Joined January 2011
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Very excited this is out! I did a deep dive into Mythos' cyber capabilities, and while the story has some complexity, I think it is undeniable we are moving into a scary regime for cyber security,
How big a leap is Mythos in cyber capabilities? @timotheechauvin, @AlexBarry4, @js_denain, and @ansonwhho compiled the public evidence and found that while it’s unclear if Mythos was ahead of trend in discovering vulnerabilities, it represents a big jump in exploiting them. 🧵
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Alexander Barry retweeted
My takeaways from chats with @AlexBarry4: For previous models, if you spend enough tokens they could find vulnerabilities but couldn't do much with them. Mythos (and to a lesser extent 5.5) is much more capable at using those vulnerabilities to create exploits for e.g. arbitrary code execution ‼️More than that, when Microsoft releases a public patch to Windows, it can take a weekish to propagate to all computers. Mythos can sometimes build exploits from that patch release in a few hours which can run on all computers who hadn't received that update yet. (5.5 can occasionally do this) Basically before a model of this cyber capability is open sourced, we need to radically change how we do cybersecurity! This is substantially scary!
How big a leap is Mythos in cyber capabilities? @timotheechauvin, @AlexBarry4, @js_denain, and @ansonwhho compiled the public evidence and found that while it’s unclear if Mythos was ahead of trend in discovering vulnerabilities, it represents a big jump in exploiting them. 🧵
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Continuing with tradition I used Opus 4.8's AECI values to predict its METR time horizon: estimated 50% time horizon of 20.0 hours, 80% time horizon of 2.8 hours. See more details (including why METR's early Mythos Preview results have been misinterpreted) in my post below
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Chance to (indirectly) tell me what to do by telling us what Epoch outputs you find most valuable
Help us produce the most useful work on AI by taking our 5-minute survey: docs.google.com/forms/d/e/1F… (You can sign up at the end to join our compensated user research panel.)
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Alexander Barry retweeted
(1) We are likely on track to develop AI systems capable of causing human extinction/permanent disempowerment, quite possibly within the next few years
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Excited to announce I am joining @EpochAIResearch as a senior researcher. My remit will include managing the Epoch Capabilities Index, as well as other projects to understand progress trends. If you have any ideas for improvements/extensions to the ECI please reach out!
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Was fun to work on this as a first application of the domain-specific ECI. I think this (and other) approaches should expand our ability to understand LLM abilities in a more fine-grained way.
Claude is typically better at software engineering and worse at math than frontier competitors. Aggregating benchmarks to create our domain-specific ECI, we find the Claude family has an average SWE-ECI 2.7 points higher than their general ECI, and a Math-ECI 1.8 points lower.
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I used GPT 5.5's ECI values to predict the METR Time Horizon values it will receive. This predicts it will have a 50% time horizon of 10 hours, and an 80% time horizon of 1.6 hours. These are below my predictions for Opus 4.7 (but would beat the current best 80% TH).
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These results are influenced by GPT 5.3-codex and GPT 5.4 having quite low time horizon values compared to their ECIs. This might be partially caused by an unusual amount of reward hacking attempts. Removing them gives a somewhat different fit:
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I used Anthropic's internal ECI values from the Opus 4.7 model card to predict the METR Time Horizon values they would receive. This predicts Mythos will have a 50% TH of 40 hours, and Opus 4.7 19 hours. 80% THs are 5.5 and 2.5 hours respectively.
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Notably both of these 50% TH values are above what I expect METR to be able to reliably measure with the TH1.1 task suite, as the longest task it contains is only 30 hours (and very few are beyond 16 hours). They should be able to produce reasonable 80% TH results though.
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For the full AECI values and some more information see my substack post: open.substack.com/pub/abstat…

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Interesting to work on this report with Epoch. We found that AI progress speeds have been accelerating since ~mid 2024 (on 3/4 of the metrics we considered). Treating reasoning models as a trendbreak made the best predictions, but not enough data to be very confident.
Have AI capabilities accelerated? On 3 out of the 4 AI capability metrics we investigated, we found strong evidence of acceleration, around when reasoning models emerged.
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I made an update to the interactive task-success-rate plot for METR time horizon. You can now see how the performance on the TH task suite has evolved over time by walking through model releases (with optional point jittering for increased visibility).
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As METR’s Time Horizon task suite saturates, the results become more sensitive to analysis choices. I did a deep dive and explored how reasonable alternative modelling choices impact time horizon results.
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Some of the alternative analyses I considered included: using different curves to connect task length to success probability, including Weibull (survival) fits, and nonparametric approaches.
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