diff --git a/renderer/app.js b/renderer/app.js
index 203eb1b..0fa7e2f 100644
--- a/renderer/app.js
+++ b/renderer/app.js
@@ -801,6 +801,7 @@ function _setHeaderUpdateLabel(text) {
 
 function _syncHeaderUpdateState() {
   const button = document.getElementById('headerUpdateBtn');
+  const slot = document.getElementById('headerUpdateSlot');
   const available = !!(_knownUpdateInfo && _knownUpdateInfo.available);
   const version = available ? String(_knownUpdateInfo.remoteVersion || '').replace(/^v/i, '') : '';
   const hint = _updateCheckBusy
@@ -808,10 +809,15 @@ function _syncHeaderUpdateState() {
     : available
       ? `Update v${version || 'unbekannt'} verfügbar. Klicken zum Installieren.`
       : 'Nach Aktualisierungen suchen';
+  if (slot) {
+    slot.classList.toggle('is-visible', available);
+    slot.setAttribute('aria-hidden', available ? 'false' : 'true');
+  }
   if (button) {
     button.classList.toggle('update-available', available);
     button.classList.toggle('is-checking', _updateCheckBusy);
-    button.disabled = _updateCheckBusy;
+    button.disabled = !available || _updateCheckBusy;
+    button.tabIndex = available ? 0 : -1;
     button.setAttribute('aria-busy', _updateCheckBusy ? 'true' : 'false');
     button.setAttribute('aria-label', hint);
     button.title = hint;
@@ -843,6 +849,7 @@ async function requestUpdateCheck({ forceRefresh = true } = {}) {
     } else if (result && result.error) {
       showCopyToast('Updateprüfung fehlgeschlagen');
     } else {
+      _knownUpdateInfo = null;
       showCopyToast('Kein Update verfügbar');
     }
     return result;
diff --git a/renderer/index.html b/renderer/index.html
index 0224fad..584830d 100644
--- a/renderer/index.html
+++ b/renderer/index.html
@@ -54,6 +54,12 @@
     </div>
     <div class="header-spacer" aria-hidden="true"></div>
     <div class="header-cluster header-utilities">
+      <div class="header-update-slot" id="headerUpdateSlot" aria-hidden="true">
+        <button class="header-update-button" id="headerUpdateBtn" title="Nach Aktualisierungen suchen" aria-label="Nach Aktualisierungen suchen" data-tooltip="Nach Aktualisierungen suchen" tabindex="-1" disabled>
+          <svg class="header-action-icon" aria-hidden="true"><use href="#icon-download"></use></svg>
+          <span class="header-update-label">Update</span>
+        </button>
+      </div>
       <div class="upload-speed-sparkline" id="uploadSpeedSparkline" title="Aktuelle Upload-Geschwindigkeit" aria-label="Aktuelle Upload-Geschwindigkeit">
         <span class="upload-speed-chart" aria-hidden="true">
           <span class="upload-speed-baseline"></span>
@@ -61,10 +67,6 @@
         </span>
         <strong id="uploadSpeedValue">0 B/s</strong>
       </div>
-      <button class="header-update-button" id="headerUpdateBtn" title="Nach Aktualisierungen suchen" aria-label="Nach Aktualisierungen suchen" data-tooltip="Nach Aktualisierungen suchen">
-        <svg class="header-action-icon" aria-hidden="true"><use href="#icon-download"></use></svg>
-        <span class="header-update-label">Update</span>
-      </button>
       <span class="header-divider" aria-hidden="true"></span>
       <nav class="menu-bar" id="menuBar" aria-label="Anwendungsmenüs">
         <div class="menu-bar-item" data-menu="datei">
diff --git a/renderer/styles.css b/renderer/styles.css
index 1952c95..bd9f81f 100644
--- a/renderer/styles.css
+++ b/renderer/styles.css
@@ -2109,6 +2109,29 @@ select.hs-input { max-width: none; width: auto; min-width: 140px; }
   border: 0;
 }
 
+.header-update-slot {
+  width: 0;
+  flex: 0 0 0;
+  height: 32px;
+  margin-right: -4px;
+  overflow: hidden;
+  opacity: 0;
+  visibility: hidden;
+  pointer-events: none;
+  transition: width .28s cubic-bezier(.22, 1, .36, 1), flex-basis .28s cubic-bezier(.22, 1, .36, 1), margin-right .28s cubic-bezier(.22, 1, .36, 1), opacity .18s ease, visibility 0s linear .28s;
+}
+
+.header-update-slot.is-visible {
+  width: 146px;
+  flex-basis: 146px;
+  margin-right: 0;
+  overflow: visible;
+  opacity: 1;
+  visibility: visible;
+  pointer-events: auto;
+  transition-delay: 0s;
+}
+
 .header-update-button {
   position: relative;
   width: 146px;
@@ -2127,7 +2150,16 @@ select.hs-input { max-width: none; width: auto; min-width: 140px; }
   font: inherit;
   font-size: 12px;
   font-weight: 700;
-  transition: background-color .14s, transform .14s;
+  opacity: 0;
+  transform: translateX(14px);
+  pointer-events: none;
+  transition: background-color .14s, transform .28s cubic-bezier(.22, 1, .36, 1), opacity .18s ease;
+}
+
+.header-update-slot.is-visible .header-update-button {
+  opacity: 1;
+  transform: translateX(0);
+  pointer-events: auto;
 }
 
