Fig. 1. Interactive comparison of embeddings for 50,000 words from three different corpora (a), using Emblaze within a Jupyter notebook. Given a selection, in this case a group of words about winemaking (b), the Star Trail visualization (c) highlights points near the group in the high-dimensional space whose neighborhoods change significantly. The plot can be manually interpolated between the two embedding spaces using a slider (d). In the sidebar, the neighborhood comparisons for the current selection (e) show a greater emphasis on recreational wine-related activities in Twitter data, such as "tastings" and "Sonoma. " The sidebar can alternatively display Suggested Selections relevant to the current visualization state (f), including clusters of wine varieties and other beverages.Modern machine learning techniques commonly rely on complex, high-dimensional embedding representations to capture underlying structure in the data and improve performance. In order to characterize model flaws and choose a desirable representation, model builders often need to compare across multiple embedding spaces, a challenging analytical task supported by few existing tools. We first interviewed nine embedding experts in a variety of fields to characterize the diverse challenges they face and techniques they use when analyzing embedding spaces. Informed by these perspectives, we developed a novel system called Emblaze that integrates embedding space comparison within a computational notebook environment. Emblaze uses an animated, interactive scatter plot with a novel Star Trail augmentation to enable visual comparison. It also employs novel neighborhood analysis and clustering procedures to dynamically suggest groups of points with interesting changes between spaces. Through a series of case studies with ML experts, we demonstrate how interactive comparison with Emblaze can help gain new insights into embedding space structure. CCS Concepts: • Human-centered computing → Visualization systems and tools; • Computing methodologies → Learning latent representations.