Pinterest is shifting its AI investments towards fine-tuned open-source models to achieve similar performance at a lower cost. Open-source models are improving, especially in cost efficiency against their performance. Pinterest finds that compact, fit-for-purpose models outperform general-purpose LLMs on specific tasks. This approach allows them to leverage domain-specific data and product integration for differentiation. User modeling, visual, and text foundation models are built, bought, or adapted based on modalities. The shift to open-source is driven by the leveling of model capabilities and the emphasis on fine-tuning. Pinterest’s assistant leverages Pinterest-native tools and an LLM for query understanding and tool calling. Advantages include reduced costs, better personalization, and the ability to align models with brand values. Pinterest will continue using a mix of internally developed, fine-tuned open-source, and third-party AI models. The long-term strategy involves leveraging data to build efficient models and partnering to address capability gaps.