Shared Global and Local Geometry of Language Model Embeddings (2503.21073v2)

Abstract: Researchers have recently suggested that models share common representations. In our work, we find that token embeddings of LLMs exhibit common geometric structure. First, we find ``global'' similarities: token embeddings often share similar relative orientations. Next, we characterize local geometry in two ways: (1) by using Locally Linear Embeddings, and (2) by defining a simple measure for the intrinsic dimension of each token embedding. Our intrinsic dimension demonstrates that token embeddings lie on a lower dimensional manifold. We qualitatively show that tokens with lower intrinsic dimensions often have semantically coherent clusters, while those with higher intrinsic dimensions do not. Both characterizations allow us to find similarities in the local geometry of token embeddings. Perhaps most surprisingly, we find that alignment in token embeddings persists through the hidden states of LLMs, allowing us to develop an application for interpretability. Namely, we introduce Emb2Emb, a simple method to transfer steering vectors from one LLM to another, despite the two models having different dimensions.