Per-Response Model Identity Disclosure in Frontier AI APIs: Cross-Vendor Comparison Data (June 2026)

Controlled comparison of per-response model identity disclosure across Google Gemini API and Anthropic Claude API. Google returns model_version and x-gemini-service-tier in every response (8/8 tests). Anthropic returns no equivalent fields (0/4 tests); response.model echoes the requested model without confirming the served model. Demonstrates that routing transparency is technically feasible and its absence is a design choice.