libsignal

Google Expands Gemini 4 Carbon Access After AI Agents Formally Verify Signal Protocol Code

Google has broadened access to its Gemini 4 Carbon model, allowing paying developers, businesses, and Google AI Ultra subscribers to use it through the Gemini API and Gemini for business. The expansion follows the successful use of Carbon-based AI agents to formally verify core security properties of the Signal protocol implementation in libsignal. Google DeepMind also introduced AlphaProof Code, which combines human experts with AI agents to generate millions of lines of Lean proofs that confirm guarantees such as forward secrecy and post-compromise security at the machine-code level. The verification effort, completed in four weeks by five researchers, also demonstrated the method's ability to detect previously patched flaws when they were reintroduced. In parallel, Carbon for cyber helped Wiz discover zero-days at two major SaaS providers and assisted Google's Cloud Vulnerability Research team in confirming the exploitability of two bugs in a popular open-source project. Google is releasing the specifications and proofs publicly while noting that the work applies to its own build of the code rather than Signal's production applications.