diff --git a/package.json b/package.json
index b81ca3cde11..48dece8de52 100644
--- a/package.json
+++ b/package.json
@@ -183,7 +183,7 @@
     {
       "path": "lib/components/internal/widget-exports.js",
       "brotli": false,
-      "limit": "1450 kB",
+      "limit": "1470 kB",
       "ignore": "react-dom"
     }
   ],
diff --git a/pages/control-group/validation.page.tsx b/pages/control-group/validation.page.tsx
new file mode 100644
index 00000000000..8f679e789ed
--- /dev/null
+++ b/pages/control-group/validation.page.tsx
@@ -0,0 +1,63 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+import React from 'react';
+
+import FormField from '~components/form-field';
+import ControlGroup, { ControlGroupProps } from '~components/internal/components/control-group';
+
+import { PermutationsPage } from '../app/templates';
+import createPermutations from '../utils/permutations';
+import PermutationsView from '../utils/permutations-view';
+import { input, multiselect, segmentedControl, select } from './common';
+
+type ValidationPermutation = ControlGroupProps & { errorText?: string; warningText?: string };
+
+const children = [
+  <>
+    {input}
+    {select}
+  </>,
+  <>
+    {input}
+    {segmentedControl}
+  </>,
+  <>
+    {select}
+    {multiselect}
+  </>,
+];
+
+const directions: ReadonlyArray<ControlGroupProps['direction']> = ['horizontal', 'vertical'];
+
+const actionButtons: ReadonlyArray<ControlGroupProps['actionButton']> = [
+  undefined,
+  { iconName: 'remove', ariaLabel: 'Remove' },
+];
+
+const labels = [undefined, 'Label'];
+
+const permutations = createPermutations<ValidationPermutation>([
+  { children, errorText: ['This value is required'], direction: directions, actionButton: actionButtons },
+  {
+    children,
+    warningText: ['Double-check this value'],
+    direction: directions,
+    actionButton: actionButtons,
+    inlineLabelText: labels,
+  },
+]);
+
+export default function ControlGroupValidation() {
+  return (
+    <PermutationsPage title="Control group validation" i18n={{}}>
+      <PermutationsView
+        permutations={permutations}
+        render={({ errorText, warningText, ...controlGroupProps }) => (
+          <FormField errorText={errorText} warningText={warningText}>
+            <ControlGroup {...controlGroupProps} />
+          </FormField>
+        )}
+      />
+    </PermutationsPage>
+  );
+}
diff --git a/pages/multiselect/validation-focus.page.tsx b/pages/multiselect/validation-focus.page.tsx
new file mode 100644
index 00000000000..15cad0242b3
--- /dev/null
+++ b/pages/multiselect/validation-focus.page.tsx
@@ -0,0 +1,46 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+import React from 'react';
+
+import Multiselect from '~components/multiselect';
+import SpaceBetween from '~components/space-between';
+
+import { SimplePage } from '../app/templates';
+import FocusTarget from '../common/focus-target';
+
+const options = [
+  { value: 'option1', label: 'Option 1' },
+  { value: 'option2', label: 'Option 2' },
+  { value: 'option3', label: 'Option 3' },
+];
+
+export default function MultiselectValidationFocusPage() {
+  return (
+    <SimplePage
+      title="Multiselect validation focus"
+      screenshotArea={{ disableAnimations: true }}
+      settings={<FocusTarget />}
+    >
+      <SpaceBetween size="m">
+        <Multiselect
+          data-testid="multiselect-invalid"
+          ariaLabel="multiselect invalid"
+          invalid={true}
+          options={options}
+          selectedOptions={[]}
+          placeholder="Choose options"
+          onChange={() => {}}
+        />
+        <Multiselect
+          data-testid="multiselect-warning"
+          ariaLabel="multiselect warning"
+          warning={true}
+          options={options}
+          selectedOptions={[]}
+          placeholder="Choose options"
+          onChange={() => {}}
+        />
+      </SpaceBetween>
+    </SimplePage>
+  );
+}
diff --git a/pages/select/validation-focus.page.tsx b/pages/select/validation-focus.page.tsx
new file mode 100644
index 00000000000..304e14d3293
--- /dev/null
+++ b/pages/select/validation-focus.page.tsx
@@ -0,0 +1,42 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+import React from 'react';
+
+import Select from '~components/select';
+import SpaceBetween from '~components/space-between';
+
+import { SimplePage } from '../app/templates';
+import FocusTarget from '../common/focus-target';
+
+const options = [
+  { value: 'option1', label: 'Option 1' },
+  { value: 'option2', label: 'Option 2' },
+  { value: 'option3', label: 'Option 3' },
+];
+
+export default function SelectValidationFocusPage() {
+  return (
+    <SimplePage title="Select validation focus" screenshotArea={{ disableAnimations: true }} settings={<FocusTarget />}>
+      <SpaceBetween size="m">
+        <Select
+          data-testid="select-invalid"
+          ariaLabel="select invalid"
+          invalid={true}
+          options={options}
+          selectedOption={null}
+          placeholder="Choose an option"
+          onChange={() => {}}
+        />
+        <Select
+          data-testid="select-warning"
+          ariaLabel="select warning"
+          warning={true}
+          options={options}
+          selectedOption={null}
+          placeholder="Choose an option"
+          onChange={() => {}}
+        />
+      </SpaceBetween>
+    </SimplePage>
+  );
+}
diff --git a/src/button/styles.scss b/src/button/styles.scss
index e77ee13e364..3b701539502 100644
--- a/src/button/styles.scss
+++ b/src/button/styles.scss
@@ -10,6 +10,7 @@
 @use '../internal/generated/custom-css-properties/index.scss' as custom-props;
 @use '@cloudscape-design/component-toolkit/internal/focus-visible' as focus-visible;
 @use './constants' as constants;
+@use '../internal/styles/forms/constants' as form-constants;
 @use '../internal/styles/style-api' as style-api;
 
