Anthropic stands alone as 4 major AI labs back open-weight models

More than two dozen technology companies — including OpenAI, Google, Microsoft, Nvidia, Meta, and SpaceX — signed an open letter urging Washington to support open-weight AI models, leaving Anthropic as the sole holdout among major frontier labs.

"The entire tech industry (save for Anthropic) has come out in favor of open source AI," David Sacks, a venture capitalist and former AI czar for the Trump administration, said in a post on X.

The letter, titled "Open Weights and American AI Leadership," was released Friday and signed by over two dozen companies. By Monday, OpenAI, Google, and SpaceX had added their names. Anthropic did not respond to a request for comment. Bill Gurley, a general partner at Benchmark, suggested the company was protecting its commercial position. "Excited to see Anthropic acknowledge the real problem with open is it competes with their corporate economic strategy," Gurley wrote on X.

The divide comes as Washington considers restrictions on Chinese open-weight models, including potential sanctions against models found to have distilled from US rivals. Anthropic CEO Dario Amodei has previously warned that developers lose control of frontier AI once model weights are released, favoring gated access through initiatives like Project Glasswing.

The debate over open models has intensified since the launch of Kimi K3, an open-weight model from Chinese lab Moonshot that rivals top US closed models on some benchmarks. Last week, a top White House official accused Moonshot of using Anthropic's Fable AI model to train K3 through distillation, a practice Treasury Secretary Scott Bessent suggested could trigger US sanctions.

Hugging Face, the AI development platform, boosted the case for open models last week when it said it used a model from China's Z.ai to defend against a hack from OpenAI's rogue AI agent, noting it could not use closed models because of restrictions.

The China Factor

China has broadly pursued a more open approach to AI than the US, and the success of models like Kimi K3 has supercharged the policy debate. Kai-Fu Lee, a former Google and Microsoft executive who founded Chinese open-model startup 01.AI, highlighted Anthropic's absence from the letter by tagging Claude AI in a post that said "Who DIDN'T sign the Open Weight letter is far more interesting than who did."

Nvidia on Monday announced the launch of the Open Secure AI Alliance, an initiative advocating for open AI models in cybersecurity, backed by Microsoft, SpaceX, and other tech firms — further isolating Anthropic's position.

Anthropic's refusal to endorse open models risks alienating developer communities and could influence how regulators approach the safety-versus-openness debate. The company has favored a gated-access model that preserves its commercial advantage, but the unified stance of its largest competitors — OpenAI, Google, and Microsoft — puts pressure on Anthropic's positioning as the industry coalesces around open-weight development. Anthropic, which has raised billions from Amazon and other investors, faces a strategic choice as Washington weighs restrictions that could reshape the competitive dynamics.

This article is for informational purposes only and does not constitute investment advice.