Anthropic not giving up on the blue teams just yet
Anthropic just released Opus 5, with some good news for the cybersecurity teams. The cybersecurity safeguards will be more lax and let us use the model for some defence tasks as Anthropic is confident for its lack of skill in executing offensive ones like creating exploits:<br>As with its predecessor, Opus 4.8, we’ve intentionally avoided training Opus 5 on cyber tasks. The model has nevertheless improved substantially on these tasks as a result of becoming more generally capable, and it comes close to Mythos 5 at finding cybersecurity vulnerabilities. However, it remains substantially behind Mythos 5 on the exploitation of those vulnerabilities
This is illustrated by Opus 5’s performance on OSS-Fuzz, an evaluation we’ve developed to assess how well models can find and then exploit vulnerabilities without extensive human guidance. Although Mythos 5 and Opus 5 identify vulnerabilities with similar success, Opus 5’s score on the development of exploits is far behind that of Mythos 5.
This is a very positive change as it felt like US models were going into a dead end since the release of Fable 5 and Mythos 5. Mythos is only accessible to a small list of companies vetted by the US government and Fable's safeguards on cybersecurity and biology topics are extremely sensitive. Trying to execute a task even remotely tied to cybersecurity, like reviewing a piece of code tied to authentication, would immediately downgrade you to Opus 4.8. OpenAI and Google have since then followed a similar path, branching the cybersecurity part of their latest model in a separate product only accessible to a handful of companies.<br>These restrictions have put a huge blow in blue team AI initiatives. Hugging Face was forced to switch to Chinese Open Weight models in the middle of a security incident as frontier US models refused to assist.<br>This will need actual testing, but the announcement specifically addresses this part:<br>Claude Opus 5’s safeguards are designed to allow beneficial uses of the model in both cybersecurity and biology. They are similar to those we applied to Opus 4.8, with the exception of some stronger guardrails on a narrow range of cyber tasks.
Cybersecurity. Opus 5’s cyber classifiers are proportionally less restrictive than those on Fable 5. They allow Opus 5 to find vulnerabilities in source code , but block “binary-based” vulnerability scanning (a method more likely to be associated with malicious actors), penetration testing, and exploit generation.
Based on our testing, we expect the classifiers to intervene around 85% less often than they do for Fable 5 .<br>Digging into the system card gives us more information. The safeguards are using the same foundations as Fable, but they explicitly allowed vulnerability finding.<br>They also have extra sensitivity threshold they can lift for companies that applied to their Cyber Verification Program, unlocking red team tasks like pentests:<br>The Fable cyber classifier we have previously discussed also applies to Claude Opus 5 , with one notable exception: for Claude Opus 5 , we’ve unblocked vulnerability finding in source code to help our coding customers develop more secure code.
If you are a cyber defender and are experiencing blocks on Claude Opus 5 , we are also offering exemptions through our Cyber Verification Program, which will remove blocks to enable activities such as bug bounty hunting and vulnerability research and verification.
Enterprise customers can also apply to join the Cyber Verification Program to have<br>mitigations removed to enable penetration testing.<br>Yet CVP has restrictions. It doesn't work with some inference providers like AWS Bedrock, and requires activating data retention on the associated workspace, a blocker for most companies.<br>Speaking of data retention, Opus 5 will not force the 30-days retention clause they added with Fable 5:<br>Consistent with prior Opus models, Opus 5 does not have data retention requirements for general access.<br>I'm a bit puzzled by this release. If they are so confident in the specificity of their new safeguards with Opus 5, why aren't they retroactively applied to Fable? How can Mythos access be so tightly restricted but Opus 5 allowed for any company, even non-US ones, as long as they fill the necessary paperworks for their CVP?<br>While Opus 5 is not as good as Mythos in producing exploits, it's still much better than Opus 4.8, finding six times more full exploits in Firefox:<br>As part of a collaboration between Anthropic and Mozilla, we’ve developed an evaluation that assesses a model’s ability to develop exploits of vulnerabilities in Firefox 147 [...]
The model is tasked with developing an exploit that can successfully read and copy a secret to another directory. These actions require arbitrary code execution beyond what is available in JavaScript.. [...]
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