Kimi K3.1 Pro: Open Weights, Almost Opus

Moonshot just released Kimi K3.1 Pro, an open-weight mixture of experts model with 2.8 trillion total parameters, about 104 billion active, and a 1 million token context window. It’s the same size as Kimi K3, post-trained with a lot more reinforcement learning. On Moonshot’s own Terminal-Bench 4.0 numbers it scores 65.7%, less than a point behind Claude Opus 5.5 (66.4%) and ahead of GPT-6 Astra (58.2%), at about a third of Opus’s cost per task on their chart. Moonshot also removed cyber-related data from training before the open release. Even so, it solves 81% of their internal exploit tasks a