gamut-styles/src/themes/__tests__/__snapshots__/theme.test.ts.snap
+++ b/packages/gamut-styles/src/themes/__tests__/__snapshots__/theme.test.ts.snap
@@ -79,7 +79,7 @@ exports[`themes admin - theme shape 1`] = `
         "base": "4rem",
         "md": "5rem",
       },
-      "headerZ": 15,
+      "headerZ": 300,
     },
     "modes": {
       "dark": {
@@ -151,6 +151,17 @@ exports[`themes admin - theme shape 1`] = `
         "text-secondary": "rgba(16,22,47,0.75)",
       },
     },
+    "zIndexes": {
+      "appBar": 300,
+      "base": 0,
+      "floating": 200,
+      "flyout": 400,
+      "foreground": 100,
+      "modal": 500,
+      "popover": 600,
+      "topmost": 700,
+      "underlay": -100,
+    },
   },
   "_variables": {
     "mode": {
@@ -257,7 +268,16 @@ exports[`themes admin - theme shape 1`] = `
       "--color-yellow-500": "#FFD300",
       "--color-yellow-900": "#211B00",
       "--elements-headerHeight": "4rem",
-      "--elements-headerZ": 15,
+      "--elements-headerZ": 300,
+      "--zIndexes-appBar": 300,
+      "--zIndexes-base": 0,
+      "--zIndexes-floating": 200,
+      "--zIndexes-flyout": 400,
+      "--zIndexes-foreground": 100,
+      "--zIndexes-modal": 500,
+      "--zIndexes-popover": 600,
+      "--zIndexes-topmost": 700,
+      "--zIndexes-underlay": -100,
       "@media only screen and (min-width: 1024px)": {
         "--elements-headerHeight": "5rem",
       },
@@ -513,6 +533,17 @@ monospace",
     "8": "0.5rem",
     "96": "6rem",
   },
+  "zIndexes": {
+    "appBar": "var(--zIndexes-appBar)",
+    "base": "var(--zIndexes-base)",
+    "floating": "var(--zIndexes-floating)",
+    "flyout": "var(--zIndexes-flyout)",
+    "foreground": "var(--zIndexes-foreground)",
+    "modal": "var(--zIndexes-modal)",
+    "popover": "var(--zIndexes-popover)",
+    "topmost": "var(--zIndexes-topmost)",
+    "underlay": "var(--zIndexes-underlay)",
+  },
 }
 `;
 
@@ -595,7 +626,7 @@ exports[`themes core - theme shape 1`] = `
         "base": "4rem",
         "md": "5rem",
       },
-      "headerZ": 15,
+      "headerZ": 300,
     },
     "modes": {
       "dark": {
@@ -667,6 +698,17 @@ exports[`themes core - theme shape 1`] = `
         "text-secondary": "rgba(16,22,47,0.75)",
       },
     },
+    "zIndexes": {
+      "appBar": 300,
+      "base": 0,
+      "floating": 200,
+      "flyout": 400,
+      "foreground": 100,
+      "modal": 500,
+      "popover": 600,
+      "topmost": 700,
+      "underlay": -100,
+    },
   },
   "_variables": {
     "mode": {
@@ -773,7 +815,16 @@ exports[`themes core - theme shape 1`] = `
       "--color-yellow-500": "#FFD300",
       "--color-yellow-900": "#211B00",
       "--elements-headerHeight": "4rem",
-      "--elements-headerZ": 15,
+      "--elements-headerZ": 300,
+      "--zIndexes-appBar": 300,
+      "--zIndexes-base": 0,
+      "--zIndexes-floating": 200,
+      "--zIndexes-flyout": 400,
+      "--zIndexes-foreground": 100,
+      "--zIndexes-modal": 500,
+      "--zIndexes-popover": 600,
+      "--zIndexes-topmost": 700,
+      "--zIndexes-underlay": -100,
       "@media only screen and (min-width: 1024px)": {
         "--elements-headerHeight": "5rem",
       },
@@ -1029,6 +1080,17 @@ monospace",
     "8": "0.5rem",
     "96": "6rem",
   },
+  "zIndexes": {
+    "appBar": "var(--zIndexes-appBar)",
+    "base": "var(--zIndexes-base)",
+    "floating": "var(--zIndexes-floating)",
+    "flyout": "var(--zIndexes-flyout)",
+    "foreground": "var(--zIndexes-foreground)",
+    "modal": "var(--zIndexes-modal)",
+    "popover": "var(--zIndexes-popover)",
+    "topmost": "var(--zIndexes-topmost)",
+    "underlay": "var(--zIndexes-underlay)",
+  },
 }
 `;
 
@@ -1114,7 +1176,7 @@ exports[`themes lxStudio - theme shape 1`] = `
         "base": "4rem",
         "md": "5rem",
       },
-      "headerZ": 15,
+      "headerZ": 300,
     },
     "modes": {
       "dark": {
@@ -1186,6 +1248,17 @@ exports[`themes lxStudio - theme shape 1`] = `
         "text-secondary": "rgba(16,22,47,0.75)",
       },
     },
+    "zIndexes": {
+      "appBar": 300,
+      "base": 0,
+      "floating": 200,
+      "flyout": 400,
+      "foreground": 100,
+      "modal": 500,
+      "popover": 600,
+      "topmost": 700,
+      "underlay": -100,
+    },
   },
   "_variables": {
     "mode": {
@@ -1295,7 +1368,16 @@ exports[`themes lxStudio - theme shape 1`] = `
       "--color-yellow-500": "#FFD300",
       "--color-yellow-900": "#211B00",
       "--elements-headerHeight": "4rem",
-      "--elements-headerZ": 15,
+      "--elements-headerZ": 300,
+      "--zIndexes-appBar": 300,
+      "--zIndexes-base": 0,
+      "--zIndexes-floating": 200,
+      "--zIndexes-flyout": 400,
+      "--zIndexes-foreground": 100,
+      "--zIndexes-modal": 500,
+      "--zIndexes-popover": 600,
+      "--zIndexes-topmost": 700,
+      "--zIndexes-underlay": -100,
       "@media only screen and (min-width: 1024px)": {
         "--elements-headerHeight": "5rem",
       },
@@ -1556,6 +1638,17 @@ monospace",
     "8": "0.5rem",
     "96": "6rem",
   },
+  "zIndexes": {
+    "appBar": "var(--zIndexes-appBar)",
+    "base": "var(--zIndexes-base)",
+    "floating": "var(--zIndexes-floating)",
+    "flyout": "var(--zIndexes-flyout)",
+    "foreground": "var(--zIndexes-foreground)",
+    "modal": "var(--zIndexes-modal)",
+    "popover": "var(--zIndexes-popover)",
+    "topmost": "var(--zIndexes-topmost)",
+    "underlay": "var(--zIndexes-underlay)",
+  },
 }
 `;
 
