On the Theoretical Limitations of Embedding-Based Retrieval

Authors: Orion Weller, Michael Boratko, Iftekhar Naim, Jinhyuk Lee

License: CC BY 4.0

Results of the summarizing process for the arXiv paper: 2508.21038v1

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In recent years, vector embeddings have been increasingly utilized for a wide range of retrieval tasks. These include reasoning, instruction-following, and coding. These new applications have pushed embeddings to adapt to various queries and notions of relevance. While previous studies have highlighted theoretical limitations of vector embeddings, there has been a prevailing belief that these challenges stem from unrealistic queries and can be overcome with improved training data and larger models. However, a recent study by Orion Weller et al. challenges this assumption by demonstrating that these theoretical limitations can manifest in realistic scenarios even with simple queries. By drawing connections to learning theory, the researchers show that the number of top-k subsets of documents retrievable for a given query is constrained by the dimensionality of the embedding space. Even when focusing on k=2 subsets, this limitation persists as evidenced through empirical testing with parameterized embeddings on test sets. To further investigate these constraints, the researchers introduce a new dataset called LIMIT designed to stress test models based on these theoretical findings. Surprisingly, state-of-the-art models struggle to perform well on this dataset despite its straightforward nature. This study sheds light on the boundaries of embedding models operating within the single vector paradigm and underscores the need for future research to develop innovative methods capable of addressing this fundamental limitation in retrieval tasks. In conclusion, highlights the intricate challenges faced by embedding models in handling diverse retrieval tasks and emphasizes of exploring novel approaches to overcome inherent limitations in current methodologies.
AI-generated keywords: Vector embeddings Retrieval tasks Limitations Learning theory Innovative methods

AI-generated Key Points

  • Vector embeddings increasingly used for retrieval tasks
  • Applications include reasoning, instruction-following, and coding
  • Challenges in adapting to various queries and notions of relevance
  • Theoretical limitations of vector embeddings highlighted in previous studies
  • Recent study by Orion Weller et al. challenges assumption that challenges stem from unrealistic queries
  • Number of top-k subsets retrievable constrained by dimensionality of embedding space
  • Limitations persist even when focusing on k=2 subsets
  • Introduction of new dataset called LIMIT to stress test models based on theoretical findings
  • State-of-the-art models struggle on the LIMIT dataset despite its straightforward nature
  • Need for future research to develop innovative methods addressing fundamental limitations in retrieval tasks
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Abstract: Vector embeddings have been tasked with an ever-increasing set of retrieval tasks over the years, with a nascent rise in using them for reasoning, instruction-following, coding, and more. These new benchmarks push embeddings to work for any query and any notion of relevance that could be given. While prior works have pointed out theoretical limitations of vector embeddings, there is a common assumption that these difficulties are exclusively due to unrealistic queries, and those that are not can be overcome with better training data and larger models. In this work, we demonstrate that we may encounter these theoretical limitations in realistic settings with extremely simple queries. We connect known results in learning theory, showing that the number of top-k subsets of documents capable of being returned as the result of some query is limited by the dimension of the embedding. We empirically show that this holds true even if we restrict to k=2, and directly optimize on the test set with free parameterized embeddings. We then create a realistic dataset called LIMIT that stress tests models based on these theoretical results, and observe that even state-of-the-art models fail on this dataset despite the simple nature of the task. Our work shows the limits of embedding models under the existing single vector paradigm and calls for future research to develop methods that can resolve this fundamental limitation.

Submitted to arXiv on 28 Aug. 2025

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