 $props: style-api.combine(style-api.$surface, (box-shadow, padding-block, padding-inline), style-api.$focus-ring);
@@ -100,6 +101,9 @@ $tokens: style-api.resolve($props, carrier);
   @include styles.styles-reset;
   @include styles.text-wrapping;
   @include styles.font-button;
+
+  $focus-border-color: var(#{custom-props.$styleFocusRingBorderColor}, awsui.$color-border-item-focused);
+
   letter-spacing: awsui.$font-button-letter-spacing;
   border-start-start-radius: style-api.value($tokens, border-radius, awsui.$border-radius-button);
   border-start-end-radius: style-api.value($tokens, border-radius, awsui.$border-radius-button);
@@ -128,10 +132,9 @@ $tokens: style-api.resolve($props, carrier);
   @include focus-visible.when-visible {
     $radius: var(#{custom-props.$styleFocusRingBorderRadius}, awsui.$border-radius-control-default-focus-ring);
     $width: var(#{custom-props.$styleFocusRingBorderWidth}, foundation.$box-shadow-focused-width);
-    $color: var(#{custom-props.$styleFocusRingBorderColor}, awsui.$color-border-item-focused);
 
     &:not(.variant-control-group-action) {
-      @include style-api.focus-highlight($radius: $radius, $width: $width, $color: $color);
+      @include style-api.focus-highlight($radius: $radius, $width: $width, $color: $focus-border-color);
     }
 
     &.variant-icon,
@@ -141,7 +144,7 @@ $tokens: style-api.resolve($props, carrier);
         $gutter-block: awsui.$space-button-icon-focus-outline-gutter-vertical,
         $radius: $radius,
         $width: $width,
-        $color: $color
+        $color: $focus-border-color
       );
     }
 
@@ -152,14 +155,7 @@ $tokens: style-api.resolve($props, carrier);
         $gutter-inline: awsui.$space-button-inline-icon-focus-outline-gutter,
         $radius: $radius,
         $width: $width,
-        $color: $color
-      );
-    }
-
-    &.variant-control-group-action {
-      @include styles.form-focus-element(
-        $border-color: $color,
-        $box-shadow: var(#{custom-props.$styleBoxShadowFocus}, foundation.$box-shadow-focused-light)
+        $color: $focus-border-color
       );
     }
   }
@@ -219,6 +215,18 @@ $tokens: style-api.resolve($props, carrier);
     padding-block: awsui.$space-field-vertical;
     padding-inline: awsui.$space-xs;
     min-block-size: awsui.$size-vertical-input;
+
+    &,
+    &:hover {
+      border-inline-start-color: transparent;
+    }
+
+    @include focus-visible.when-visible {
+      @include styles.form-focus-element(
+        $border-color: $focus-border-color,
+        $box-shadow: var(#{custom-props.$styleBoxShadowFocus}, foundation.$box-shadow-focused-light)
+      );
+    }
   }
 
