diff --git a/BREAKING.md b/BREAKING.md
index c47e098e609..a90892ff430 100644
--- a/BREAKING.md
+++ b/BREAKING.md
@@ -26,6 +26,7 @@ This is a comprehensive list of the breaking changes introduced in the major ver
   - [Radio Group](#version-9x-radio-group)
   - [Spinner](#version-9x-spinner)
   - [Textarea](#version-9x-textarea)
+  - [Thumbnail](#version-9x-thumbnail)
 
 <h2 id="version-9x-global-styles">Global Styles</h2>
 
@@ -245,3 +246,28 @@ Additionally, the `radio-group-wrapper` div element has been removed, causing sl
 Converted `ion-textarea` to use [Shadow DOM](https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_shadow_DOM).
 
 If you were targeting the internals of `ion-textarea` in your CSS, you will need to target the `wrapper`, `container`, `label`, `native`, `supporting-text`, `helper-text`, `error-text`, `counter`, or `bottom` [Shadow Parts](https://ionicframework.com/docs/theming/css-shadow-parts) instead, or use the provided CSS Variables.
+
+<h4 id="version-9x-thumbnail">Thumbnail</h4>
+
+The following breaking changes apply to `ion-thumbnail`:
+
+1. `--size` has been split into separate `--ion-thumbnail-width` and `--ion-thumbnail-height` CSS variables.
+2. `--border-radius` has been replaced.
+3. Theme classes (`ion-thumbnail.md`, `ion-thumbnail.ios`) are no longer supported.
+
+<h5>Removed CSS variables</h5>
+
+`--size` and `--border-radius` have been removed. Use the new token structure for global styles, or the corresponding CSS variable for component-specific overrides:
+
+| Old (8.x) | New token (global) | New CSS variable (component-specific) |
+|---|---|---|
+| `--size` | `IonThumbnail.width` | `--ion-thumbnail-width` |
+| `--size` | `IonThumbnail.height` | `--ion-thumbnail-height` |
+| `--border-radius` | `IonThumbnail.border.radius` | `--ion-thumbnail-border-radius` |
+
+> [!NOTE]
+> Code that previously set `--size: 48px` on `ion-thumbnail` must now set both `--ion-thumbnail-width: 48px` and `--ion-thumbnail-height: 48px`.
+
+<h5>Theme classes</h5>
+
+Remove any instances that target the theme classes: `ion-thumbnail.md`, `ion-thumbnail.ios`.
diff --git a/core/api.txt b/core/api.txt
index bc8bb22dba9..49dd1f3b6d8 100644
--- a/core/api.txt
+++ b/core/api.txt
@@ -2806,9 +2806,9 @@ ion-textarea,part,wrapper
 
 ion-thumbnail,shadow
 ion-thumbnail,prop,mode,"ios" | "md",undefined,false,false
-ion-thumbnail,prop,theme,"ios" | "md" | "ionic",undefined,false,false
-ion-thumbnail,css-prop,--border-radius
-ion-thumbnail,css-prop,--size
+ion-thumbnail,css-prop,--ion-thumbnail-border-radius
+ion-thumbnail,css-prop,--ion-thumbnail-height
+ion-thumbnail,css-prop,--ion-thumbnail-width
 
 ion-title,shadow
 ion-title,prop,color,"danger" | "dark" | "light" | "medium" | "primary" | "secondary" | "success" | "tertiary" | "warning" | string & Record<never, never> | undefined,undefined,false,true
diff --git a/core/scripts/vercel-build.sh b/core/scripts/vercel-build.sh
index 99c83b22adc..a456d847e2e 100755
--- a/core/scripts/vercel-build.sh
+++ b/core/scripts/vercel-build.sh
@@ -48,6 +48,7 @@ echo "Copying core output..."
 cp -r "${CORE_DIR}/src" "${OUTPUT_DIR}/src"
 cp -r "${CORE_DIR}/dist" "${OUTPUT_DIR}/dist"
 cp -r "${CORE_DIR}/css" "${OUTPUT_DIR}/css"
+cp -r "${CORE_DIR}/themes" "${OUTPUT_DIR}/themes"
 mkdir -p "${OUTPUT_DIR}/scripts"
 cp -r "${CORE_DIR}/scripts/testing" "${OUTPUT_DIR}/scripts/testing"
 
