How do you enable thinking on Claude Opus 5?

On Claude Opus 5, thinking is already enabled by default for requests that don't configure it explicitly, a change from every prior Opus model, where thinking needed to be explicitly turned on with something like thinking: {"type": "adaptive"}.

Because of this, developers migrating from Opus 4.8 generally don't need to add anything to get thinking behavior on Opus 5 - if anything, they need to actively opt out if they want it disabled.

To disable thinking instead, a request can set thinking: {"type": "disabled"}, but this is only accepted at effort level high or below - attempting to disable thinking at xhigh or max effort returns an HTTP 400 error, since Anthropic requires thinking to stay on at those higher effort levels.

Invest now in Acorns!!! 🚀
Join Acorns and get your $5 bonus!

Acorns is a micro-investing app that automatically invests your "spare change" from daily purchases into diversified, expert-built portfolios of ETFs. It is designed for beginners, allowing you to start investing with as little as $5. The service automates saving and investing. Disclosure: I may receive a referral bonus.

Invest now!!! Get Free equity stock (US, UK only)!

Use Robinhood app to invest in stocks. It is safe and secure. Use the Referral link to claim your free stock when you sign up!.

The Robinhood app makes it easy to trade stocks, crypto and more.

Webull! Receive free stock by signing up using the link: Webull signup.