March 9, 2026
Is legal the same as legitimate: AI reimplementation and the erosion of copyleft
Last week, Dan Blanchard, the maintainer of chardet—a Python library for detecting text encodings used by roughly 130 million projects a month—released a new version. Version 7.0 is 48 times faster than its predecessor, supports multiple cores, and was redesigned from the ground up. Anthropic's Claude is listed as a contributor. The license changed from LGPL to MIT.
Blanchard's account is that he never looked at the existing source code directly. He fed only the API and the test suite to Claude and asked it to reimplement the library from scratch. The resulting code shares less than 1.3% similarity with any prior version, as measured by JPlag. His conclusion: this is an independent new work, and he is under no obligation to carry forward the LGPL. Mark Pilgrim, the library's original author, opened a GitHub issue to object. The LGPL requires that modifications be distributed under the same license, and a reimplementation produced with ample exposure to the original codebase cannot, in Pilgrim's view, pass as a clean-room effort.
The dispute drew responses from two prominent figures in the open source world. Armin Ronacher, the creator of Flask, welcomed the relicensing. Salvatore Sanfilippo (antirez), the creator of Redis, published a broader defense of AI reimplementation, grounding it in copyright law and the history of the GNU project. Both conclude, by different routes, that what Blanchard did is legitimate. I respect both writers, and I think both are wrong—or more precisely, both are evading the question that actually matters.
That question is this: does legal mean legitimate? Neither piece answers it. Both move from “this is legally permissible” to “this is therefore fine,” without pausing at the gap between those two claims. Law sets a floor; clearing it does not mean the conduct is right. That gap is where this essay begins.
The analogy points the wrong way
Antirez builds his case on history. When the GNU project reimplemented the UNIX userspace, it was lawful. So was Linux. Copyright law prohibits copying “protected expressions”—the actual code, its structure, its specific mechanisms—but it does not protect ideas or behavior. AI-assisted reimplementation occupies the same legal ground. Therefore, it is lawful.
The legal analysis is largely correct, and I am not disputing it. The problem lies in what antirez does next: he presents the legal conclusion as if it were also a social one, and uses a historical analogy that, examined more carefully, argues against his own position.
When GNU reimplemented the UNIX userspace, the vector ran from proprietary to free. Stallman was using the limits of copyright law to turn proprietary software into free software. The ethical force of that project did not come from its legal permissibility—it came from the direction it was moving, from the fact that it was expanding the commons. That is why people cheered.
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