diff --git a/.changeset/mosaic-card-footer-button-width.md b/.changeset/mosaic-card-footer-button-width.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/mosaic-card-footer-button-width.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/packages/mosaic/src/blocks/confirmation/confirmation.tsx b/packages/mosaic/src/blocks/confirmation/confirmation.tsx
index b7e91ce72de..c41fc8008bc 100644
--- a/packages/mosaic/src/blocks/confirmation/confirmation.tsx
+++ b/packages/mosaic/src/blocks/confirmation/confirmation.tsx
@@ -57,7 +57,6 @@ export function Confirmation<Payload = void>({ color = 'negative', ...props }: C
                 <Button
                   color='neutral'
                   variant='outline'
-                  fullWidth
                 >
                   {cancelLabel}
                 </Button>
@@ -65,7 +64,6 @@ export function Confirmation<Payload = void>({ color = 'negative', ...props }: C
             />
             <SubmitButton
               type='button'
-              fullWidth
               color={color}
               isPending={isPending}
               onClick={confirm}
diff --git a/packages/mosaic/src/blocks/destructive/destructive.tsx b/packages/mosaic/src/blocks/destructive/destructive.tsx
index 057bb973466..31527a6de6a 100644
--- a/packages/mosaic/src/blocks/destructive/destructive.tsx
+++ b/packages/mosaic/src/blocks/destructive/destructive.tsx
@@ -88,7 +88,6 @@ function DestructiveStep<Payload>({
             <Button
               color='neutral'
               variant='outline'
-              fullWidth
             >
               {cancelLabel}
             </Button>
@@ -96,7 +95,6 @@ function DestructiveStep<Payload>({
         />
         <SubmitButton
           form={formId}
-          fullWidth
           color='negative'
           isPending={isPending}
           disabled={!isConfirmed}
diff --git a/packages/mosaic/src/components/button/button.context.ts b/packages/mosaic/src/components/button/button.context.ts
index 60d0f84fd36..05f1d3edd85 100644
--- a/packages/mosaic/src/components/button/button.context.ts
+++ b/packages/mosaic/src/components/button/button.context.ts
@@ -5,10 +5,12 @@ import React from 'react';
 
 import type { ButtonProps } from './button';
 
-export const ButtonContext = React.createContext<
-  Pick<ButtonProps, 'size' | 'shape' | 'variant' | 'color' | 'disabled'> & {
-    styles?: StyleXStyles;
-    sizeStyles?: StyleXStyles;
-    iconStyles?: StyleXStyles;
-  }
->({});
+type ButtonDefaults = Pick<ButtonProps, 'size' | 'shape' | 'variant' | 'color' | 'disabled' | 'fullWidth'> & {
+  styles?: StyleXStyles;
+  sizeStyles?: StyleXStyles;
+  iconStyles?: StyleXStyles;
+};
+
+export const NO_BUTTON_DEFAULTS: ButtonDefaults = {};
+
+export const ButtonContext = React.createContext<ButtonDefaults>(NO_BUTTON_DEFAULTS);
diff --git a/packages/mosaic/src/components/button/button.tsx b/packages/mosaic/src/components/button/button.tsx
index 9d107a20986..92dbd1b0d5a 100644
--- a/packages/mosaic/src/components/button/button.tsx
+++ b/packages/mosaic/src/components/button/button.tsx
@@ -61,7 +61,7 @@ export const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(function
     variant: variantProp,
     size: sizeProp,
     shape: shapeProp,
-    fullWidth = false,
+    fullWidth: fullWidthProp,
     touchTarget = true,
     disabled: disabledProp,
     focusableWhenDisabled = false,
@@ -76,6 +76,7 @@ export const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(function
   const variant = variantProp ?? defaults.variant ?? 'filled';
   const size = sizeProp ?? defaults.size ?? 'md';
   const shape = shapeProp ?? defaults.shape ?? 'default';
+  const fullWidth = fullWidthProp ?? defaults.fullWidth ?? false;
   const disabled = defaults.disabled || disabledProp || false;
   const isIconShape = shape === 'square' || shape === 'circle';
   const hasTouchTarget = touchTarget && variant !== 'link';
diff --git a/packages/mosaic/src/components/card/card.test.tsx b/packages/mosaic/src/components/card/card.test.tsx
index 89739b7814d..f2a3277c0e5 100644
--- a/packages/mosaic/src/components/card/card.test.tsx
+++ b/packages/mosaic/src/components/card/card.test.tsx
@@ -4,6 +4,8 @@ import userEvent from '@testing-library/user-event';
 import React from 'react';
 import { afterEach, describe, expect, it, vi } from 'vitest';
 
+import { Button, SubmitButton } from '../button';
+import { ButtonContext } from '../button/button.context';
 import { Dialog } from '../dialog';
 import { Flow } from '../flow';
 import { Card } from './card';
@@ -753,6 +755,55 @@ describe('Mosaic Card', () => {
   });
 });
 
