From Sparse to Dense: GPT-4 Summarization with Chain of Density Prompting

From Sparse to Dense: GPT-4 Summarization with Chain of Density Prompting
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Original Paper
Selecting the ``right'' amount of information to include in a summary is a difficult task. A good summary should be detailed and entity-centric without being overly dense and hard to follow. To better understand this tradeoff, we solicit increasingly dense GPT-4 summaries with what we refer to as a ``Chain of Density'' (CoD) prompt. Specifically, GPT-4 generates an initial entity-sparse summary before iteratively incorporating missing salient entities without increasing the length. Summaries generated by CoD are more abstractive, exhibit more fusion, and have less of a lead bias than GPT-4 summaries generated by a vanilla prompt. We conduct a human preference study on 100 CNN DailyMail articles and find that that humans prefer GPT-4 summaries that are more dense than those generated by a vanilla prompt and almost as dense as human written summaries. Qualitative analysis supports the notion that there exists a tradeoff between informativeness and readability. 500 annotated CoD summaries, as well as an extra 5,000 unannotated summaries, are freely available on HuggingFace (

Summary Notes

Blog Post: Simplifying Summary Generation with GPT-4: Exploring Information Density

The field of natural language processing (NLP) is rapidly evolving, with automatic summarization at the forefront, especially with advancements in large language models (LLMs) like GPT-4.
A recent study introduces the concept of information density as a key to enhancing the quality of generated summaries and proposes a new method called the "Chain of Density" (CoD) prompting technique.
This post is designed for AI Engineers at enterprise companies and aims to explain the methodology, evaluation, and implications of adjusting information density to create more informative and readable summaries.


Recent progress has shown that using zero-shot prompting with LLMs can lead to concise yet content-rich summaries. The challenge, though, is achieving the right balance of information—avoiding summaries that are too sparse or too dense. The discussed study explores this by presenting a way to adjust the information density without changing the summary length, potentially changing how we think about automatic summarization.

Chain of Density Prompting

The CoD Method

The CoD technique seeks to iteratively refine summaries by increasing their entity density, making them more informative without altering their length. The process includes:
  • Starting with a basic summary: Initially focusing on a few key entities.
  • Iterative refinement: Adding 1-3 more relevant entities in each iteration to enrich the summary without making it longer.
  • Focusing on specificity and relevance: Each additional entity should significantly enhance the summary's informativeness.

Refining Summaries Iteratively

This method is unique in its approach to adding details that improve the summary's quality by focusing on specific, novel, and relevant entities. Examples in the study show how summaries can become significantly more detailed and informative through CoD's successive iterations.


The CoD method's effectiveness was tested through human preferences and automatic evaluations focusing on entity density.
  • Human Preference Judgments: Evaluations showed a clear preference for CoD-generated summaries, especially those that matched the density of summaries crafted by humans.
  • Automatic Evaluation: This measured the summaries' entity density and its correlation with human judgments on quality, informativeness, and readability, finding a strong correlation between increased density and better summary quality up to an optimal point.


The study revealed a preference for CoD-generated summaries over traditional GPT-4 summaries, identifying:
  • Optimal Density Level: There's an ideal level of density that balances informativeness and readability.
  • Entity Incorporation Methods: The method of incorporating entities affects the summary's perceived quality.


The research contributes to the NLP and automatic summarization field by:
  • Introducing a Novel Iterative Method: The CoD technique enhances summary informativeness without increasing text length.
  • Providing Insights on Informativeness vs. Readability: It gives valuable insights into balancing a summary's information content with its readability.
  • Making a Dataset Available: A dataset of CoD summaries is now available for further research, encouraging advancements in summary generation.


Manipulating information density in summary generation holds great promise for making automatic summaries more informative and enjoyable to read.
However, finding the right information density balance is complex, as too much density can harm readability. The study acknowledges these challenges and opens up its dataset for further exploration, setting the stage for future innovations in automatic summarization.

Figures and Tables

The study includes figures and tables that:
  • Show how summaries evolve from sparse to dense using the CoD technique.
  • Highlight the relationship between entity density and human preferences, emphasizing the need for an optimal density level in summary generation.

Data Availability

For AI Engineers and researchers interested in this field, the study's authors have made the CoD summaries and annotations publicly available.
This encourages further research and collaboration in developing sophisticated summarization models and exploring new domains, fostering innovation in automatic summarization solutions.

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