diff --git a/api-goldens/element-ng/accordion/index.api.md b/api-goldens/element-ng/accordion/index.api.md
index 62ed1ce08c..b1c7f1e4cc 100644
--- a/api-goldens/element-ng/accordion/index.api.md
+++ b/api-goldens/element-ng/accordion/index.api.md
@@ -6,6 +6,7 @@
 
 import { AfterContentInit } from '@angular/core';
 import * as _angular_core from '@angular/core';
+import * as i1 from '@angular/aria/accordion';
 import { OnChanges } from '@angular/core';
 import { Subject } from 'rxjs';
 import { TranslatableString } from '@siemens/element-translate-ng/translate';
diff --git a/projects/element-ng/accordion/si-accordion.component.ts b/projects/element-ng/accordion/si-accordion.component.ts
index a7c062aed5..95918b9001 100644
--- a/projects/element-ng/accordion/si-accordion.component.ts
+++ b/projects/element-ng/accordion/si-accordion.component.ts
@@ -2,6 +2,7 @@
  * Copyright (c) Siemens 2016 - 2026
  * SPDX-License-Identifier: MIT
  */
+import { AccordionGroup } from '@angular/aria/accordion';
 import {
   AfterContentInit,
   booleanAttribute,
@@ -31,7 +32,8 @@ const PANEL_MIN_HEIGHT = 100;
   host: {
     '[class.full-height]': 'fullHeight()',
     '[class.hcollapsed]': 'collapsed()'
-  }
+  },
+  hostDirectives: [AccordionGroup]
 })
 export class SiAccordionComponent implements AfterContentInit, OnChanges {
   /**
diff --git a/projects/element-ng/accordion/si-accordion.service.ts b/projects/element-ng/accordion/si-accordion.service.ts
index 707a7c2b9e..b8d05f79bf 100644
--- a/projects/element-ng/accordion/si-accordion.service.ts
+++ b/projects/element-ng/accordion/si-accordion.service.ts
@@ -5,15 +5,15 @@
 import { Injectable, signal } from '@angular/core';
 import { Subject } from 'rxjs';
 
+import type { SiCollapsiblePanelComponent } from './si-collapsible-panel.component';
+
 /** @internal */
 @Injectable({
   providedIn: null
 })
 export class SiAccordionService {
-  /**
-   * Emit an item in the accordion which should be toggled.
-   */
-  readonly toggle$ = new Subject<any>();
+  /** Emit the panel that was toggled so sibling panels can close. */
+  readonly toggle$ = new Subject<SiCollapsiblePanelComponent>();
   /**
    * Subject to emit when the items should be expanded to their full height or restored to normal height.
    *
diff --git a/projects/element-ng/accordion/si-collapsible-panel.component.html b/projects/element-ng/accordion/si-collapsible-panel.component.html
index 9c5a365e87..9b7e888534 100644
--- a/projects/element-ng/accordion/si-collapsible-panel.component.html
+++ b/projects/element-ng/accordion/si-collapsible-panel.component.html
@@ -1,65 +1,74 @@
-<div
-  role="button"
-  placement="start"
-  [siTooltip]="hcollapsed() && heading() ? (heading()! | translate) : ''"
-  [class]="`collapsible-header focus-inside ${headerCssClasses()}`"
-  [class.px-5]="hcollapsed()"
-  [class.px-6]="!hcollapsed()"
-  [attr.tabindex]="disabled() ? '' : '0'"
-  [id]="headerId"
-  [class.open]="opened()"
-  [class.disabled]="disabled()"
-  [attr.aria-expanded]="opened() && !hcollapsed()"
-  [attr.aria-disabled]="disabled()"
-  [attr.aria-controls]="controlId"
-  [attr.aria-label]="hcollapsed() ? (heading() | translate) : ''"
-  (keydown)="keydown($event)"
-  (click)="doToggle($event)"
->
-  @let headerIcon = icon();
-  @if (headerIcon) {
-    <si-icon
-      class="icon"
-      [class.p-1]="hcollapsed()"
-      [class.pe-2]="!hcollapsed()"
-      [icon]="headerIcon"
-      [class.collapsed-icon]="isHCollapsible"
+@if (accordionService) {
+  <ng-container [ngTemplateOutlet]="panelTemplate" />
+} @else {
+  <div #standaloneAccordionGroup class="d-contents" ngAccordionGroup>
+    <ng-container
+      [ngTemplateOutlet]="panelTemplate"
+      [ngTemplateOutletInjector]="accordionGroupInjector()"
     />
-  }
-  @if (icon() && badge() !== undefined && badge() !== '') {
-    <span class="badge-text">
-      {{ badge() }}
-    </span>
-  }
-  <div class="si-h5 autohide">
-    {{ heading() | translate }}
-    <ng-content select="[si-panel-heading]" />
   </div>
+}
+
+<ng-template #panelTemplate>
+  <div
+    ngAccordionTrigger
+    placement="start"
+    [panel]="panel"
+    [siTooltip]="hcollapsed() && heading() ? (heading()! | translate) : ''"
+    [class]="`collapsible-header focus-inside ${headerCssClasses()}`"
+    [class.px-5]="hcollapsed()"
+    [class.px-6]="!hcollapsed()"
+    [class.open]="opened()"
+    [class.disabled]="disabled()"
+    [disabled]="disabled()"
+    [attr.aria-label]="hcollapsed() ? (heading() | translate) : ''"
+    [(expanded)]="opened"
+    (expandedChange)="doToggle($event)"
+  >
+    @let headerIcon = icon();
+    @if (headerIcon) {
+      <si-icon
+        class="icon"
+        [class.p-1]="hcollapsed()"
+        [class.pe-2]="!hcollapsed()"
+        [icon]="headerIcon"
+        [class.collapsed-icon]="isHCollapsible"
+      />
+    }
+    @if (icon() && badge() !== undefined && badge() !== '') {
+      <span class="badge-text">
+        {{ badge() }}
+      </span>
+    }
+    <div class="si-h5 autohide">
+      {{ heading() | translate }}
+      <ng-content select="[si-panel-heading]" />
+    </div>
 