+describe('Card.Footer buttons', () => {
+  it('makes buttons full width by default', () => {
+    render(
+      <Card.Footer>
+        <Button>Cancel</Button>
+        <SubmitButton>Save</SubmitButton>
+      </Card.Footer>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Cancel' })).toHaveAttribute('data-full-width', '');
+    expect(screen.getByRole('button', { name: 'Save' })).toHaveAttribute('data-full-width', '');
+  });
+
+  it('lets a button opt out', () => {
+    render(
+      <Card.Footer>
+        <Button fullWidth={false}>Sign in</Button>
+      </Card.Footer>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Sign in' })).not.toHaveAttribute('data-full-width');
+  });
+
+  it('keeps button defaults from an enclosing provider', () => {
+    render(
+      <ButtonContext.Provider value={{ disabled: true }}>
+        <Card.Footer>
+          <Button>Save</Button>
+        </Card.Footer>
+      </ButtonContext.Provider>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Save' })).toBeDisabled();
+  });
+
+  it('leaves buttons outside the footer alone', () => {
+    render(
+      <Card.Root>
+        <Card.Content>
+          <Button>Inside content</Button>
+        </Card.Content>
+        <Card.Footer />
+      </Card.Root>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Inside content' })).not.toHaveAttribute('data-full-width');
+  });
+});
+
 describe('Card surface', () => {
   // Written out rather than imported, so a drift from `card.styles.ts` fails here instead of passing silently.
   const probe = stylex.create({
diff --git a/packages/mosaic/src/components/card/card.tsx b/packages/mosaic/src/components/card/card.tsx
index 631b12ab3c6..4fc2766ac6e 100644
--- a/packages/mosaic/src/components/card/card.tsx
+++ b/packages/mosaic/src/components/card/card.tsx
@@ -13,6 +13,7 @@ import type { BannerRootProps } from '../banner';
 import { Banner } from '../banner';
 import { Branding } from '../branding';
 import { Button } from '../button';
+import { ButtonContext } from '../button/button.context';
 import type { DialogContextValue } from '../dialog';
 import { Dialog, DialogContext, isInDialog } from '../dialog';
 import { Icon } from '../icon';
@@ -251,7 +252,9 @@ const Footer = React.forwardRef<HTMLDivElement, MosaicComponentProps<'div'>>(fun
   ref,
 ) {
   const elevation = React.useContext(CardContext)?.elevation ?? DEFAULT_ELEVATION;
-  return useRender({
+  const parentButtonDefaults = React.useContext(ButtonContext);
+  const buttonDefaults = React.useMemo(() => ({ ...parentButtonDefaults, fullWidth: true }), [parentButtonDefaults]);
+  const element = useRender({
     defaultTagName: 'div',
     render,
     ref,
@@ -263,6 +266,8 @@ const Footer = React.forwardRef<HTMLDivElement, MosaicComponentProps<'div'>>(fun
       ),
     },
   });
+
+  return <ButtonContext.Provider value={buttonDefaults}>{element}</ButtonContext.Provider>;
 });
 
 /**
diff --git a/packages/mosaic/src/components/dialog/__tests__/dialog.test.tsx b/packages/mosaic/src/components/dialog/__tests__/dialog.test.tsx
index 7a2587396d1..af6605da7f1 100644
--- a/packages/mosaic/src/components/dialog/__tests__/dialog.test.tsx
+++ b/packages/mosaic/src/components/dialog/__tests__/dialog.test.tsx
@@ -6,6 +6,8 @@ import { afterEach, describe, expect, it, vi } from 'vitest';
 
 import type { MosaicComponentProps } from '../../../props';
 import { colorVars, radiusVars, space } from '../../../tokens.stylex';
+import { Button } from '../../button';
+import { ButtonContext } from '../../button/button.context';
 import { Card } from '../../card';
 import type { DialogVariant } from '../dialog';
 import { Dialog } from '../dialog';
@@ -395,6 +397,38 @@ describe('stacked backdrops', () => {
   });
 });
 
+describe('button defaults', () => {
+  it('does not inherit full width from a card footer it is opened from', () => {
+    render(
+      <Card.Footer>
+        <Dialog.Root defaultOpen>
+          <Dialog.Popup>
+            <Surface title='Nested' />
+            <Button>Inside popup</Button>
+          </Dialog.Popup>
+        </Dialog.Root>
+      </Card.Footer>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Inside popup' })).not.toHaveAttribute('data-full-width');
+  });
+
+  it('does not inherit disabled from an enclosing provider', () => {
+    render(
+      <ButtonContext.Provider value={{ disabled: true }}>
+        <Dialog.Root defaultOpen>
+          <Dialog.Popup>
+            <Surface title='Nested' />
+            <Button>Inside popup</Button>
+          </Dialog.Popup>
+        </Dialog.Root>
+      </ButtonContext.Provider>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Inside popup' })).toBeEnabled();
+  });
+});
+
 describe('Dialog.CloseButton', () => {
   it('closes the dialog and carries a default accessible name', async () => {
     const user = userEvent.setup();
diff --git a/packages/mosaic/src/components/dialog/dialog.tsx b/packages/mosaic/src/components/dialog/dialog.tsx
index 9ef61a4566a..e142b13cc20 100644
--- a/packages/mosaic/src/components/dialog/dialog.tsx
+++ b/packages/mosaic/src/components/dialog/dialog.tsx
@@ -16,6 +16,7 @@ import type { MosaicComponentProps } from '../../props';
 import { mergeStyleProps, themeProps } from '../../props';
 import { reset } from '../../styles/reset.styles';
 import { Button } from '../button';
+import { ButtonContext, NO_BUTTON_DEFAULTS } from '../button/button.context';
 import { Icon } from '../icon';
 import { ToastProvider } from '../toast/toast';
 import {
@@ -475,7 +476,11 @@ const Popup = React.forwardRef<HTMLDivElement, DialogPopupProps>(function Dialog
   );
 
   return (
-    <Primitive.Portal>{holdsProfile(variant) ? <ToastProvider>{viewport}</ToastProvider> : viewport}</Primitive.Portal>
+    <Primitive.Portal>
+      <ButtonContext.Provider value={NO_BUTTON_DEFAULTS}>
+        {holdsProfile(variant) ? <ToastProvider>{viewport}</ToastProvider> : viewport}
+      </ButtonContext.Provider>
+    </Primitive.Portal>
   );
 });
 
diff --git a/packages/mosaic/src/components/popover/popover.test.tsx b/packages/mosaic/src/components/popover/popover.test.tsx
index 5271670f381..7a42e87f753 100644
--- a/packages/mosaic/src/components/popover/popover.test.tsx
+++ b/packages/mosaic/src/components/popover/popover.test.tsx
@@ -4,6 +4,9 @@ import userEvent from '@testing-library/user-event';
 import React from 'react';
 import { afterEach, describe, expect, it, vi } from 'vitest';
 
