diff --git a/resources/boost/skills/livewire-material-development/SKILL.md b/resources/boost/skills/livewire-material-development/SKILL.md
index 145cc8e0..359d50a8 100644
--- a/resources/boost/skills/livewire-material-development/SKILL.md
+++ b/resources/boost/skills/livewire-material-development/SKILL.md
@@ -280,7 +280,7 @@ Clusters: `<x-menu-separator />` draws M3's line, `<x-menu-group gap>` M3 Expres
 
 ### `<x-button-group>`
 
-A row of `<x-button>`s: `<x-button-group label="View" size="md">…</x-button-group>`. `connected` sets them 2px apart with small inner corners (a selected toggle rounds fully). Pass the `size` of the buttons inside.
+A row of `<x-button>`s: `<x-button-group label="View" size="md">…</x-button-group>`. `connected` sets them 2px apart with small inner corners (a selected toggle rounds fully). Pass the `size` of the buttons inside. `shape="square"` is M3's square group and covers every button in it, so do not write `shape` on each one: a connected group's ends square to the corner its inner edges take, a standard group's buttons take the square corner scale, and a selected button still rounds — M3 has the toggle morph the other way.
 
 ### `<x-group>`
 
@@ -294,7 +294,7 @@ A choice between a few options as a connected button group of native radios (che
 ]" hint="Recipients lose access after that" />
 ```
 
-Props: `label`, `hint`, `hint-class` (classes for the hint, as on the fields; a colour there paints it), `name` (required with `x-model`), `options`, `option-value` (`id`), `option-label` (`name`), `option-icon` (`icon`), `size`, `variant` (`tonal`, `filled`, `outlined`), `multiple`, `inline` (intrinsic width instead of sharing the row). A validation error for the bound property replaces the hint.
+Props: `label`, `hint`, `hint-class` (classes for the hint, as on the fields; a colour there paints it), `name` (required with `x-model`), `options`, `option-value` (`id`), `option-label` (`name`), `option-icon` (`icon`), `size`, `variant` (`tonal`, `filled`, `outlined`), `shape` (`round`, `square`), `multiple`, `inline` (intrinsic width instead of sharing the row). A validation error for the bound property replaces the hint.
 
 ### `<x-split-button>`
 
diff --git a/resources/css/components/groups.css b/resources/css/components/groups.css
index 6058a39a..de21ac79 100644
--- a/resources/css/components/groups.css
+++ b/resources/css/components/groups.css
@@ -13,6 +13,16 @@
  * full, the inner corners small, smaller still while pressed, and a selected segment fully round
  * (ConnectedButtonGroupSmallTokens and the M3 Expressive connected button group spec).
  *
+ * Shape (`shape="square"`, M3's "Default shape | Round, square" configuration): `--group-outer`
+ * is what the two ends of a group round to — half the height for a round group, and for a square
+ * one the same corner its inner edges take, which is the square table M3 publishes for connected
+ * groups (4/8/8/16/20dp by size). A square *standard* group has no inner edges, so it hands its
+ * buttons the square corner scale `<x-button shape="square">` draws (`--group-square`, and
+ * `--group-square-pressed` under the finger) instead of asking the caller to write it on each
+ * one. Selection morphs the other way in both: M3 has a toggle inside a group "swap shape
+ * square/round on selection", so a selected button in a square group turns round, which is why
+ * the selected rules keep `--group-full` rather than `--group-outer`.
