Prediction: AI will make formal verification go mainstream

Summary

Prediction: AI will make formal verification go mainstream Published by Martin Kleppmann on 08 Dec 2025. Much has been said about the effects that AI will have on software development, but there is an angle I haven’t seen talked about: I believe that AI will bring formal verification, which for decades has been a bit of a fringe pursuit, into the software engineering mainstream. Proof assistants and proof-oriented programming languages such as Rocq, Isabelle, Lean, F*, and Agda have been around for a long time. They make it possible to write a formal specification that some piece of code is supposed to satisfy, and then mathematically prove that the code always satisfies that spec (even on weird edge cases that you didn’t think of testing). These tools have been used to develop some large formally verified software systems, such as an operating system kernel, a C compiler, and a cryptographic protocol stack. At present, formal verification is mostly used by research projects, and it is uncommon for industrial software engineers to use formal methods (even those working on classic high-assurance software such as medical devices and aircraft). The reason is that writing those proofs is both very difficult (requiring PhD-level training) and very laborious. For example, as of 2009, the formally verified seL4 microkernel consisted of 8,700 lines of C code, but proving it correct required 20 person-years and 200,000 lines of Isabelle code – or 23 lines of proof and half a person-day for every single line of implementation. Moreover, there are maybe a few hundred people in the world (wild guess) who know how to write such proofs, since it requires a lot of arcane knowledge about the proof system. To put it in simple economic terms: for most systems, the expected cost of bugs is lower than the expected cost of using the proof techniques that would eliminate those bugs. Part of the reason is perhaps that bugs are a negative externality: it’s not the software developer who be...