diff --git a/core/src/components.d.ts b/core/src/components.d.ts
index a9299aaee9a..bda9768f20b 100644
--- a/core/src/components.d.ts
+++ b/core/src/components.d.ts
@@ -4239,10 +4239,6 @@ export namespace Components {
           * The mode determines the platform behaviors of the component.
          */
         "mode"?: "ios" | "md";
-        /**
-          * The theme determines the visual appearance of the component.
-         */
-        "theme"?: "ios" | "md" | "ionic";
     }
     interface IonTitle {
         /**
@@ -10335,10 +10331,6 @@ declare namespace LocalJSX {
           * The mode determines the platform behaviors of the component.
          */
         "mode"?: "ios" | "md";
-        /**
-          * The theme determines the visual appearance of the component.
-         */
-        "theme"?: "ios" | "md" | "ionic";
     }
     interface IonTitle {
         /**
diff --git a/core/src/components/item-divider/item-divider.scss b/core/src/components/item-divider/item-divider.scss
index 024e59a4f06..086f3d4335f 100644
--- a/core/src/components/item-divider/item-divider.scss
+++ b/core/src/components/item-divider/item-divider.scss
@@ -308,15 +308,15 @@
 
 // Thumbnail
 ::slotted(ion-thumbnail) {
-  // TODO(FW-6862): separate width and height tokens for thumbnails
-  --size: var(--ion-item-divider-thumbnail-width);
-
   @include mixins.margin(
     var(--ion-item-divider-thumbnail-margin-top),
     var(--ion-item-divider-thumbnail-margin-end),
     var(--ion-item-divider-thumbnail-margin-bottom),
     var(--ion-item-divider-thumbnail-margin-start)
   );
+
+  width: var(--ion-item-divider-thumbnail-width, revert-layer);
+  height: var(--ion-item-divider-thumbnail-height, revert-layer);
 }
 
 ::slotted(ion-thumbnail[slot="start"]) {
diff --git a/core/src/components/item/item.ios.scss b/core/src/components/item/item.ios.scss
index b6d2b0447d0..7f34002a0e1 100644
--- a/core/src/components/item/item.ios.scss
+++ b/core/src/components/item/item.ios.scss
@@ -161,7 +161,9 @@
 // --------------------------------------------------
 
 ::slotted(ion-thumbnail) {
-  --size: #{$item-ios-thumbnail-size};
+  // TODO(FW-6847): replace $item-md-thumbnail-* to revert-layer pattern used in item-divider.scss. Assuming the --ion-item-thumbnail-width/height tokens will be used in the migration, else update them.
+  width: var(--ion-item-thumbnail-width, $item-ios-thumbnail-width);
+  height: var(--ion-item-thumbnail-height, $item-ios-thumbnail-height);
 }
 
 // iOS Item Avatar/Thumbnail
diff --git a/core/src/components/item/item.ios.vars.scss b/core/src/components/item/item.ios.vars.scss
index 223b08125f3..39dc56f1929 100644
--- a/core/src/components/item/item.ios.vars.scss
+++ b/core/src/components/item/item.ios.vars.scss
@@ -33,8 +33,11 @@ $item-ios-avatar-width: 36px;
 /// @prop - Height of the avatar in the item
 $item-ios-avatar-height: $item-ios-avatar-width;
 
-/// @prop - Size of the thumbnail in the item
-$item-ios-thumbnail-size: 56px;
+/// @prop - Width of the thumbnail in the item
+$item-ios-thumbnail-width: 56px;
+
+/// @prop - Height of the thumbnail in the item
+$item-ios-thumbnail-height: $item-ios-thumbnail-width;
 
 /// @prop - Padding top for the item content
 $item-ios-padding-top: 10px;
diff --git a/core/src/components/item/item.md.scss b/core/src/components/item/item.md.scss
index 7ecb4dd009e..2651fffe9f9 100644
--- a/core/src/components/item/item.md.scss
+++ b/core/src/components/item/item.md.scss
@@ -172,7 +172,9 @@
 // --------------------------------------------------
 
 ::slotted(ion-thumbnail) {
-  --size: #{$item-md-thumbnail-size};
+  // TODO(FW-6847): replace $item-md-thumbnail-* to revert-layer pattern used in item-divider.scss. Assuming the --ion-item-thumbnail-width/height tokens will be used in the migration, else update them.
+  width: var(--ion-item-thumbnail-width, $item-md-thumbnail-width);
+  height: var(--ion-item-thumbnail-height, $item-md-thumbnail-height);
 }
 