 .header-update-button.update-available {
@@ -4040,6 +4072,11 @@ input[type="checkbox"] {
     padding: 0;
   }
 
+  .header-update-slot.is-visible {
+    width: 34px;
+    flex-basis: 34px;
+  }
+
   .header-update-label,
   .version-label {
     display: none;
diff --git a/tests/startup-renderer.test.js b/tests/startup-renderer.test.js
index 02c2539..23212bb 100644
--- a/tests/startup-renderer.test.js
+++ b/tests/startup-renderer.test.js
@@ -154,11 +154,16 @@ test('header occupies its final geometry before asynchronous initialization', ()
   const mainSource = fs.readFileSync(path.join(projectRoot, 'main.js'), 'utf8');
   const css = fs.readFileSync(path.join(projectRoot, 'renderer', 'styles.css'), 'utf8');
   const updateButton = html.match(/<button class="header-update-button"[^>]*id="headerUpdateBtn"[^>]*>/u)?.[0] || '';
+  const updateSlotIndex = html.indexOf('class="header-update-slot"');
+  const speedWidgetIndex = html.indexOf('id="uploadSpeedSparkline"');
   const firstFrameInitialization = appSource.lastIndexOf('\ninitializeStaticHeader();');
   const asynchronousInitialization = appSource.lastIndexOf('\ninit().then(');
 
   assert.doesNotMatch(updateButton, /\shidden(?:\s|>)/u);
-  assert.match(css, /\.header-update-button\s*\{[^}]*width:\s*146px;[^}]*flex:\s*0 0 146px;/su);
+  assert.ok(updateSlotIndex >= 0 && updateSlotIndex < speedWidgetIndex);
+  assert.match(css, /\.header-update-slot\s*\{[^}]*width:\s*0;[^}]*flex:\s*0 0 0;[^}]*overflow:\s*hidden;/su);
+  assert.match(css, /\.header-update-slot\.is-visible\s*\{[^}]*width:\s*146px;[^}]*flex-basis:\s*146px;/su);
+  assert.match(css, /\.header-update-slot\.is-visible\s+\.header-update-button\s*\{[^}]*opacity:\s*1;[^}]*transform:\s*translateX\(0\);/su);
   assert.match(css, /\.version-badge\s*\{[^}]*min-width:\s*48px;/su);
   assert.notEqual(firstFrameInitialization, -1);
   assert.ok(firstFrameInitialization < asynchronousInitialization);
diff --git a/tests/ui-smoke.js b/tests/ui-smoke.js
index 08006c9..08b1160 100644
--- a/tests/ui-smoke.js
+++ b/tests/ui-smoke.js
@@ -185,8 +185,8 @@ setTimeout(async () => {
   }
 
   try {
-    const startupUpdateState = await wc.executeJavaScript('(() => { const button = document.getElementById("headerUpdateBtn"); return [_knownUpdateInfo?.remoteVersion, button?.hidden, getComputedStyle(button).display, document.getElementById("updateBanner")?.style.display].join("|"); })()');
-    check('Startup update survives pending renderer initialization', startupUpdateState === '9.9.8|false|flex|flex');
+    const startupUpdateState = await wc.executeJavaScript('(() => { const slot = document.getElementById("headerUpdateSlot"); return [_knownUpdateInfo?.remoteVersion, slot?.classList.contains("is-visible"), slot?.getAttribute("aria-hidden"), document.getElementById("updateBanner")?.style.display].join("|"); })()');
+    check('Startup update survives pending renderer initialization', startupUpdateState === '9.9.8|true|false|flex');
     await wc.executeJavaScript('_knownUpdateInfo = null; closeUpdateDialog(); _syncHeaderUpdateState();');
 
     const germanStartupReady = await waitUntil(() => wc.executeJavaScript('document.documentElement.lang + "|" + document.getElementById("languageInput")?.value + "|" + [...document.querySelectorAll(".tab")].map(tab => tab.textContent.trim()).join(",")'));
@@ -290,8 +290,8 @@ setTimeout(async () => {
     const headerUpdateButtonExists = await wc.executeJavaScript('Boolean(document.getElementById("headerUpdateBtn"))');
     check('App header exposes the update action', headerUpdateButtonExists);
 
