San Francisco-based AI lab Arcee made waves last year for being one of the only U.S. companies to train large language models (LLMs) from scratch and release them under open or partially open source licenses to the public—enabling developers, solo entrepreneurs, and even medium-to-large enterprises to use the powerful AI models for free and customize them at will.Now Arcee is back again this week with the release of its largest, most performant open language model to date: Trinity Large, a 400-billion parameter mixture-of-experts (MoE), available now in preview,Alongside the flagship release, Arcee is shipping a “raw” checkpoint model, Trinity-Large-TrueBase, that allows researchers to study what a 400B sparse MoE learns from raw data alone, before instruction tuning and reinforcement has been applied.By providing a clean slate at the 10-trillion-token mark, Arcee enables AI builders in highly regulated industries to perform authentic audits and conduct their own specialized alignments without inheriting the “black box” biases or formatting quirks of a general-purpose chat model. This transparency allows for a deeper understanding of the distinction between a model’s intrinsic reasoning capabilities and the helpful behaviors dialed in during the final stages of post-training.This launch arrives as powerful Chinese open-source LLM alternatives from the likes of Alibaba (Qwen), z.AI (Zhipu), DeepSeek, Moonshot, and Baidu have flooded the market, effectively leading the category with high-efficiency architectures. Trinity Large also comes after Meta has notably retreated from the frontier open-source landscape. Following the April 2025 debut of Llama 4, which was met with a mixed reception, and former Meta AI researcher Yann LeCun later admitted the company used multiple specialized versions of the model to inflate scores on third-party benchmarks. Amidst this domestic vacuum, only OpenAI—with its gpt-oss family released in the summer of 2025—and Arcee are currently carrying the mantle of new U.S.-made open-source models trained entirely from scratch.As sparse as they comeTrinity Large is noteworthy for the extreme sparsity of its attention mechanism. An MoE architecture, “sparsity” refers to the model’s ability to selectively activate only a tiny fraction of its total parameters for any …
