diff --git a/src/components/message-item.tsx b/src/components/message-item.tsx
index 7acd15e2..6782eaea 100644
--- a/src/components/message-item.tsx
+++ b/src/components/message-item.tsx
@@ -6,6 +6,7 @@ interface MessageItemProps {
   message: Message
   messageInfo?: any
   isQueued?: boolean
+  parts?: any[]
   onRevert?: (messageId: string) => void
 }
 
@@ -16,6 +17,8 @@ export default function MessageItem(props: MessageItemProps) {
     return date.toLocaleTimeString([], { hour: "2-digit", minute: "2-digit" })
   }
 
+  const messageParts = () => props.parts ?? props.message.parts
+
   const errorMessage = () => {
     if (!props.messageInfo?.error) return null
 
@@ -36,7 +39,7 @@ export default function MessageItem(props: MessageItemProps) {
   }
 
   const hasContent = () => {
-    return props.message.parts.length > 0 || errorMessage() !== null
+    return messageParts().length > 0 || errorMessage() !== null
   }
 
   const isGenerating = () => {
@@ -81,7 +84,7 @@ export default function MessageItem(props: MessageItemProps) {
           </div>
         </Show>
 
-        <For each={props.message.parts}>{(part) => <MessagePart part={part} />}</For>
+        <For each={messageParts()}>{(part) => <MessagePart part={part} />}</For>
       </div>
 
       <Show when={props.message.status === "sending"}>
diff --git a/src/components/message-stream.tsx b/src/components/message-stream.tsx
index 3980df60..d0db98d6 100644
--- a/src/components/message-stream.tsx
+++ b/src/components/message-stream.tsx
@@ -1,11 +1,11 @@
 import { For, Show, createSignal, createEffect, createMemo } from "solid-js"
-import type { Message } from "../types/message"
+import type { Message, MessageDisplayParts } from "../types/message"
 import MessageItem from "./message-item"
 import ToolCall from "./tool-call"
 import { sseManager } from "../lib/sse-manager"
 import Kbd from "./kbd"
 import { preferences } from "../stores/preferences"
-import { providers, getSessionInfo } from "../stores/sessions"
+import { providers, getSessionInfo, computeDisplayParts } from "../stores/sessions"
 
 // Calculate session tokens and cost from messagesInfo (matches TUI logic)
 function calculateSessionInfo(messagesInfo?: Map<string, any>, instanceId?: string) {
@@ -120,17 +120,46 @@ interface MessageStreamProps {
   onRevert?: (messageId: string) => void
 }
 
-interface DisplayItem {
-  type: "message" | "tool"
-  data: any
+interface MessageDisplayItem {
+  type: "message"
+  message: Message
+  combinedParts: any[]
+  isQueued: boolean
   messageInfo?: any
 }
 
+interface ToolDisplayItem {
+  type: "tool"
+  key: string
+  toolPart: any
+  messageInfo?: any
+}
+
+type DisplayItem = MessageDisplayItem | ToolDisplayItem
+
+interface MessageCacheEntry {
+  version: number
+  showThinking: boolean
+  isQueued: boolean
+  messageInfo?: any
+  displayParts: MessageDisplayParts
+  item: MessageDisplayItem
+}
+
+interface ToolCacheEntry {
+  toolPart: any
+  messageInfo?: any
+  item: ToolDisplayItem
+}
+
 export default function MessageStream(props: MessageStreamProps) {
   let containerRef: HTMLDivElement | undefined
   const [autoScroll, setAutoScroll] = createSignal(true)
   const [showScrollButton, setShowScrollButton] = createSignal(false)
 
+  let messageItemCache = new Map<string, MessageCacheEntry>()
+  let toolItemCache = new Map<string, ToolCacheEntry>()
+
   const connectionStatus = () => sseManager.getStatus(props.instanceId)
 
   const sessionInfo = createMemo(() => {
@@ -180,9 +209,11 @@ export default function MessageStream(props: MessageStreamProps) {
 
   const displayItems = createMemo(() => {
     // Ensure memo reacts to preference changes
-    preferences().showThinkingBlocks
+    const showThinking = preferences().showThinkingBlocks
 
     const items: DisplayItem[] = []
+    const newMessageCache = new Map<string, MessageCacheEntry>()
+    const newToolCache = new Map<string, ToolCacheEntry>()
 
     let lastAssistantIndex = -1
     for (let i = props.messages.length - 1; i >= 0; i--) {
@@ -201,35 +232,82 @@ export default function MessageStream(props: MessageStreamProps) {
         break
       }
 
