When to use extended thinking across Claude models in the Claude App and Claude Code
Generated by Claude Opus 4.5 (with extended thinking)
Extended thinking gives Claude a "scratchpad" to reason through problems before responding. It's the same model with more time to deliberate — not a separate model. Performance on complex tasks improves logarithmically with thinking tokens allocated.
Key insight: Extended thinking isn't universally better. Research shows it can hurt performance by up to 36% on certain task types — similar to how humans perform worse when overthinking intuitive tasks.
| App | Model | Default | When to Enable | When to Keep Off |
|---|---|---|---|---|
| Claude App | Sonnet 4.5 | Off | Complex reasoning, debugging, analysis | Simple Q&A, creative writing, lookups |
| Claude App | Opus 4.5 | On (Max) | Leave on for most tasks | Quick chat, pattern recognition |
| Claude App | Haiku 4.5 | Off | Hard problems where speed matters less | Real-time tasks, rapid iteration |
| Claude Code | Sonnet 4.5 | Off | Architecture, complex bugs, planning | Routine edits, boilerplate |
| Claude Code | Opus 4.5 | Off | System design, multi-codebase work | Most tasks — Opus is already strong |
| Claude Code | Haiku 4.5 | Off | When stuck in loops, multi-step logic | Prototyping, scaffolding |
- Click "Search and tools" button (lower left)
- Toggle "Extended thinking" on
| Plan | Models Available |
|---|---|
| Free | Sonnet 4.5, Haiku 4.5 |
| Pro | Sonnet 4.5, Haiku 4.5 |
| Max | All models (Opus 4.5 is default) |
Use thinking for:
- Multi-step math or logic problems
- Debugging complex code
- Architectural planning
- Legal/financial analysis
- When accuracy matters more than speed
Keep thinking off for:
- Simple factual questions
- Quick translations
- Summarisation
- Creative writing (style/voice)
- Pattern recognition tasks
Opus is a hybrid model — reasons deeply even without extended thinking. For Max users, defaults to thinking on.
Use thinking for:
- Leave it on for most tasks
- Complex multi-step analysis
- Deep research and synthesis
Keep thinking off for:
- Quick chat, simple Q&A
- When latency matters
- Pattern matching / classification
First Haiku with extended thinking. Use when you need speed + occasional depth.
Use thinking for:
- Complex coding problems
- Multi-step reasoning
- When stuck on a hard problem
Keep thinking off for:
- Quick lookups, simple chat
- Real-time interactions
- High-throughput tasks
Method 1: Tab key
- Press
Tabto toggle thinking on/off - Sticky across sessions
Method 2: Keywords in prompts
| Keyword | Tokens | Use Case |
|---|---|---|
think |
~4,000 | Routine debugging, basic refactoring |
think hard / megathink |
~10,000 | Architectural decisions, complex problems |
think harder / ultrathink |
~32,000 | Hardest tasks, deep sustained reasoning |
| Plan | Models Available |
|---|---|
| Pro | Sonnet 4.5, Haiku 4.5 (no Opus) |
| Max | All models including Opus 4.5 |
1. EXPLORE → Let Claude read files (don't write code yet)
2. PLAN → "ultrathink. Analyse this and propose a plan. Don't code yet."
3. CODE → Implement based on confirmed plan
4. COMMIT → Ask Claude to commit and create PR
Steps 1–2 are crucial. Without them, Claude jumps straight to coding.
Trigger thinking for:
ultrathinkbefore architectural decisionsthink hardfor complex debugging- When Claude gets stuck in a loop
- Multi-file refactoring
- Before writing code — ask for a plan first
No keyword needed for:
- Simple file edits
- Routine refactoring
- Generating boilerplate
- Quick questions about code
Trigger thinking for:
- Complex system design
- Multi-codebase refactoring
- Debugging subtle concurrency issues
No keyword needed for:
- Most tasks — Opus is already strong
- Simple changes
- When speed matters
Note: Opus 4.5 uses fewer tokens than Sonnet to solve the same problems.
Trigger thinking for:
- When Claude gets stuck
- Complex logic problems
- Multi-step analysis
No keyword needed for:
- Rapid prototyping
- UI scaffolding
- Simple file operations
Research shows thinking can degrade performance on these task types:
| Task Type | Why Thinking Hurts |
|---|---|
| Pattern recognition | Intuition beats deliberation |
| Visual classification | Statistical learning is implicit |
| Classification with exceptions | Overthinking misses edge cases |
| Implicit learning tasks | Analysis interferes with pattern matching |
Rule of thumb: If a human would do worse by "thinking too hard," so will Claude.
Simple question → OFF
Complex reasoning → ON
Creative writing → OFF
Code debugging → ON
Quick lookup → OFF
Analysis/research → ON
Pattern matching → OFF
Quick fix → No keyword
Routine refactor → "think"
Architecture → "ultrathink" + plan first
Stuck in loop → "ultrathink"
Simple edit → No keyword
New feature → "think hard" + plan first
Prototyping → No keyword
| Metric | Haiku 4.5 | Sonnet 4.5 | Opus 4.5 |
|---|---|---|---|
| SWE-bench | 73.3% | 77.2% | 80.9% |
| Speed | Fastest (2x Sonnet) | Fast | Slower |
| Best for | High-volume, real-time | Daily development | Complex/critical tasks |
| Extended thinking | First Haiku with it | Recommended for coding | Usually unnecessary |
- Start without thinking — enable when you hit problems needing deeper analysis
- Plan before coding — especially with
ultrathinkin Claude Code - Opus rarely needs thinking — it's already a strong reasoner
- Haiku + thinking — unlocks near-Sonnet performance when needed
- Avoid thinking for pattern tasks — it can hurt performance significantly
- Keywords only work in Claude Code — not in the Claude App or API
Last updated: November 2025