+ *
  * Split button (`<x-split-button>`): the same idea for two halves, on its own corner scale —
  * SplitButton*Tokens gives the inner corner 4/4/4/8/12px at rest and *grows* it to 8/12/12/20/20px
  * under the finger, the opposite of a connected group, so `--split-inner*` is separate from
@@ -34,13 +44,32 @@
     --group-inner: var(--md-sys-shape-corner-sm);
     --group-inner-pressed: var(--md-sys-shape-corner-xs);
     --group-full: 1.25rem;
+    --group-square: var(--md-sys-shape-corner-md);
+    --group-square-pressed: var(--md-sys-shape-corner-sm);
+    --group-outer: var(--group-full);
 }
 
 [data-button-group][data-size='xs'] { --group-pad: 1rem; --group-grow: 4px; --group-inner: var(--md-sys-shape-corner-xs); --group-inner-pressed: 2px; --group-full: 1rem; }
 [data-button-group][data-size='sm'] { --group-pad: 1rem; --group-grow: 6px; --group-full: 1.25rem; }
-[data-button-group][data-size='md'] { --group-pad: 1.5rem; --group-grow: 8px; --group-full: 1.75rem; }
-[data-button-group][data-size='lg'] { --group-pad: 3rem; --group-grow: 16px; --group-inner: var(--md-sys-shape-corner-lg); --group-inner-pressed: var(--md-sys-shape-corner-md); --group-full: 3rem; }
-[data-button-group][data-size='xl'] { --group-pad: 4rem; --group-grow: 20px; --group-inner: var(--md-sys-shape-corner-lg-increased); --group-inner-pressed: var(--md-sys-shape-corner-lg); --group-full: 4.25rem; }
+[data-button-group][data-size='md'] { --group-pad: 1.5rem; --group-grow: 8px; --group-full: 1.75rem; --group-square: var(--md-sys-shape-corner-lg); --group-square-pressed: var(--md-sys-shape-corner-md); }
+[data-button-group][data-size='lg'] { --group-pad: 3rem; --group-grow: 16px; --group-inner: var(--md-sys-shape-corner-lg); --group-inner-pressed: var(--md-sys-shape-corner-md); --group-full: 3rem; --group-square: var(--md-sys-shape-corner-xl); --group-square-pressed: var(--md-sys-shape-corner-lg); }
+[data-button-group][data-size='xl'] { --group-pad: 4rem; --group-grow: 20px; --group-inner: var(--md-sys-shape-corner-lg-increased); --group-inner-pressed: var(--md-sys-shape-corner-lg); --group-full: 4.25rem; --group-square: var(--md-sys-shape-corner-xl); --group-square-pressed: var(--md-sys-shape-corner-lg); }
+
+/* A square group's ends take the corner its inner edges take — M3's square table for connected
+   groups — and a square standard group hands its buttons the button's own square scale. */
+[data-button-group][data-shape='square'] { --group-outer: var(--group-inner); }
+
+[data-button-group='standard'][data-shape='square'] > * {
+    border-radius: var(--group-square);
+}
+
+[data-button-group='standard'][data-shape='square'] > :active:not(:disabled, [aria-disabled='true']) {
+    border-radius: var(--group-square-pressed);
+}
+
+[data-button-group='standard'][data-shape='square'] > [aria-pressed='true'] {
+    border-radius: var(--group-full);
+}
 
 [data-button-group='standard'] > :not([data-icon-button]):active:not(:disabled, [aria-disabled='true']) {
     padding-inline: calc(var(--group-pad) + var(--group-grow));
@@ -107,14 +136,14 @@
 
 [data-button-group='connected'] > :first-child,
 [data-split='leading'] {
-    border-start-start-radius: var(--group-full);
-    border-end-start-radius: var(--group-full);
+    border-start-start-radius: var(--group-outer);
+    border-end-start-radius: var(--group-outer);
 }
 
 [data-button-group='connected'] > :last-child,
 [data-split='trailing'] {
-    border-start-end-radius: var(--group-full);
-    border-end-end-radius: var(--group-full);
+    border-start-end-radius: var(--group-outer);
+    border-end-end-radius: var(--group-outer);
 }
 
 /*
diff --git a/resources/views/components/button-group.blade.php b/resources/views/components/button-group.blade.php
index 8a670aa5..f8935067 100644
--- a/resources/views/components/button-group.blade.php
+++ b/resources/views/components/button-group.blade.php
@@ -11,6 +11,13 @@
      the size of the buttons inside, so the spacing and corners match. For a choice bound to a
      property, `<x-group>` draws a connected group of radios.