+import { Button } from '../button';
+import { ButtonContext } from '../button/button.context';
+import { Card } from '../card';
 import { Popover } from './popover';
 
 afterEach(() => cleanup());
@@ -14,6 +17,36 @@ const settle = () =>
     await new Promise(resolve => setTimeout(resolve, 0));
   });
 
+describe('button defaults', () => {
+  it('does not inherit full width from a card footer it is opened from', () => {
+    render(
+      <Card.Footer>
+        <Popover.Root defaultOpen>
+          <Popover.Popup aria-label='Panel'>
+            <Button>Inside popup</Button>
+          </Popover.Popup>
+        </Popover.Root>
+      </Card.Footer>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Inside popup' })).not.toHaveAttribute('data-full-width');
+  });
+
+  it('does not inherit disabled from an enclosing provider', () => {
+    render(
+      <ButtonContext.Provider value={{ disabled: true }}>
+        <Popover.Root defaultOpen>
+          <Popover.Popup aria-label='Panel'>
+            <Button>Inside popup</Button>
+          </Popover.Popup>
+        </Popover.Root>
+      </ButtonContext.Provider>,
+    );
+
+    expect(screen.getByRole('button', { name: 'Inside popup' })).toBeEnabled();
+  });
+});
+
 describe('Mosaic Popover', () => {
   it('uses a custom anchor and restores the trigger when it is removed', async () => {
     const anchor = document.createElement('div');
diff --git a/packages/mosaic/src/components/popover/popover.tsx b/packages/mosaic/src/components/popover/popover.tsx
index fb728d5da00..d79f6e65a0e 100644
--- a/packages/mosaic/src/components/popover/popover.tsx
+++ b/packages/mosaic/src/components/popover/popover.tsx
@@ -7,6 +7,7 @@ import { Popover as Primitive } from '../../primitives/popover';
 import type { MosaicComponentProps } from '../../props';
 import { mergeStyleProps, themeProps } from '../../props';
 import { reset } from '../../styles/reset.styles';
+import { ButtonContext, NO_BUTTON_DEFAULTS } from '../button/button.context';
 import { sizes, styles } from './popover.styles';
 
