Verified PPLX-11 implementation is complete: **Perplexity API Integration (backend/perplexity_client.py)** - PerplexityService class with OpenAI-compatible SDK - API key from env var or constructor parameter - Model mapping: search→sonar, research→sonar-pro, labs→sonar-deep-research - Streaming response with generator pattern - Rich metadata extraction: search_results, related_questions, videos, images - Usage/cost tracking fields **API Endpoint (backend/routers/queries.py)** - POST /api/queries with SSE streaming response - Rate limiting: 10 requests/minute - Conversation history support for follow-up questions - Database persistence of all response data - Error handling with SSE error events **Test Coverage** - 19 tests in test_queries_api.py covering all functionality - All 212 backend tests pass Implementation verified complete.