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## Summary GPT-5 introduced the concept of [custom tools](https://platform.openai.com/docs/guides/function-calling#custom-tools), which allow the model to send a raw string result back, simplifying json-escape issues. We are migrating gpt-5 to use this by default. However, gpt-oss models do not support custom tools, only normal functions. So we keep both tool definitions, and provide whichever one the model family supports. ## Testing - [x] Tested locally with various models - [x] Unit tests pass