diff --git a/.changeset/blankslate-size-scale.md b/.changeset/blankslate-size-scale.md
new file mode 100644
index 00000000000..27f011a27d5
--- /dev/null
+++ b/.changeset/blankslate-size-scale.md
@@ -0,0 +1,5 @@
+---
+'@primer/react': minor
+---
+
+Blankslate: Add compact-default sizing and default-sized primary actions behind the default-off `primer_react_blankslate_compact_default` feature flag. The `small` size remains supported.
diff --git a/packages/react/src/Blankslate/Blankslate.module.css b/packages/react/src/Blankslate/Blankslate.module.css
index 8604a1dcb12..106e492f366 100644
--- a/packages/react/src/Blankslate/Blankslate.module.css
+++ b/packages/react/src/Blankslate/Blankslate.module.css
@@ -137,3 +137,52 @@
     }
   }
 }
+
+.Blankslate:where([data-compact-default][data-size='medium']) {
+  --blankslate-heading-text: var(--text-title-shorthand-small);
+  --blankslate-heading-margin-block: 0 var(--base-size-4);
+  --blankslate-description-text: var(--text-body-shorthand-medium);
+  --blankslate-description-margin-block: 0;
+  --blankslate-padding: var(--base-size-16);
+  --blankslate-action-margin-block-end: var(--base-size-12);
+  --blankslate-visual-size: var(--base-size-24);
+
+  &:where([data-spacious]) {
+    --blankslate-padding: var(--base-size-44) var(--base-size-28);
+  }
+}
+
+.Blankslate:where([data-compact-default][data-size='large']) {
+  --blankslate-heading-text: var(--text-title-shorthand-medium);
+  --blankslate-heading-margin-block: 0 var(--base-size-4);
+  --blankslate-description-text: var(--text-body-shorthand-large);
+  --blankslate-description-margin-block: 0;
+  --blankslate-padding: var(--base-size-32);
+  --blankslate-action-margin-block-end: var(--base-size-16);
+
+  &:where([data-spacious]) {
+    --blankslate-padding: var(--base-size-80) var(--base-size-40);
+  }
+}
+
+.Blankslate:where([data-compact-default]) {
+  & .Action {
+    margin-block-start: var(--base-size-16);
+  }
+
+  &[data-size='medium'] .Action:last-of-type {
+    margin-block-end: var(--base-size-12);
+  }
+
+  &[data-size='large'] .Action:last-of-type {
+    margin-block-end: var(--base-size-16);
+  }
+
+  & .Visual {
+    margin-block-end: var(--base-size-8);
+  }
+}
+
+.Blankslate:where([data-compact-default][data-size='large']) .Visual {
+  max-width: none;
+}
diff --git a/packages/react/src/Blankslate/Blankslate.test.tsx b/packages/react/src/Blankslate/Blankslate.test.tsx
index 912d0e02daa..38b3e51ffca 100644
--- a/packages/react/src/Blankslate/Blankslate.test.tsx
+++ b/packages/react/src/Blankslate/Blankslate.test.tsx
@@ -2,6 +2,7 @@ import {describe, expect, it, vi} from 'vitest'
 import {render, screen} from '@testing-library/react'
 import userEvent from '@testing-library/user-event'
 import {Blankslate} from '../Blankslate'
+import {FeatureFlags} from '../FeatureFlags'
 import {implementsClassName} from '../utils/testing'
 import classes from './Blankslate.module.css'
 
@@ -23,11 +24,12 @@ function getCSSStyleRules(): Array<CSSStyleRule> {
   })
 }
 
-function getSizePadding(size: 'small' | 'medium' | 'large') {
+function getSizePadding(size: 'small' | 'medium' | 'large', compactDefault = false) {
   const rule = getCSSStyleRules().find(cssRule => {
     return (
       cssRule.selectorText.includes(`.${classes.Blankslate}`) &&
       cssRule.selectorText.includes(`data-size="${size}"`) &&
+      cssRule.selectorText.includes('data-compact-default') === compactDefault &&
       !cssRule.selectorText.includes('data-spacious')
     )
   })
@@ -59,6 +61,39 @@ describe('Blankslate', () => {
     expect(getSizePadding('small')).toMatch(/^var\(--base-size-16/)
   })
 
+  it('keeps the existing size scale when the compact default feature is disabled', () => {
+    const {container} = render(<Blankslate size="small">Test content</Blankslate>)
+    const blankslate = container.querySelector('[data-component="Blankslate"]')
+
+    expect(blankslate).toHaveAttribute('data-size', 'small')
+    expect(blankslate).not.toHaveAttribute('data-compact-default')
+  })
+
+  it('uses the compact default size scale when the feature is enabled', () => {
+    const {container} = render(
+      <FeatureFlags flags={{primer_react_blankslate_compact_default: true}}>
+        <Blankslate>Test content</Blankslate>
+      </FeatureFlags>,
+    )
+    const blankslate = container.querySelector('[data-component="Blankslate"]')
+
+    expect(blankslate).toHaveAttribute('data-size', 'medium')
+    expect(blankslate).toHaveAttribute('data-compact-default', '')
+    expect(getSizePadding('medium', true)).toMatch(/^var\(--base-size-16/)
+    expect(getSizePadding('large', true)).toMatch(/^var\(--base-size-32/)
+  })
+
+  it('maps the legacy small size to the compact default size when the feature is enabled', () => {
+    const {container} = render(
+      <FeatureFlags flags={{primer_react_blankslate_compact_default: true}}>
+        <Blankslate size="small">Test content</Blankslate>
+      </FeatureFlags>,
+    )
+    const blankslate = container.querySelector('[data-component="Blankslate"]')
+
+    expect(blankslate).toHaveAttribute('data-size', 'medium')
+  })
+
   it('renders data-component attributes', () => {
     const {container} = render(
       <Blankslate>
@@ -146,6 +181,28 @@ describe('Blankslate', () => {
       expect(screen.getByRole('button', {name: 'Primary action'})).toBeInTheDocument()
     })
 