 export type PopoverSize = 'sm' | 'md' | 'lg' | 'anchor';
@@ -98,14 +99,16 @@ const Popup = React.forwardRef<HTMLDivElement, PopoverPopupProps>(function Popov
         {...(ariaLabel == null ? {} : { 'aria-label': ariaLabel })}
         {...(ariaLabelledby == null ? {} : { 'aria-labelledby': ariaLabelledby })}
       >
-        <Primitive.Popup
-          ref={ref}
-          {...mergeStyleProps(
-            themeProps('popover-popup', { size }),
-            stylex.props(reset.base, styles.popup, sizes[size], xstyle),
-            rest,
-          )}
-        />
+        <ButtonContext.Provider value={NO_BUTTON_DEFAULTS}>
+          <Primitive.Popup
+            ref={ref}
+            {...mergeStyleProps(
+              themeProps('popover-popup', { size }),
+              stylex.props(reset.base, styles.popup, sizes[size], xstyle),
+              rest,
+            )}
+          />
+        </ButtonContext.Provider>
       </Positioner>
     </Primitive.Portal>
   );
diff --git a/packages/mosaic/src/features/api-keys/create-api-key.dialog.tsx b/packages/mosaic/src/features/api-keys/create-api-key.dialog.tsx
index 95fee435a9b..3a49e5d7506 100644
--- a/packages/mosaic/src/features/api-keys/create-api-key.dialog.tsx
+++ b/packages/mosaic/src/features/api-keys/create-api-key.dialog.tsx
@@ -163,7 +163,6 @@ function CreateKeyStep(props: CreateAPIKeyDialogProps & { inputRef: Ref<HTMLInpu
       <Card.Footer>
         <SubmitButton
           form={form.id}
-          fullWidth
           isPending={form.isSubmitting}
           disabled={!form.canSubmit}
           focusableWhenDisabled
@@ -223,12 +222,7 @@ function CopyKeyStep(props: CreateAPIKeyDialogProps) {
         </Field.Root>
       </Card.Content>
       <Card.Footer>
-        <SubmitButton
-          form={formId}
-          fullWidth
-        >
-          {m.copyAndClose}
-        </SubmitButton>
+        <SubmitButton form={formId}>{m.copyAndClose}</SubmitButton>
       </Card.Footer>
     </>
   );
diff --git a/packages/mosaic/src/features/create-organization/create-organization.view.tsx b/packages/mosaic/src/features/create-organization/create-organization.view.tsx
index 3497d22088f..717c8f285eb 100644
--- a/packages/mosaic/src/features/create-organization/create-organization.view.tsx
+++ b/packages/mosaic/src/features/create-organization/create-organization.view.tsx
@@ -147,7 +147,6 @@ function CreateStep({ form, slugEnabled, onNameChange, onCancel }: CreateOrganiz
           <Button
             variant='outline'
             color='neutral'
-            fullWidth
             disabled={form.isSubmitting}
             onClick={onCancel}
           >
@@ -156,7 +155,6 @@ function CreateStep({ form, slugEnabled, onNameChange, onCancel }: CreateOrganiz
         ) : null}
         <SubmitButton
           form={form.id}
-          fullWidth
           isPending={form.isSubmitting}
           disabled={!form.canSubmit}
           focusableWhenDisabled
@@ -303,7 +301,6 @@ function InviteStep({ invite, onFinish }: CreateOrganizationStepsProps) {
         <Button
           variant='outline'
           color='neutral'
-          fullWidth
           disabled={invite.isPending}
           onClick={onFinish}
         >
@@ -311,7 +308,6 @@ function InviteStep({ invite, onFinish }: CreateOrganizationStepsProps) {
         </Button>
         <SubmitButton
           form={formId}
-          fullWidth
           isPending={invite.isPending}
           disabled={!canSubmit}
           focusableWhenDisabled
@@ -336,7 +332,6 @@ function SentStep({ onFinish }: CreateOrganizationStepsProps) {
       <Card.Footer>
         <Button
           ref={finishButton}
-          fullWidth
           onClick={onFinish}
         >
           {m.sent.finish}
diff --git a/packages/mosaic/src/features/organization-list/organization-list.view.tsx b/packages/mosaic/src/features/organization-list/organization-list.view.tsx
index 3ff8a2e00fc..14bbb47869a 100644
--- a/packages/mosaic/src/features/organization-list/organization-list.view.tsx
+++ b/packages/mosaic/src/features/organization-list/organization-list.view.tsx
@@ -151,7 +151,6 @@ function ListStep({
             ref={createButton}
             variant='outline'
             color='neutral'
-            fullWidth
             disabled={Boolean(pendingKey)}
             focusableWhenDisabled
             onClick={onCreateOrganization}
diff --git a/packages/mosaic/src/features/organization-profile/organization-profile-members-panel/organization-profile-invite-members.dialog.tsx b/packages/mosaic/src/features/organization-profile/organization-profile-members-panel/organization-profile-invite-members.dialog.tsx
index 0356ac54ee0..0736d17d40b 100644
--- a/packages/mosaic/src/features/organization-profile/organization-profile-members-panel/organization-profile-invite-members.dialog.tsx
+++ b/packages/mosaic/src/features/organization-profile/organization-profile-members-panel/organization-profile-invite-members.dialog.tsx
@@ -104,7 +104,6 @@ export function OrganizationProfileInviteMembersDialog({
                 <Button
                   variant='outline'
                   color='neutral'
-                  fullWidth
                 >
                   {m.cancel}
                 </Button>
@@ -112,7 +111,6 @@ export function OrganizationProfileInviteMembersDialog({
             />
             <SubmitButton
               form={formId}
-              fullWidth
               isPending={isPending}
               disabled={!canSubmit}
               focusableWhenDisabled
diff --git a/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-name.dialog.tsx b/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-name.dialog.tsx
index e5d4d2b80d8..8dca956b855 100644
--- a/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-name.dialog.tsx
+++ b/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-name.dialog.tsx
@@ -83,7 +83,6 @@ export function OrganizationProfileEditNameDialog({
                 <Button
                   variant='outline'
                   color='neutral'
-                  fullWidth
                 />
               }
             >
@@ -91,7 +90,6 @@ export function OrganizationProfileEditNameDialog({
             </Dialog.Close>
             <SubmitButton
               form={form.id}
-              fullWidth
               isPending={form.isSubmitting}
               disabled={!form.canSubmit}
               focusableWhenDisabled