   > .icon-left {
diff --git a/src/input/styles.scss b/src/input/styles.scss
index 9236921d3aa..c5814aad830 100644
--- a/src/input/styles.scss
+++ b/src/input/styles.scss
@@ -162,7 +162,15 @@
       var(#{custom-props.$styleColorDefault}, awsui.$color-text-form-secondary)
     );
     background-color: var(#{custom-props.$styleBackgroundFocus}, awsui.$color-background-input-default);
-    @include styles.input-focus-styles;
+    &:not(.grouped-validation) {
+      @include styles.input-focus-styles;
+    }
+    &.grouped-validation {
+      @include styles.form-focus-element(
+        $border-color: false,
+        $box-shadow: var(#{custom-props.$styleBoxShadowFocus}, foundation.$box-shadow-focused-light)
+      );
+    }
   }
 
   // Keep disabled styles before validation modifiers so invalid/warning border colors win when both modifiers are present.
@@ -186,6 +194,9 @@
     }
 
     &:focus-within {
+      // Re-assert the validation border under focus so the neutral focus color
+      // (.input-field:focus-within, equal specificity) does not win by order.
+      border-color: var(#{custom-props.$styleBorderColorDefault}, awsui.$color-text-status-error);
       box-shadow: var(#{custom-props.$styleBoxShadowFocus}, foundation.$box-shadow-focused-light-invalid);
     }
   }
@@ -200,6 +211,9 @@
     }
 
     &:focus-within {
+      // Re-assert the validation border under focus so the neutral focus color
+      // (.input-field:focus-within, equal specificity) does not win by order.
+      border-color: var(#{custom-props.$styleBorderColorDefault}, awsui.$color-text-status-warning);
       box-shadow: var(#{custom-props.$styleBoxShadowFocus}, foundation.$box-shadow-focused-light-invalid);
     }
   }
@@ -226,6 +240,15 @@
 
   &.grouped {
     @include styles.grouped-control;
+
+    // The grouped inset (bar + cph) assumes a single-element control. Input's
+    // inner native .input already supplies its own cph, so the wrapper adds only
+    // one border width; wrapper(1px) + inner(cph) nets the same bar + invalid gap
+    // as single-element controls. The doubled selector matches the grouped-control
+    // validation rule's specificity and wins by source order.
+    &#{&}-validation {
+      padding-inline-start: awsui.$border-width-field;
+    }
   }
 }
 
@@ -262,8 +285,11 @@
   cursor: default;
 }
 
-// The wider invalid/warning start border is absorbed by the first cell, so the content does not shift.
-// The first cell is the prefix when present, otherwise the native input.
+// Standalone only: the wider invalid/warning start border is absorbed by the first
+// cell, so the content does not shift. The first cell is the prefix when present,
+// otherwise the native input. Grouped controls keep their 1px gray border under the
+// overlay bar and get their inset from the grouped wrapper, so the inner cell keeps
+// its normal cph (no re-pad here).
 .input-field-invalid,
 .input-field-warning {
   > .input-prefix,
diff --git a/src/internal/components/button-trigger/styles.scss b/src/internal/components/button-trigger/styles.scss
index d550bb574ee..87bc1a862fe 100644
--- a/src/internal/components/button-trigger/styles.scss
+++ b/src/internal/components/button-trigger/styles.scss
@@ -128,8 +128,10 @@ $icon-offset: awsui.$space-xxxs;
   }
 
   &:not(.in-filtering-token):not(.compact) {
-    @include focus-visible.when-visible {
-      @include styles.form-focus-element();
+    &:not(.grouped) {
+      @include focus-visible.when-visible {
+        @include styles.form-focus-element();
+      }
     }
 
     &:invalid {
@@ -146,6 +148,15 @@ $icon-offset: awsui.$space-xxxs;
     &.warning:focus {
       @include styles.form-warning-control();
     }
+
+    @include focus-visible.when-visible {
+      &.invalid {
+        border-color: awsui.$color-text-status-error;
+      }
+      &.warning {
+        border-color: awsui.$color-text-status-warning;
+      }
+    }
   }
 