@@ -1654,7 +1747,7 @@ exports[`themes percipio - theme shape 1`] = `
         "base": "4rem",
         "md": "5rem",
       },
-      "headerZ": 15,
+      "headerZ": 300,
     },
     "modes": {
       "dark": {
@@ -1726,6 +1819,17 @@ exports[`themes percipio - theme shape 1`] = `
         "text-secondary": "rgba(34, 35, 37, 0.75)",
       },
     },
+    "zIndexes": {
+      "appBar": 300,
+      "base": 0,
+      "floating": 200,
+      "flyout": 400,
+      "foreground": 100,
+      "modal": 500,
+      "popover": 600,
+      "topmost": 700,
+      "underlay": -100,
+    },
   },
   "_variables": {
     "mode": {
@@ -1848,7 +1952,16 @@ exports[`themes percipio - theme shape 1`] = `
       "--color-yellow-500": "#FFD300",
       "--color-yellow-900": "#211B00",
       "--elements-headerHeight": "4rem",
-      "--elements-headerZ": 15,
+      "--elements-headerZ": 300,
+      "--zIndexes-appBar": 300,
+      "--zIndexes-base": 0,
+      "--zIndexes-floating": 200,
+      "--zIndexes-flyout": 400,
+      "--zIndexes-foreground": 100,
+      "--zIndexes-modal": 500,
+      "--zIndexes-popover": 600,
+      "--zIndexes-topmost": 700,
+      "--zIndexes-underlay": -100,
       "@media only screen and (min-width: 1024px)": {
         "--elements-headerHeight": "5rem",
       },
@@ -2120,6 +2233,17 @@ sans-serif",
     "8": "0.5rem",
     "96": "6rem",
   },
+  "zIndexes": {
+    "appBar": "var(--zIndexes-appBar)",
+    "base": "var(--zIndexes-base)",
+    "floating": "var(--zIndexes-floating)",
+    "flyout": "var(--zIndexes-flyout)",
+    "foreground": "var(--zIndexes-foreground)",
+    "modal": "var(--zIndexes-modal)",
+    "popover": "var(--zIndexes-popover)",
+    "topmost": "var(--zIndexes-topmost)",
+    "underlay": "var(--zIndexes-underlay)",
+  },
 }
 `;
 
@@ -2222,7 +2346,7 @@ exports[`themes platform - theme shape 1`] = `
         "base": "4rem",
         "md": "5rem",
       },
-      "headerZ": 15,
+      "headerZ": 300,
     },
     "modes": {
       "dark": {
@@ -2346,6 +2470,17 @@ exports[`themes platform - theme shape 1`] = `
         "text-secondary": "rgba(16,22,47,0.75)",
       },
     },
+    "zIndexes": {
+      "appBar": 300,
+      "base": 0,
+      "floating": 200,
+      "flyout": 400,
+      "foreground": 100,
+      "modal": 500,
+      "popover": 600,
+      "topmost": 700,
+      "underlay": -100,
+    },
   },
   "_variables": {
     "mode": {
@@ -2498,7 +2633,16 @@ exports[`themes platform - theme shape 1`] = `
       "--color-yellow-500": "#FFD300",
       "--color-yellow-900": "#211B00",
       "--elements-headerHeight": "4rem",
-      "--elements-headerZ": 15,
+      "--elements-headerZ": 300,
+      "--zIndexes-appBar": 300,
+      "--zIndexes-base": 0,
+      "--zIndexes-floating": 200,
+      "--zIndexes-flyout": 400,
+      "--zIndexes-foreground": 100,
+      "--zIndexes-modal": 500,
+      "--zIndexes-popover": 600,
+      "--zIndexes-topmost": 700,
+      "--zIndexes-underlay": -100,
       "@media only screen and (min-width: 1024px)": {
         "--elements-headerHeight": "5rem",
       },
@@ -2852,5 +2996,16 @@ monospace",
     "8": "0.5rem",
     "96": "6rem",
   },
+  "zIndexes": {
+    "appBar": "var(--zIndexes-appBar)",
+    "base": "var(--zIndexes-base)",
+    "floating": "var(--zIndexes-floating)",
+    "flyout": "var(--zIndexes-flyout)",
+    "foreground": "var(--zIndexes-foreground)",
+    "modal": "var(--zIndexes-modal)",
+    "popover": "var(--zIndexes-popover)",
+    "topmost": "var(--zIndexes-topmost)",
+    "underlay": "var(--zIndexes-underlay)",
+  },
 }
 `;
diff --git a/packages/gamut-styles/src/themes/core.ts b/packages/gamut-styles/src/themes/core.ts
index 3a6da844330..e41a089abea 100644
--- a/packages/gamut-styles/src/themes/core.ts
+++ b/packages/gamut-styles/src/themes/core.ts
@@ -11,6 +11,7 @@ import {
   lineHeight,
   mediaQueries,
   spacing,
+  zIndexes,
 } from '../variables';
 
 /**
@@ -28,6 +29,7 @@ export const coreTheme = createTheme({
   fontWeight,
   spacing,
   elements,
+  zIndexes,
 })
   .addColors(corePalette)
   .addColorModes('light', {
@@ -141,6 +143,7 @@ export const coreTheme = createTheme({
     2: `2px solid ${colors['border-primary']}`,
   }))
   .createScaleVariables('elements')
+  .createScaleVariables('zIndexes')
   .addName('core')
   .build();
 
diff --git a/packages/gamut-styles/src/variables/elements.ts b/packages/gamut-styles/src/variables/elements.ts
index 25bc743bd83..c9e39f7a21e 100644
--- a/packages/gamut-styles/src/variables/elements.ts
+++ b/packages/gamut-styles/src/variables/elements.ts
@@ -1,9 +1,12 @@
+import { zIndexes } from './zIndexes';
+
 export const elements = {
   headerHeight: { base: '4rem', md: '5rem' },
 
   /**
-   * Semi-arbitrary z-index for global page headers.
-   * @remarks PLEASE talk to web platform before adding new z-index constants!
+   * z-index for global page headers. Aliases the `appBar` token from the `zIndexes`
+   * scale so consumers still reading `elements.headerZ` stay in sync with the scale.
+   * Prefer `zIndex="appBar"` in new code.
    */
-  headerZ: 15,
+  headerZ: zIndexes.appBar,
 } as const;
diff --git a/packages/gamut-styles/src/variables/index.ts b/packages/gamut-styles/src/variables/index.ts
index d4f074462ef..5fd8de5cd3e 100644
--- a/packages/gamut-styles/src/variables/index.ts
+++ b/packages/gamut-styles/src/variables/index.ts
@@ -5,3 +5,4 @@ export * from './responsive';
 export * from './spacing';
 export * from './timing';
 export * from './typography';
+export * from './zIndexes';
diff --git a/packages/gamut-styles/src/variables/zIndexes.ts b/packages/gamut-styles/src/variables/zIndexes.ts
new file mode 100644
index 00000000000..69bcc1e6d00
--- /dev/null
+++ b/packages/gamut-styles/src/variables/zIndexes.ts
@@ -0,0 +1,55 @@
+import { Globals } from 'csstype';
+
+/**
+ * Semantic z-index scale. Every z-index in Gamut should reference a token here rather than a
+ * magic number.
+ *
+ * The `zIndex` system prop accepts a token name directly (e.g. `zIndex="modal"`), this object's
+ * numeric values (e.g. `zIndex={zIndexes.modal}`), a raw in-between number as an escape hatch
+ * (e.g. `zIndex={550}`), or arithmetic on a token (e.g. `zIndexes.foreground - 2`).
+ *
+ * Values are spaced by 100 so in-between escape-hatch numbers are available. `floating` (200) is
+ * the floor of the portal band and the default for `BodyPortal`.
+ *
+ * @remarks PLEASE talk to web platform before adding new z-index tokens.
+ */
+export const zIndexes = {
+  /** Decorative layer behind content (underlines, backdrops, shadows). */
+  underlay: -100,
+  /** Ground layer — establishes a local stacking context without lifting above siblings. */
+  base: 0,
+  /**
+   * The raised in-flow layer: an element in front of what sits/scrolls behind it, but below
+   * all portal overlays. Covers content lifted above an `underlay` (e.g. text over its
+   * underline) and sticky content headers (e.g. a sticky table `thead`).
+   */
+  foreground: 100,
+  /**
+   * Portal floor: the default for `BodyPortal`, and the layer for persistent floating page
+   * furniture at rest (e.g. an AI chat launcher, help bubble). Above page content, below the
+   * app nav and all overlays.
+   */
+  floating: 200,
+  /** Global app header / nav bar. Aliased by the legacy `elements.headerZ` constant. */
+  appBar: 300,
+  /** Portaled side panel (the `Flyout` component = `Drawer` inside `Overlay`). */
+  flyout: 400,
+  /** `Overlay`, `Modal`, and `Dialog` (they share one portal primitive). */
+  modal: 500,
+  /** Portal-mode `Popover` and the portaled `SelectDropdown` menu — above modal. */
+  popover: 600,
+  /**
+   * Top-most transient overlays that must never be clipped: floating tooltips (`FloatingTip`)
+   * and toasts / notifications (`Toaster`). Highest layer — nothing in Gamut sits above it.
+   */
+  topmost: 700,
+} as const;
+
+/**
+ * A `zIndexes` token name (e.g. `'foreground'`), a raw number as an escape hatch
+ * (e.g. `550`, or `zIndexes.foreground + 1`), or a CSS global (`'initial'`, `'inherit'`, …).
+ * Use this for component `zIndex` props that forward to a `Box`-like `zIndex` system prop or
+ * `BodyPortal`. The scale still resolves token names to `var(--zIndexes-*)` at runtime; this
+ * type just also permits the numeric/global escape hatches the scale type alone would reject.
+ */
+export type ZIndexType = keyof typeof zIndexes | number | Globals;
diff --git a/packages/gamut-styles/src/variance/config.ts b/packages/gamut-styles/src/variance/config.ts
index ad2b6e3fc23..7dff05a366f 100644
--- a/packages/gamut-styles/src/variance/config.ts
+++ b/packages/gamut-styles/src/variance/config.ts
@@ -328,7 +328,10 @@ export const positioning = {
     resolveProperty: getPropertyMode,
     transform: transformSize,
   },
-  zIndex: { property: 'zIndex' },
+  // `scale: 'zIndexes'` resolves token names (e.g. `zIndex="modal"`) to `var(--zIndexes-*)`.
+  // `allowRawValue` keeps the numeric/global escape hatch (e.g. `zIndex={550}`,
+  // `zIndex={zIndexes.foreground + 1}`) that scaled props otherwise reject.
+  zIndex: { property: 'zIndex', scale: 'zIndexes', allowRawValue: true },
   opacity: { property: 'opacity' },
 } as const;
 
