Late last year, the Chinese start-up DeepSeek released A.I. models that were built upon Llama but were more advanced and required fewer resources to create. Meta's open-source strategy, once seen as a competitive advantage, appeared to have let others get a leg up on it. Mr. Zuckerberg knew he needed to act. Around that time, outside A.I. researchers began receiving emails from him, asking if they would be interested in joining Meta, two people familiar with the outreach said. In April, Meta released two new versions of Llama, asserting that the models performed as well as or better than comparable ones from OpenAI and Google. To prove its claim, Meta cited its own testing benchmarks. On Instagram, Mr. Zuckerberg championed the releases in a video selfie. But some independent researchers quickly deduced that Meta's benchmarks were designed to make one of its models look more advanced than it was. They became incensed. Mr.