diff --git a/packages/ui/src/components/message-block.tsx b/packages/ui/src/components/message-block.tsx
index fc152de6..b42d6be0 100644
--- a/packages/ui/src/components/message-block.tsx
+++ b/packages/ui/src/components/message-block.tsx
@@ -1,4 +1,5 @@
 import { For, Match, Show, Switch, createEffect, createMemo, createSignal } from "solid-js"
+import { FoldVertical } from "lucide-solid"
 import MessageItem from "./message-item"
 import ToolCall from "./tool-call"
 import type { InstanceMessageStore } from "../stores/message-v2/instance-store"
@@ -192,7 +193,15 @@ type ReasoningDisplayItem = {
   defaultExpanded: boolean
 }
 
-type MessageBlockItem = ContentDisplayItem | ToolDisplayItem | StepDisplayItem | ReasoningDisplayItem
+type CompactionDisplayItem = {
+  type: "compaction"
+  key: string
+  part: ClientPart
+  messageInfo?: MessageInfo
+  accentColor?: string
+}
+
+type MessageBlockItem = ContentDisplayItem | ToolDisplayItem | StepDisplayItem | ReasoningDisplayItem | CompactionDisplayItem
 
 interface MessageDisplayBlock {
   record: MessageRecord
@@ -330,6 +339,21 @@ export default function MessageBlock(props: MessageBlockProps) {
         return
       }
 
+      if (part.type === "compaction") {
+        flushContent()
+        const key = `${current.id}:${part.id ?? partIndex}:compaction`
+        const isAuto = Boolean((part as any)?.auto)
+        items.push({
+          type: "compaction",
+          key,
+          part,
+          messageInfo: info,
+          accentColor: isAuto ? "var(--session-status-compacting-fg)" : USER_BORDER_COLOR,
+        })
+        lastAccentColor = isAuto ? "var(--session-status-compacting-fg)" : USER_BORDER_COLOR
+        return
+      }
+
       if (part.type === "step-start") {
         flushContent()
         return
@@ -477,6 +501,9 @@ export default function MessageBlock(props: MessageBlockProps) {
                     borderColor={(item as StepDisplayItem).accentColor}
                   />
                 </Match>
+                <Match when={item.type === "compaction"}>
+                  <CompactionCard part={(item as CompactionDisplayItem).part} messageInfo={(item as CompactionDisplayItem).messageInfo} borderColor={(item as CompactionDisplayItem).accentColor} />
+                </Match>
                 <Match when={item.type === "reasoning"}>
                   <ReasoningCard
                     part={(item as ReasoningDisplayItem).part}
@@ -505,6 +532,29 @@ interface StepCardProps {
   borderColor?: string
 }
 
+function CompactionCard(props: { part: ClientPart; messageInfo?: MessageInfo; borderColor?: string }) {
+  const isAuto = () => Boolean((props.part as any)?.auto)
+  const label = () => (isAuto() ? "Session auto-compacted" : "Session compacted by you")
+  const borderColor = () => props.borderColor ?? (isAuto() ? "var(--session-status-compacting-fg)" : USER_BORDER_COLOR)
+
+  const containerClass = () =>
+    `message-compaction-card ${isAuto() ? "message-compaction-card--auto" : "message-compaction-card--manual"}`
+
+  return (
+    <div
+      class={containerClass()}
+      style={{ "border-left": `4px solid ${borderColor()}` }}
+      role="status"
+      aria-label="Session compaction"
+    >
+      <div class="message-compaction-row">
+        <FoldVertical class="message-compaction-icon w-4 h-4" aria-hidden="true" />
+        <span class="message-compaction-label">{label()}</span>
+      </div>
+    </div>
+  )
+}
+
 function StepCard(props: StepCardProps) {
   const timestamp = () => {
     const value = props.messageInfo?.time?.created ?? (props.part as any)?.time?.start ?? Date.now()
diff --git a/packages/ui/src/components/message-timeline.tsx b/packages/ui/src/components/message-timeline.tsx
index 3f63bda2..df3f28f3 100644
--- a/packages/ui/src/components/message-timeline.tsx
+++ b/packages/ui/src/components/message-timeline.tsx
@@ -5,9 +5,9 @@ import type { ClientPart } from "../types/message"
 import type { MessageRecord } from "../stores/message-v2/types"
 import { buildRecordDisplayData } from "../stores/message-v2/record-display-cache"
 import { getToolIcon } from "./tool-call/utils"
-import { User as UserIcon, Bot as BotIcon } from "lucide-solid"
+import { User as UserIcon, Bot as BotIcon, FoldVertical } from "lucide-solid"
 
-export type TimelineSegmentType = "user" | "assistant" | "tool"
+export type TimelineSegmentType = "user" | "assistant" | "tool" | "compaction"
 
 export interface TimelineSegment {
   id: string
@@ -16,6 +16,7 @@ export interface TimelineSegment {
   label: string
   tooltip: string
   shortLabel?: string
+  variant?: "auto" | "manual"
 }
 
 interface MessageTimelineProps {
@@ -31,6 +32,7 @@ const SEGMENT_LABELS: Record<TimelineSegmentType, string> = {
   user: "You",
   assistant: "Asst",
   tool: "Tool",
+  compaction: "Compaction",
 }
 
 const TOOL_FALLBACK_LABEL = "Tool Call"
@@ -215,6 +217,21 @@ export function buildTimelineSegments(instanceId: string, record: MessageRecord)
       continue
     }
  