-    const initialHeaderUpdateVisibility = await wc.executeJavaScript('(() => { const button = document.getElementById("headerUpdateBtn"); return [button?.hidden, getComputedStyle(button).display].join("|"); })()');
-    check('Header update action keeps its layout slot before an update is available', initialHeaderUpdateVisibility === 'false|flex');
+    const initialHeaderUpdateVisibility = await wc.executeJavaScript('(() => { const slot = document.getElementById("headerUpdateSlot"); const button = document.getElementById("headerUpdateBtn"); return [slot?.classList.contains("is-visible"), slot?.getAttribute("aria-hidden"), Math.round(slot?.getBoundingClientRect().width || 0), button?.disabled, button?.tabIndex].join("|"); })()');
+    check('Header update action is fully collapsed before an update is available', initialHeaderUpdateVisibility === 'false|true|0|true|-1');
 
     const initialUpdateLabel = await wc.executeJavaScript('document.querySelector("#headerUpdateBtn .header-update-label")?.textContent?.trim()');
     check('App header uses the compact update label', initialUpdateLabel === 'Update');
@@ -1198,20 +1198,20 @@ setTimeout(async () => {
       document.getElementById('headerUpdateBtn').click();
     })()\`);
     await new Promise(resolve => setTimeout(resolve, 100));
-    const coordinatedUpdateBusy = await wc.executeJavaScript('(() => { const manual = document.getElementById("manualUpdateCheckBtn"); const header = document.getElementById("headerUpdateBtn"); return [manual?.disabled, manual?.getAttribute("aria-busy"), manual?.textContent?.trim(), header?.disabled, header?.getAttribute("aria-busy"), header?.hidden].join("|"); })()');
-    check('All update entry points share one in-flight check', updateCheckCallCount === 1 && coordinatedUpdateBusy === 'true|true|Prüfe…|true|true|false');
+    const coordinatedUpdateBusy = await wc.executeJavaScript('(() => { const manual = document.getElementById("manualUpdateCheckBtn"); const header = document.getElementById("headerUpdateBtn"); const slot = document.getElementById("headerUpdateSlot"); return [manual?.disabled, manual?.getAttribute("aria-busy"), manual?.textContent?.trim(), header?.disabled, header?.getAttribute("aria-busy"), slot?.classList.contains("is-visible")].join("|"); })()');
+    check('All update entry points share one in-flight check without revealing the header action', updateCheckCallCount === 1 && coordinatedUpdateBusy === 'true|true|Prüfe…|true|true|false');
     updateCheckResolvers.splice(0).forEach(resolve => resolve({ available: false, error: 'Simulierter Netzwerkfehler' }));
     await new Promise(resolve => setTimeout(resolve, 150));
-    const coordinatedUpdateError = await wc.executeJavaScript('(() => { const manual = document.getElementById("manualUpdateCheckBtn"); const header = document.getElementById("headerUpdateBtn"); return [manual?.disabled, header?.disabled, header?.hidden, manual?.textContent?.trim(), document.getElementById("copyToast")?.textContent?.trim()].join("|"); })()');
-    check('Settings update check uses the shared error contract', coordinatedUpdateError === 'false|false|false|Nach Updates suchen|Updateprüfung fehlgeschlagen');
+    const coordinatedUpdateError = await wc.executeJavaScript('(() => { const manual = document.getElementById("manualUpdateCheckBtn"); const header = document.getElementById("headerUpdateBtn"); const slot = document.getElementById("headerUpdateSlot"); return [manual?.disabled, header?.disabled, slot?.classList.contains("is-visible"), manual?.textContent?.trim(), document.getElementById("copyToast")?.textContent?.trim()].join("|"); })()');
+    check('Settings update check uses the shared error contract', coordinatedUpdateError === 'false|true|false|Nach Updates suchen|Updateprüfung fehlgeschlagen');
     await wc.executeJavaScript('document.getElementById("copyToast")?.classList.remove("show")');
 
     await wc.executeJavaScript('requestUpdateCheck(); true');
     await new Promise(resolve => setTimeout(resolve, 100));
     updateCheckResolvers.splice(0).forEach(resolve => resolve({ available: false }));
     await new Promise(resolve => setTimeout(resolve, 150));
-    const noUpdateHeaderVisibility = await wc.executeJavaScript('(() => { const button = document.getElementById("headerUpdateBtn"); return [button?.hidden, getComputedStyle(button).display].join("|"); })()');
-    check('Successful no-update result keeps the header action in its stable slot', noUpdateHeaderVisibility === 'false|flex');
+    const noUpdateHeaderVisibility = await wc.executeJavaScript('(() => { const slot = document.getElementById("headerUpdateSlot"); const button = document.getElementById("headerUpdateBtn"); return [slot?.classList.contains("is-visible"), Math.round(slot?.getBoundingClientRect().width || 0), button?.disabled].join("|"); })()');
+    check('Successful no-update result keeps the header action collapsed', noUpdateHeaderVisibility === 'false|0|true');
 
     const settingsNavigation = await wc.executeJavaScript('(() => { const buttons = [...document.querySelectorAll(".settings-nav-button")]; return [buttons.length, buttons.map(button => button.textContent.trim()).join("|"), document.querySelector(".settings-nav-button.active")?.dataset.settingsPage, document.getElementById("settingsSearchInput")?.placeholder].join("::"); })()');
     check('Settings use the task-based sidebar navigation', settingsNavigation === '8::Allgemein|Uploads|Automatik|Benachrichtigungen|Logs & Support|Fernsteuerung|Diagnose-Zugriff|Backup & Übertragen::allgemein::Einstellungen durchsuchen');