 // Material Design Item Avatar/Thumbnail
diff --git a/core/src/components/item/item.md.vars.scss b/core/src/components/item/item.md.vars.scss
index 4e38c76ec26..3aad826bf17 100644
--- a/core/src/components/item/item.md.vars.scss
+++ b/core/src/components/item/item.md.vars.scss
@@ -18,8 +18,11 @@ $item-md-avatar-width: 40px;
 /// @prop - Height of the avatar in the item
 $item-md-avatar-height: $item-md-avatar-width;
 
-/// @prop - Size of the thumbnail in the item
-$item-md-thumbnail-size: 56px;
+/// @prop - Width of the thumbnail in the item
+$item-md-thumbnail-width: 56px;
+
+/// @prop - Height of the thumbnail in the item
+$item-md-thumbnail-height: $item-md-thumbnail-width;
 
 /// @prop - Padding top for the item content
 $item-md-padding-top: 10px;
diff --git a/core/src/components/thumbnail/test/basic/index.html b/core/src/components/thumbnail/test/basic/index.html
index 7d412f65c28..5bd8694408e 100644
--- a/core/src/components/thumbnail/test/basic/index.html
+++ b/core/src/components/thumbnail/test/basic/index.html
@@ -33,6 +33,13 @@
           </ion-thumbnail>
           <ion-label>Item Thumbnail</ion-label>
         </ion-item>
+
+        <ion-item-divider id="ion-item-divider">
+          <ion-thumbnail slot="start">
+            <img src="/src/components/thumbnail/test/thumbnail.svg" />
+          </ion-thumbnail>
+          <ion-label>Item Divider Thumbnail</ion-label>
+        </ion-item-divider>
       </ion-content>
     </ion-app>
   </body>
diff --git a/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts b/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts
index 49b4c6dfcc2..28e645edbc8 100644
--- a/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts
+++ b/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts
@@ -2,7 +2,7 @@ import { expect } from '@playwright/test';
 import { configs, test } from '@utils/test/playwright';
 
 /**
- * ion-thumbnail does not have mode/RTL-specific logic
+ * This behavior does not vary across modes/directions
  */
 configs({ modes: ['ios'], directions: ['ltr'] }).forEach(({ title, screenshot, config }) => {
   test.describe(title('thumbnail: rendering'), () => {
@@ -22,8 +22,15 @@ configs({ modes: ['ios'], directions: ['ltr'] }).forEach(({ title, screenshot, c
 
       await page.setContent(
         `
+          <style>
+            ion-thumbnail {
+              --ion-item-thumbnail-width: 20px;
+              --ion-item-thumbnail-height: 20px;
+            }
+          </style>
+
           <ion-item>
-            <ion-thumbnail style="--size: 20px">
+            <ion-thumbnail>
               <img src="/src/components/thumbnail/test/thumbnail.svg" />
             </ion-thumbnail>
           </ion-item>
@@ -34,6 +41,29 @@ configs({ modes: ['ios'], directions: ['ltr'] }).forEach(({ title, screenshot, c
       const item = page.locator('ion-item');
       await expect(item).toHaveScreenshot(screenshot(`thumbnail-ion-item-size-diff`));
     });
+
+    test('size should be customizable in <ion-item-divider>', async ({ page }) => {
+      await page.setContent(
+        `
+          <style>
+            ion-item-divider {
+              --ion-item-divider-thumbnail-width: 20px;
+              --ion-item-divider-thumbnail-height: 20px;
+            }
+          </style>
+
+          <ion-item-divider>
+            <ion-thumbnail>
+              <img src="/src/components/thumbnail/test/thumbnail.svg" />
+            </ion-thumbnail>
+          </ion-item-divider>
+        `,
+        config
+      );
+
+      const itemDivider = page.locator('ion-item-divider');
+      await expect(itemDivider).toHaveScreenshot(screenshot(`thumbnail-ion-item-divider-size`));
+    });
   });
 });
 
