Two technologies with opposite strengths
It is worth being precise about what each technology is good at, because the complementarity is not where most commentary places it.
Modern AI is probabilistic, data-hungry and, in practice, highly centralised: the frontier is set by a small number of organisations with access to very large compute clusters. It produces output that is fluent, cheap and — crucially — difficult to attribute or verify after the fact.
A blockchain is close to the opposite. It is deterministic, replicated and expensive per unit of computation. What it is genuinely good at is producing a shared, tamper-evident record that multiple parties who do not trust each other can agree on, without appointing one of them as the referee.
Stated that way, the useful connection becomes clearer. It is not that blockchains will run AI models — for the most part they cannot, economically. It is that one technology is increasingly good at generating content and actions at scale, and the other is a machine for establishing what is true about a record.