diff --git a/packages/gamut/src/Anchor/index.tsx b/packages/gamut/src/Anchor/index.tsx
index 287ff0e6d37..7bb43b900a9 100644
--- a/packages/gamut/src/Anchor/index.tsx
+++ b/packages/gamut/src/Anchor/index.tsx
@@ -21,7 +21,7 @@ const outlineFocusVisible = {
     border: 2,
     borderColor: 'primary',
     opacity: 0,
-    zIndex: 0,
+    zIndex: 'base',
   },
 
   [ButtonSelectors.OUTLINE_FOCUS_VISIBLE]: {
diff --git a/packages/gamut/src/BarChart/layout/GridLines.tsx b/packages/gamut/src/BarChart/layout/GridLines.tsx
index 14db738f132..154a639a703 100644
--- a/packages/gamut/src/BarChart/layout/GridLines.tsx
+++ b/packages/gamut/src/BarChart/layout/GridLines.tsx
@@ -12,7 +12,7 @@ const GridLineWrapper = styled(Box)(
     inset: 0,
     pointerEvents: 'none',
     position: 'absolute',
-    zIndex: 0,
+    zIndex: 'base',
   })
 );
 
diff --git a/packages/gamut/src/BodyPortal/__tests__/BodyPortal.test.tsx b/packages/gamut/src/BodyPortal/__tests__/BodyPortal.test.tsx
new file mode 100644
index 00000000000..0961f2e8c54
--- /dev/null
+++ b/packages/gamut/src/BodyPortal/__tests__/BodyPortal.test.tsx
@@ -0,0 +1,50 @@
+import { setupRtl } from '@codecademy/gamut-tests';
+
+import { BodyPortal, BodyPortalProps } from '..';
+
+const BodyPortalTest = (props?: Partial<BodyPortalProps>) => (
+  <main>
+    <BodyPortal {...props}>
+      <div data-testid="portal-content">Howdy!</div>
+    </BodyPortal>
+  </main>
+);
+
+const renderView = setupRtl(BodyPortalTest, {});
+
+describe('BodyPortal', () => {
+  it('renders children outside its mounting container', () => {
+    const { view } = renderView();
+
+    const content = view.getByTestId('portal-content');
+    expect(content.closest('main')).toBe(null);
+    expect(document.body).toContainElement(content);
+  });
+
+  it('applies the floating z-index token by default', () => {
+    const { view } = renderView();
+
+    const content = view.getByTestId('portal-content');
+    expect(content.parentElement).toHaveStyle({
+      zIndex: 'var(--zIndexes-floating)',
+    });
+  });
+
+  it('resolves a custom z-index token to its CSS variable', () => {
+    const { view } = renderView({ zIndex: 'modal' });
+
+    const content = view.getByTestId('portal-content');
+    expect(content.parentElement).toHaveStyle({
+      zIndex: 'var(--zIndexes-modal)',
+    });
+  });
+
+  it('passes through a raw numeric z-index escape hatch', () => {
+    const { view } = renderView({ zIndex: 550 });
+
+    const content = view.getByTestId('portal-content');
+    expect(content.parentElement).toHaveStyle({
+      zIndex: 550,
+    });
+  });
+});
diff --git a/packages/gamut/src/BodyPortal/index.tsx b/packages/gamut/src/BodyPortal/index.tsx
index 5da951b486b..267d6f35fa9 100644
--- a/packages/gamut/src/BodyPortal/index.tsx
+++ b/packages/gamut/src/BodyPortal/index.tsx
@@ -1,4 +1,9 @@
-import { ColorMode, system, useCurrentMode } from '@codecademy/gamut-styles';
+import {
+  ColorMode,
+  system,
+  useCurrentMode,
+  ZIndexType,
+} from '@codecademy/gamut-styles';
 import styled from '@emotion/styled';
 import { useState } from 'react';
 import * as React from 'react';
@@ -17,18 +22,13 @@ const PortalWrapper = styled
   )
   .withComponent(ColorMode);
 
-interface BodyPortalProps {
-  /**
-   * TEMPORARY: a stopgap solution to avoid zIndex conflicts -
-   * will be reworked with: GM-624
-   * previously, zIndex was set to 1 in the CSS function
-   */
-  zIndex?: number;
+export interface BodyPortalProps {
+  zIndex?: ZIndexType;
 }
 