@@ -53,5 +83,11 @@ configs().forEach(({ title, screenshot, config }) => {
 
       await expect(referenceEl).toHaveScreenshot(screenshot(`thumbnail-ion-item-diff`));
     });
+
+    test('should not have visual regressions when rendering inside of an <ion-item-divider>', async ({ page }) => {
+      const referenceEl = page.locator('#ion-item-divider');
+
+      await expect(referenceEl).toHaveScreenshot(screenshot('thumbnail-ion-item-divider'));
+    });
   });
 });
diff --git a/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts-snapshots/thumbnail-ion-item-divider-ios-ltr-Mobile-Chrome-linux.png b/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts-snapshots/thumbnail-ion-item-divider-ios-ltr-Mobile-Chrome-linux.png
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diff --git a/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts-snapshots/thumbnail-ion-item-divider-md-ltr-Mobile-Chrome-linux.png b/core/src/components/thumbnail/test/basic/thumbnail.e2e.ts-snapshots/thumbnail-ion-item-divider-md-ltr-Mobile-Chrome-linux.png
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new file mode 100644
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diff --git a/core/src/components/thumbnail/thumbnail.interfaces.ts b/core/src/components/thumbnail/thumbnail.interfaces.ts
new file mode 100644
index 00000000000..d3b02bd1688
--- /dev/null
+++ b/core/src/components/thumbnail/thumbnail.interfaces.ts
@@ -0,0 +1,8 @@
+export type IonThumbnailRecipe = {
+  height?: string;
+  width?: string;
+
+  border?: {
+    radius?: string;
+  };
+};
diff --git a/core/src/components/thumbnail/thumbnail.scss b/core/src/components/thumbnail/thumbnail.scss
index 48fea442a83..aa0ddfe4e5f 100644
--- a/core/src/components/thumbnail/thumbnail.scss
+++ b/core/src/components/thumbnail/thumbnail.scss
@@ -1,27 +1,25 @@
-@import "../../themes/native/native.globals";
+@use "../../themes/mixins" as mixins;
 
 // Thumbnail
 // --------------------------------------------------
 
 :host {
   /**
-   * @prop --border-radius: Border radius of the thumbnail
-   * @prop --size: Size of the thumbnail
+   * @prop --ion-thumbnail-width: Width of the thumbnail
+   * @prop --ion-thumbnail-height: Height of the thumbnail
+   * @prop --ion-thumbnail-border-radius: Border radius of the thumbnail and the slotted image
    */
-  --size: 48px; // TODO(FW-6862): separate width and height tokens for thumbnails
-  --border-radius: 0;
-
-  @include border-radius(var(--border-radius));
+  @include mixins.border-radius(var(--ion-thumbnail-border-radius));
 
   display: block;
 
-  width: var(--size, 48px);
-  height: var(--size, 48px);
+  width: var(--ion-thumbnail-width);
+  height: var(--ion-thumbnail-height);
 }
 
 ::slotted(ion-img),
 ::slotted(img) {
-  @include border-radius(var(--border-radius));
+  @include mixins.border-radius(var(--ion-thumbnail-border-radius));
 
   width: 100%;
   height: 100%;
diff --git a/core/src/components/thumbnail/thumbnail.tsx b/core/src/components/thumbnail/thumbnail.tsx
index 05479cfc288..321f6e39871 100644
--- a/core/src/components/thumbnail/thumbnail.tsx
+++ b/core/src/components/thumbnail/thumbnail.tsx
@@ -1,11 +1,8 @@
 import type { ComponentInterface } from '@stencil/core';
 import { Component, Host, h } from '@stencil/core';
 
