Writing is a well-established practice to support ideation and creativity. While Large Language Models (LLMs) have become ubiquitous in providing different kinds of writing assistance to different writers, LLM-powered writing systems often fall short in capturing the nuanced personalization and control necessary for effective support and creative exploration. To address these challenges, we introduce GhostWriter, an AI-enhanced writing design probe that enables users to exercise enhanced agency and personalization. GhostWriter leverages LLMs to implicitly learn the user's intended writing style for seamless personalization, while exposing explicit teaching moments for style refinement and reflection. We study 18 participants who use GhostWriter for editing and creative tasks, observing that it helps users craft personalized text and empowers them by providing multiple ways to steer system output. Based on this study, we present insights on people's relationships with AI-assisted writing and offer design recommendations to promote user agency in similar co-creative systems.

翻译：写作是一种支持构思与创造力的成熟实践。尽管大型语言模型（LLM）已普遍应用于为不同写作者提供多样化的写作辅助，但基于LLM的写作系统往往难以捕捉有效支持和创意探索所需的细致个性化与可控性。为应对这些挑战，我们推出GhostWriter——一种增强人工智能的写作设计探针，使用户能够行使更强的自主权并实现个性化。GhostWriter利用LLM隐式学习用户的预期写作风格以实现无缝个性化，同时提供明确的风格优化与反思教学契机。我们通过对18名参与者使用GhostWriter进行编辑与创意任务的研究发现，该系统能帮助用户创作个性化文本，并通过提供多种引导系统输出的方式增强用户掌控力。基于此项研究，我们提出关于人与AI辅助写作关系的见解，并为促进类似共创系统中用户自主性提供设计建议。