Meta’s Muse Spark Open lands in Arena for public testing

Meta’s newest AI model is now in front of the toughest audience in tech: other developers. Muse Spark Open, the first open-weight release from Meta’s Muse Spark series, is now available in Arena.ai’s Agent Arena and Code Arena. There, users can test it on complex tasks and score how it actually performs. Meta announced the model on October 15, 2026. Arena.ai confirmed the integration and live testing on launch day. What Meta actually built Muse Spark Open is a multimodal model with 816 billion total parameters. Of those, 42 billion are active. The model also comes with a 1M-token context window. Muse Spark Open can take in images, video, and audio as inputs. Meta is pitching the model at three jobs in particular: long-horizon agentic workflows, complex coding, and multi-step reasoning. On the coding side, Meta says it supports workflows such as analyzing entire repositories and handling complicated refactors that span multiple files. Where you can get it Muse Spark Open became available on October 15, 2026, through a range of API platforms and cloud marketplaces. API access runs through providers including Baseten and Fireworks AI, among many others. Teams that want the weights the...