Anthropic bill is higher than expected with thinking on: reasoning tokens are billed as output tokens

TL;DR

For budgets above 32k, use batch processing: long thinking runs hit network timeouts on live requests. Compare thinking\_tokens before and after the change on the same task.

Steps

1. Read usage.output_tokens_details.thinking_tokens on the response. That field reports how many of the billed output tokens were internal reasoning. The budget is a target, not a cap: actual usage varies, and max_tokens is the hard ceiling on total output. A 16k budget on a task the model could solve in 2k of thinking is pure overspend.
2. Start near the 1024-token minimum for simple tasks and raise incrementally; start around 16k only for genuinely complex ones.
3. On adaptive-thinking models, lower effort settings let the model skip thinking entirely on easy inputs.
4. For budgets above 32k, use batch processing: long thinking runs hit network timeouts on live requests.
5. Compare thinking_tokens before and after the change on the same task. Quality holding steady while thinking tokens drop is the win; if quality drops, you found the floor.

When to use

You are seeing this: Costs jump after enabling thinking, well beyond what the visible answer length would suggest. Use this skill when you run into "Anthropic bill is higher than expected with thinking on: reasoning tokens are billed as output tokens".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

Read usage.output\tokens\details.thinking\_tokens on the response.

Thinking tokens billed as output, the thinking_tokens usage field, the budget target-not-cap rule, and the 32k batch guidance are documented on the extended thinking page. Verified live at https://docs.anthropic.com/en/docs/build-with-claude/extended-thinking.