-      // Use precomputed displayParts, fallback to empty arrays if not available
-      const displayParts = message.displayParts || { text: [], tool: [], reasoning: [] }
-      const textParts = displayParts.text
-      const toolParts = displayParts.tool
-      const reasoningParts = displayParts.reasoning
+      const baseDisplayParts = message.displayParts
+      const displayParts: MessageDisplayParts =
+        baseDisplayParts && baseDisplayParts.showThinking === showThinking
+          ? baseDisplayParts
+          : computeDisplayParts(message, showThinking)
 
+      const combinedParts = displayParts.combined
+      const version = message.version ?? 0
       const isQueued = message.type === "user" && (lastAssistantIndex === -1 || index > lastAssistantIndex)
 
-      if (textParts.length > 0 || reasoningParts.length > 0 || messageInfo?.error) {
-        items.push({
+      const cacheEntry = messageItemCache.get(message.id)
+      if (
+        cacheEntry &&
+        cacheEntry.version === version &&
+        cacheEntry.showThinking === showThinking &&
+        cacheEntry.isQueued === isQueued &&
+        cacheEntry.messageInfo === messageInfo
+      ) {
+        cacheEntry.displayParts = displayParts
+        cacheEntry.version = version
+        cacheEntry.showThinking = showThinking
+        cacheEntry.isQueued = isQueued
+        cacheEntry.messageInfo = messageInfo
+        cacheEntry.item.message = message
+        cacheEntry.item.combinedParts = combinedParts
+        cacheEntry.item.isQueued = isQueued
+        cacheEntry.item.messageInfo = messageInfo
+        newMessageCache.set(message.id, cacheEntry)
+        items.push(cacheEntry.item)
+      } else {
+        const messageItem: MessageDisplayItem = {
           type: "message",
-          data: {
-            ...message,
-            parts: [...textParts, ...reasoningParts],
-            isQueued,
-          },
+          message,
+          combinedParts,
+          isQueued,
           messageInfo,
+        }
+        newMessageCache.set(message.id, {
+          version,
+          showThinking,
+          isQueued,
+          messageInfo,
+          displayParts,
+          item: messageItem,
         })
+        items.push(messageItem)
       }
 
-      for (const toolPart of toolParts) {
-        items.push({
-          type: "tool",
-          data: toolPart,
-          messageInfo,
-        })
+      for (let toolIndex = 0; toolIndex < displayParts.tool.length; toolIndex++) {
+        const toolPart = displayParts.tool[toolIndex]
+        const toolKey = typeof toolPart?.id === "string" ? toolPart.id : `${message.id}-tool-${toolIndex}`
+
+        const toolEntry = toolItemCache.get(toolKey)
+        if (toolEntry && toolEntry.toolPart === toolPart && toolEntry.messageInfo === messageInfo) {
+          toolEntry.item.toolPart = toolPart
+          toolEntry.item.messageInfo = messageInfo
+          toolEntry.toolPart = toolPart
+          toolEntry.messageInfo = messageInfo
+          newToolCache.set(toolKey, toolEntry)
+          items.push(toolEntry.item)
+        } else {
+          const toolItem: ToolDisplayItem = {
+            type: "tool",
+            key: toolKey,
+            toolPart,
+            messageInfo,
+          }
+          newToolCache.set(toolKey, { toolPart, messageInfo, item: toolItem })
+          items.push(toolItem)
+        }
       }
     }
 
+    messageItemCache = newMessageCache
+    toolItemCache = newToolCache
+
     return items
   })
 
@@ -301,29 +379,30 @@ export default function MessageStream(props: MessageStreamProps) {
         </Show>
 
