Muse Spark 1.3 Contributor

Muse Spark 1.3 is the latest release in Meta's Muse Spark line, published on September 2, 2026, by Artificial Analysis's count the fourth Muse Spark release in five months and the one Mark Zuckerberg described as Meta's largest step forward yet on coding and agent work. It works across a 1 million token context, accepts text, images, and video, and supports tool use, structured output, and selectable reasoning effort up to a max setting that Meta held back for extra safety testing at launch and has since opened up. The headline change is efficiency in agent loops: in comparisons by Meta's own engineers it finishes coding tasks with roughly a fifth fewer tool calls and a quarter fewer tokens than Muse Spark 1.2, taking fewer turns and writing less when the task does not need it. Independent testing by Artificial Analysis put the xhigh setting at 61 on its Intelligence Index, tied with GPT-5.6 Sol and a few points behind Claude Fable 5.1, with 85% on Terminal-Bench 2.1, 94% on GPQA Diamond, and 79% on the AA-LCR long-context test, a four-point drop from 1.2. Muse Spark 1.3 suits coding agents, long-running tool-driven workflows, and long-form instruction following, and Meta reports stronger adversarial robustness and better calibration on which actions are irreversible.