The search index is provided by Brave: https://simonwillison.net/2025/Mar/21/anthropic-use-brave/
- Brave is now listed as a subprocessor on the Anthropic Trust Center portal
- Search results for "interesting pelican facts" from Claude and Brave were an exact match
- If you ask Claude for the definition of its web_search tool one of the properties is called "BraveSearchParams"