Anastasios Nikolas Angelopoulos(@ml_angelopoulos):Kimi K3.1 is out; it is the #1 OSS model. It places similarly to Opus 5, which was released 3 months ago. Thus, China is lagging the frontier by about 3 months. The Kimi K3 release was #1 on Code Arena, at the time better than all US labs. K3.1 is close, but substantially off from Opus 5.5. On a performance vs cost-per-task basis, the combo of Sonnet 5.5 and DeepSeek V4.1 flash together dominate this model. The race is so tight!!! Congrats to the Moonshot team on a great release. And now, back to work. The frontier never sleeps!

Anastasios Nikolas Angelopoulos

@ml_angelopoulos

Co-Founder and CEO of @arena PhD @Berkeley_EECS EE @StanfordEng SR @GoogleDeepMind

Joined September 2019

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Anastasios Nikolas Angelopoulos@ml_angelopoulos

2026.10.23 17:51

Kimi K3.1 is out; it is the #1# OSS model. It places similarly to Opus 5, which was released 3 months ago. Thus, China is lagging the frontier by about 3 months. The Kimi K3 release was #1# on Code Arena, at the time better than all US labs. K3.1 is close, but substantially off from Opus 5.5. On a performance vs cost-per-task basis, the combo of Sonnet 5.5 and DeepSeek V4.1 flash together dominate this model. The race is so tight!!! Congrats to the Moonshot team on a great release. And now, back to work. The frontier never sleeps!