It's actually fine to use MIT code and publish it under GPL, or to switch from MIT to GPL. You can still do that today on the repo, btw. It's the other direction that is thorny. Just fyi

...thus implying that you'd rather the preeminent safety-focused lab not have used your interpretibility research, as they're technically a for-profit company with various closed-source assets?

I am certainly biased by a passionate distaste for IP law in general, but I am honestly curious to hear the reasoning behind it in this case.

In case it helps: this is a "research prototype", so I'd assume that seeing one or more aspects used in a highly impactful paper would be about the best possible outcome. Is this about publish-or-perish stuff, perhaps (e.g. citation "importance" for the algos)? Or maybe you're okay with this in general, but are regretful because it's Anthropic in particular?

Doesn’t matter. AI bros don’t care. AI wash it and release it closed. What are you going to do? Sue them?