-import { getIonTheme } from '../../global/ionic-global';
-
 /**
  * @virtualProp {"ios" | "md"} mode - The mode determines the platform behaviors of the component.
- * @virtualProp {"ios" | "md" | "ionic"} theme - The theme determines the visual appearance of the component.
  */
 @Component({
   tag: 'ion-thumbnail',
@@ -14,13 +11,8 @@ import { getIonTheme } from '../../global/ionic-global';
 })
 export class Thumbnail implements ComponentInterface {
   render() {
-    const theme = getIonTheme(this);
     return (
-      <Host
-        class={{
-          [theme]: true,
-        }}
-      >
+      <Host>
         <slot></slot>
       </Host>
     );
diff --git a/core/src/themes/ionic/default.tokens.ts b/core/src/themes/ionic/default.tokens.ts
index bde15b539a0..9e4789b43ef 100644
--- a/core/src/themes/ionic/default.tokens.ts
+++ b/core/src/themes/ionic/default.tokens.ts
@@ -803,5 +803,14 @@ export const defaultTheme: DefaultTheme = {
         },
       },
     },
+
+    IonThumbnail: {
+      height: 'var(--ion-scaling-xl)',
+      width: 'var(--ion-scaling-xl)',
+
+      border: {
+        radius: 'var(--ion-radii-xxxxs)',
+      },
+    },
   },
 };
diff --git a/core/src/themes/ios/default.tokens.ts b/core/src/themes/ios/default.tokens.ts
index 00f09285cec..a47d43d58fb 100644
--- a/core/src/themes/ios/default.tokens.ts
+++ b/core/src/themes/ios/default.tokens.ts
@@ -831,5 +831,14 @@ export const defaultTheme: DefaultTheme = {
         },
       },
     },
+
+    IonThumbnail: {
+      height: 'var(--ion-scaling-xxxl)',
+      width: 'var(--ion-scaling-xxxl)',
+
+      border: {
+        radius: 'var(--ion-radii-xxxxs)',
+      },
+    },
   },
 };
diff --git a/core/src/themes/md/default.tokens.ts b/core/src/themes/md/default.tokens.ts
index 48cbb301023..cb2c9e85a8c 100644
--- a/core/src/themes/md/default.tokens.ts
+++ b/core/src/themes/md/default.tokens.ts
@@ -956,5 +956,14 @@ export const defaultTheme: DefaultTheme = {
         },
       },
     },
+
+    IonThumbnail: {
+      height: 'var(--ion-scaling-xxxl)',
+      width: 'var(--ion-scaling-xxxl)',
+
+      border: {
+        radius: 'var(--ion-radii-xxxxs)',
+      },
+    },
   },
 };
diff --git a/core/src/themes/themes.interfaces.ts b/core/src/themes/themes.interfaces.ts
index 4d552c77be7..d45a4717b60 100644
--- a/core/src/themes/themes.interfaces.ts
+++ b/core/src/themes/themes.interfaces.ts
@@ -3,6 +3,7 @@ import type { IonChipConfig, IonChipRecipe } from '../components/chip/chip.inter
 import type { IonItemDividerRecipe } from '../components/item-divider/item-divider.interfaces';
 import type { IonProgressBarConfig, IonProgressBarRecipe } from '../components/progress-bar/progress-bar.interfaces';
 import type { IonSpinnerConfig, IonSpinnerRecipe } from '../components/spinner/spinner.interfaces';
+import type { IonThumbnailRecipe } from '../components/thumbnail/thumbnail.interfaces';
 import type { IonicConfig as IonicGlobalConfig } from '../utils/config';
 
 // Platform-specific theme
@@ -290,6 +291,7 @@ type Components = {
   IonItemDivider?: IonItemDividerRecipe;
   IonProgressBar?: IonProgressBarRecipe;
   IonSpinner?: IonSpinnerRecipe;
+  IonThumbnail?: IonThumbnailRecipe;
 
   IonCard?: any;
   IonItem?: any;
diff --git a/packages/angular/src/directives/proxies.ts b/packages/angular/src/directives/proxies.ts
index 64d4888724b..fa5571aacba 100644
--- a/packages/angular/src/directives/proxies.ts
+++ b/packages/angular/src/directives/proxies.ts
@@ -2489,14 +2489,14 @@ the user clears the textarea by performing a keydown event.
 
 
 @ProxyCmp({
-  inputs: ['mode', 'theme']
+  inputs: ['mode']
 })
 @Component({
   selector: 'ion-thumbnail',
   changeDetection: ChangeDetectionStrategy.OnPush,
   template: '<ng-content></ng-content>',
   // eslint-disable-next-line @angular-eslint/no-inputs-metadata-property
-  inputs: ['mode', 'theme'],
+  inputs: ['mode'],
 })
 export class IonThumbnail {
   protected el: HTMLIonThumbnailElement;
diff --git a/packages/angular/standalone/src/directives/proxies.ts b/packages/angular/standalone/src/directives/proxies.ts
index bf79b098440..68407deee87 100644
--- a/packages/angular/standalone/src/directives/proxies.ts
+++ b/packages/angular/standalone/src/directives/proxies.ts
@@ -2185,14 +2185,14 @@ export declare interface IonText extends Components.IonText {}
 
 @ProxyCmp({
   defineCustomElementFn: defineIonThumbnail,
-  inputs: ['mode', 'theme']
+  inputs: ['mode']
 })
 @Component({
   selector: 'ion-thumbnail',
   changeDetection: ChangeDetectionStrategy.OnPush,
   template: '<ng-content></ng-content>',
   // eslint-disable-next-line @angular-eslint/no-inputs-metadata-property
-  inputs: ['mode', 'theme'],
+  inputs: ['mode'],
   standalone: true
 })
 export class IonThumbnail {