   &.custom-option {
diff --git a/src/internal/components/control-group/grouped-control-styles.ts b/src/internal/components/control-group/grouped-control-styles.ts
index 0f6f81f7e12..08a3a999d06 100644
--- a/src/internal/components/control-group/grouped-control-styles.ts
+++ b/src/internal/components/control-group/grouped-control-styles.ts
@@ -11,11 +11,25 @@ import { GroupedControlContextProps } from '../../context/control-group-context'
  */
 export function getGroupedControlClassNames(
   styles: Record<string, string>,
-  { position, direction, hasAction }: GroupedControlContextProps
+  { position, direction, hasAction, validation }: GroupedControlContextProps
 ): string[] {
   if (!position) {
     return [];
   }
-  const baseClassNames = [styles.grouped, styles[`grouped-${direction}-${position}`]];
-  return hasAction ? [...baseClassNames, styles['grouped-with-action']] : baseClassNames;
+  const classNames = [styles.grouped, styles[`grouped-${direction}-${position}`]];
+  if (hasAction) {
+    classNames.push(styles['grouped-with-action']);
+  }
+  if (validation) {
+    // State class drives the outward validation color (and invalid ring) in SCSS.
+    // Every control gets it so each re-asserts its own outward edges on focus.
+    classNames.push(validation === 'error' ? styles['grouped-in-error'] : styles['grouped-in-warning']);
+    // Only the leading (inline-start) controls draw the thick validation seam:
+    // the first/only control horizontally, every control vertically.
+    const isLeading = direction === 'vertical' || position === 'first' || position === 'only';
+    if (isLeading) {
+      classNames.push(styles['grouped-validation']);
+    }
+  }
+  return classNames;
 }
diff --git a/src/internal/components/control-group/index.tsx b/src/internal/components/control-group/index.tsx
index ca3da291077..bc3089d494f 100644
--- a/src/internal/components/control-group/index.tsx
+++ b/src/internal/components/control-group/index.tsx
@@ -8,6 +8,7 @@ import { useUniqueId } from '@cloudscape-design/component-toolkit/internal';
 import { InternalButton } from '../../../button/internal';
 import { getBaseProps } from '../../base-component';
 import { GroupedControlContext, GroupedControlPosition } from '../../context/control-group-context';
+import { FormFieldContext, useFormFieldContext } from '../../context/form-field-context';
 import { flattenChildren } from '../../utils/flatten-children';
 import { ControlGroupProps } from './interfaces';
 
@@ -26,6 +27,10 @@ export default function ControlGroup({
   const baseProps = getBaseProps(props);
   const labelId = useUniqueId('control-group-label');
 
+  const formFieldContext = useFormFieldContext({});
+  const isInvalid = !!formFieldContext.invalid;
+  const isWarning = !!formFieldContext.warning && !isInvalid;
+
   const flattenedChildren = flattenChildren(children, 'ControlGroup');
   const controlCount = flattenedChildren.length;
 
