diff --git a/src/components/ChatMessage.tsx b/src/components/ChatMessage.tsx
index 9ed5c98..ae4dfc5 100644
--- a/src/components/ChatMessage.tsx
+++ b/src/components/ChatMessage.tsx
@@ -10,7 +10,7 @@ import { CodeBlock } from './CodeBlock';
 import { ToolCall } from './ToolCall';
 import { ImageBlock } from './ImageBlock';
 import { buildImageSrc } from '../lib/image';
-import { Bot, User, Wrench, Copy, Check, CheckCheck, RefreshCw, Zap, Info, Webhook, Braces, Clock, AlertCircle, Bookmark } from 'lucide-react';
+import { Bot, User, Wrench, Copy, Check, CheckCheck, RefreshCw, Zap, Info, Webhook, Braces, Clock, AlertCircle, Bookmark, ChevronDown } from 'lucide-react';
 import { t, getLocale } from '../lib/i18n';
 import { useLocale } from '../hooks/useLocale';
 import { stripWebhookScaffolding, hasWebhookScaffolding } from '../lib/systemEvent';
@@ -199,6 +199,49 @@ function MarkdownLink(props: React.AnchorHTMLAttributes<HTMLAnchorElement>) {
 
 const markdownComponents = { pre: CodeBlock, img: MarkdownImage, a: MarkdownLink };
 
+/** Threshold (in characters) above which assistant messages are collapsed by default */
+const COLLAPSE_THRESHOLD = 3000;
+const COLLAPSED_MAX_HEIGHT = 400; // px
+
+/** Wrapper that collapses long content with a gradient fade and "Show more" button */
+function CollapsibleContent({ content, isStreaming, children }: { content: string; isStreaming?: boolean; children: React.ReactNode }) {
+  const [expanded, setExpanded] = useState(false);
+  const shouldCollapse = !isStreaming && content.length > COLLAPSE_THRESHOLD;
+
+  if (!shouldCollapse || expanded) {
+    return (
+      <>
+        {children}
+        {shouldCollapse && expanded && (
+          <button
+            onClick={() => setExpanded(false)}
+            className="mt-2 flex items-center gap-1 text-xs text-pc-accent-light hover:text-pc-accent transition-colors"
+          >
+            <ChevronDown size={12} className="rotate-180" />
+            <span>{t('message.showLess')}</span>
+          </button>
+        )}
+      </>
+    );
+  }
+
+  return (
+    <div className="relative">
+      <div style={{ maxHeight: `${COLLAPSED_MAX_HEIGHT}px`, overflow: 'hidden' }}>
+        {children}
+      </div>
+      <div className="absolute bottom-0 left-0 right-0 h-24 bg-gradient-to-t from-[var(--pc-bg-elevated)] to-transparent pointer-events-none" />
+      <button
+        onClick={() => setExpanded(true)}
+        className="relative mt-1 flex items-center gap-1 text-xs text-pc-accent-light hover:text-pc-accent transition-colors"
+      >
+        <ChevronDown size={12} />
+        <span>{t('message.showMore')}</span>
+      </button>
+    </div>
+  );
+}
+
 function renderTextBlocks(blocks: MessageBlock[]) {
   return getTextBlocks(blocks).map((block, i) => (
     <div key={`text-${i}`} className="markdown-body">
@@ -516,12 +559,24 @@ export const ChatMessageComponent = memo(function ChatMessageComponent({ message
             </button>
           )}
           {/* User-visible text */}
-          {message.blocks.length > 0 ? renderTextBlocks(message.blocks) : (
-            <div className="markdown-body">
-              <LazyMarkdown components={markdownComponents}>
-                {autoFormatText(message.content)}
-              </LazyMarkdown>
-            </div>
+          {!isUser ? (
+            <CollapsibleContent content={message.content || ''} isStreaming={message.isStreaming}>
+              {message.blocks.length > 0 ? renderTextBlocks(message.blocks) : (
+                <div className="markdown-body">
+                  <LazyMarkdown components={markdownComponents}>
+                    {autoFormatText(message.content)}
+                  </LazyMarkdown>
+                </div>
+              )}
+            </CollapsibleContent>
+          ) : (
+            message.blocks.length > 0 ? renderTextBlocks(message.blocks) : (
+              <div className="markdown-body">
+                <LazyMarkdown components={markdownComponents}>
+                  {autoFormatText(message.content)}
+                </LazyMarkdown>
+              </div>
+            )
           )}
 
