One of the concerns with modern AI chatbots is their tendency to "hallucinate" - to generate fictional facts and information that has no basis in reality. This issue came to prominence recently when a law firm got in trouble for submitting fake legal opinions generated by the AI tool ChatGPT. To better understand this problem, the company Vectara has created an "AI Hallucination Leaderboard" that ranks various leading chatbots based on their rate of hallucination.

Vectara's Evaluation Approach


Vectara's approach involves feeding over 800 short reference documents to various LLMs and requesting factual summaries. The responses are then analyzed by a model that detects any introduced data not present in the source materials.

The Evaluation Criteria

The key evaluation metric is the rate of hallucination, determined by the frequency of inaccuracies or fabrications in the LLM-generated summaries.

The Hallucination Leaderboard

AI Hallucination Leaderboard: This bar chart illustrates the percentage of hallucinations for each model, while the line graph depicts the accuracy of each model.

Current Standings

GPT-4 currently leads with the lowest hallucination rate, suggesting superior accuracy. In contrast, Google's Palm-Chat exhibited a significantly higher rate of hallucination, questioning its reliability for factual summarization.

The initial leaderboard shows some striking differences between the top performers and poor performers:

  • GPT-4 had the lowest hallucination rate at just 3.8%. Its responses were highly accurate to the source material.
  • Google's Palm-Chat scored worst with a 27.1% hallucination rate. Its summaries contained significant fabricated information.
  • Other models like Anthropic's Claude and Meta's Blenderbot ranked in the middle.

Ongoing Monitoring

Vectara plans to periodically update the leaderboard to reflect advancements in LLM technology and the introduction of new models.

Understanding AI Hallucinations

The Problem

AI hallucinations refer to the generation of fabricated or inaccurate content by AI systems, particularly in contexts where factual accuracy is paramount. This issue is not just a technical challenge but also a matter of reliability and trust in AI applications.

High-Profile Cases

The Levidow case, involving made-up legal decisions like 'Martinez v. Delta Air Lines', exemplifies the potential dangers of unchecked AI hallucinations. These errors, often indistinguishable from real data, can have serious consequences in fields like law, healthcare, and defence.

Why Measuring Hallucinations Matters

The rankings provide insight into a critical AI safety issue. Chatbots that frequently hallucinate and generate false information cannot be reliably deployed in domains like healthcare, finance, or other areas where accuracy is paramount. As the authors note, "building a model that is free of hallucinations is much harder than building one that can simply detect them."

The leaderboard creates an important benchmark to evaluate progress. It puts pressure on AI teams to enhance truthfulness and minimize imagination. As new models are developed, the rankings provide a standardized way to assess their trustworthiness.

Responses to the Leaderboard

The leaderboard has already prompted discussion within the AI community:

  • Some argue the test methodology favours certain models over others. The prompts and documents may play to the strengths/weaknesses of some chatbots.
  • Others note the leaderboard focuses narrowly on factual accuracy over other dimensions of chatbot quality. Creativity, personality and nuanced language understanding are not measured.
  • Many agree the leaderboard provides a useful starting point to address the critical issue of hallucination. More rigorous testing frameworks will evolve over time.

The Path Ahead

Reducing hallucinations will be a pivotal challenge as chatbots grow more powerful. Testing frameworks like Vectara's leaderboard are a first step toward accountability and transparency. As chatbot creators refine their models, hallucination rates should gradually improve. But perfectly truthful AI may remain elusive for some time. Striking the right balance between creativity and accuracy will require continued research and responsible development.


Vectara's AI Hallucination Leaderboard highlights the variance in factual accuracy between leading chatbots today. Minimizing false information from AI systems is critical as they take on greater roles in society. While imperfect, the leaderboard provides an initial benchmark to incentivize greater truthfulness in AI conversational agents. Ongoing work to refine hallucination detection and reduce imagination-driven errors will be vital to building trust in this rapidly advancing technology.

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