Large Language Models (LLMs) hold promise in supporting creative writing, yet the role of proactive AI in collaborative writing remains underexplored due to concerns around human agency and disruption. To investigate effective strategies for proactive AI support, we conducted a Wizard-of-Oz study simulating two suggestion styles: intrusive suggestions (next-sentence completions) and non-intrusive suggestions (exploratory proposals), where participants completed two story outlining tasks under each style, receiving real-time proactive suggestions from a human wizard acting as the AI. Both quantitative and qualitative results show that proactive AI can enhance creativity and accelerate writing. However, we observed a trade-off between AI involvement and perceived human agency. This trade-off was moderated by how strongly AI stimulated users–greater inspiration led to stronger perceived agency even under high AI involvement. Based on wizards’ behavior, we offer guidance on suggestion style and timing to better balance creativity and agency for future proactive AI writing systems.

Collaborative Mixed Reality (MR) systems that help extend expertise for physical tasks to remote environments often situate experts in an immersive view of the task environment to bring the collaboration closer to collocated settings. In this paper, we design UnMapped, an alternative interface for remote experts that combines a live 3D view of the active space within the novice’s environment with a static 3D recreation of the expert’s own workspace to leverage their existing spatial memories within it. We evaluate the impact of this approach on single and repeated use of collaborative MR systems for remote guidance through a comparative study. Our results indicate that despite having a limited understanding of the novice’s environment, using an UnMapped interface increased performance and communication efficiency while reducing experts’ task load. We also outline the various affordances of providing remote experts with a familiar and spatially-stable environment to assist novices.