         <For each={displayItems()} fallback={null}>
-          {(item, index) => {
-            const key = item.type === "message" ? `msg-${item.data.id}` : `tool-${item.data.id}`
-            return (
-              <Show
-                when={item.type === "message"}
-                fallback={
-                  <div class="tool-call-message" data-key={key}>
-                    <div class="tool-call-header-label">
-                      <span class="tool-call-icon">🔧</span>
-                      <span>Tool Call</span>
-                      <span class="tool-name">{item.data?.tool || "unknown"}</span>
-                    </div>
-                    <ToolCall toolCall={item.data} toolCallId={item.data.id} />
-                  </div>
-                }
-              >
+          {(item) => {
+            if (item.type === "message") {
+              return (
                 <MessageItem
-                  message={item.data}
+                  message={item.message}
                   messageInfo={item.messageInfo}
-                  isQueued={item.data.isQueued}
+                  isQueued={item.isQueued}
+                  parts={item.combinedParts}
                   onRevert={props.onRevert}
                 />
-              </Show>
+              )
+            }
+
+            const toolPart = item.toolPart
+
+            return (
+              <div class="tool-call-message" data-key={item.key}>
+                <div class="tool-call-header-label">
+                  <span class="tool-call-icon">🔧</span>
+                  <span>Tool Call</span>
+                  <span class="tool-name">{toolPart?.tool || "unknown"}</span>
+                </div>
+                <ToolCall toolCall={toolPart} toolCallId={toolPart?.id} />
+              </div>
             )
           }}
         </For>
diff --git a/src/stores/sessions.ts b/src/stores/sessions.ts
index 8ddababe..1fddfae0 100644
--- a/src/stores/sessions.ts
+++ b/src/stores/sessions.ts
@@ -82,7 +82,7 @@ function removeSessionIndexes(instanceId: string) {
   sessionIndexes.delete(instanceId)
 }
 
-function computeDisplayParts(message: Message, showThinking: boolean): MessageDisplayParts {
+export function computeDisplayParts(message: Message, showThinking: boolean): MessageDisplayParts {
   const text: any[] = []
   const tool: any[] = []
   const reasoning: any[] = []
@@ -97,7 +97,10 @@ function computeDisplayParts(message: Message, showThinking: boolean): MessageDi
     }
   }
 
-  return { text, tool, reasoning }
+  const combined = reasoning.length > 0 ? [...text, ...reasoning] : [...text]
+  const version = typeof message.version === "number" ? message.version : 0
+
+  return { text, tool, reasoning, combined, showThinking, version }
 }
 
 function withSession(instanceId: string, sessionId: string, updater: (session: Session) => void) {
@@ -710,6 +713,7 @@ async function loadMessages(instanceId: string, sessionId: string, force = false
         parts: apiMessage.parts || [],
         timestamp: info.time?.created || Date.now(),
         status: "complete" as const,
+        version: 0,
       }
 
       message.displayParts = computeDisplayParts(message, preferences().showThinkingBlocks)
@@ -824,6 +828,7 @@ function handleMessageUpdate(instanceId: string, event: any): void {
         parts: [part],
         timestamp: Date.now(),
         status: "streaming" as const,
+        version: 0,
       }
 
       newMessage.displayParts = computeDisplayParts(newMessage, preferences().showThinkingBlocks)
@@ -841,6 +846,9 @@ function handleMessageUpdate(instanceId: string, event: any): void {
     } else {
       // Update existing message
       const message = session.messages[messageIndex]
+      if (typeof message.version !== "number") {
+        message.version = 0
+      }
 
       // Strip synthetic parts when real data arrives
       let filteredSynthetics = false
@@ -864,14 +872,32 @@ function handleMessageUpdate(instanceId: string, event: any): void {
         index.partIndex.set(message.id, partMap)
       }
 
