diff --git a/pkg/tui/components/messages/messages.go b/pkg/tui/components/messages/messages.go
index a96fd4399..b817639c3 100644
--- a/pkg/tui/components/messages/messages.go
+++ b/pkg/tui/components/messages/messages.go
@@ -56,6 +56,7 @@ type Model interface {
 	LoadFromSession(sess *session.Session) tea.Cmd
 
 	ScrollToBottom() tea.Cmd
+	AdjustBottomSlack(delta int)
 }
 
 // renderedItem represents a cached rendered message with position information
@@ -1229,6 +1230,13 @@ func (m *model) ScrollToBottom() tea.Cmd {
 	}
 }
 
+func (m *model) AdjustBottomSlack(delta int) {
+	if delta == 0 {
+		return
+	}
+	m.bottomSlack = max(0, m.bottomSlack+delta)
+}
+
 // contentWidth returns the width available for content.
 // Always reserves 2 chars for scrollbar (space + bar) to prevent layout shifts.
 func (m *model) contentWidth() int {
diff --git a/pkg/tui/page/chat/chat.go b/pkg/tui/page/chat/chat.go
index 81eeaedc8..da4f7f0f6 100644
--- a/pkg/tui/page/chat/chat.go
+++ b/pkg/tui/page/chat/chat.go
@@ -421,14 +421,47 @@ func (p *chatPage) setWorking(working bool) tea.Cmd {
 
 // setPendingResponse sets the pending response state.
 // When true, a spinner is shown below the messages while waiting for the first chunk.
+// Resizes messages to leave room for the spinner; bottomSlack smooths the transition.
 func (p *chatPage) setPendingResponse(pending bool) tea.Cmd {
-	p.pendingResponse = pending
 	if pending {
-		// Reset spinner to get a fresh random phrase
+		p.pendingResponse = pending
+
+		// Resize messages to account for spinner space (3 lines: 2 newlines + 1 spinner)
+		mainWidth, messagesHeight := p.messagesSize()
+		resizeCmd := p.messages.SetSize(mainWidth, messagesHeight)
+
 		p.pendingSpinner = p.pendingSpinner.Reset()
-		return p.pendingSpinner.Init()
+		return tea.Batch(resizeCmd, p.pendingSpinner.Init())
 	}
-	return nil
+
+	p.pendingResponse = pending
+
+	// Resize messages to reclaim spinner space and add slack to prevent a visual jump.
+	mainWidth, messagesHeight := p.messagesSize()
+	resizeCmd := p.messages.SetSize(mainWidth, messagesHeight)
+	p.messages.AdjustBottomSlack(pendingSpinnerHeight)
+
+	return resizeCmd
+}
+
+// pendingSpinnerHeight is the space taken by the pending spinner (2 newlines + 1 line)
+const pendingSpinnerHeight = 3
+
+func (p *chatPage) messagesSize() (int, int) {
+	innerWidth := p.width - 2
+	var mainWidth int
+	if p.width >= minWindowWidth {
+		mainWidth = max(1, innerWidth-sidebarWidth)
+	} else {
+		mainWidth = max(innerWidth, 1)
+	}
+
+	messagesHeight := p.chatHeight
+	if p.pendingResponse {
+		messagesHeight -= pendingSpinnerHeight
+	}
+
+	return mainWidth, max(1, messagesHeight)
 }
 
 // View renders the chat page
@@ -453,13 +486,12 @@ func (p *chatPage) View() string {
 		}
 	}
 
-	if p.width >= minWindowWidth {
-		// Ensure we don't exceed available space
-		chatWidth := max(1, innerWidth-sidebarWidth)
+	mainWidth, _ := p.messagesSize()
 
+	if p.width >= minWindowWidth {
 		chatView := styles.ChatStyle.
 			Height(p.chatHeight).
-			Width(chatWidth).
+			Width(mainWidth).
 			Render(messagesView)
 
 		sidebarView := lipgloss.NewStyle().
@@ -478,7 +510,7 @@ func (p *chatPage) View() string {
 
 		chatView := styles.ChatStyle.
 			Height(p.chatHeight).
-			Width(innerWidth).
+			Width(mainWidth).
 			Render(messagesView)
 
 		sidebarView := lipgloss.NewStyle().
@@ -551,7 +583,6 @@ func (p *chatPage) SetSize(width, height int) tea.Cmd {
 		)
 	} else {
 		const horizontalSidebarHeight = 3
-		mainWidth = max(innerWidth, 1)
 		p.chatHeight = max(1, height-actualEditorHeight-horizontalSidebarHeight-2) // -1 for resize handle, -1 for empty line before status bar
 		p.sidebar.SetMode(sidebar.ModeHorizontal)
 		cmds = append(cmds,
@@ -562,8 +593,9 @@ func (p *chatPage) SetSize(width, height int) tea.Cmd {
 	}
 
 	// Set component sizes
+	mainWidth, messagesHeight := p.messagesSize()
 	cmds = append(cmds,
-		p.messages.SetSize(mainWidth, p.chatHeight),
+		p.messages.SetSize(mainWidth, messagesHeight),
 	)
 
 	return tea.Batch(cmds...)