Who’s Harry Potter? Approximate Unlearning in LLMs: Conclusion, Acknowledgment, and References

3 Jul 2024


(1) Ronen Eldan, Microsoft Research (email: roneneldan@microsoft.com);

(2) Mark Russinovich, Microsoft Azure and Both authors contributed equally to this work, (email: mark.russinovich@microsoft.com).

5 Conclusion

The ambitious endeavor of teaching a Large Language Model (LLM) to selectively forget, or ”unlearn”, is a testament to the nuanced complexities inherent in the world of artificial intelligence and machine learning. Widely regarded as a daunting task, any attempt at enabling such a functionality in LLMs stands at the vanguard of innovative solutions, and in this light, our proof of concept arguably underscores progress.

Firstly, our research demonstrates that unlearning, though challenging, is not an insurmountable task, as the positive outcomes in our experiments with the Llama2-7b model suggest. Yet, this achievement must be contextualized with prudence. Our current methodology—basing our evaluation on prompts presented to the model and assessing the resultant completions—though effective in certain scenarios, could potentially be blind to more adversarial means of extracting information. It’s conceivable that non-traditional or intricate methods, such as delving into token probability distributions, might inadvertently reveal the model’s latent familiarity with unlearned content.

Diving deeper into the potential generality of our technique, a pertinent observation emerges when considering the unique attributes of the Harry Potter series. The books are replete with idiosyncratic expressions and distinctive names—traits that, in hindsight, may have abetted our unlearning strategy. The pronounced presence of Harry Potter themes across the training data of many LLMs further compounds the challenge. Given such widespread representation, even the slightest hint in a prompt might stir a cascade of related completions, underscoring the depth of memory ingrained in the model.

A nuance of our methodology involves a reliance on GPT-4’s existing knowledge of the Harry Potter universe. To detect specific anchored terms and devise generic counterparts, the expertise of GPT-4 proved useful. This raises the question whether our technique achieve similar efficacy when stripped of such vast prior knowledge. Preliminary experiments show that entity extraction can still be effective when this knowledge is absent, and we speculate that the lack of familiarity with idiosyncratic expressions can be addressed with simple n-gram frequency analysis but we leave a more thorough study for future work.

Extending our approach to other types of content, particularly non-fiction or textbooks, presents its own set of challenges. Unlike the fictional universe of Harry Potter, non-fiction content will not possess the same density of unique terms or phrases. Furthermore, non-fictional texts often embed higher-level constructs such as ideas, concepts, or cultural perspectives. It remains uncertain to what extent our technique can effectively address and unlearn these more abstract elements. This would clearly necessitate adaptations of our technique.

In conclusion, while our technique offers a promising start, its applicability across various content types remains to be thoroughly tested. The presented approach offers a foundation, but further research is needed to refine and extend the methodology for broader unlearning tasks in LLMs.


The authors would like to thank Yanan Cai for helping to configure and manage the Azure GPU VMs used for this work.


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