@@ -38,6 +43,7 @@ export default function ControlGroup({
       className={clsx(
         styles.controls,
         styles[`controls-${direction}`],
+        actionButton && styles['controls-with-action'],
         !actionButton && !inlineLabelText && rootClassnames
       )}
     >
@@ -45,13 +51,33 @@ export default function ControlGroup({
         const key = child && typeof child === 'object' ? (child as Record<'key', unknown>).key : undefined;
         const position: GroupedControlPosition =
           controlCount === 1 ? 'only' : index === 0 ? 'first' : index === controlCount - 1 ? 'last' : 'middle';
+        // Only the leading (inline-start) slots host the thick validation bar:
+        // the first/only control horizontally, every control vertically. Mirrors
+        // the isLeading rule in grouped-control-styles.ts.
+        const isLeading = direction === 'vertical' || position === 'first' || position === 'only';
         return (
           <div
             key={key ? String(key) : index}
-            className={clsx(styles.control, styles[`control-${position}-${direction}`])}
+            className={clsx(
+              styles.control,
+              styles[`control-${position}-${direction}`],
+              isLeading && (isInvalid || isWarning) && styles['control-validation'],
+              isLeading && isInvalid && styles['control-in-error'],
+              isLeading && isWarning && styles['control-in-warning']
+            )}
           >
-            <GroupedControlContext.Provider value={{ position, direction, hasAction: !!actionButton }}>
-              {child}
+            <GroupedControlContext.Provider
+              value={{
+                position,
+                direction,
+                hasAction: !!actionButton,
+                validation: isInvalid ? 'error' : isWarning ? 'warning' : null,
+              }}
+            >
+              {/* Mask the form-field flags so inner controls do not color their own seams. */}
+              <FormFieldContext.Provider value={{ ...formFieldContext, invalid: false, warning: false }}>
+                {child}
+              </FormFieldContext.Provider>
             </GroupedControlContext.Provider>
           </div>
         );
@@ -67,7 +93,7 @@ export default function ControlGroup({
       {controls}
       <div className={styles['action-slot']}>
         <InternalButton
-          className={testUtilStyles['action-button']}
+          className={clsx(testUtilStyles['action-button'])}
           variant="control-group-action"
           formAction="none"
           iconName={actionButton.iconName}
diff --git a/src/internal/components/control-group/styles.scss b/src/internal/components/control-group/styles.scss
index 7e0d69b2f7f..72b3a1144f7 100644
--- a/src/internal/components/control-group/styles.scss
+++ b/src/internal/components/control-group/styles.scss
@@ -6,6 +6,7 @@
 @use '../../styles' as styles;
 @use '../../styles/tokens' as awsui;
 @use '../../styles/forms/mixins' as forms;
+@use '../../styles/forms/constants' as constants;
 
 $margin-overlap: calc(-1 * #{awsui.$border-width-field});
 
@@ -66,6 +67,53 @@ $margin-overlap: calc(-1 * #{awsui.$border-width-field});
       margin-block-start: $margin-overlap;
     }
   }
+
+  // Thick leading validation bar. Drawn on the slot <div> (not the control) so it
+  // is a flat rectangle that cannot miter against the control's thin block seams
+  // and renders for replaced-element controls (Input/Autosuggest). Offset one
+  // border width outboard and widened to match so it sits flush with the control's
+  // outer edge and overpaints the control's 1px gray leading border. z-index: 1
+  // keeps it above the control's border/box-shadow phase; the slot's own
+  // isolation keeps it from reaching an adjacent slot.
+  &-validation {
+    position: relative;
+
+    &::before {
+      content: '';
+      position: absolute;
+      inset-block: 0;
+      inline-size: calc(#{constants.$invalid-control-left-border} + #{awsui.$border-width-field});
+      z-index: 1;
+    }
+
+    // Per-position leading corner radii. border-radius is not inherited and the
+    // slot carries none, so match the leading corners each position rounds in
+    // grouped-control.scss so the bar's rounded corners coincide with the group's
+    // outer corners (and stay square where the group is square).
+    // Leading horizontal positions (first/only) round both leading corners.
+    &.control-first-horizontal::before,
+    &.control-only-horizontal::before,
+    &.control-only-vertical::before {
+      border-start-start-radius: constants.$control-border-radius;
+      border-end-start-radius: constants.$control-border-radius;
+    }
+    // Vertical first rounds only the top-leading corner.
+    &.control-first-vertical::before {
+      border-start-start-radius: constants.$control-border-radius;
+    }
+    // Vertical last rounds only the bottom-leading corner.
+    &.control-last-vertical::before {
+      border-end-start-radius: constants.$control-border-radius;
+    }
+    // Vertical middle rounds neither (no radius rule needed).
+
+    &.control-in-error::before {
+      background-color: awsui.$color-text-status-error;
+    }
+    &.control-in-warning::before {
+      background-color: awsui.$color-text-status-warning;
+    }
+  }
 }
 
 .action-slot,
diff --git a/src/internal/context/control-group-context.tsx b/src/internal/context/control-group-context.tsx
index 7acd0a97818..089ee2eb095 100644
--- a/src/internal/context/control-group-context.tsx
+++ b/src/internal/context/control-group-context.tsx
@@ -6,6 +6,8 @@ export type GroupedControlPosition = 'first' | 'middle' | 'last' | 'only';
 
 export type GroupedControlDirection = 'horizontal' | 'vertical';
 