+      let shouldIncrementVersion = filteredSynthetics || replacedTemp
       const partIndex = partMap.get(part.id)
+
       if (partIndex === undefined) {
         baseParts.push(part)
         if (part.id && typeof part.id === "string") {
           partMap.set(part.id, baseParts.length - 1)
         }
+        shouldIncrementVersion = true
       } else {
+        const previousPart = baseParts[partIndex]
+        const textUnchanged =
+          !filteredSynthetics &&
+          !replacedTemp &&
+          part.type === "text" &&
+          previousPart?.type === "text" &&
+          previousPart.text === part.text
+
+        if (textUnchanged) {
+          return
+        }
+
         baseParts[partIndex] = part
+        if (part.type !== "text" || !previousPart || previousPart.text !== part.text) {
+          shouldIncrementVersion = true
+        }
       }
 
       const oldId = message.id
@@ -879,7 +905,16 @@ function handleMessageUpdate(instanceId: string, event: any): void {
       message.status = message.status === "sending" ? "streaming" : message.status
       message.parts = baseParts
 
-      message.displayParts = computeDisplayParts(message, preferences().showThinkingBlocks)
+      if (shouldIncrementVersion) {
+        message.version += 1
+        message.displayParts = computeDisplayParts(message, preferences().showThinkingBlocks)
+      } else if (
+        !message.displayParts ||
+        message.displayParts.showThinking !== preferences().showThinkingBlocks ||
+        message.displayParts.version !== message.version
+      ) {
+        message.displayParts = computeDisplayParts(message, preferences().showThinkingBlocks)
+      }
 
       // Update message index if ID changed
       if (oldId !== message.id) {
@@ -947,11 +982,17 @@ function handleMessageUpdate(instanceId: string, event: any): void {
       if (tempMessageIndex > -1) {
         // Replace queued message
         const message = session.messages[tempMessageIndex]
+        if (typeof message.version !== "number") {
+          message.version = 0
+        }
+
         const oldId = message.id
         message.id = info.id
         message.type = (info.role === "user" ? "user" : "assistant") as "user" | "assistant"
         message.timestamp = info.time?.created || Date.now()
         message.status = "complete" as const
+        message.version += 1
+        message.displayParts = computeDisplayParts(message, preferences().showThinkingBlocks)
 
         if (oldId !== message.id) {
           index.messageIndex.delete(oldId)
@@ -971,6 +1012,7 @@ function handleMessageUpdate(instanceId: string, event: any): void {
           parts: [],
           timestamp: info.time?.created || Date.now(),
           status: "complete" as const,
+          version: 0,
         }
 
         newMessage.displayParts = computeDisplayParts(newMessage, preferences().showThinkingBlocks)
@@ -989,16 +1031,21 @@ function handleMessageUpdate(instanceId: string, event: any): void {
     } else {
       // Update existing message status
       const message = session.messages[messageIndex]
+      if (typeof message.version !== "number") {
+        message.version = 0
+      }
       message.status = "complete" as const
+      message.version += 1
+      message.displayParts = computeDisplayParts(message, preferences().showThinkingBlocks)
+
+      session.messagesInfo.set(info.id, info)
+
+      withSession(instanceId, info.sessionID, (session) => {
+        // Session already mutated in place
+      })
+
+      updateSessionInfo(instanceId, info.sessionID)
     }
-
-    session.messagesInfo.set(info.id, info)
-
-    withSession(instanceId, info.sessionID, (session) => {
-      // Session already mutated in place
-    })
-
-    updateSessionInfo(instanceId, info.sessionID)
   }
 }
 
@@ -1110,6 +1157,7 @@ async function sendMessage(
     parts: optimisticParts,
     timestamp: Date.now(),
     status: "sending",
+    version: 0,
   }
 
   optimisticMessage.displayParts = computeDisplayParts(optimisticMessage, preferences().showThinkingBlocks)
diff --git a/src/types/message.ts b/src/types/message.ts
index 01dbe187..c2a54ec8 100644
--- a/src/types/message.ts
+++ b/src/types/message.ts
@@ -2,6 +2,9 @@ export interface MessageDisplayParts {
   text: any[]
   tool: any[]
   reasoning: any[]
+  combined: any[]
+  showThinking: boolean
+  version: number
 }
 
 export interface Message {
@@ -11,5 +14,6 @@ export interface Message {
   parts: any[]
   timestamp: number
   status: "sending" | "sent" | "streaming" | "complete" | "error"
+  version: number
   displayParts?: MessageDisplayParts
 }