 export const BodyPortal: React.FC<React.PropsWithChildren<BodyPortalProps>> = ({
   children,
-  zIndex = 1,
+  zIndex = 'floating',
 }) => {
   const [ready, setReady] = useState(false);
   const mode = useCurrentMode();
diff --git a/packages/gamut/src/Box/props.ts b/packages/gamut/src/Box/props.ts
index 536ff575392..390fcef7f45 100644
--- a/packages/gamut/src/Box/props.ts
+++ b/packages/gamut/src/Box/props.ts
@@ -24,7 +24,7 @@ export const sharedStates = system.states({
   },
   context: {
     position: 'relative',
-    zIndex: 1,
+    zIndex: 'foreground',
   },
   'no-select': {
     WebkitTouchCallout: 'none',
diff --git a/packages/gamut/src/Button/shared/styles.ts b/packages/gamut/src/Button/shared/styles.ts
index 9bcf0cbed8f..02b608cf9ac 100644
--- a/packages/gamut/src/Button/shared/styles.ts
+++ b/packages/gamut/src/Button/shared/styles.ts
@@ -67,7 +67,7 @@ export const buttonStyles = system.css({
     border: 2,
     inset: -5,
     opacity: 0,
-    zIndex: 0,
+    zIndex: 'base',
   },
   [ButtonSelectors.OUTLINE_FOCUS_VISIBLE]: {
     opacity: 1,
diff --git a/packages/gamut/src/DataList/EmptyRows.tsx b/packages/gamut/src/DataList/EmptyRows.tsx
index 3684664b57e..7203fa90718 100644
--- a/packages/gamut/src/DataList/EmptyRows.tsx
+++ b/packages/gamut/src/DataList/EmptyRows.tsx
@@ -15,7 +15,7 @@ export const EmptyRows = () => {
       position="sticky"
       top="calc(50% - 66px)"
       width="320px"
-      zIndex={1}
+      zIndex="foreground"
     >
       <FlexBox as="tr" center column gap={16} width="100%">
         <th>
diff --git a/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/CalendarWrapper.tsx b/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/CalendarWrapper.tsx
index 425348fa6dd..ac6bde63f72 100644
--- a/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/CalendarWrapper.tsx
+++ b/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/CalendarWrapper.tsx
@@ -12,7 +12,7 @@ export const CalendarWrapper: React.FC<WithChildrenProp> = ({ children }) => (
       border={1}
       borderRadius="sm"
       position="relative"
-      zIndex={1}
+      zIndex="foreground"
     >
       {children}
     </Box>
diff --git a/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/utils/elements.tsx b/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/utils/elements.tsx
index b5a7354e8d7..ca91002442b 100644
--- a/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/utils/elements.tsx
+++ b/packages/gamut/src/DatePicker/DatePickerCalendar/Calendar/utils/elements.tsx
@@ -119,7 +119,7 @@ export const DateCell = styled.td<DateCellProps>(
       borderRadius: 'lg',
       border: 2,
       opacity: 0,
-      zIndex: 0,
+      zIndex: 'base',
     },
     '&:focus-visible::before': {
       opacity: 1,
diff --git a/packages/gamut/src/Flyout/index.tsx b/packages/gamut/src/Flyout/index.tsx
index 8bd38fc0ccf..7a5218feb19 100644
--- a/packages/gamut/src/Flyout/index.tsx
+++ b/packages/gamut/src/Flyout/index.tsx
@@ -52,6 +52,7 @@ export const Flyout: React.FC<FlyoutProps> = ({
       escapeCloses
       isOpen={expanded}
       shroud
+      zIndex="flyout"
       onRequestClose={onClose}
     >
       <Background bg={bg}>
diff --git a/packages/gamut/src/Form/SelectDropdown/SelectDropdown.tsx b/packages/gamut/src/Form/SelectDropdown/SelectDropdown.tsx
index f31839eaa46..603b626cbfe 100644
--- a/packages/gamut/src/Form/SelectDropdown/SelectDropdown.tsx
+++ b/packages/gamut/src/Form/SelectDropdown/SelectDropdown.tsx
@@ -276,6 +276,9 @@ export const SelectDropdown: React.FC<SelectDropdownProps> = ({
         isOptionDisabled={(option) => option.disabled}
         isSearchable={isSearchable}
         menuAlignment={menuAlignment}
+        menuPortalTarget={
+          typeof document !== 'undefined' ? document.body : undefined
+        }
         name={name}
         options={selectOptions}
         placeholder={placeholder}
diff --git a/packages/gamut/src/Form/SelectDropdown/styles.ts b/packages/gamut/src/Form/SelectDropdown/styles.ts
index ba9178c113c..b250b0b9ed5 100644
--- a/packages/gamut/src/Form/SelectDropdown/styles.ts
+++ b/packages/gamut/src/Form/SelectDropdown/styles.ts
@@ -3,6 +3,7 @@ import {
   states,
   theme as GamutTheme,
   variant,
+  ZIndexType,
 } from '@codecademy/gamut-styles';
 import { StylesConfig } from 'react-select';
 
@@ -25,7 +26,6 @@ import { BaseSelectComponentProps } from './types/styles';
 const selectDropdownStyles = css({
   ...formBaseFieldStylesObject,
   display: 'flex',
-  zIndex: 3,
 });
 
 const selectFocusStyles = {
@@ -61,7 +61,7 @@ const dropdownBorderStates = states({
   error: { borderColorTop: 'feedback-error' },
 });
 
-const dropdownBorderStyles = (zIndex = 2) =>
+const dropdownBorderStyles = (zIndex: ZIndexType = 'popover') =>
   css({
     ...formBaseComponentStyles,
     border: 1,
@@ -91,7 +91,7 @@ const placeholderColor = css({
 
 export const getMemoizedStyles = (
   theme: typeof GamutTheme,
-  zIndex?: number
+  zIndex?: ZIndexType
 ): StylesConfig<any, false> => {
   return {
     clearIndicator: (provided) => ({
@@ -164,6 +164,12 @@ export const getMemoizedStyles = (
           : {}),
       };
     },
+    menuPortal: (provided) => ({
+      ...provided,
+      // The menu is portaled to the body, so it stacks at the page root as a popover —
+      // above sticky headers and modal content. A raw `zIndex` prop overrides as an escape hatch.
+      zIndex: zIndex ?? 'popover',
+    }),
     menuList: (provided, state: BaseSelectComponentProps) => {
       const sizeInteger = state.selectProps.size === 'small' ? 2 : 3;
       const maxHeight = `${
diff --git a/packages/gamut/src/Form/SelectDropdown/types/styles.ts b/packages/gamut/src/Form/SelectDropdown/types/styles.ts
index 3be7acbd824..6ab89ef6756 100644
--- a/packages/gamut/src/Form/SelectDropdown/types/styles.ts
+++ b/packages/gamut/src/Form/SelectDropdown/types/styles.ts
@@ -1,3 +1,4 @@
+import { ZIndexType } from '@codecademy/gamut-styles';
 import { StyleProps } from '@codecademy/variance';
 
 import { conditionalBorderStates } from '../styles';
@@ -24,7 +25,7 @@ export interface SharedProps extends InternalInputsProps, SelectDropdownSizes {
    */
   menuAlignment?: 'left' | 'right';
   /** Z-index for the dropdown menu */
-  zIndex?: number;
+  zIndex?: ZIndexType;
 }
 
 /**
diff --git a/packages/gamut/src/Form/__tests__/SelectDropdown.test.tsx b/packages/gamut/src/Form/__tests__/SelectDropdown.test.tsx
index 3b068aaaa93..da13bd8f81d 100644
--- a/packages/gamut/src/Form/__tests__/SelectDropdown.test.tsx
+++ b/packages/gamut/src/Form/__tests__/SelectDropdown.test.tsx
@@ -100,6 +100,46 @@ describe('SelectDropdown', () => {
     expect(view.getByRole('listbox')).toHaveStyle({ maxHeight: '8rem' });
   });
 
