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!

Arena has raised a $200M Series B at a $3.1B valuation. We are using this momentum to evaluate agentic utility in real workflows from every economically valuable industry on Earth. We seek to give everyone universal and frictionless access to the best intelligence. The @arena platform has 10s of millions of monthly users doing complex coding and agentic work tasks. We have gone way beyond human preference, and most of our tokens go to deep, single threaded workflows with dozens of turns where we can evaluate agents while humans are in their true flow state. And we make leaderboards by observing whether they get their jobs done. This is how benchmarks should be: representative of actual human value, so we incentivize AI to benefit humanity. Today, we are releasing one of the most exciting developments in the history of our platform. The Arena Alignment Index. In observing how humans collaborate with agents, we have witnessed that in a surprisingly large fraction of cases, agents are attempting to deceive users or take unauthorized actions beyond what the user intended or permissioned. Agents are deleting files and lying to users about what they did or didn’t do. The longer conversations go, the higher the probability that an agent will violate alignment. The results are really striking; see the plot below. And because this represents in-the-wild usage, the probability that those of us reading this have experienced some form of misalignment from our agents is nearly 100%. And we may not even have noticed. This is exactly why it’s important to have a neutral 3rd party that is evaluating AI alignment on the distribution of actual user-agent interactions. Arena is excited to step into that role. We are also incredibly grateful for the incredible and experienced investors backing our vision. Our Series B is co-led by @lightspeedvp and @khoslaventures with participation from @SalesforceVC, @01Advisors, @DellTechCapital and @endvr_catalyst. This round includes support from our existing investors @a16z, @felicis, @amppublic, @QuantumLightVC, @thehousefund, and others. Which brings me to the real headline: we're hiring, across ML, product engineering, design, marketing, BD, and more. If evaluation and alignment at the frontier is your thing, and you’re looking for an environment with exceptional research and engineering, come join us. Job board link in @arena’s bio and in the thread below LFG (safely)!

When we started @arena as a project at UC Berkeley, we were ranking eight models. Today we evaluate the performance of over 500 models, with new releases arriving every week. It was great catching up with @mamoonha and @Joubinmir to talk Arena’s mission, and how it’s helping power frontier AI capabilities made for real-world use. Thanks for having me on Grit @kleinerperkins

This is the only primary-source interview on the METR report I have seen. This is one of the most important topics in AI this year, given the severity of the incident, we should all be listening to hear how we can put proper guardrails to ensure agents are securely and reliably deployed.

Cyber defense in AI is a collective responsibility. As intelligence and capabilities advance, we have invest in protecting the systems and institutions society relies on. @arena has joined @openai's call for a global surge in cyber defense.

What makes Ion special? He's deeply in the details. In the office every day, these days. Writing PRDs like an IC PM. Ion loves the game. Nothing/no-one is below him. Nothing is taken for granted. Here he is next to me, working on Arena, literally right now. A true 🐐