+export type GroupedControlValidation = 'error' | 'warning';
+
 export interface GroupedControlContextProps {
   /**
    * The control's position within a control group,
@@ -22,12 +24,19 @@ export interface GroupedControlContextProps {
    * inline-end corners facing the action so it owns the only rounded ones.
    */
   hasAction?: boolean;
+  /**
+   * The surrounding control group's validation state, or `null` for none. The
+   * group owns the validation border; individual controls do not independently
+   * paint it.
+   */
+  validation?: GroupedControlValidation | null;
 }
 
 export const GroupedControlContext = createContext<GroupedControlContextProps>({
   position: null,
   direction: 'horizontal',
   hasAction: false,
+  validation: null,
 });
 
 export function useGroupedControlContext() {
@@ -41,11 +50,15 @@ export function useGroupedControlContext() {
  * content) should wrap that content with this provider. Otherwise a nested
  * control rendered inside such a slot would inherit the surrounding group's
  * `position` and incorrectly pick up the grouped-control styling
- * where adjacent borders lose their border radii.
+ * where adjacent borders lose their border radii. The group's `validation`
+ * state is also cleared so nested custom-slot controls never inherit the
+ * group's validation styling.
  */
 export function ResetGroupedControlContext({ children }: { children: React.ReactNode }) {
   const { direction } = useGroupedControlContext();
   return (
-    <GroupedControlContext.Provider value={{ position: null, direction }}>{children}</GroupedControlContext.Provider>
+    <GroupedControlContext.Provider value={{ position: null, direction, validation: null }}>
+      {children}
+    </GroupedControlContext.Provider>
   );
 }
diff --git a/src/internal/generated/styles/tokens.d.ts b/src/internal/generated/styles/tokens.d.ts
index b42ce787d0a..c29e9bbf787 100644
--- a/src/internal/generated/styles/tokens.d.ts
+++ b/src/internal/generated/styles/tokens.d.ts
@@ -62,6 +62,10 @@ export const colorChartsThresholdPositive: string;
 export const colorChartsThresholdInfo: string;
 export const colorChartsThresholdNeutral: string;
 
+// Status text colors
+export const colorTextStatusError: string;
+export const colorTextStatusWarning: string;
+
 // Spacing
 export const spaceXs: string;
 export const spaceXxs: string;
diff --git a/src/internal/styles/forms/grouped-control.scss b/src/internal/styles/forms/grouped-control.scss
index 2e29f0808ea..58a3dd2f92f 100644
--- a/src/internal/styles/forms/grouped-control.scss
+++ b/src/internal/styles/forms/grouped-control.scss
@@ -1,12 +1,61 @@
 // Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
+@use 'sass:list';
 @use '../tokens' as awsui;
 @use '../utils' as styles;
+@use '../foundation' as foundation;
 @use './constants' as constants;
+@use '@cloudscape-design/component-toolkit/internal/focus-visible' as focus-visible;
 
 $grouped-control-border-radius: constants.$control-border-radius;
 
+$grouped-control-error-marker: '.grouped-in-error';
+$grouped-control-warning-marker: '.grouped-in-warning';
+
+// Sets the given color on the outward-facing border edges of `$edges`.
+// Inner borders stay neutral.
+@mixin grouped-control-edge-color($edges, $color) {
+  @if list.index($edges, inline-start) {
+    border-inline-start-color: $color;
+  }
+  @if list.index($edges, inline-end) {
+    border-inline-end-color: $color;
+  }
+  @if list.index($edges, block-start) {
+    border-block-start-color: $color;
+  }
+  @if list.index($edges, block-end) {
+    border-block-end-color: $color;
+  }
+}
+
+@mixin grouped-control-status-edges($edges) {
+  @each $marker,
+    $color
+      in (
+        $grouped-control-error-marker: awsui.$color-text-status-error,
+        $grouped-control-warning-marker: awsui.$color-text-status-warning
+      )
+  {
+    &#{$marker},
+    &#{$marker}:hover,
+    &#{$marker}:focus {
+      @include grouped-control-edge-color($edges, $color);
+    }
+    &#{$marker} {
+      @include focus-visible.when-visible {
+        @include grouped-control-edge-color($edges, $color);
+      }
+    }
+  }
+}
+
+@mixin grouped-control-outer-border-color($edges) {
+  @include grouped-control-edge-color($edges, awsui.$color-border-input-default);
+  @include grouped-control-status-edges($edges);
+}
+
 @mixin grouped-control-base {
   @include styles.logical-radius($grouped-control-border-radius);
 }
@@ -37,29 +86,58 @@ $grouped-control-border-radius: constants.$control-border-radius;
   &-horizontal {
     &-first {
       @include grouped-control-horizontal-first;
+      @include grouped-control-outer-border-color((inline-start, block-start, block-end));
     }
     &-middle {
       @include grouped-control-middle;
+      @include grouped-control-outer-border-color((block-start, block-end));
     }
     &-last {
       @include grouped-control-horizontal-last;
+      @include grouped-control-outer-border-color((inline-end, block-start, block-end));
     }
   }
 