+  describe('menu portal', () => {
+    // The menu portals to `document.body` (rather than rendering inline) so it can't be
+    // clipped by an `overflow: hidden` ancestor. This changed the DOM location of every
+    // menu's options in every consuming app, so it's covered explicitly here.
+    const getPortalNode = (view: ReturnType<typeof renderView>['view']) => {
+      const listbox = view.getByRole('listbox');
+      const portal = listbox.parentElement?.parentElement;
+      if (!portal) throw new Error('Expected portal node to exist');
+      return portal;
+    };
+
+    it('renders the options menu in a portal appended to document.body', async () => {
+      const { view } = renderView();
+
+      await openDropdown(view);
+
+      const listbox = view.getByRole('listbox');
+      expect(view.container).not.toContainElement(listbox);
+      expect(document.body).toContainElement(listbox);
+    });
+
+    it('applies the popover z-index token to the portaled menu by default', async () => {
+      const { view } = renderView();
+
+      await openDropdown(view);
+
+      expect(getPortalNode(view)).toHaveStyle({
+        zIndex: 'popover',
+      });
+    });
+
+    it('applies a raw zIndex override to the portaled menu when provided', async () => {
+      const { view } = renderView({ zIndex: 12345 });
+
+      await openDropdown(view);
+
+      expect(getPortalNode(view)).toHaveStyle({ zIndex: 12345 });
+    });
+  });
+
   it('renders a dropdown with icons', async () => {
     const { view } = renderView({ options: optionsIconsArray });
 
diff --git a/packages/gamut/src/List/TableHeader.tsx b/packages/gamut/src/List/TableHeader.tsx
index 60810da9c91..6d470b0c957 100644
--- a/packages/gamut/src/List/TableHeader.tsx
+++ b/packages/gamut/src/List/TableHeader.tsx
@@ -12,7 +12,13 @@ export const TableHeader = forwardRef<HTMLTableRowElement, TableHeaderProps>(
   ({ children, ...rest }, ref) => {
     const { spacing, scrollable, variant } = useListContext();
     return (
-      <Box as="thead" display="block" position="sticky" top={0} zIndex={2}>
+      <Box
+        as="thead"
+        display="block"
+        position="sticky"
+        top={0}
+        zIndex="foreground"
+      >
         <HeaderRowEl
           {...rest}
           ref={ref}
diff --git a/packages/gamut/src/List/elements.tsx b/packages/gamut/src/List/elements.tsx
index 3f4b3476fe3..1daa9d2ee05 100644
--- a/packages/gamut/src/List/elements.tsx
+++ b/packages/gamut/src/List/elements.tsx
@@ -217,7 +217,7 @@ export const HeaderRowEl = styled('tr', styledOptions)<HeaderProps>(
     flexDirection: { _: 'row', c_base: 'column', c_sm: 'row' },
     top: 0,
     bg: 'background-current',
-    zIndex: 2,
+    zIndex: 'foreground',
     fontFamily: 'accent',
     pb: { _: 0, c_base: 8, c_sm: 0 },
   }),
@@ -468,7 +468,7 @@ export const StickyHeaderColWrapper = styled.th(
       height: '100%',
       top: 0,
       left: 0,
-      zIndex: -1,
+      zIndex: 'underlay',
     },
     '&:after': {
       content: '""',
@@ -482,7 +482,7 @@ export const StickyHeaderColWrapper = styled.th(
       height: '100%',
       top: 0,
       left: 0,
-      zIndex: -1,
+      zIndex: 'underlay',
     },
     // p: 0 removes the browser's default padding of 1px
     p: 0,
@@ -490,7 +490,7 @@ export const StickyHeaderColWrapper = styled.th(
     flexShrink: 0,
     position: 'sticky',
     left: 0,
-    zIndex: 1,
+    zIndex: 'foreground',
     bg: { _: 'inherit', c_base: 'transparent', c_sm: 'inherit' },
     '&:not(:first-of-type)': {
       left: { _: 16, c_base: 0, c_sm: 16 },
diff --git a/packages/gamut/src/Menu/elements.tsx b/packages/gamut/src/Menu/elements.tsx
index f8eea4af20d..69b0d6640c1 100644
--- a/packages/gamut/src/Menu/elements.tsx
+++ b/packages/gamut/src/Menu/elements.tsx
@@ -88,7 +88,7 @@ const interactiveVariants = system.variant({
     alignItems: 'center',
     cursor: 'pointer',
     width: 1,
-    zIndex: 1,
+    zIndex: 'foreground',
     px: 24,
     py: 12,
     position: 'relative',
@@ -108,7 +108,7 @@ const interactiveVariants = system.variant({
       border: 2,
       borderColor: 'primary',
       opacity: 0,
-      zIndex: -1,
+      zIndex: 'underlay',
     },
     [MenuItemSelectors.OUTLINE_FOCUS_VISIBLE]: {
       opacity: 1,
@@ -224,7 +224,7 @@ const StyledListLink = styled('a', styledOptions<'a'>())<ListLinkProps>(
 export const ListLink = forwardRef<
   HTMLAnchorElement,
   ComponentProps<typeof StyledListLink>
->(({ zIndex = 1, ...rest }, ref) => (
+>(({ zIndex = 'foreground', ...rest }, ref) => (
   <StyledListLink ref={ref} zIndex={zIndex} {...rest} />
 ));
 
diff --git a/packages/gamut/src/Overlay/index.tsx b/packages/gamut/src/Overlay/index.tsx
index 9ddda4854d0..ad3bd6a1e53 100644
--- a/packages/gamut/src/Overlay/index.tsx
+++ b/packages/gamut/src/Overlay/index.tsx
@@ -1,4 +1,4 @@
-import { states } from '@codecademy/gamut-styles';
+import { states, ZIndexType } from '@codecademy/gamut-styles';
 import styled from '@emotion/styled';
 import { useCallback } from 'react';
 import * as React from 'react';
@@ -34,10 +34,11 @@ export type OverlayProps = {
   /** Whether the overlay allows scroll */
   allowScroll?: boolean;
   /**
-   * z-index for the Overlay. Defaults to 3 to appear above common UI elements
-   * like headers . Can be overridden when needed for custom stacking orders.
+   * Stacking layer for the Overlay. Pass a `zIndexes` token or a raw number (escape
+   * hatch). Defaults to `"modal"`; a portaled side panel should pass
+   * `"flyout"` to sit below modals.
    */
-  zIndex?: number;
+  zIndex?: ZIndexType;
 };
 
 const OverlayContainer = styled(FlexBox)(
@@ -61,7 +62,7 @@ export const Overlay: React.FC<OverlayProps> = ({
   onRequestClose,
   isOpen,
   allowScroll = false,
-  zIndex = 3,
+  zIndex = 'modal',
 }) => {
   const handleOutsideClick = useCallback(() => {
     if (clickOutsideCloses) {
diff --git a/packages/gamut/src/PatternBackdrop/PatternBackdrop.tsx b/packages/gamut/src/PatternBackdrop/PatternBackdrop.tsx
index c3d6bcd8b15..f431b8171ae 100644
--- a/packages/gamut/src/PatternBackdrop/PatternBackdrop.tsx
+++ b/packages/gamut/src/PatternBackdrop/PatternBackdrop.tsx
@@ -13,7 +13,7 @@ const PatternBackdropBody = styled('div', styledOptions)<
 >(
   system.css({
     position: 'relative',
-    zIndex: 1,
+    zIndex: 'foreground',
     bg: 'background',
     border: 1,
     maxWidth: 1,
@@ -29,7 +29,12 @@ type PatternBackdropProps = ComponentProps<typeof PatternBackdropBody>;
  */
 export const PatternBackdrop = forwardRef<HTMLDivElement, PatternBackdropProps>(
   ({ children, ...rest }, ref) => (
-    <Box display="inline-block" maxWidth="100%" position="relative" zIndex={1}>
+    <Box
+      display="inline-block"
+      maxWidth="100%"
+      position="relative"
+      zIndex="foreground"
+    >
       <CheckerDense
         dimensions={1}
         left="-0.5rem"
diff --git a/packages/gamut/src/Popover/elements.tsx b/packages/gamut/src/Popover/elements.tsx
index 04908315050..22b80080349 100644
--- a/packages/gamut/src/Popover/elements.tsx
+++ b/packages/gamut/src/Popover/elements.tsx
@@ -66,7 +66,7 @@ export const PopoverPortal: React.FC<
   animation ? (
     <AnimatePresence>
       {isOpen && (
-        <BodyPortal>
+        <BodyPortal zIndex="popover">
           <motion.div
             animate={{ opacity: 1 }}
             exit={{ opacity: 0 }}
@@ -81,7 +81,7 @@ export const PopoverPortal: React.FC<
       )}
     </AnimatePresence>
   ) : (
-    <BodyPortal {...rest} />
+    <BodyPortal zIndex="popover" {...rest} />
   );
 