 
+     `shape` is M3's "Default shape | Round, square" configuration, and covers every button in the
+     group so it need not be written on each one: `square` squares a connected group's two ends to
+     the corner its inner edges take (M3's square table, 4/8/8/16/20dp by size) and gives a
+     standard group's buttons the square corner scale `<x-button shape="square">` draws. Selection
+     still morphs the other way — M3 has a toggle inside a group "swap shape square/round on
+     selection" — so a selected button in a square group rounds.
+
      A group never wraps to a second line — M3's rule, and the press expansion only reaches a
      neighbour on the same line anyway. Where a row is too long for its window the answer is a
      smaller `size` or fewer buttons, or two groups stacked.
@@ -22,10 +29,12 @@
     'connected' => false,
     'size' => 'sm',
     'label' => null,
+    'shape' => 'round',
 ])
 
 @php
     $size = in_array($size, ['xs', 'sm', 'md', 'lg', 'xl'], true) ? $size : 'sm';
+    $shape = $shape === 'square' ? 'square' : 'round';
 @endphp
 
 <div
@@ -33,6 +42,7 @@
     @if ($label) aria-label="{{ $label }}" @endif
     data-button-group="{{ $connected ? 'connected' : 'standard' }}"
     data-size="{{ $size }}"
+    data-shape="{{ $shape }}"
     {{ $attributes->class([
         'inline-flex items-center',
         'gap-0.5' => $connected,
diff --git a/resources/views/components/group.blade.php b/resources/views/components/group.blade.php
index d5bbef1e..c64e453e 100644
--- a/resources/views/components/group.blade.php
+++ b/resources/views/components/group.blade.php
@@ -15,9 +15,14 @@
      you never to reduce. Corners move on the spatial spring and colours on the effects one
      (`state-transition-fast`).
 
+     `shape` is M3's "Default shape | Round, square" configuration: `square` squares the two ends
+     of the group to the corner its inner edges take (M3's square table, 4/8/8/16/20dp by size),
+     and the chosen segment still rounds fully, so selection reads the same either way.
+
      ReStride's props, kept: `label`, `hint`, `hint-class`, `name` (needed with `x-model`, which
      names no property), `options`, `option-value`, `option-label`; plus `option-icon`, `size`,
-     `variant`, `multiple`, `inline`. A validation message for the bound property replaces the hint.
+     `variant`, `shape`, `multiple`, `inline`. A validation message for the bound property replaces
+     the hint.
 
      `hint-class` adds classes to the hint, as on `<x-field>`: a colour there paints it
      (`hint-class="text-warning"` for a hint that warns). The hint's own colour then carries no
@@ -35,6 +40,7 @@
     'optionIcon' => 'icon',
     'size' => 'sm',
     'variant' => 'tonal',
+    'shape' => 'round',
     'multiple' => false,
     'inline' => false,
 ])
@@ -46,6 +52,9 @@
     $errorKey = $model ?? (filled($attributes->get('name')) ? str_replace(['[]', '[', ']'], ['', '.', ''], (string) $attributes->get('name')) : null);
     $messages = $errorKey !== null && isset($errors) ? \Illuminate\Support\Arr::flatten($errors->get($errorKey)) : [];
     $size = in_array($size, ['xs', 'sm', 'md', 'lg', 'xl'], true) ? $size : 'sm';
+    // M3's "Default shape | Round, square": a square group's ends take the corner its inner edges
+    // take; the chosen segment still rounds fully, which is the cue selection has always carried.
+    $shape = $shape === 'square' ? 'square' : 'round';
     // M3: an xs or sm connected segment keeps a 48px target and a 48px minimum width, whatever
     // its 32px/40px container measures. From md the segment is wider than that on its own.