   &-vertical {
     &-first {
       @include grouped-control-vertical-first;
+      @include grouped-control-outer-border-color((block-start, inline-start, inline-end));
     }
     &-middle {
       @include grouped-control-middle;
+      @include grouped-control-outer-border-color((inline-start, inline-end));
     }
     &-last {
       @include grouped-control-vertical-last;
+      @include grouped-control-outer-border-color((block-end, inline-start, inline-end));
     }
   }
 
+  &-horizontal-only,
+  &-vertical-only {
+    @include grouped-control-outer-border-color((inline-start, inline-end, block-start, block-end));
+  }
+
   &-with-action {
     border-start-end-radius: 0;
     border-end-end-radius: 0;
   }
+
+  // Invalid focus ring, position-independent. Keyed on the state markers with
+  // :focus-within so it fires for the button-trigger (focus on self) and the
+  // Input .input-field wrapper (focus on the inner native input).
+  &#{$grouped-control-error-marker}:focus-within,
+  &#{$grouped-control-warning-marker}:focus-within {
+    box-shadow: foundation.$box-shadow-focused-light-invalid;
+  }
+  &#{$grouped-control-error-marker},
+  &#{$grouped-control-warning-marker} {
+    @include focus-visible.when-visible {
+      box-shadow: foundation.$box-shadow-focused-light-invalid;
+    }
+  }
+
+  &#{&}-validation {
+    padding-inline-start: calc(#{constants.$invalid-control-left-border} + #{constants.$invalid-control-left-padding});
+  }
 }
diff --git a/src/internal/styles/forms/mixins.scss b/src/internal/styles/forms/mixins.scss
index 209f2090fcc..59a313cd265 100644
--- a/src/internal/styles/forms/mixins.scss
+++ b/src/internal/styles/forms/mixins.scss
@@ -124,8 +124,13 @@
   // See focus-highlight above.
   outline: 2px dotted transparent;
 
-  border-block: awsui.$border-width-field solid $border-color;
-  border-inline: awsui.$border-width-field solid $border-color;
+  border-block-style: solid;
+  border-inline-style: solid;
+
+  @if $border-color {
+    border-block-color: $border-color;
+    border-inline-color: $border-color;
+  }
 
   box-shadow: $box-shadow;
 }
@@ -198,12 +203,20 @@
 ) {
   color: $color;
   border-color: $border-color;
-  padding-inline-start: constants.$invalid-control-left-padding;
-  border-inline-start-width: constants.$invalid-control-left-border;
+  // Standalone only: thicken the real leading border and reduce the padding so
+  // text stays at the neutral position. Grouped controls get the overlay bar and
+  // a bar+cph content inset instead (grouped-control.scss), so they must not pull
+  // a real thick border here. @content is scoped to the standalone path so a
+  // caller (Input) can zero the wrapper padding when an inner cell owns the
+  // compensation, at the same specificity as the padding above.
+  &:not(.grouped) {
+    padding-inline-start: constants.$invalid-control-left-padding;
+    border-inline-start-width: constants.$invalid-control-left-border;
+    @content;
+  }
   &:focus {
     box-shadow: $focus-box-shadow;
   }
-  @content;
 }
 
