Emotion representations in transformer language models localize at approximately 50% depth following an architecture-invariant U-shaped pattern across model scales from 124M to 3B parameters

Jeong's systematic investigation across nine models from five architectural families (124M to 3B parameters) found that emotion representations consistently cluster in middle transformer layers at approximately 50% depth, following a U-shaped localization curve that is 'architecture-invariant.' This finding extends Anthropic's emotion vector work from frontier-scale models (Claude Sonnet 4.5) down to small models, demonstrating that the localization pattern is not an artifact of scale or specific training procedures but a structural property of transformer architectures themselves. The generation-based extraction method produced statistically superior emotion separation (p = 0.007) compared to comprehension-based methods, and steering experiments achieved 92% success rate with three distinct behavioral regimes: surgical (coherent transformation), repetitive collapse, and explosive (text degradation). The architecture-invariance across such a wide parameter range (spanning nearly two orders of magnitude) suggests that emotion representations are a fundamental organizational principle in transformers, making emotion vector steering a potentially general-purpose alignment mechanism applicable across model scales.