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“Learning to Interpret Weight Differences in Language Models” by avichal


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Audio note: this article contains 38 uses of latex notation, so the narration may be difficult to follow. There's a link to the original text in the episode description.

Paper | Github | Demo Notebook

This post is about our recent paper Learning to Interpret Weight Differences in Language Models (Goel et al. Oct. 2025). We introduce a method for training a LoRA adapter that gives a finetuned model the ability to accurately describe the effects of its finetuning.

Figure 1: A demonstration of our method on Qwen3-8B. With the adapter applied, a model is able to answer questions about its finetuning changes. Try it yourself here.

WeightDiffQA

Our paper introduces and attempts to solve a task we call WeightDiffQA[1]:

Given a language model _M_, a weight diff _delta_, and a natural language question _q_ about _delta_, output a correct natural language answer to _q_.

Here, a "weight [...]

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Outline:

(00:57) WeightDiffQA

(03:17) Diff Interpretation Tuning

(05:09) Eval #1: Reporting hidden behaviors

(07:17) Eval #2: Summarizing finetuned knowledge

(08:26) Limitations

(09:50) Takeaways

The original text contained 8 footnotes which were omitted from this narration.

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First published:

October 23rd, 2025

Source:

https://www.lesswrong.com/posts/EKhTrhrCz2rNg7FmG/learning-to-interpret-weight-differences-in-language-models-1

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