diff --git a/cli/src/components/__tests__/thinking.test.tsx b/cli/src/components/__tests__/thinking.test.tsx
new file mode 100644
index 0000000000..e20a5273c3
--- /dev/null
+++ b/cli/src/components/__tests__/thinking.test.tsx
@@ -0,0 +1,95 @@
+import { beforeAll, describe, expect, test } from 'bun:test'
+import { createTestRenderer } from '@opentui/core/testing'
+import { createRoot, flushSync } from '@opentui/react'
+import React from 'react'
+
+import { Thinking } from '../thinking'
+import { initializeThemeStore } from '../../hooks/use-theme'
+
+beforeAll(() => {
+  initializeThemeStore()
+})
+
+describe('Thinking component', () => {
+  const content = 'Line 1 of reasoning.\nLine 2 of reasoning.\nLine 3 of reasoning.'
+
+  test('renders in preview state with preview lines', async () => {
+    const setup = await createTestRenderer({ width: 80, height: 10 })
+    const root = createRoot(setup.renderer)
+    flushSync(() => {
+      root.render(
+        <Thinking
+          content={content}
+          thinkingCollapseState="preview"
+          isThinkingComplete={true}
+          onToggle={() => {}}
+          availableWidth={80}
+        />,
+      )
+    })
+
+    try {
+      await setup.renderOnce()
+      const frame = setup.captureCharFrame()
+      expect(frame).toContain('Thinking')
+      expect(frame).toContain('Line')
+    } finally {
+      flushSync(() => root.unmount())
+      setup.renderer.destroy()
+    }
+  })
+
+  test('renders in hidden state without preview text', async () => {
+    const setup = await createTestRenderer({ width: 80, height: 10 })
+    const root = createRoot(setup.renderer)
+    flushSync(() => {
+      root.render(
+        <Thinking
+          content={content}
+          thinkingCollapseState="hidden"
+          isThinkingComplete={true}
+          onToggle={() => {}}
+          availableWidth={80}
+        />,
+      )
+    })
+
+    try {
+      await setup.renderOnce()
+      const frame = setup.captureCharFrame()
+      expect(frame).toContain('Thinking')
+      expect(frame).toContain('▸')
+      expect(frame).not.toContain('Line 1 of reasoning.')
+    } finally {
+      flushSync(() => root.unmount())
+      setup.renderer.destroy()
+    }
+  })
+
+  test('renders in expanded state with expanded text', async () => {
+    const setup = await createTestRenderer({ width: 80, height: 10 })
+    const root = createRoot(setup.renderer)
+    flushSync(() => {
+      root.render(
+        <Thinking
+          content={content}
+          thinkingCollapseState="expanded"
+          isThinkingComplete={true}
+          onToggle={() => {}}
+          availableWidth={80}
+        />,
+      )
+    })
+
+    try {
+      await setup.renderOnce()
+      const frame = setup.captureCharFrame()
+      expect(frame).toContain('Thinking')
+      expect(frame).toContain('▾')
+      expect(frame).toContain('Line 1 of reasoning.')
+    } finally {
+      flushSync(() => root.unmount())
+      setup.renderer.destroy()
+    }
+  })
+})
diff --git a/cli/src/components/blocks/thinking-block.tsx b/cli/src/components/blocks/thinking-block.tsx
index a29f5ff2c2..cdb3f569a1 100644
--- a/cli/src/components/blocks/thinking-block.tsx
+++ b/cli/src/components/blocks/thinking-block.tsx
@@ -27,10 +27,13 @@ export const ThinkingBlock = memo(
   }: ThinkingBlockProps) => {
     const firstBlock = blocks[0]
     const thinkingId = firstBlock?.thinkingId
-    const combinedContent = blocks
-      .map((b) => b.content)
-      .join('')
-      .trim()
+    const combinedContent =
+      blocks.length === 1
+        ? (firstBlock?.content ?? '').trim()
+        : blocks
+            .map((b) => b.content)
+            .join('')
+            .trim()
 
     const thinkingCollapseState = firstBlock?.thinkingCollapseState ?? 'preview'
     const offset = isNested ? NESTED_WIDTH_OFFSET : WIDTH_OFFSET
diff --git a/cli/src/components/thinking.tsx b/cli/src/components/thinking.tsx
index 6fbf28db50..6c77059350 100644
--- a/cli/src/components/thinking.tsx
+++ b/cli/src/components/thinking.tsx
@@ -38,21 +38,32 @@ export const Thinking = memo(
       )
     }
 
-    const width = Math.max(10, availableWidth ?? contentMaxWidth)
-    // Normalize content to single line for consistent preview (but preserve in expanded mode)
-    const normalizedContent = content.replace(/\n+/g, ' ').trim()
-    // Account for "..." prefix (3 chars) when calculating line widths
-    const effectiveWidth = width - 3
-    const { lines, hasMore } = getLastNVisualLines(
-      normalizedContent,
-      effectiveWidth,
-      PREVIEW_LINE_COUNT,
-    )
+    const showFull = thinkingCollapseState === 'expanded'
+    const isPreviewCandidate = thinkingCollapseState === 'preview'
+
+    let lines: string[] = []
+    let hasMore = false
+    if (isPreviewCandidate) {
+      const width = Math.max(10, availableWidth ?? contentMaxWidth)
+      // Normalize content to single line for consistent preview (but preserve in expanded mode)
+      const normalizedContent = content.replace(/\n+/g, ' ').trim()
+      // Account for "..." prefix (3 chars) when calculating line widths
+      const effectiveWidth = width - 3
+      const result = getLastNVisualLines(
+        normalizedContent,
+        effectiveWidth,
+        PREVIEW_LINE_COUNT,
+      )
+      lines = result.lines
+      hasMore = result.hasMore
+    }
+
     // In expanded mode, preserve original line breaks for proper markdown rendering
-    const expandedContent = content.replace(/\n\n+/g, '\n\n').trim()
+    const expandedContent = showFull
+      ? content.replace(/\n\n+/g, '\n\n').trim()
+      : ''
 
-    const showFull = thinkingCollapseState === 'expanded'
-    const showPreview = thinkingCollapseState === 'preview' && lines.length > 0
+    const showPreview = isPreviewCandidate && lines.length > 0
 
     const toggleIndicator =
       !isThinkingComplete ? '• '