Lost in Stories: Consistency Bugs in Long Story Generation by LLMs

TL;DR

This paper introduces ConStory-Bench, a comprehensive benchmark and ConStory-Checker tool to evaluate and detect consistency errors in long-form story generation by LLMs, revealing key tendencies and areas for improvement.

Contribution

It presents the first dedicated benchmark and automated detection pipeline for narrative consistency errors in long story generation by LLMs, with detailed error taxonomy and analysis.

Findings

Consistency errors are most common in factual and temporal aspects.

Errors tend to occur around the middle of narratives.

Certain error types frequently co-occur.

Abstract

What happens when a storyteller forgets its own story? Large Language Models (LLMs) can now generate narratives spanning tens of thousands of words, but they often fail to maintain consistency throughout. When generating long-form narratives, these models can contradict their own established facts, character traits, and world rules. Existing story generation benchmarks focus mainly on plot quality and fluency, leaving consistency errors largely unexplored. To address this gap, we present ConStory-Bench, a benchmark designed to evaluate narrative consistency in long-form story generation. It contains 2,000 prompts across four task scenarios and defines a taxonomy of five error categories with 19 fine-grained subtypes. We also develop ConStory-Checker, an automated pipeline that detects contradictions and grounds each judgment in explicit textual evidence. Evaluating a range of LLMs through five research questions, we find that consistency errors show clear tendencies: they are most common in factual and temporal dimensions, tend to appear around the middle of narratives, occur in text segments with higher token-level entropy, and certain error types tend to co-occur. These findings can inform future efforts to improve consistency in long-form narrative generation. Our project page is available at https://picrew.github.io/constory-bench.github.io/.