     $small = in_array($size, ['xs', 'sm'], true);
@@ -78,7 +87,7 @@
         <legend class="mb-2 type-label-lg text-on-surface-variant">{{ $label }}</legend>
     @endif
 
-    <div data-button-group="connected" data-size="{{ $size }}" @class(['flex gap-0.5', 'w-full' => ! $inline, 'w-fit' => $inline])>
+    <div data-button-group="connected" data-size="{{ $size }}" data-shape="{{ $shape }}" @class(['flex gap-0.5', 'w-full' => ! $inline, 'w-fit' => $inline])>
         @foreach ($options as $option)
             <label @class([
                 'state-layer relative flex cursor-pointer select-none items-center justify-center whitespace-nowrap',
diff --git a/resources/views/showcase/sections/buttons.blade.php b/resources/views/showcase/sections/buttons.blade.php
index cc9d634e..69bd916b 100644
--- a/resources/views/showcase/sections/buttons.blade.php
+++ b/resources/views/showcase/sections/buttons.blade.php
@@ -76,6 +76,27 @@
                 <x-button icon="format_underlined" aria-label="Underline" variant="tonal" :selected="false" />
             </x-button-group>
             BLADE,
+        'Square groups (hold a button down)' => <<<'BLADE'
+            <x-button-group label="Square standard" size="md" shape="square">
+                <x-button label="Day" variant="tonal" size="md" />
+                <x-button label="Week" variant="tonal" size="md" />
+                <x-button label="Month" variant="tonal" size="md" />
+            </x-button-group>
+
+            <x-button-group label="Square formatting" connected shape="square">
+                <x-button icon="format_bold" aria-label="Bold" variant="tonal" :selected="true" />
+                <x-button icon="format_italic" aria-label="Italic" variant="tonal" :selected="false" />
+                <x-button icon="format_underlined" aria-label="Underline" variant="tonal" :selected="false" />
+            </x-button-group>
+
+            <div x-data="{ density: 'cosy' }" class="w-full">
+                <x-group label="Density" name="showcase-density" shape="square" x-model="density" inline :options="[
+                    ['id' => 'compact', 'name' => 'Compact'],
+                    ['id' => 'cosy', 'name' => 'Cosy'],
+                    ['id' => 'roomy', 'name' => 'Roomy'],
+                ]" />
+            </div>
+            BLADE,
         'A choice as a connected group' => <<<'BLADE'
             <div x-data="{ theme: 'system', days: ['mon'] }" class="grid w-full gap-6 medium:grid-cols-2">
                 <x-group label="Theme" name="showcase-theme" x-model="theme" :options="[
diff --git a/tests/Feature/Components/ButtonGroupTest.php b/tests/Feature/Components/ButtonGroupTest.php
index fbf43af5..d5eb2896 100644
--- a/tests/Feature/Components/ButtonGroupTest.php
+++ b/tests/Feature/Components/ButtonGroupTest.php
@@ -20,6 +20,22 @@ it('connects buttons 2px apart', function () {
         ->toContain('gap-0.5');
 });
 
+it('squares a group, and a choice drawn as one', function () {
+    // M3 lists "Default shape | Round, square" as a button-group configuration; the shape covers
+    // every button in the group, so it need not be written on each one.
+    expect((string) $this->blade('<x-button-group shape="square"><x-button label="Day" /></x-button-group>'))
+        ->toContain('data-shape="square"')
+        ->and((string) $this->blade('<x-button-group connected shape="square"><x-button label="Day" /></x-button-group>'))
+        ->toContain('data-button-group="connected"')
+        ->toContain('data-shape="square"')
+        ->and((string) $this->blade('<x-button-group><x-button label="Day" /></x-button-group>'))
+        ->toContain('data-shape="round"')
+        ->and((string) $this->blade('<x-group shape="square" name="x" :options="[[\'id\' => \'a\', \'name\' => \'A\']]" />'))
+        ->toContain('data-shape="square"')
+        ->and((string) $this->blade('<x-group name="x" :options="[[\'id\' => \'a\', \'name\' => \'A\']]" />'))
+        ->toContain('data-shape="round"');
+});
+
 it('never wraps a group onto a second line', function () {
     expect((string) $this->blade('<x-button-group><x-button label="Day" /></x-button-group>'))
         ->not->toContain('flex-wrap');