Simon WillisonMar 5
The chardet open source library relicensed from LGPL to MIT two days ago thanks to a Claude Code assisted "clean room" rewrite - but original author Mark Pilgrim is disputing that the way this was done justifies the change in license - my notes here: https://simonwillison.net/2026/Mar/5/chardet/
Can coding agents relicense open source through a “clean room” implementation of code?

Over the past few months it’s become clear that coding agents are extraordinarily good at building a weird version of a “clean room” implementation of code. The most famous version …

Simon Willison’s Weblog
Show threadǝʌɐpMar 5
@simon lots of public conversation logs for the courts to pour over when the time comes
Show threadǝʌɐpMar 5
@simon I think I'm of the opinion that it's impossible to clean room something that is open source with an LLM because the exact source is in the training corpus
Show threadCassandrichMar 5

RE: https://social.treehouse.systems/@dvshkn/116177633529242686

@dvshkn @simon Bingo.

Show threadMagnus Ahltorp

@dalias @dvshkn @simon Yes, and this phrase is especially clueless:

”explicitly instructed Claude not to base anything on LGPL/GPL-licensed code”

Is there any evidence, or even indication, that putting this into the ”instructions” has any effect whatsoever?

Mar 9 at 10:06amWeb
Show threadCassandrichMar 9
@ahltorp @dvshkn @simon Nope. 🙃