When to use Extended Thinking — and when not to

Extended Thinking is Claude's mode for working through complex problems step by step before responding. In standard mode, Claude reads your message and produces a response. In Extended Thinking mode, Claude reasons through the problem — exploring approaches, checking its logic, considering edge cases — before writing the final answer.

The tradeoff is simple: Extended Thinking takes longer and uses more tokens. In exchange, it produces better reasoning on problems that actually require it.

What Extended Thinking improves

Multi-step reasoning problems. When getting from question to answer requires holding multiple pieces of logic in sequence — mathematical proofs, legal analysis, complex planning problems, code architecture — Extended Thinking produces more reliable answers. Standard Claude can handle simpler versions of these, but longer chains of reasoning are where it tends to drop threads.

Problems with many valid approaches. When the question has multiple plausible answers and you want Claude to evaluate them against each other before committing — strategic decisions, architectural choices, competing interpretations — Extended Thinking gives Claude time to work through the options rather than defaulting to the first plausible one.

Tasks where systematic coverage matters. Reviewing a contract for risk, auditing a plan for gaps, checking an argument for logical flaws — tasks where missing something has a cost. Extended Thinking gives Claude time to be more thorough.

Hard coding and technical problems. Complex algorithms, debugging non-obvious issues, designing systems with multiple interacting components. This is where Extended Thinking's benefits are clearest to most users.

What Extended Thinking does not improve

Simple questions. If the answer does not require reasoning — factual recall, basic summarisation, straightforward writing tasks — Extended Thinking adds time and cost without improving quality. Use standard Claude for 90% of tasks.

Creative tasks. Writing, brainstorming, ideation — Extended Thinking can make Claude more systematic but often makes it less fluent and creative. The reasoning process is a constraint as much as a capability for open-ended creative work.

Tasks where speed matters more than depth. Customer support drafts, quick Q&A, anything where responsiveness is part of the value. Use standard Claude.

How to activate it

In Claude.ai, Extended Thinking is available in certain plans and can be toggled per conversation. Look for the "Extended" or "Think" option in the interface. For API users, it is available as a parameter in the messages API.

Not every plan includes Extended Thinking — check your plan's feature set. It is available on Pro and above.

A practical test

If you are not sure whether Extended Thinking is right for your task, run it both ways: once with Extended Thinking, once without. Compare the outputs. For tasks that genuinely benefit, the difference will be obvious — more thorough reasoning, fewer gaps. For tasks that don't, you'll get similar results and can save the additional processing time.

The general rule: if you would want a smart person to think carefully before answering rather than answering immediately, Extended Thinking is probably the right mode. If you want a quick, fluent response, standard Claude is better.

Extended Thinking and Adaptive Thinking

Adaptive Thinking is the automatic version — Claude decides when to think deeply based on the complexity of the question, without you having to specify. Extended Thinking is the explicit version — you tell Claude to think carefully regardless of how complex it judges the question to be.

For most users, Adaptive Thinking is sufficient. Extended Thinking is for when you have a specific hard problem and want to be sure Claude is giving it full attention.