 export type PopoverContainerProps = Pick<PopoverProps, 'position' | 'align'>;
diff --git a/packages/gamut/src/Popover/styles/base.ts b/packages/gamut/src/Popover/styles/base.ts
index d3aae9f9c2c..9f4eabb16ee 100644
--- a/packages/gamut/src/Popover/styles/base.ts
+++ b/packages/gamut/src/Popover/styles/base.ts
@@ -31,7 +31,7 @@ export const popoverStates = states({
 
 export const raisedDivVariants = variant({
   base: {
-    zIndex: 1,
+    zIndex: 'foreground',
   },
   defaultVariant: 'primary',
   variants: {
diff --git a/packages/gamut/src/Popover/styles/variants.ts b/packages/gamut/src/Popover/styles/variants.ts
index 1ebf78d59e7..f8001fe58d1 100644
--- a/packages/gamut/src/Popover/styles/variants.ts
+++ b/packages/gamut/src/Popover/styles/variants.ts
@@ -47,7 +47,7 @@ const beakVariantStyles = createVariantsFromAlignments(
 export const beakVariants = variant({
   base: {
     background: 'transparent',
-    zIndex: 1,
+    zIndex: 'foreground',
     position: 'fixed',
   },
   prop: 'beak',
diff --git a/packages/gamut/src/PopoverContainer/PopoverContainer.tsx b/packages/gamut/src/PopoverContainer/PopoverContainer.tsx
index c93f1965bc8..128582075a6 100644
--- a/packages/gamut/src/PopoverContainer/PopoverContainer.tsx
+++ b/packages/gamut/src/PopoverContainer/PopoverContainer.tsx
@@ -282,5 +282,5 @@ export const PopoverContainer: React.FC<PopoverContainerProps> = ({
 
   if (inline) return content;
 
-  return <BodyPortal>{content}</BodyPortal>;
+  return <BodyPortal zIndex="popover">{content}</BodyPortal>;
 };
diff --git a/packages/gamut/src/Tabs/TabButton.tsx b/packages/gamut/src/Tabs/TabButton.tsx
index 0cbaf3f2582..f376ac16209 100644
--- a/packages/gamut/src/Tabs/TabButton.tsx
+++ b/packages/gamut/src/Tabs/TabButton.tsx
@@ -29,7 +29,7 @@ const focusVisibleStyles = {
     borderColor: 'primary',
     position: 'absolute',
     inset: 0,
-    zIndex: 0,
+    zIndex: 'base',
     borderRadiusTop: 'md',
     borderRadiusBottom: 'none',
   },
@@ -48,7 +48,7 @@ export const tabVariants = variant({
     color: 'text',
     font: 'inherit',
     cursor: 'pointer',
-    zIndex: 1,
+    zIndex: 'foreground',
     [TabSelectors.DISABLED]: {
       opacity: 0.25,
       cursor: 'not-allowed',
diff --git a/packages/gamut/src/Tabs/Tabs.tsx b/packages/gamut/src/Tabs/Tabs.tsx
index 3194df06756..05c26d9d6af 100644
--- a/packages/gamut/src/Tabs/Tabs.tsx
+++ b/packages/gamut/src/Tabs/Tabs.tsx
@@ -25,10 +25,10 @@ export const Tabs: React.FC<TabsProps> = (props) => {
       {/* currently only supporting dark mode for the LE variant. */}
       {props.variant === 'block' ? (
         <Background bg="navy-800" height="100%">
-          <TabsBase position="relative" zIndex={0} {...props} />
+          <TabsBase position="relative" zIndex="base" {...props} />
         </Background>
       ) : (
-        <TabsBase position="relative" zIndex={0} {...props} />
+        <TabsBase position="relative" zIndex="base" {...props} />
       )}
     </TabProvider>
   );
diff --git a/packages/gamut/src/Tabs/styles.tsx b/packages/gamut/src/Tabs/styles.tsx
index 68d2579f9fb..b6b955fa910 100644
--- a/packages/gamut/src/Tabs/styles.tsx
+++ b/packages/gamut/src/Tabs/styles.tsx
@@ -15,7 +15,7 @@ export const tabContainerVariants = variant({
         bg: 'text',
         position: 'absolute',
         bottom: 0,
-        zIndex: 0,
+        zIndex: 'base',
         width: '100%',
       },
     },
diff --git a/packages/gamut/src/Tip/PreviewTip/elements.tsx b/packages/gamut/src/Tip/PreviewTip/elements.tsx
index 6f42308c3c4..34bad35c6fb 100644
--- a/packages/gamut/src/Tip/PreviewTip/elements.tsx
+++ b/packages/gamut/src/Tip/PreviewTip/elements.tsx
@@ -1,5 +1,5 @@
 import { CheckerDense } from '@codecademy/gamut-patterns';
-import { css, variant } from '@codecademy/gamut-styles';
+import { css, variant, zIndexes } from '@codecademy/gamut-styles';
 import styled from '@emotion/styled';
 import { useMemo } from 'react';
 
@@ -143,11 +143,19 @@ export const PreviewTipShadow: React.FC<PreviewTipShadowProps> = ({
   zIndex,
 }) => {
   const shadowAlignment = getShadowAlignment(alignment);
+  // The shadow sits two layers below the tip. Resolve a token name to its numeric value so
+  // we can offset it; a raw number is used directly; anything else (a CSS global) falls back.
+  const numericZIndex =
+    typeof zIndex === 'number'
+      ? zIndex
+      : typeof zIndex === 'string' && zIndex in zIndexes
+      ? zIndexes[zIndex as keyof typeof zIndexes]
+      : undefined;
 
   return (
     <PreviewTipPattern
       aria-hidden
-      zIndex={zIndex ? zIndex - 2 : -1}
+      zIndex={numericZIndex ? numericZIndex - 2 : 'underlay'}
       {...shadowAlignment}
     >
       <CheckerDense />
diff --git a/packages/gamut/src/Tip/shared/InlineTip.tsx b/packages/gamut/src/Tip/shared/InlineTip.tsx
index 871cfaac1ac..7cdf1b7a1a6 100644
--- a/packages/gamut/src/Tip/shared/InlineTip.tsx
+++ b/packages/gamut/src/Tip/shared/InlineTip.tsx
@@ -55,7 +55,7 @@ export const InlineTip: React.FC<TipWrapperProps> = ({
   const tipBody = (
     <InlineTipBodyWrapper
       alignment={alignment}
-      zIndex={zIndex ?? 1}
+      zIndex={zIndex ?? 'foreground'}
       {...inlineWrapperProps}
     >
       <TipBody
diff --git a/packages/gamut/src/Tip/shared/elements.tsx b/packages/gamut/src/Tip/shared/elements.tsx
index 8a510fea0bf..c8a1a654b88 100644
--- a/packages/gamut/src/Tip/shared/elements.tsx
+++ b/packages/gamut/src/Tip/shared/elements.tsx
@@ -83,7 +83,7 @@ export const TargetContainer = styled(Box)(
       border: 2,
       borderColor: 'primary',
       opacity: 0,
-      zIndex: 0,
+      zIndex: 'base',
     },
     [TargetSelectors.OUTLINE_FOCUS_VISIBLE]: {
       opacity: 1,
diff --git a/packages/gamut/src/Tip/shared/types.tsx b/packages/gamut/src/Tip/shared/types.tsx
index 164ed1aaf37..957aa25531c 100644
--- a/packages/gamut/src/Tip/shared/types.tsx
+++ b/packages/gamut/src/Tip/shared/types.tsx
@@ -1,3 +1,4 @@
+import { ZIndexType } from '@codecademy/gamut-styles';
 import { ComponentProps, ReactNode } from 'react';
 
