Anthropic updated billing behavior in Claude Platform for refusals occurring before output is generated for the user. According to the company's September 24 Release Notes, billing now applies when stop_details.category is bio, frontier_llm or reasoning_extraction.
Anthropic says the change focuses on categories where low false positive rates were measured.
For developers using Claude API, this means a request stopped before a visible answer can still incur charges in these scenarios. Monitor stop_details and usage data rather than assume an early refusal always costs zero.