-  @if (badge() !== undefined && badge() !== '') {
-    <span [class]="'badge autohide' + (badgeColor() ? ' bg-' + badgeColor() : '')">
-      {{ badge() }}
+    @if (badge() !== undefined && badge() !== '') {
+      <span [class]="'badge autohide' + (badgeColor() ? ' bg-' + badgeColor() : '')">
+        {{ badge() }}
+      </span>
+    }
+    <span class="ms-auto autohide">
+      <si-icon class="icon dropdown-caret" [icon]="icons.elementDown2" />
     </span>
-  }
-  <span class="ms-auto autohide">
-    <si-icon class="icon dropdown-caret" [icon]="icons.elementDown2" />
-  </span>
-</div>
-<div
-  #content
-  role="region"
-  [id]="controlId"
-  [class]="`collapsible-content ${contentBgClasses()}`"
-  [attr.aria-labelledby]="headerId"
-  [class.full-height]="fullHeight()"
->
-  @if (opened()) {
-    <div class="content-motion" animate.enter="content-enter" animate.leave="content-leave">
-      <div class="overflow-hidden">
-        <div [class]="contentCssClasses()">
-          <ng-content />
+  </div>
+  <div
+    #content
+    #panel="ngAccordionPanel"
+    ngAccordionPanel
+    [class]="`collapsible-content ${contentBgClasses()}`"
+    [class.full-height]="fullHeight()"
+  >
+    <ng-template ngAccordionContent>
+      <div class="content-motion" animate.enter="content-enter" animate.leave="content-leave">
+        <div class="overflow-hidden">
+          <div [class]="contentCssClasses()">
+            <ng-content />
+          </div>
         </div>
       </div>
-    </div>
-  }
-</div>
+    </ng-template>
+  </div>
+</ng-template>
diff --git a/projects/element-ng/accordion/si-collapsible-panel.component.ts b/projects/element-ng/accordion/si-collapsible-panel.component.ts
index c057f31fc8..ede4a6f56e 100644
--- a/projects/element-ng/accordion/si-collapsible-panel.component.ts
+++ b/projects/element-ng/accordion/si-collapsible-panel.component.ts
@@ -2,6 +2,13 @@
  * Copyright (c) Siemens 2016 - 2026
  * SPDX-License-Identifier: MIT
  */
+import {
+  AccordionContent,
+  AccordionGroup,
+  AccordionPanel,
+  AccordionTrigger
+} from '@angular/aria/accordion';
+import { NgTemplateOutlet } from '@angular/common';
 import {
   booleanAttribute,
   Component,
@@ -12,7 +19,8 @@ import {
   model,
   output,
   signal,
-  viewChild
+  viewChild,
+  ViewContainerRef
 } from '@angular/core';
 import { takeUntilDestroyed } from '@angular/core/rxjs-interop';
 import { elementDown2 } from '@siemens/element-icons';
@@ -25,11 +33,18 @@ import { filter } from 'rxjs';
 import { SiAccordionHCollapseService } from './si-accordion-hcollapse.service';
 import { SiAccordionService } from './si-accordion.service';
 