+    if (part.type === "compaction") {
+      flushPending()
+      const isAuto = Boolean((part as any)?.auto)
+      result.push({
+        id: `${record.id}:${segmentIndex}`,
+        messageId: record.id,
+        type: "compaction",
+        label: SEGMENT_LABELS.compaction,
+        tooltip: isAuto ? "Auto Compaction" : "User Compaction",
+        variant: isAuto ? "auto" : "manual",
+      })
+      segmentIndex += 1
+      continue
+    }
+
     if (part.type === "step-start" || part.type === "step-finish") {
       continue
     }
@@ -343,20 +360,26 @@ const MessageTimeline: Component<MessageTimelineProps> = (props) => {
           onCleanup(() => buttonRefs.delete(segment.id))
           const isActive = () => props.activeMessageId === segment.messageId
           const isHidden = () => segment.type === "tool" && !(showTools() || isActive())
-          const shortLabelContent = () => {
-            if (segment.type === "tool") {
-              return segment.shortLabel ?? getToolIcon("tool")
-            }
-            if (segment.type === "user") {
-              return <UserIcon class="message-timeline-icon" aria-hidden="true" />
-            }
-            return <BotIcon class="message-timeline-icon" aria-hidden="true" />
-          }
+           const shortLabelContent = () => {
+             if (segment.type === "tool") {
+               return segment.shortLabel ?? getToolIcon("tool")
+             }
+             if (segment.type === "compaction") {
+               return <FoldVertical class="message-timeline-icon" aria-hidden="true" />
+             }
+             if (segment.type === "user") {
+               return <UserIcon class="message-timeline-icon" aria-hidden="true" />
+             }
+             return <BotIcon class="message-timeline-icon" aria-hidden="true" />
+           }
+
           return (
-            <button
-              ref={(el) => registerButtonRef(segment.id, el)}
-              type="button"
-              class={`message-timeline-segment message-timeline-${segment.type} ${isActive() ? "message-timeline-segment-active" : ""} ${isHidden() ? "message-timeline-segment-hidden" : ""}`}
+             <button
+               ref={(el) => registerButtonRef(segment.id, el)}
+               type="button"
+               data-variant={segment.variant}
+               class={`message-timeline-segment message-timeline-${segment.type} ${segment.type === "compaction" ? `message-timeline-compaction-${segment.variant ?? "manual"}` : ""} ${isActive() ? "message-timeline-segment-active" : ""} ${isHidden() ? "message-timeline-segment-hidden" : ""}`}
+
               aria-current={isActive() ? "true" : undefined}
               aria-hidden={isHidden() ? "true" : undefined}
               onClick={() => props.onSegmentClick?.(segment)}
diff --git a/packages/ui/src/styles/messaging/message-base.css b/packages/ui/src/styles/messaging/message-base.css
index 31767999..eccab659 100644
--- a/packages/ui/src/styles/messaging/message-base.css
+++ b/packages/ui/src/styles/messaging/message-base.css
@@ -208,6 +208,35 @@
   border-radius: 0;
 }
 
+.message-compaction-card {
+  @apply flex flex-col gap-1 px-3 py-2 text-xs;
+  background-color: var(--message-assistant-bg);
+}
+
+.message-compaction-card--auto {
+  background-color: var(--session-status-compacting-bg);
+  color: var(--session-status-compacting-fg);
+}
+
+.message-compaction-card--manual {
+  background-color: var(--message-user-bg);
+  color: var(--text-primary);
+}
+
+.message-compaction-row {
+  @apply flex items-center gap-2;
+  justify-content: center;
+}
+
+.message-compaction-icon {
+  @apply inline-flex items-center;
+  color: inherit;
+}
+
+.message-compaction-label {
+  font-weight: var(--font-weight-medium);
+}
+
 .message-step-start {
   background-color: var(--message-assistant-bg);
   border-left: 4px solid var(--message-assistant-border);
diff --git a/packages/ui/src/styles/messaging/message-timeline.css b/packages/ui/src/styles/messaging/message-timeline.css
index b66514bf..a639a9e5 100644
--- a/packages/ui/src/styles/messaging/message-timeline.css
+++ b/packages/ui/src/styles/messaging/message-timeline.css
@@ -146,6 +146,16 @@
   background-color: var(--surface-secondary);
 }
 
+.message-timeline-compaction-auto {
+  border-color: var(--session-status-compacting-fg);
+  background-color: var(--surface-secondary);
+}
+
+.message-timeline-compaction-manual {
+  border-color: var(--message-user-border);
+  background-color: var(--message-user-bg);
+}
+
 .message-timeline-segment-active {
   background-color: #0f5b44 !important;
   border-color: transparent !important;