diff --git a/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-slug.dialog.tsx b/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-slug.dialog.tsx
index 4cb4539ffed..a4891143520 100644
--- a/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-slug.dialog.tsx
+++ b/packages/mosaic/src/features/organization-profile/organization-profile-profile-section/organization-profile-edit-slug.dialog.tsx
@@ -84,7 +84,6 @@ export function OrganizationProfileEditSlugDialog({
                 <Button
                   variant='outline'
                   color='neutral'
-                  fullWidth
                 />
               }
             >
@@ -92,7 +91,6 @@ export function OrganizationProfileEditSlugDialog({
             </Dialog.Close>
             <SubmitButton
               form={form.id}
-              fullWidth
               isPending={form.isSubmitting}
               disabled={!form.canSubmit}
               focusableWhenDisabled
diff --git a/packages/mosaic/src/features/reverification/reverification.view.tsx b/packages/mosaic/src/features/reverification/reverification.view.tsx
index 6493eb40caa..eac07391e9d 100644
--- a/packages/mosaic/src/features/reverification/reverification.view.tsx
+++ b/packages/mosaic/src/features/reverification/reverification.view.tsx
@@ -73,7 +73,6 @@ export function ReverificationError({ reason, onClose }: { reason: Reverificatio
             type='button'
             variant='outline'
             color='neutral'
-            fullWidth
             onClick={onClose}
           >
             {m.error.close}
@@ -103,6 +102,7 @@ export function ReverificationPending() {
         <Button
           type='button'
           disabled
+          fullWidth={false}
           xstyle={styles.pendingAction}
         >
           {m.continue}
diff --git a/packages/mosaic/src/features/reverification/steps/reverification-backup-code.tsx b/packages/mosaic/src/features/reverification/steps/reverification-backup-code.tsx
index d5103bf0bcc..0bde6d42a8c 100644
--- a/packages/mosaic/src/features/reverification/steps/reverification-backup-code.tsx
+++ b/packages/mosaic/src/features/reverification/steps/reverification-backup-code.tsx
@@ -90,7 +90,6 @@ export function ReverificationBackupCode({
             type='button'
             variant='outline'
             color='neutral'
-            fullWidth
             disabled={isPending}
             onClick={onCancel}
           >
@@ -99,7 +98,6 @@ export function ReverificationBackupCode({
         ) : null}
         <SubmitButton
           form={formId}
-          fullWidth
           disabled={!canSubmit}
           isPending={isPending}
           pendingLabel={messages.pendingLabel}
diff --git a/packages/mosaic/src/features/reverification/steps/reverification-help.tsx b/packages/mosaic/src/features/reverification/steps/reverification-help.tsx
index 94c2347f47b..982595df413 100644
--- a/packages/mosaic/src/features/reverification/steps/reverification-help.tsx
+++ b/packages/mosaic/src/features/reverification/steps/reverification-help.tsx
@@ -28,14 +28,12 @@ export function ReverificationHelp({ messages, onEmailSupport, onBack }: Reverif
           type='button'
           variant='outline'
           color='neutral'
-          fullWidth
           onClick={onBack}
         >
           {messages.backButton}
         </Button>
         <Button
           type='button'
-          fullWidth
           onClick={onEmailSupport}
         >
           {messages.supportButton}
diff --git a/packages/mosaic/src/features/reverification/steps/reverification-otp.tsx b/packages/mosaic/src/features/reverification/steps/reverification-otp.tsx
index b9b8efd4610..0b54f309702 100644
--- a/packages/mosaic/src/features/reverification/steps/reverification-otp.tsx
+++ b/packages/mosaic/src/features/reverification/steps/reverification-otp.tsx
@@ -121,7 +121,6 @@ export function ReverificationOTP({
             type='button'
             variant='outline'
             color='neutral'
-            fullWidth
             disabled={isPending}
             onClick={onCancel}
           >
@@ -130,7 +129,6 @@ export function ReverificationOTP({
         ) : null}
         <SubmitButton
           form={formId}
-          fullWidth
           disabled={!canSubmit}
           isPending={isPending}
           pendingLabel={messages.pendingLabel}
diff --git a/packages/mosaic/src/features/reverification/steps/reverification-passkey.tsx b/packages/mosaic/src/features/reverification/steps/reverification-passkey.tsx
index 8c9a699c43f..ee6d083d3f4 100644
--- a/packages/mosaic/src/features/reverification/steps/reverification-passkey.tsx
+++ b/packages/mosaic/src/features/reverification/steps/reverification-passkey.tsx
@@ -48,7 +48,6 @@ export function ReverificationPasskey({
             type='button'
             variant='outline'
             color='neutral'
-            fullWidth
             disabled={isPending}
             onClick={onCancel}
           >
@@ -58,7 +57,6 @@ export function ReverificationPasskey({
         <SubmitButton
           ref={useMergeRefs<HTMLElement>([focusRef, useFlowAutoFocus<HTMLButtonElement>()])}
           type='button'
-          fullWidth
           isPending={isPending}
           pendingLabel={messages.pendingLabel}
           onClick={onSubmit}
diff --git a/packages/mosaic/src/features/reverification/steps/reverification-password.tsx b/packages/mosaic/src/features/reverification/steps/reverification-password.tsx
index 401d408baf6..11525352895 100644
--- a/packages/mosaic/src/features/reverification/steps/reverification-password.tsx
+++ b/packages/mosaic/src/features/reverification/steps/reverification-password.tsx
@@ -107,7 +107,6 @@ export function ReverificationPassword({
             type='button'
             variant='outline'
             color='neutral'
-            fullWidth
             disabled={isPending}
             onClick={onCancel}
           >
@@ -116,7 +115,6 @@ export function ReverificationPassword({
         ) : null}
         <SubmitButton
           form={formId}
-          fullWidth
           disabled={!canSubmit}
           isPending={isPending}
           pendingLabel={messages.pendingLabel}
diff --git a/packages/mosaic/src/features/user-profile/user-profile-active-devices-section/user-profile-device-details.dialog.tsx b/packages/mosaic/src/features/user-profile/user-profile-active-devices-section/user-profile-device-details.dialog.tsx