 @mixin form-warning-control(
@@ -213,12 +226,17 @@
 ) {
   color: $color;
   border-color: $border-color;
-  padding-inline-start: constants.$invalid-control-left-padding;
-  border-inline-start-width: constants.$invalid-control-left-border;
+  // Symmetric with form-invalid-control: standalone only gets the thick real
+  // border + reduced padding; grouped uses the overlay bar + bar+cph inset.
+  // @content is scoped to the standalone path for the same reason.
+  &:not(.grouped) {
+    padding-inline-start: constants.$invalid-control-left-padding;
+    border-inline-start-width: constants.$invalid-control-left-border;
+    @content;
+  }
   &:focus {
     box-shadow: $focus-box-shadow;
   }
-  @content;
 }
 
 @mixin input-default-styles {
diff --git a/src/prompt-input/styles.scss b/src/prompt-input/styles.scss
index 3887fec3461..8d69e9144a6 100644
--- a/src/prompt-input/styles.scss
+++ b/src/prompt-input/styles.scss
@@ -71,11 +71,15 @@ $invalid-border-offset: constants.$invalid-control-left-padding;
   }
 
   &.textarea-invalid {
+    // The thick leading border lives on this root while the compensating reduced
+    // padding lives on inner content cells (.textarea etc.), so the root must own
+    // zero inline-start padding. Pass the zero as mixin @content so it lands inside
+    // the mixin's `:not(.grouped)` branch and wins the specificity contest against
+    // the mixin's own padding (matching the working Input pattern).
     @include styles.form-invalid-control(
       $color: var(#{custom-props.$promptInputStyleColorDefault}, awsui.$color-text-status-error),
       $border-color: var(#{custom-props.$promptInputStyleBorderColorDefault}, awsui.$color-text-status-error)
-    );
-    & {
+    ) {
       padding-inline-start: 0;
     }
 
@@ -84,8 +88,7 @@ $invalid-border-offset: constants.$invalid-control-left-padding;
       @include styles.form-invalid-control(
         $color: var(#{custom-props.$promptInputStyleColorDefault}, awsui.$color-text-status-error),
         $border-color: var(#{custom-props.$promptInputStyleBorderColorDefault}, awsui.$color-text-status-error)
-      );
-      & {
+      ) {
         padding-inline-start: 0;
         box-shadow: foundation.$box-shadow-focused-light-invalid;
       }
@@ -99,11 +102,13 @@ $invalid-border-offset: constants.$invalid-control-left-padding;
   }
 
   &.textarea-warning {
+    // Symmetric with the invalid state: pass the root's zero inline-start padding
+    // as mixin @content so it wins the specificity contest against the mixin's own
+    // padding, keeping text at the neutral x-position next to the thick border.
     @include styles.form-warning-control(
       $color: var(#{custom-props.$promptInputStyleColorDefault}, awsui.$color-text-status-warning),
       $border-color: var(#{custom-props.$promptInputStyleBorderColorDefault}, awsui.$color-text-status-warning)
-    );
-    & {
+    ) {
       padding-inline-start: 0;
     }
 
@@ -112,8 +117,7 @@ $invalid-border-offset: constants.$invalid-control-left-padding;
       @include styles.form-warning-control(
         $color: var(#{custom-props.$promptInputStyleColorDefault}, awsui.$color-text-status-warning),
         $border-color: var(#{custom-props.$promptInputStyleBorderColorDefault}, awsui.$color-text-status-warning)
-      );
-      & {
+      ) {
         padding-inline-start: 0;
         box-shadow: foundation.$box-shadow-focused-light-invalid;
       }
diff --git a/src/segmented-control/styles.scss b/src/segmented-control/styles.scss
index aa5deb60e44..0f07763fa99 100644
--- a/src/segmented-control/styles.scss
+++ b/src/segmented-control/styles.scss
@@ -8,6 +8,7 @@
 @use 'sass:list' as list;
 @use '../internal/styles/tokens' as awsui;
 @use '../internal/styles/utils/theming' as theming;
+@use '@cloudscape-design/component-toolkit/internal/focus-visible' as focus-visible;
 
 @function repeatValue($value, $times) {
   $result: ();
@@ -69,6 +70,17 @@
   &.grouped-horizontal-last {
     border-inline-start: none;
   }
+
+  // The focused inner segment option draws its own ring, so suppress the group's.
+  &.grouped-in-error,
+  &.grouped-in-warning {
+    &:focus-within {
+      box-shadow: none;
+    }
+    @include focus-visible.when-visible {
+      box-shadow: none;
+    }
+  }
 }
 
 .select {