Following OpenAI's introduction of GPTs, a surge in GPT apps has led to the launch of dedicated LLM app stores. Nevertheless, given its debut, there is a lack of sufficient understanding of this new ecosystem. To fill this gap, this paper presents a first comprehensive longitudinal (5-month) study of the evolution, landscape, and vulnerability of the emerging LLM app ecosystem, focusing on two GPT app stores: \textit{GPTStore.AI} and the official \textit{OpenAI GPT Store}. Specifically, we develop two automated tools and a TriLevel configuration extraction strategy to efficiently gather metadata (\ie names, creators, descriptions, \etc) and user feedback for all GPT apps across these two stores, as well as configurations (\ie system prompts, knowledge files, and APIs) for the top 10,000 popular apps. Our extensive analysis reveals: (1) the user enthusiasm for GPT apps consistently rises, whereas creator interest plateaus within three months of GPTs' launch; (2) nearly 90\% system prompts can be easily accessed due to widespread failure to secure GPT app configurations, leading to considerable plagiarism and duplication among apps. Our findings highlight the necessity of enhancing the LLM app ecosystem by the app stores, creators, and users.

OpenAI is an unconventional company in many ways, but last November it borrowed a page from the standard tech industry playbook: It held a developer conference where CEO Sam Altman urged software makers to build on top of ChatGPT. The company said it would soon launch a marketplace where developers and non-techies alike could create custom functions for the chatbot and make money by sharing them with the world. The reaction to that news was mixed, with some hailing the birth of a new platform and others turning a laundry app demoed onstage into a meme. But whether meme-worthy or momentous, OpenAI's app store is part of a broader strategy to maintain its edge in the competitive AI landscape. Like Apple and Google's YouTube have done so well, OpenAI now wants to incentivize developers and creators to supply fresh content for its platform, so that it can keep offering new experiences that draw in users.