index aadc6f9c539..12b70b037c5 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-active-devices-section/user-profile-device-details.dialog.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-active-devices-section/user-profile-device-details.dialog.tsx
@@ -136,7 +136,6 @@ function DeviceDetails({
         {onSignOut && !device.isCurrent ? (
           <SubmitButton
             type='button'
-            fullWidth
             isPending={isSigningOut}
             onClick={onSignOut}
           >
@@ -147,7 +146,6 @@ function DeviceDetails({
             render={
               <Button
                 color='neutral'
-                fullWidth
                 variant='outline'
               />
             }
diff --git a/packages/mosaic/src/features/user-profile/user-profile-email-section/user-profile-add-email.dialog.tsx b/packages/mosaic/src/features/user-profile/user-profile-email-section/user-profile-add-email.dialog.tsx
index 5c21748f209..daea0360f3a 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-email-section/user-profile-add-email.dialog.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-email-section/user-profile-add-email.dialog.tsx
@@ -190,7 +190,6 @@ function EnterEmailStep(props: EnterEmailStepProps) {
       <Card.Footer>
         <SubmitButton
           form={emailFormId}
-          fullWidth
           disabled={!props.canSubmit}
           isPending={props.isPending}
           pendingLabel={m.email.pending}
@@ -275,7 +274,6 @@ function VerifyEmailStep(props: VerifyEmailStepProps) {
             <Button
               variant='outline'
               color='neutral'
-              fullWidth
             />
           }
         >
@@ -283,7 +281,6 @@ function VerifyEmailStep(props: VerifyEmailStepProps) {
         </Dialog.Close>
         <SubmitButton
           form={verifyFormId}
-          fullWidth
           isPending={props.isPending}
           disabled={!props.canSubmit || props.isResending}
           pendingLabel={m.verify.pending}
@@ -332,7 +329,6 @@ function VerifyLinkStep(props: VerifyLinkStepProps) {
             <Button
               variant='outline'
               color='neutral'
-              fullWidth
             />
           }
         >
@@ -406,7 +402,6 @@ function VerifySsoStep(props: VerifySsoStepProps) {
             <Button
               variant='outline'
               color='neutral'
-              fullWidth
             />
           }
         >
diff --git a/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-authenticator.view.tsx b/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-authenticator.view.tsx
index 3a8a0d5c6b3..93d31879c45 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-authenticator.view.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-authenticator.view.tsx
@@ -78,7 +78,6 @@ export function UserProfileAddAuthenticatorView({
           type='button'
           variant='outline'
           color='neutral'
-          fullWidth
           disabled={isPending}
           onClick={onBack}
         >
@@ -88,7 +87,6 @@ export function UserProfileAddAuthenticatorView({
           ref={actionRef}
           type='submit'
           form={formId}
-          fullWidth
           isPending={isPending}
           disabled={code.length !== 6}
           focusableWhenDisabled
diff --git a/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-sms.view.tsx b/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-sms.view.tsx
index 1958a79f8d6..248625e1b6e 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-sms.view.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-add-sms.view.tsx
@@ -161,7 +161,6 @@ function SelectPhoneStep(props: UserProfileAddSmsViewProps & { inputRef?: Ref<HT
           type='button'
           variant='outline'
           color='neutral'
-          fullWidth
           disabled={props.isPending}
           onClick={props.onBack}
         >
@@ -169,7 +168,6 @@ function SelectPhoneStep(props: UserProfileAddSmsViewProps & { inputRef?: Ref<HT
         </Button>
         <SubmitButton
           form={formId}
-          fullWidth
           isPending={props.isPending}
           disabled={!props.selectedPhoneId}
           pendingLabel={m.pending}
diff --git a/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-backup-codes.view.tsx b/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-backup-codes.view.tsx
index b064ab5e121..c73bb012277 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-backup-codes.view.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-mfa-section/user-profile-backup-codes.view.tsx
@@ -104,7 +104,6 @@ export function UserProfileBackupCodesView({
                 type='button'
                 variant='outline'
                 color='neutral'
-                fullWidth
                 disabled={!hasCodes}
                 onClick={onPrint}
               >
@@ -115,7 +114,6 @@ export function UserProfileBackupCodesView({
               type='button'
               variant='outline'
               color='neutral'
-              fullWidth
               isPending={pendingAction === 'download'}
               disabled={!hasCodes || pendingAction === 'copy'}
               pendingLabel={m.downloading}
@@ -133,7 +131,6 @@ export function UserProfileBackupCodesView({
             type='button'
             variant='outline'
             color='neutral'
-            fullWidth
             disabled={Boolean(pendingAction)}
             onClick={onBack ?? onCancel}
           >
@@ -142,7 +139,6 @@ export function UserProfileBackupCodesView({
         )}
         <SubmitButton
           type='button'
-          fullWidth
           isPending={pendingAction === 'copy'}
           disabled={showSaveActions && (!hasCodes || pendingAction === 'download')}
           focusableWhenDisabled
diff --git a/packages/mosaic/src/features/user-profile/user-profile-passkeys-section/user-profile-rename-passkey.dialog.tsx b/packages/mosaic/src/features/user-profile/user-profile-passkeys-section/user-profile-rename-passkey.dialog.tsx
index e55d7b6cb89..56ef7c60a42 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-passkeys-section/user-profile-rename-passkey.dialog.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-passkeys-section/user-profile-rename-passkey.dialog.tsx
@@ -82,7 +82,6 @@ export function UserProfileRenamePasskeyDialog({
                 <Button
                   color='neutral'
                   variant='outline'
-                  fullWidth
                   disabled={form.isSubmitting}
                 >
                   {m.cancel}
