Text settings Story text Size Small Standard Large Width * Standard Wide Links Standard Orange * Subscribers only Learn more Minimize to nav Last month, Anthropic made a big deal about the supposedly outsize cybersecurity threat represented by its Mythos Preview model, leading the company to restrict the initial release to “critical industry partners.” But new research from the UK’s AI Security Institute (AISI) suggests that OpenAI’s GPT-5.5, which launched publicly last week, reached “a similar level of performance on our cyber evaluations” as Mythos Preview, which the group evaluated last month.
Since 2023, the AISI has run a variety of frontier AI models through 95 different Capture the Flag challenges designed to test capabilities on cybersecurity tasks, such as reverse engineering, web exploitation, and cryptography. On the highest-level “Expert” tasks, GPT-5.5 passed an average of 71.4 percent, slightly higher than the 68.6 percent achieved by Mythos Preview (though within the margin of error). In one particularly difficult task that involved building a disassembler to decode a Rust binary, AISI notes that “GPT-5.5 solved the challenge in 10 minutes and 22 seconds with no human assistance at a cost of $1.73” in API calls.
GPT-5.5 also matched Mythos Preview in its progress on “The Last Ones” (TLO), an AISI test range set up to simulate a 32-step data extraction attack on a corporate network. GPT-5.5 succeeded in 3 of 10 attempts on TLO, compared to 2 of 10 for Mythos Preview—no previous model had ever succeeded at the test even once. But GPT-5.5 still fails at AISI’s more difficult “Cooling Tower” simulation of an attempted disruption of the control software for a power plant, as every previously tested AI model also has.
The new results for GPT-5.5 suggest that, when it comes to cybersecurity risk, Mythos Preview was likely not “a breakthrough specific to one model” but rather “a byproduct of more general improvements in long-horizon autonomy, reasoning, and coding,” AISI writes.
In a recent interview with the Core Memory podcast, OpenAI CEO Sam Altman criticized what he calls “fear-based marketing” in promoting limited releases for certain AI models. While he said he’s “sure Mythos is a great model for cybersecurity,” he added that “it is clearly incredible marketing to say, ‘We have built a bomb. We are about to drop it on your head. We will sell you a bomb shelter for $100 million.’”
“There will be a lot more rhetoric about models that are too dangerous to release,” Altman continued. “There will also be very dangerous models that will have to be released in different ways.”
In February, OpenAI rolled out its Trusted Access for Cyber pilot program, letting security researchers and enterprises verify their identities and register their interest in studying OpenAI’s frontier models for “legitimate defensive work.” Last month, OpenAI said it was using that trusted access list to control the limited launch of GPT-5.4-Cyber, a model variant that it says is “purposely fine-tuned for additional cyber capabilities and with fewer capability restrictions.”
On Thursday, OpenAI CEO Sam Altman said on social media that the initial release of GPT-5.5-Cyber would similarly be limited “to critical cyber defenders in the next few days.”
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