-let controlIdCounter = 1;
-
 @Component({
   selector: 'si-collapsible-panel',
-  imports: [SiIconComponent, SiTranslatePipe, SiTooltipDirective],
+  imports: [
+    AccordionContent,
+    AccordionGroup,
+    AccordionPanel,
+    AccordionTrigger,
+    NgTemplateOutlet,
+    SiIconComponent,
+    SiTranslatePipe,
+    SiTooltipDirective
+  ],
   templateUrl: './si-collapsible-panel.component.html',
   styleUrl: './si-collapsible-panel.component.scss',
   host: {
@@ -106,19 +121,23 @@ export class SiCollapsiblePanelComponent {
     () => this.accordionHCollapseService?.hcollapsed() ?? false
   );
   protected readonly fullHeight = computed(() => this.accordionService?.fullHeight() ?? false);
-  protected controlId = '__si-collapsible-' + controlIdCounter++;
-  protected headerId = this.controlId + '-header';
+  private readonly standaloneAccordionGroupView = viewChild('standaloneAccordionGroup', {
+    read: ViewContainerRef
+  });
+  protected readonly accordionGroupInjector = computed(
+    () => this.standaloneAccordionGroupView()?.injector
+  );
   protected isHCollapsible = false;
   protected readonly icons = addIcons({ elementDown2 });
   protected readonly disableAnimation = signal(false);
 
-  private readonly accordionService = inject(SiAccordionService, { optional: true });
+  protected readonly accordionService = inject(SiAccordionService, { optional: true });
   private readonly accordionHCollapseService = inject(SiAccordionHCollapseService, {
     optional: true
   });
   /** Restore the content scroll position between open/close of the panel. */
   private lastScrollPos = 0;
-  private readonly contentRef = viewChild.required<ElementRef<HTMLElement>>('content');
+  private readonly contentRef = viewChild<ElementRef<HTMLElement>>('content');
 
   constructor() {
     this.isHCollapsible = !!this.accordionHCollapseService;
@@ -142,32 +161,23 @@ export class SiCollapsiblePanelComponent {
     if (open) {
       // Restore scroll position after opening
       setTimeout(() => {
-        this.contentRef().nativeElement.scrollTop = this.lastScrollPos;
+        const content = this.contentRef();
+        if (content) {
+          content.nativeElement.scrollTop = this.lastScrollPos;
+        }
       });
     } else {
       // Save scroll position before closing
-      this.lastScrollPos = this.contentRef().nativeElement.scrollTop;
+      this.lastScrollPos = this.contentRef()?.nativeElement.scrollTop ?? 0;
     }
   }
 
-  protected doToggle(event?: Event): void {
-    if (this.disabled()) {
-      return;
-    }
-
-    event?.preventDefault();
-    const opened = this.opened();
-    this.panelToggle.emit(!opened);
-    this.openClose(this.hcollapsed() || !opened);
+  protected doToggle(open: boolean): void {
+    this.panelToggle.emit(open);
+    this.openClose(this.hcollapsed() || open);
     this.accordionService?.toggle$.next(this);
     if (this.hcollapsed()) {
       this.accordionHCollapseService?.open$.next(this);
     }
   }
-
-  protected keydown(event: KeyboardEvent): void {
-    if (event.key === 'Enter' || event.key === 'Space' || event.key === ' ') {
-      this.doToggle(undefined);
-    }
-  }
 }