According to DeepLearning.AI, researchers at Anthropic and several safety institutions have identified 'persona vectors'—distinct patterns in large language model (LLM) layer outputs that correlate with character traits such as sycophancy or hallucination tendency (source: DeepLearning.AI, Dec 8, 2025). By averaging LLM outputs from trait-specific examples and subtracting outputs of opposing traits, engineers can isolate and proactively control these characteristics. This breakthrough enables screening of fine-tuning datasets to predict and manage personality shifts before training, resulting in safer and more predictable LLM behavior. The study demonstrates that high-level LLM behaviors are structured and editable, unlocking new market opportunities for robust, customizable AI applications in industries with strict safety and compliance requirements (source: DeepLearning.AI, 2025).