 import { Text } from '../../Typography';
@@ -54,7 +55,7 @@ export interface TipNewBaseProps {
 }
 export interface TipInlineProps extends TipNewBaseProps {
   placement?: 'inline';
-  zIndex?: number;
+  zIndex?: ZIndexType;
 }
 export interface TipFloatingProps extends TipNewBaseProps {
   placement: 'floating';
@@ -83,5 +84,5 @@ export type TipPlacementComponentProps = Omit<
     | ((node: HTMLDivElement | null) => void);
   type: 'info' | 'tool' | 'preview';
   wrapperRef?: React.RefObject<HTMLDivElement>;
-  zIndex?: number;
+  zIndex?: ZIndexType;
 } & React.PropsWithChildren;
diff --git a/packages/gamut/src/Toaster/index.tsx b/packages/gamut/src/Toaster/index.tsx
index 809d08aade6..0cbaac7fdd9 100644
--- a/packages/gamut/src/Toaster/index.tsx
+++ b/packages/gamut/src/Toaster/index.tsx
@@ -26,7 +26,7 @@ export const Toaster: React.FC<ToasterProps> = ({
   colorMode = 'light',
 }) => {
   return (
-    <BodyPortal>
+    <BodyPortal zIndex="topmost">
       <ColorMode mode={colorMode}>
         <Box aria-live="polite" bottom={88} position="fixed" right={16}>
           <AnimatePresence>
diff --git a/packages/gamut/src/Typography/Text.tsx b/packages/gamut/src/Typography/Text.tsx
index 173661b8632..d8bdfcfbcd8 100644
--- a/packages/gamut/src/Typography/Text.tsx
+++ b/packages/gamut/src/Typography/Text.tsx
@@ -76,7 +76,7 @@ const textStates = states({
     fontWeight: 'bold',
     minWidth: '0.4rem',
     position: 'relative',
-    zIndex: 1,
+    zIndex: 'foreground',
     // the text is more legible against the background color with text smoothing
     MozOsxFontSmoothing: 'grayscale',
     WebkitFontSmoothing: 'antialiased',
@@ -90,7 +90,7 @@ const textStates = states({
       position: 'absolute',
       top: '50%',
       width: 'calc(100% + 0.4rem)',
-      zIndex: -1,
+      zIndex: 'underlay',
     },
   },
   screenreader: {
diff --git a/packages/styleguide/src/lib/Foundations/ZIndex.mdx b/packages/styleguide/src/lib/Foundations/ZIndex.mdx
new file mode 100644
index 00000000000..03e1911c96f
--- /dev/null
+++ b/packages/styleguide/src/lib/Foundations/ZIndex.mdx
@@ -0,0 +1,52 @@
+import { Meta } from '@storybook/addon-docs/blocks';
+
+import { ComponentHeader, TokenTable } from '~styleguide/blocks';
+
+import * as TABLES from './shared/elements';
+
+export const parameters = {
+  title: 'Z-Index',
+  subtitle:
+    'A single semantic scale for coordinating stacking order across Gamut.',
+  status: 'static',
+};
+
+<Meta title="Foundations/Z-Index" />
+
+<ComponentHeader {...parameters} />
+
+z-index should only be used when necessary to override the default stacking order. When possible, use the default stacking order and avoid using z-index.
+
+To standardize z-index values across the application, Gamut exposes one semantic z-index scale, `zIndexes`, so stacking order is coordinated by name
+instead of by scattered magic numbers. Import it from `@codecademy/gamut-styles` and pass a token to
+the `zIndex` prop:
+
+```tsx
+import { zIndexes } from '@codecademy/gamut-styles';
+
+<Box zIndex={zIndexes.modal}>…</Box>;
+```
+
+## The scale
+
+<TokenTable {...TABLES.zIndexes} />
+
+## Custom z-index values
+
+The `zIndex` prop is left **numeric**. `zIndexes` is just a numeric object you reference by name; the prop still accepts a raw number. This is deliberate in situations where you need to set a z-index that is not part of the scale.
+
+```tsx
+<Overlay zIndex={zIndexes.modal + 5}>…</Overlay>; // just above modal
+<Box zIndex={605}>…</Box>; // deliberate one-off
+```
+
+These situations should be rare, but when they do arise, you can use the scale as a reference point.
+
+## Guidance
+
+- **Reach for a token first.** `zIndexes.modal`, `zIndexes.foreground`, etc. — the name documents
+  intent far better than a number.
+- **Escape hatch sparingly.** A raw number is fine for a genuine one-off, but prefer
+  `token ± n` so the relationship to the scale stays visible, and leave a comment.
+- **Third-party widgets** (e.g. injected marketing/chat scripts) set their own z-index and are out
+  of Gamut's control; `topmost` is the highest Gamut layer.
diff --git a/packages/styleguide/src/lib/Foundations/shared/elements.tsx b/packages/styleguide/src/lib/Foundations/shared/elements.tsx
index 1ec160156af..a77a5957cb2 100644
--- a/packages/styleguide/src/lib/Foundations/shared/elements.tsx
+++ b/packages/styleguide/src/lib/Foundations/shared/elements.tsx
@@ -6,6 +6,7 @@ import {
   lxStudioColors,
   theme,
   trueColors,
+  zIndexes as zIndexesTokens,
 } from '@codecademy/gamut-styles';
 // eslint-disable-next-line gamut/import-paths
 import * as ALL_PROPS from '@codecademy/gamut-styles/src/variance/config';
@@ -438,6 +439,84 @@ export const borderRadii = {
   ],
 };
 
+// Representative components that use each token, linked to their Storybook stories.
+// Story ids are the folder path under `src/lib` (Storybook auto-title).
+const zIndexExamples: Record<string, { label: string; id: string }[]> = {
+  underlay: [
+    { label: 'Text', id: 'Typography/Text' },
+    { label: 'Menu', id: 'Molecules/Menu' },
+  ],
+  base: [
+    { label: 'Tabs', id: 'Molecules/Tabs' },
+    { label: 'Anchor', id: 'Typography/Anchor' },
+  ],
+  foreground: [
+    { label: 'Text', id: 'Typography/Text' },
+    { label: 'Tabs', id: 'Molecules/Tabs' },
+    { label: 'DataList', id: 'Organisms/Lists & Tables/DataList' },
+  ],
+  flyout: [{ label: 'Flyout', id: 'Molecules/Flyout' }],
+  modal: [
+    { label: 'Modal', id: 'Molecules/Modals/Modal' },
+    { label: 'Dialog', id: 'Molecules/Modals/Dialog' },
+  ],
+  popover: [
+    { label: 'Popover', id: 'Molecules/Popover' },
+    { label: 'SelectDropdown', id: 'Atoms/FormInputs/SelectDropdown' },
+  ],
+  topmost: [
+    { label: 'ToolTip', id: 'Molecules/Tips/ToolTip' },
+    { label: 'Toaster', id: 'Molecules/Toasts/Toaster' },
+  ],
+};
+
+// Tokens with no single component example get a short note instead of links.
+const zIndexNotes: Record<string, string> = {
+  floating: 'BodyPortal default; floating launchers (e.g. AI chat button)',
+  appBar: 'App header / nav (app-owned)',
+};
+
+export const zIndexes = {
+  // Object insertion order runs low → high (underlay … tooltip).
+  rows: Object.entries(zIndexesTokens).map(([id, value]) => ({
+    id,
+    value,
+  })),
+  columns: [
+    { ...PROP_COLUMN, name: 'Token' },
+    {
+      ...PATH_COLUMN,
+      render: ({ id }: any) => <Code>zIndexes.{id}</Code>,
+    },
+    VALUE_COLUMN,
+    {
+      key: 'usedBy',
+      name: 'Used by',
+      size: 'lg',
+      render: ({ id }: any) => {
+        const examples = zIndexExamples[id];
+        if (!examples?.length) {
+          return <Box color="text-secondary">{zIndexNotes[id] ?? '—'}</Box>;
+        }
+        return (
+          <>
+            {examples.flatMap((example, i) => {
+              const link = (
+                <LinkTo id={example.id} key={example.id}>
+                  {example.label}
+                </LinkTo>
+              );
+              return i === 0
+                ? [link]
+                : [<span key={`sep-${example.id}`}>, </span>, link];
+            })}
+          </>
+        );
+      },
+    },
+  ],
+};
+
 export const LightModeTable = () => (
   <Background bg="white">
     <TokenTable bg={false} {...(lightMode as any)} />
diff --git a/packages/styleguide/src/lib/Meta/ESLint rules.mdx b/packages/styleguide/src/lib/Meta/ESLint rules.mdx
index fcc82dc92dd..c7201b4ffdf 100644
--- a/packages/styleguide/src/lib/Meta/ESLint rules.mdx	
+++ b/packages/styleguide/src/lib/Meta/ESLint rules.mdx	
@@ -176,6 +176,57 @@ import { theme } from '@codecademy/gamut-styles';
 
