Constantine Cannon Files Amicus Brief Supporting Anthropic in AI Copyright Case

By the Constantine Cannon Antitrust Team

On April 27, 2026, Constantine Cannon partner Seth Greenstein filed an amicus brief[1] on behalf of technology innovation advocacy groups Chamber of Progress[2] and Engine Advocacy[3] in support of leading AI developer Anthropic PBC in a copyright suit brought by major music publishers.  The case, Concord Music Group, Inc. v. Anthropic PBC, Case 5:24-cv-03811-EKL, alleges that Anthropic infringes the publishers’ copyrighted lyrics by including the lyrics in Claude’s training sets and in the output responding to certain user prompts.

While other courts have concluded that training AI models and their output can be non-infringing fair uses under copyright law, the publishers make the highly controversial contention that the ability of Claude to generate lyrics and music that can compete with the publishers’ copyrighted works threatens the market for copyrighted lyrics.  As a result of this alleged “market dilution,” the publishers claim that Claude’s commercial nature and effects preclude a finding of fair use.

The Amicus Brief Challenge

The amicus brief challenges the publishers’ “market dilution” theory as unconstitutional and contrary to the text of the Copyright Act.  Copyright under the Constitution is intended primarily to promote the public interest, not just the private remuneration of copyright owners.

According to Greenstein: “Copyright under the Constitution and the Copyright Act focus on individual creations, not entire categories of works (e.g., lyrics of a group of copyright owners).  By seeking protection against the market effects of all AI-generated works, plaintiffs seek to turn copyright into a competition law—more accurately, an anti-competition law.”

What Does the Brief Explain?

More fundamentally, the brief explains how copyright was not intended to stifle development of new and innovative technologies like AI models.  To the contrary, the fair use doctrine under copyright law is designed to protect “transformational” uses of copyrighted works by AI systems, which draw from non-protectable factual elements of copyrighted works and not the specific expression that copyright protects.

The Chamber of Progress and Engine Advocacy brief supports Anthropic’s motion for summary judgment, and opposes the Plaintiffs’ motion for partial summary judgment.  The Court has set a hearing on these dispositive motions for October 21, 2026.

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Sources:

[1] See https://ecf.cand.uscourts.gov/doc1/035127052204.

[2] See https://progresschamber.org/.

[3] See https://www.engine.is/. 

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