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# OpenAI Claims Major Drop in Hallucinations with GPT-5
- URL: https://www.theleftshift.com/openai-claims-major-drop-in-hallucinations-with-gpt-5/
- Published: 2025-08-08T07:30:05.000Z
- Updated: 2025-08-08T07:30:05.000Z
- Description: OpenAI claims GPT-5 is ~45% less likely to produce factual errors than GPT-4o on real-world queries.
- Author: The Left Shift Bureau
- Tags: AI News

OpenAI has announced the launch of GPT-5, which the startup claims is the most advanced AI model yet. It also claims its latest AI model delivers significantly more accurate answers compared to its predecessors, with a notable [reduction in hallucinations. ](https://www.theleftshift.com/detecting-hallucinations-in-llms-is-possible-new-research-says/)

According to the company, [GPT-5 is \~45% less likely](https://openai.com/index/introducing-gpt-5/?ref=theleftshift.com) to produce factual errors than GPT-4o on real-world queries with web search enabled, and \~80% less likely when using its “thinking” mode—OpenAI’s term for deeper reasoning.

The improvements are particularly visible in complex, open-ended questions. OpenAI stress-tested GPT-5 using public factuality benchmarks like LongFact and FActScore. The results showed that “GPT-5 thinking” produces around six times fewer hallucinations than its earlier o3 model, demonstrating a significant leap in long-form factual accuracy.

In addition to factual reliability, GPT-5 also shows enhanced instruction-following and reduced sycophancy. The model’s performance is especially strong in writing, coding, and health-related queries—three of ChatGPT’s most common use cases. 

Recently, [OpenAI also released two open-source models- GPT-OSS-120B and GPT-OSS-20B](https://www.theleftshift.com/openai-launches-open-source-models-tops-hugging-face-leaderboard/)\- which also hallucinate significantly more compared to older models. 

"gpt-oss-120b and gpt-oss-20b underperform OpenAI o4-mini on both our SimpleQA and PersonQA evaluations," OpenAI [admitted](https://cdn.openai.com/pdf/419b6906-9da6-406c-a19d-1bb078ac7637/oai%5Fgpt-oss%5Fmodel%5Fcard.pdf?ref=theleftshift.com#page16).

Previously, OpenAI admitted that their earlier models– o3 and o4 mini– [hallucinate more often than older reasoning models](https://www.theleftshift.com/openai-admits-newer-models-hallucinate-even-more/) like o1, o1-mini, and o3-mini, as well as traditional models such as GPT-4.

The startup said “more research is needed” to explain why hallucinations increase as reasoning capabilities scale.