 ---
 
+### `gamut/no-raw-z-index`
+
+**Level:** `error`
+
+Discourages raw numeric `z-index` values in favor of semantic tokens from the `zIndexes` scale exported by `gamut-styles`. This applies to both JSX `zIndex` props (e.g. `<Box zIndex={2} />`) and style object properties (`zIndex` / `'z-index'` in `css()` or styled-component style objects).
+
+**Why?** Magic z-index numbers make stacking order hard to reason about and prone to regressions as new overlapping UI gets added. The `zIndexes` scale (`underlay`, `base`, `foreground`, `floating`, `appBar`, `flyout`, `modal`, `popover`, `topmost`) gives every layer a named, semantic role so stacking intent stays legible and consistent across the app.
+
+#### ❌ Incorrect
+
+```tsx
+// Raw number in a JSX prop
+<Box position="relative" zIndex={2} />;
+
+// Raw number in a style object
+const styles = css({
+  position: 'absolute',
+  zIndex: 100,
+});
+```
+
+#### ✅ Correct
+
+```tsx
+import { zIndexes } from '@codecademy/gamut-styles';
+
+// Use a semantic token
+<Box position="relative" zIndex={zIndexes.foreground} />
+
+// Token arithmetic is allowed for a deliberate offset within a layer
+<Box position="relative" zIndex={zIndexes.foreground + 1} />
+
+const styles = css({
+  position: 'absolute',
+  zIndex: zIndexes.popover,
+});
+```
+
+#### Disabling the rule
+
+For a deliberate in-between value that doesn't map to an existing token, disable the rule inline with a comment justifying the choice:
+
+```tsx
+// eslint-disable-next-line gamut/no-raw-z-index -- must sit one layer below the legacy FCN nav (12)
+<Box zIndex={11} />
+```
+
+<Callout text="Please talk to web platform before adding a new token to the zIndexes scale." />
+
+---
+
 ### `gamut/prefer-themed`
 
 **Level:** `off` (by default)
@@ -222,6 +273,7 @@ module.exports = {
     'gamut/no-inline-style': 'error',
     'gamut/no-css-standalone': 'error',
     'gamut/import-paths': 'error',
+    'gamut/no-raw-z-index': 'error',
     'gamut/prefer-themed': 'off',
   },
 };
diff --git a/packages/styleguide/src/lib/Molecules/Tips/InfoTip/InfoTip.stories.tsx b/packages/styleguide/src/lib/Molecules/Tips/InfoTip/InfoTip.stories.tsx
index bd0e2c435ed..80404fd33eb 100644
--- a/packages/styleguide/src/lib/Molecules/Tips/InfoTip/InfoTip.stories.tsx
+++ b/packages/styleguide/src/lib/Molecules/Tips/InfoTip/InfoTip.stories.tsx
@@ -10,6 +10,7 @@ import {
   Text,
 } from '@codecademy/gamut';
 import { SparkleIcon } from '@codecademy/gamut-icons';
+import { zIndexes } from '@codecademy/gamut-styles';
 import type { Meta, StoryObj } from '@storybook/react';
 import { useState } from 'react';
 
@@ -292,18 +293,18 @@ export const InfoTipInsideModal: Story = {
 export const ZIndex: Story = {
   args: {
     info: 'I am inline, cool',
-    zIndex: 5,
+    zIndex: zIndexes.foreground,
   },
   render: (args) => (
     <FlexBox center flexDirection="column" m={24} py={64}>
-      <Box bg="background-primary" zIndex={3}>
+      <Box bg="background-primary" zIndex={zIndexes.base}>
         I will not be behind the infotip, sad + unreadable
       </Box>
       <InfoTip
         ariaLabel="z-index example without override"
         info="I am inline, cool"
       />
-      <Box bg="background-primary" zIndex={3}>
+      <Box bg="background-primary" zIndex={zIndexes.base}>
         I will be behind the infotip, nice + great
       </Box>
       <InfoTip {...args} ariaLabel="z-index example with override" />
diff --git a/packages/variance/src/types/config.ts b/packages/variance/src/types/config.ts
index c4dc0be88eb..b56c841b569 100644
--- a/packages/variance/src/types/config.ts
+++ b/packages/variance/src/types/config.ts
@@ -35,6 +35,13 @@ export interface Prop extends BaseProperty {
     props?: AbstractProps
   ) => string | number | CSSObject;
   resolveProperty?: (useLogicalProperties: boolean) => PropertyMode;
+  /**
+   * Keep the raw CSS-value escape hatch (arbitrary numbers, globals) available on a
+   * scale-backed prop, alongside the scale's token names. Without this a scale-backed prop
+   * is token-only. Runtime is unaffected — the parser already falls back to the raw value
+   * for anything that isn't a scale token; this only widens the accepted type.
+   */
+  allowRawValue?: boolean;
 }
 
 export interface AbstractPropTransformer extends Prop {
@@ -60,19 +67,30 @@ export type PropertyValues<
 // Uses 'physical' for directional properties (both physical/logical have same value types)
 type BasePropertyKey<P> = P extends DirectionalProperty ? P['physical'] : P;
 
+// When a scale-backed prop opts into `allowRawValue`, also permit the full raw CSS value
+// type (the same type an unscaled prop gets), which includes arbitrary numbers and globals.
+type RawValueEscapeHatch<Config extends Prop> = Config extends {
+  allowRawValue: true;
+}
+  ? PropertyValues<BasePropertyKey<Config['property']>, true>
+  : never;
+
 export type ScaleValue<Config extends Prop> =
   Config['scale'] extends keyof Theme
     ?
         | keyof Theme[Config['scale']]
         | PropertyValues<BasePropertyKey<Config['property']>>
+        | RawValueEscapeHatch<Config>
     : Config['scale'] extends MapScale
     ?
         | keyof Config['scale']
         | PropertyValues<BasePropertyKey<Config['property']>>
+        | RawValueEscapeHatch<Config>
     : Config['scale'] extends ArrayScale
     ?
         | Config['scale'][number]
         | PropertyValues<BasePropertyKey<Config['property']>>
+        | RawValueEscapeHatch<Config>
     : PropertyValues<BasePropertyKey<Config['property']>, true>;
 
 export type Scale<Config extends Prop> = ResponsiveProp<