77 companies have signed the open-weights letter. Anthropic hasn't.

The list tripled in three days, drawing in Google, OpenAI, AMD and SpaceX. Anthropic has not signed and has not commented, and one of its own researchers is a public critic.

Agent-drafted, human-editedPublished July 27, 2026

Reviewed by Trevor Brown

Sundar Pichai, during the meeting at the European Commission in Brussels, Belgium.

Google and Alphabet chief executive Sundar Pichai at the European Commission in Brussels in 2023. File photo. European Union / Lukasz Kobus, CC BY 4.0 (source)

An industry letter defending open-weight AI models had 25 signatories when it was published on Friday. By Monday it had 77.

Anthropic has not signed it, and has not commented on it.

Why it matters: The letter has become a public register of where each AI company stands on open models. Microsoft, Meta, NVIDIA, Google and OpenAI are all on it.

What it says: "Open Weights and American AI Leadership," dated July 24, defines open weight models as ones "anyone can download, inspect, modify, and run on their own infrastructure." It asks Washington to expand compute access for startups and researchers and to keep "the frontier plural by avoiding premature restrictions on open models."

That is not the same as open source. As Georgia Tech's Jeffrey Young explains for The Conversation and PBS NewsHour, open-source AI also requires public training data and code; open-weight models release only the weights.

The letter also asks policymakers not to "conflate legitimate model-development techniques with misappropriation," naming distillation — training one model on another's outputs — as legitimate.

How it grew: Jensen Huang launched it with the first post of his life on X, past 62 million views by Monday. Satya Nadella called open-weight models "essential to a healthy AI ecosystem."

Still in the Loop counted the names at four stages. Microsoft's PDF carries the original 25. NVIDIA's PDF went to 35 on Saturday morning, adding OpenAI. Microsoft's canonical page reached 50 by Saturday night and 77 by Monday.

Google, AMD and SpaceX joined along the way. Sundar Pichai endorsed it "on behalf of Google" on Saturday morning, hours before Google itself appeared on the list.

Sundar Pichai

@sundarpichai

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Very happy to support this on behalf of Google. We have long benefited from open source, are big contributors to open source and in fact have consistently made open weights models with Gemma available from @GoogleDeepMind @demishassabis . Onwards!

2:39 PM · Jul 25, 2026

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Provenance & disclosure

AI use

Agent-drafted, human-edited

Disclosure

Agent-drafted for review and editing by Trevor Brown. Still in the Loop counted the letter's signatories directly from the published documents at four stages between July 24 and July 27 rather than relying on reported figures, and read the letter in full. Quotes are taken from the principals' own posts. Julian Schrittwieser posts as an individual and does not speak for Anthropic, which has not commented. The signatory list is still growing.

Reviewed by

Trevor Brown — Editor-in-chief

Sources

Official sourceOpen Weights and American AI Leadership (Microsoft, canonical page)
Official sourceOpen Weights and American AI Leadership (Microsoft-hosted PDF, original 25 signatories)
Official sourceOpen Weights and American AI Leadership (NVIDIA-hosted PDF)
Social reaction

He later said he does not want open models banned, but called it "interesting how some historically extremely anti-open source companies are suddenly all in favor of openness." He posts as an individual. Anthropic itself has said nothing.

The backdrop: Two days before the letter, White House science and technology policy director Michael Kratsios said the government has "information that Moonshot AI distilled Anthropic's Fable for the development of its K3 model." The letter does not mention China, Moonshot or the allegation.

Anthropic has its own published position on the practice. A February post called illicit distillation a security threat and named Moonshot, DeepSeek and MiniMax.

What we could not confirm: Whether Anthropic was asked to sign, or why it has not commented. Kratsios has published no evidence, and Moonshot has not publicly denied the allegation.