diff --git a/CHANGELOG.md b/CHANGELOG.md
index f2176cffb..7a8763e17 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -17,6 +17,7 @@
 - Model: `/model` output now includes auth source location (env/auth.json/models.json).
 - Docs: clarify auth storage, migration, and OpenAI Codex OAuth onboarding.
 - Sandbox: copy inbound media into sandbox workspaces so agent tools can read attachments.
+- Control UI: show a reading indicator bubble while the assistant is responding.
 - Status: show runtime (docker/direct) and move shortcuts to `/help`.
 - Status: show model auth source (api-key/oauth).
 
diff --git a/ui/src/styles/components.css b/ui/src/styles/components.css
index 78a14c295..7c7c4df03 100644
--- a/ui/src/styles/components.css
+++ b/ui/src/styles/components.css
@@ -595,6 +595,56 @@
   }
 }
 
+.chat-bubble.chat-reading-indicator {
+  width: fit-content;
+  padding: 10px 14px;
+}
+
+.chat-reading-indicator__dots {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+  height: 10px;
+}
+
+.chat-reading-indicator__dots > span {
+  width: 6px;
+  height: 6px;
+  border-radius: 999px;
+  background: var(--chat-text);
+  opacity: 0.55;
+  transform: translateY(0);
+  animation: chatReadingDot 1.1s ease-in-out infinite;
+}
+
+.chat-reading-indicator__dots > span:nth-child(2) {
+  animation-delay: 0.12s;
+}
+
+.chat-reading-indicator__dots > span:nth-child(3) {
+  animation-delay: 0.24s;
+}
+
+@keyframes chatReadingDot {
+  0%,
+  80%,
+  100% {
+    opacity: 0.45;
+    transform: translateY(0);
+  }
+  40% {
+    opacity: 0.95;
+    transform: translateY(-2px);
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .chat-reading-indicator__dots > span {
+    animation: none;
+    opacity: 0.75;
+  }
+}
+
 .chat-text {
   overflow-wrap: anywhere;
   word-break: break-word;
diff --git a/ui/src/ui/views/chat.ts b/ui/src/ui/views/chat.ts
index 90660d319..f78a67a8f 100644
--- a/ui/src/ui/views/chat.ts
+++ b/ui/src/ui/views/chat.ts
@@ -78,15 +78,17 @@ export function renderChat(props: ChatProps) {
       <div class="chat-thread" role="log" aria-live="polite">
         ${props.loading ? html`<div class="muted">Loading chat…</div>` : nothing}
         ${props.messages.map((m) => renderMessage(m))}
-        ${props.stream
-          ? renderMessage(
-              {
-                role: "assistant",
-                content: [{ type: "text", text: props.stream }],
-                timestamp: Date.now(),
-              },
-              { streaming: true },
-            )
+        ${props.stream !== null
+          ? props.stream.trim().length > 0
+            ? renderMessage(
+                {
+                  role: "assistant",
+                  content: [{ type: "text", text: props.stream }],
+                  timestamp: Date.now(),
+                },
+                { streaming: true },
+              )
+            : renderReadingIndicator()
           : nothing}
       </div>
 
@@ -171,6 +173,20 @@ function resolveSessionOptions(
   return result;
 }
 
+function renderReadingIndicator() {
+  return html`
+    <div class="chat-line assistant">
+      <div class="chat-msg">
+        <div class="chat-bubble chat-reading-indicator" aria-hidden="true">
+          <span class="chat-reading-indicator__dots">
+            <span></span><span></span><span></span>
+          </span>
+        </div>
+      </div>
+    </div>
+  `;
+}
+
 function renderMessage(message: unknown, opts?: { streaming?: boolean }) {
   const m = message as Record<string, unknown>;
   const role = typeof m.role === "string" ? m.role : "unknown";