+    it('uses the default button size when the compact default feature is enabled', () => {
+      render(
+        <FeatureFlags flags={{primer_react_blankslate_compact_default: true}}>
+          <Blankslate size="small">
+            <Blankslate.PrimaryAction>Primary action</Blankslate.PrimaryAction>
+          </Blankslate>
+        </FeatureFlags>,
+      )
+
+      expect(screen.getByRole('button', {name: 'Primary action'})).toHaveAttribute('data-size', 'medium')
+    })
+
+    it('keeps the small button size when the compact default feature is disabled', () => {
+      render(
+        <Blankslate size="small">
+          <Blankslate.PrimaryAction>Primary action</Blankslate.PrimaryAction>
+        </Blankslate>,
+      )
+
+      expect(screen.getByRole('button', {name: 'Primary action'})).toHaveAttribute('data-size', 'small')
+    })
+
     it('should handle click events on the button', async () => {
       const user = userEvent.setup()
       const onClick = vi.fn()
diff --git a/packages/react/src/Blankslate/Blankslate.tsx b/packages/react/src/Blankslate/Blankslate.tsx
index fa785e9991b..21908142cb9 100644
--- a/packages/react/src/Blankslate/Blankslate.tsx
+++ b/packages/react/src/Blankslate/Blankslate.tsx
@@ -2,6 +2,7 @@ import {clsx} from 'clsx'
 import {useMemo} from 'react'
 import type React from 'react'
 import {Button} from '../Button'
+import {useFeatureFlag} from '../FeatureFlags'
 import Link from '../Link'
 import {Provider, useBlankslate} from './BlankslateContext'
 import classes from './Blankslate.module.css'
@@ -34,11 +35,13 @@ type BlankslateProps = React.HTMLAttributes<HTMLElement> & {
 }
 
 function Blankslate({border, children, narrow, spacious, className, size = 'medium', ...rest}: BlankslateProps) {
+  const compactDefault = useFeatureFlag('primer_react_blankslate_compact_default')
   const value = useMemo(() => {
     return {
       size,
+      compactDefault,
     }
-  }, [size])
+  }, [size, compactDefault])
 
   return (
     <Provider value={value}>
@@ -49,7 +52,8 @@ function Blankslate({border, children, narrow, spacious, className, size = 'medi
           data-border={border ? '' : undefined}
           data-narrow={narrow ? '' : undefined}
           data-spacious={spacious ? '' : undefined}
-          data-size={size}
+          data-compact-default={compactDefault ? '' : undefined}
+          data-size={compactDefault && size === 'small' ? 'medium' : size}
         >
           {children}
         </div>
@@ -108,7 +112,7 @@ type BlankslatePrimaryActionProps =
     }>
 
 function PrimaryAction({children, href, ...props}: BlankslatePrimaryActionProps) {
-  const {size} = useBlankslate()
+  const {size, compactDefault} = useBlankslate()
   return (
     <div className={clsx('Blankslate-Action', classes.Action)} data-component="Blankslate.PrimaryAction">
       <Button
@@ -116,7 +120,7 @@ function PrimaryAction({children, href, ...props}: BlankslatePrimaryActionProps)
         as={href ? 'a' : 'button'}
         href={href}
         variant="primary"
-        size={size === 'small' ? 'small' : undefined}
+        size={!compactDefault && size === 'small' ? 'small' : undefined}
       >
         {children}
       </Button>
diff --git a/packages/react/src/Blankslate/BlankslateContext.ts b/packages/react/src/Blankslate/BlankslateContext.ts
index 59bed1202bc..0c8afaa5890 100644
--- a/packages/react/src/Blankslate/BlankslateContext.ts
+++ b/packages/react/src/Blankslate/BlankslateContext.ts
@@ -2,6 +2,7 @@ import {createContext, useContext} from 'react'
 
 type BlankslateContextType = {
   size: 'small' | 'medium' | 'large'
+  compactDefault: boolean
 }
 
 const BlankslateContext = createContext<BlankslateContextType | null>(null)
diff --git a/packages/react/src/FeatureFlags/DefaultFeatureFlags.ts b/packages/react/src/FeatureFlags/DefaultFeatureFlags.ts
index 0862870621f..726bcd42906 100644
--- a/packages/react/src/FeatureFlags/DefaultFeatureFlags.ts
+++ b/packages/react/src/FeatureFlags/DefaultFeatureFlags.ts
@@ -11,4 +11,5 @@ export const DefaultFeatureFlags = FeatureFlagScope.create({
   primer_react_timeline_list_semantics: false,
   primer_react_merged_forwarded_refs: false,
   primer_react_button_loading_disabled_styles: false,
+  primer_react_blankslate_compact_default: false,
 })