@@ -91,7 +90,6 @@ export function UserProfileRenamePasskeyDialog({
             />
             <SubmitButton
               form={form.id}
-              fullWidth
               isPending={form.isSubmitting}
               disabled={!form.canSubmit}
               focusableWhenDisabled
diff --git a/packages/mosaic/src/features/user-profile/user-profile-password-section/user-profile-edit-password.dialog.tsx b/packages/mosaic/src/features/user-profile/user-profile-password-section/user-profile-edit-password.dialog.tsx
index 50a2799d07a..24d5c2f4274 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-password-section/user-profile-edit-password.dialog.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-password-section/user-profile-edit-password.dialog.tsx
@@ -121,7 +121,6 @@ export function UserProfileEditPasswordDialog({
             <Button
               variant='outline'
               color='neutral'
-              fullWidth
             >
               {m.cancel}
             </Button>
@@ -129,7 +128,6 @@ export function UserProfileEditPasswordDialog({
         />
         <SubmitButton
           form={form.id}
-          fullWidth
           isPending={form.isSubmitting}
           disabled={!form.canSubmit}
           focusableWhenDisabled
diff --git a/packages/mosaic/src/features/user-profile/user-profile-phone.steps.tsx b/packages/mosaic/src/features/user-profile/user-profile-phone.steps.tsx
index 4b909999d0c..b89641c7f0d 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-phone.steps.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-phone.steps.tsx
@@ -78,7 +78,6 @@ export function EnterPhoneStep(props: EnterPhoneStepProps) {
         {props.secondaryAction}
         <SubmitButton
           form={phoneFormId}
-          fullWidth
           disabled={!canSubmit}
           isPending={props.isPending}
           pendingLabel={m.phone.pending}
@@ -188,7 +187,6 @@ export function VerifyPhoneStep(props: VerifyPhoneStepProps) {
               <Button
                 variant='outline'
                 color='neutral'
-                fullWidth
               />
             }
           >
@@ -197,7 +195,6 @@ export function VerifyPhoneStep(props: VerifyPhoneStepProps) {
         )}
         <SubmitButton
           form={verifyFormId}
-          fullWidth
           isPending={props.isPending}
           disabled={!canSubmit || props.isResending}
           pendingLabel={m.verify.pending}
diff --git a/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-name.dialog.tsx b/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-name.dialog.tsx
index 07f10510048..2949ce14fac 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-name.dialog.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-name.dialog.tsx
@@ -109,7 +109,6 @@ export function UserProfileEditNameDialog({
                 <Button
                   variant='outline'
                   color='neutral'
-                  fullWidth
                 >
                   {m.name.cancel}
                 </Button>
@@ -117,7 +116,6 @@ export function UserProfileEditNameDialog({
             />
             <SubmitButton
               form={form.id}
-              fullWidth
               isPending={form.isSubmitting}
               disabled={!form.canSubmit}
               focusableWhenDisabled
diff --git a/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-username.dialog.tsx b/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-username.dialog.tsx
index 2f466e7b3e9..0e6af09f3e9 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-username.dialog.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-profile-section/user-profile-edit-username.dialog.tsx
@@ -74,7 +74,6 @@ export function UserProfileEditUsernameDialog({
             <Button
               variant='outline'
               color='neutral'
-              fullWidth
             >
               {m.cancel}
             </Button>
@@ -82,7 +81,6 @@ export function UserProfileEditUsernameDialog({
         />
         <SubmitButton
           form={form.id}
-          fullWidth
           isPending={form.isSubmitting}
           disabled={!form.canSubmit}
           focusableWhenDisabled
diff --git a/packages/mosaic/src/features/user-profile/user-profile-web3-wallets-section/user-profile-solana-wallet.view.tsx b/packages/mosaic/src/features/user-profile/user-profile-web3-wallets-section/user-profile-solana-wallet.view.tsx
index ffb75b244bd..c83ec69bdf9 100644
--- a/packages/mosaic/src/features/user-profile/user-profile-web3-wallets-section/user-profile-solana-wallet.view.tsx
+++ b/packages/mosaic/src/features/user-profile/user-profile-web3-wallets-section/user-profile-solana-wallet.view.tsx
@@ -79,7 +79,6 @@ export function UserProfileSolanaWalletView({
             <Button
               variant='outline'
               color='neutral'
-              fullWidth
               disabled={pending}
             >
               {m.solanaDialog.cancel}
diff --git a/packages/mosaic/src/features/waitlist/waitlist.view.tsx b/packages/mosaic/src/features/waitlist/waitlist.view.tsx
index b62a2c9fe1f..3ab11d17c8a 100644
--- a/packages/mosaic/src/features/waitlist/waitlist.view.tsx
+++ b/packages/mosaic/src/features/waitlist/waitlist.view.tsx
@@ -51,6 +51,7 @@ export function WaitlistView({ step, form, renderBranding, isRedirecting, onSign
             type='button'
             variant='link'
             size='sm'
+            fullWidth={false}
             onClick={onSignIn}
           >
             {m.signIn.action}
diff --git a/packages/swingset/src/app/(clerk)/live/misc/reverification/page.tsx b/packages/swingset/src/app/(clerk)/live/misc/reverification/page.tsx
index 82e3ba48662..dd2beab0f78 100644
--- a/packages/swingset/src/app/(clerk)/live/misc/reverification/page.tsx
+++ b/packages/swingset/src/app/(clerk)/live/misc/reverification/page.tsx
@@ -243,7 +243,6 @@ function DialogHarness() {
                     <Card.Footer>
                       <Button
                         color='negative'
-                        fullWidth
                         onClick={continueDelete}
                         disabled={requestPending}
                       >
diff --git a/packages/swingset/src/stories/card.component.mdx b/packages/swingset/src/stories/card.component.mdx
index 16d3e551269..3882d6984ef 100644
--- a/packages/swingset/src/stories/card.component.mdx
+++ b/packages/swingset/src/stories/card.component.mdx
@@ -31,6 +31,8 @@ import { Card } from '@clerk/mosaic/components/card';
 