           {/* Inline images */}
diff --git a/src/lib/i18n.ts b/src/lib/i18n.ts
index 7870871..c672e7c 100644
--- a/src/lib/i18n.ts
+++ b/src/lib/i18n.ts
@@ -91,6 +91,8 @@ const en = {
   'message.copy': 'Copy message',
   'message.copied': 'Copied!',
   'message.retry': 'Resend message',
+  'message.showMore': 'Show more',
+  'message.showLess': 'Show less',
   'message.metadata': 'Message details',
   'message.rawJson': 'Raw JSON',
   'message.hideRawJson': 'Hide raw JSON',
@@ -255,6 +257,8 @@ const fr: Record<keyof typeof en, string> = {
   'message.copy': 'Copier le message',
   'message.copied': 'Copié !',
   'message.retry': 'Renvoyer le message',
+  'message.showMore': 'Afficher plus',
+  'message.showLess': 'Afficher moins',
   'message.metadata': 'Détails du message',
   'message.rawJson': 'JSON brut',
   'message.hideRawJson': 'Masquer le JSON brut',
@@ -411,6 +415,8 @@ const es: Record<keyof typeof en, string> = {
   'message.copy': 'Copiar mensaje',
   'message.copied': '¡Copiado!',
   'message.retry': 'Reenviar mensaje',
+  'message.showMore': 'Ver más',
+  'message.showLess': 'Ver menos',
   'message.metadata': 'Detalles del mensaje',
   'message.rawJson': 'JSON sin formato',
   'message.hideRawJson': 'Ocultar JSON sin formato',
@@ -569,6 +575,8 @@ const de: Record<keyof typeof en, string> = {
   'message.copy': 'Nachricht kopieren',
   'message.copied': 'Kopiert!',
   'message.retry': 'Nachricht erneut senden',
+  'message.showMore': 'Mehr anzeigen',
+  'message.showLess': 'Weniger anzeigen',
   'message.metadata': 'Nachrichtendetails',
   'message.rawJson': 'Roh-JSON',
   'message.hideRawJson': 'Roh-JSON ausblenden',
@@ -725,6 +733,8 @@ const ja: Record<keyof typeof en, string> = {
   'message.copy': 'メッセージをコピー',
   'message.copied': 'コピーしました！',
   'message.retry': 'メッセージを再送信',
+  'message.showMore': 'もっと見る',
+  'message.showLess': '折りたたむ',
   'message.metadata': 'メッセージの詳細',
   'message.rawJson': '生JSON',
   'message.hideRawJson': '生JSONを非表示',
@@ -881,6 +891,8 @@ const pt: Record<keyof typeof en, string> = {
   'message.copy': 'Copiar mensagem',
   'message.copied': 'Copiado!',
   'message.retry': 'Reenviar mensagem',
+  'message.showMore': 'Ver mais',
+  'message.showLess': 'Ver menos',
   'message.metadata': 'Detalhes da mensagem',
   'message.rawJson': 'JSON bruto',
   'message.hideRawJson': 'Ocultar JSON bruto',
@@ -1037,6 +1049,8 @@ const zh: Record<keyof typeof en, string> = {
   'message.copy': '复制消息',
   'message.copied': '已复制！',
   'message.retry': '重新发送',
+  'message.showMore': '展开更多',
+  'message.showLess': '收起',
   'message.metadata': '消息详情',
   'message.rawJson': '原始 JSON',
   'message.hideRawJson': '隐藏原始 JSON',
@@ -1193,6 +1207,8 @@ const it: Record<keyof typeof en, string> = {
   'message.copy': 'Copia messaggio',
   'message.copied': 'Copiato!',
   'message.retry': 'Reinvia messaggio',
+  'message.showMore': 'Mostra di più',
+  'message.showLess': 'Mostra meno',
   'message.metadata': 'Dettagli messaggio',
   'message.rawJson': 'JSON grezzo',
   'message.hideRawJson': 'Nascondi JSON grezzo',