Anthropic's open-weights silence after its own Fable 5 ban

This article was published on July 27, 2026 Anthropic is the last major AI lab that has not signed an open letter defending open-weight models, and Silicon Valley has spent the day saying so. Almost nobody has mentioned that six weeks ago Anthropic made the letter's argument itself, on its own behalf, when Washington switched off its most powerful model. On Friday, 25 companies signed a letter defending open-weight AI. Three big names were missing. By Monday, two of them had signed. That left Anthropic alone, and Silicon Valley noticed. Nvidia, Meta and Microsoft signed “Open Weights and American AI Leadership” on Friday. Over the weekend OpenAI, Google and SpaceX added their names, Business Insider reported. David Sacks, a venture capitalist and former AI adviser to the Trump administration, was blunt. “The entire tech industry (save for Anthropic) has come out in favor of open source AI,” he wrote on X. “They won’t stop until they kneecap open source,” he added. “The rest of the industry needs to watch these guys like a hawk.” Bill Gurley, a general partner at Benchmark, read it as commerce rather than principle. Anthropic’s reluctance, he posted, reflects that open weights compe