 `Card.Banner` sits between the header and the content and is always rendered. While its children hold a message, a `Banner` of the given `color` expands into it; once they are empty it collapses again. Give it `role='alert'` so the message is announced.
 
+Buttons in `Card.Footer` are full width by default. Pass `fullWidth={false}` to opt out. A `Dialog.Popup` or `Popover.Popup` rendered inside the footer doesn't inherit this.
+
 ---
 
 ## Examples
diff --git a/packages/swingset/src/stories/card.component.stories.tsx b/packages/swingset/src/stories/card.component.stories.tsx
index 9e6aaa35483..69986e1c14f 100644
--- a/packages/swingset/src/stories/card.component.stories.tsx
+++ b/packages/swingset/src/stories/card.component.stories.tsx
@@ -48,7 +48,7 @@ export function Default(props: Record<string, unknown>) {
         </Field.Root>
       </Card.Content>
       <Card.Footer>
-        <Button fullWidth>Continue</Button>
+        <Button>Continue</Button>
       </Card.Footer>
     </Card.Root>
   );
diff --git a/packages/swingset/src/stories/dialog.component.mdx b/packages/swingset/src/stories/dialog.component.mdx
index 649bdd2f7b4..bf3662db30e 100644
--- a/packages/swingset/src/stories/dialog.component.mdx
+++ b/packages/swingset/src/stories/dialog.component.mdx
@@ -40,8 +40,8 @@ import { Dialog } from '@clerk/mosaic/components/dialog';
         <Card.Description>Are you sure you want to proceed?</Card.Description>
       </Card.Header>
       <Card.Footer>
-        <Dialog.Close render={<Button variant='outline' fullWidth />}>Cancel</Dialog.Close>
-        <Button fullWidth>Proceed</Button>
+        <Dialog.Close render={<Button variant='outline' />}>Cancel</Dialog.Close>
+        <Button>Proceed</Button>
       </Card.Footer>
     </Card.Root>
   </Dialog.Popup>
@@ -207,8 +207,8 @@ action as its submit.
   <Input value={name} onChange={…} />
 </Card.Content>
 <Card.Footer>
-  <Dialog.Close render={<Button variant='outline' fullWidth />}>Cancel</Dialog.Close>
-  <Button type='submit' form='update-profile' fullWidth>Save</Button>
+  <Dialog.Close render={<Button variant='outline' />}>Cancel</Dialog.Close>
+  <Button type='submit' form='update-profile'>Save</Button>
 </Card.Footer>
 ```
 
diff --git a/packages/swingset/src/stories/dialog.component.stories.tsx b/packages/swingset/src/stories/dialog.component.stories.tsx
index 8d455a6fa66..c4f67d6fcc8 100644
--- a/packages/swingset/src/stories/dialog.component.stories.tsx
+++ b/packages/swingset/src/stories/dialog.component.stories.tsx
@@ -122,21 +122,11 @@ export function Alert() {
             </Card.Description>
           </Card.Header>
           <Card.Footer>
-            <Dialog.Close
-              render={
-                <Button
-                  variant='outline'
-                  fullWidth
-                />
-              }
-            >
-              Cancel
-            </Dialog.Close>
+            <Dialog.Close render={<Button variant='outline' />}>Cancel</Dialog.Close>
             {/* Not a `Dialog.Close`: the action is where the work happens, so the caller closes
                 once it resolves rather than the button closing on press. */}
             <Button
               color='negative'
-              fullWidth
               onClick={() => setOpen(false)}
             >
               Delete organization
@@ -203,20 +193,10 @@ export function Sheet() {
             />
           </Card.Content>
           <Card.Footer>
-            <Dialog.Close
-              render={
-                <Button
-                  variant='outline'
-                  fullWidth
-                />
-              }
-            >
-              Cancel
-            </Dialog.Close>
+            <Dialog.Close render={<Button variant='outline' />}>Cancel</Dialog.Close>
             <Button
               type='submit'
               form='add-email'
-              fullWidth
             >
               Add
             </Button>
@@ -291,16 +271,7 @@ export function Stacked() {
                 tree — which is what escape ordering, the stacking styles and the refcounted
                 scroll lock all read. */}
             <Dialog.Root role='alertdialog'>
-              <Dialog.Trigger
-                render={
-                  <Button
-                    variant='outline'
-                    fullWidth
-                  />
-                }
-              >
-                Cancel
-              </Dialog.Trigger>
+              <Dialog.Trigger render={<Button variant='outline' />}>Cancel</Dialog.Trigger>
               <Dialog.Popup finalFocus={nameRef}>
                 <Card.Root
                   elevation='overlay'
@@ -311,19 +282,9 @@ export function Stacked() {
                     <Card.Description>Your edits will be lost.</Card.Description>
                   </Card.Header>
                   <Card.Footer>
-                    <Dialog.Close
-                      render={
-                        <Button
-                          variant='outline'
-                          fullWidth
-                        />
-                      }
-                    >
-                      Keep editing
-                    </Dialog.Close>
+                    <Dialog.Close render={<Button variant='outline' />}>Keep editing</Dialog.Close>
                     <Button
                       color='negative'
-                      fullWidth
                       onClick={close}
                     >
                       Discard
@@ -506,13 +467,12 @@ export function CardSurface() {
                 <Button
                   {...props}
                   variant='outline'
-                  fullWidth
                 >
                   Cancel
                 </Button>
               )}
             />
-            <Button fullWidth>Continue</Button>
+            <Button>Continue</Button>
           </Card.Footer>
         </Card.Root>
       </Dialog.Popup>
diff --git a/packages/swingset/src/stories/flow.component.stories.tsx b/packages/swingset/src/stories/flow.component.stories.tsx
index 82e2ddd514a..3c7348e1a42 100644
--- a/packages/swingset/src/stories/flow.component.stories.tsx
+++ b/packages/swingset/src/stories/flow.component.stories.tsx
@@ -38,12 +38,7 @@ function FlowDemo(): JSX.Element {
                 <Card.Description>Current controller state: {state.step}</Card.Description>
               </Card.Header>
               <Card.Footer>
-                <Button
-                  fullWidth
-                  onClick={() => navigate('confirm', 1)}
-                >
-                  Continue
-                </Button>
+                <Button onClick={() => navigate('confirm', 1)}>Continue</Button>
               </Card.Footer>
             </Flow.Step>
             <Flow.Step ids={['confirm']}>
@@ -56,14 +51,13 @@ function FlowDemo(): JSX.Element {
               </Card.Header>
               <Card.Footer>
                 <Button
-                  fullWidth
                   variant='outline'
                   color='neutral'
                   onClick={() => navigate('details', -1)}
                 >
                   Back
                 </Button>
-                <Button fullWidth>Submit</Button>
+                <Button>Submit</Button>
               </Card.Footer>
             </Flow.Step>
           </>
diff --git a/packages/swingset/src/stories/popover.component.mdx b/packages/swingset/src/stories/popover.component.mdx
index 53ea83deadd..6745e1545c0 100644
--- a/packages/swingset/src/stories/popover.component.mdx
+++ b/packages/swingset/src/stories/popover.component.mdx
@@ -28,7 +28,6 @@ import { Popover } from '@clerk/mosaic/components/popover';
       <Card.Footer>
         <Button
           color='negative'
-          fullWidth
         >
           Sign out of all accounts
         </Button>
diff --git a/packages/swingset/src/stories/popover.component.stories.tsx b/packages/swingset/src/stories/popover.component.stories.tsx
index 8b905825a19..ca59356498a 100644
--- a/packages/swingset/src/stories/popover.component.stories.tsx
+++ b/packages/swingset/src/stories/popover.component.stories.tsx
@@ -35,12 +35,7 @@ export function Default() {
             <Text>ada@example.com</Text>
           </Card.Header>
           <Card.Footer>
-            <Button
-              color='negative'
-              fullWidth
-            >
-              Sign out of all accounts
-            </Button>
+            <Button color='negative'>Sign out of all accounts</Button>
           </Card.Footer>
         </Card.Root>
       </Popover.Popup>
diff --git a/packages/swingset/src/stories/table.stories.tsx b/packages/swingset/src/stories/table.stories.tsx
index 2d863bab27e..946d3d51537 100644
--- a/packages/swingset/src/stories/table.stories.tsx
+++ b/packages/swingset/src/stories/table.stories.tsx
@@ -562,7 +562,6 @@ export function ClickableRows() {
                     render={
                       <Button
                         color='neutral'
-                        fullWidth
                         variant='outline'
                       />
                     }