Muse Spark 1.3 cuts tool calls by 20% and tees up open weights

On September 2, 2026, Meta released Muse Spark 1.3, its fourth model in five months, tuned for agentic and coding work: 20% fewer tool calls, 25% fewer tokens, and better calibration on irreversible actions. It is a change of direction — an agent’s value is now measured by its cost, not just its benchmark score.