Only some of them, and the exact share depends on how you count. Lean is a programming language and proof assistant: if a proof is written in Lean, a computer can check every logical step mechanically. That makes it the fastest way to trust a result you don’t fully understand.
OpenAI said 300 top-line results across 719 manuscripts had been formalized, around 42 percent. A separate count, based on the repository’s own formalization catalog, found only 162 of the 722 papers had a computer-checked main result, about 22 percent. OpenAI’s own README warns that some of the unformalized results could have issues, and promises to add more Lean proofs as it gets them.
Even a passing Lean check has limits. It tells you the logic holds for the exact statement typed into Lean. Whether that statement is faithful to the real problem, and whether the result is fresh or worth anything, still takes a human expert to judge. Mathematicians digging through the files said the quality of the formal proofs was uneven and didn’t always line up neatly with the claims in the papers.
Kevin Buzzard of Imperial College London said only about six theorems in his own field stood out to him, and few if any appeared to be checked in Lean. That leaves him reading possibly flawed papers, waiting for others to read them, or waiting for someone to formalize them.