Sonar, R1-1776, and TransferEngine -- Perplexity's Open Source and Model Strategy

Perplexity is not just consuming AI models -- it builds and open-sources them. This module covers the proprietary Sonar model family (built on Llama 3.3 70B), the politically significant R1-1776 release that removed Chinese censorship from DeepSeek-R1, and TransferEngine, an open-source tool enabling trillion-parameter models on older GPU hardware. Understanding Perplexity's dual strategy of building custom models while remaining model-agnostic reveals their technical philosophy and is essential for engineering-focused interview conversations.