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Noam Razin

@noamrazin.bsky.social
872 followers 267 following 34 posts

Postdoctoral Fellow at Princeton Language and Intelligence | Past: Computer Science PhD at Tel Aviv University & Apple Scholar in AI/ML | Interested in the foundations of deep learning noamrazin.github.io

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Noam Razin @noamrazin.bsky.social · 11/07/2025
Joint w/ Yong Lin, Jiarui Yao, @profsanjeevarora.bsky.social This work was supported in part by the #ZuckermanSTEMLeadershipProgram. 📰 Paper: arxiv.org/abs/2507.07981 6/6
arxiv.org
Why is Your Language Model a Poor Implicit Reward Model?
Reward models are key to language model post-training and inference pipelines. Conveniently, recent work showed that every language model defines an implicit reward model (IM-RM), without requiring an...
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Noam Razin @noamrazin.bsky.social · 11/07/2025
Overall, our results highlight that seemingly minor design choices can substantially impact how RMs generalize. We hope that it will encourage further research into understanding the implicit biases of different RM types. 5/6
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Noam Razin @noamrazin.bsky.social · 11/07/2025
We also challenge the intuitive claim that IM-RMs struggle in tasks where generation is harder than verification, since they can operate both as a verifier and generator. We prove and show empirically that IM-RMs do not need to learn to generate in order to verify responses. 4/6
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Noam Razin @noamrazin.bsky.social · 11/07/2025
TL;DR: Through theory and experiments, we find that IM-RMs rely more heavily on superficial token-level cues. As a result, they often generalize worse under token-level shifts, as well as in-distribution, but actually generalize comparably or better under domain shifts. 3/6
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Noam Razin @noamrazin.bsky.social · 11/07/2025
As the DPO paper showed, every LM defines an IM-RM. However, prior work observed that IM-RMs often generalize worse than EX-RMs. The existence of a generalization gap is puzzling, since both RM types can be trained using the same LM, data, and loss. So what causes it? 2/6
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Noam Razin @noamrazin.bsky.social · 11/07/2025
Reward models (RMs) are key to language model post-training and inference pipelines. But, little is known about the relative pros and cons of different RM types. 📰 We investigate why RMs implicitly defined by language models (LMs) often generalize worse than explicit RMs 🧵 1/6
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Noam Razin @noamrazin.bsky.social · 20/03/2025
Had the pleasure of collaborating with Zixuan Wang, Hubert Strauss, Stanley Wei, @jasondeanlee.bsky.social, @profsanjeevarora.bsky.social. This work was supported in part by the #ZuckermanSTEMLeadershipProgram. 📰 Paper: arxiv.org/abs/2503.15477 10/10
arxiv.org
What Makes a Reward Model a Good Teacher? An Optimization Perspective
The success of Reinforcement Learning from Human Feedback (RLHF) critically depends on the quality of the reward model. While this quality is primarily evaluated through accuracy, it remains unclear w...
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Noam Razin @noamrazin.bsky.social · 20/03/2025
Overall, despite the importance of RMs, the understanding of what makes a good RM is limited. We hope our insights can inspire further research on RM training and evaluation protocols that account for properties beyond accuracy. 9/10
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Noam Razin @noamrazin.bsky.social · 20/03/2025
We additionally prove that the same RM can induce high reward variance and work well for one LLM, yet induce low reward variance and perform poorly for another. This reveals a fundamental limitation of evaluating RMs in isolation from the LLM they guide. 8/10
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Noam Razin @noamrazin.bsky.social · 20/03/2025
Intuitively, accuracy and reward variance measure distinct properties of an RM. Reward variance is determined by how well the RM separates outputs that are likely under the LLM being aligned. In contrast, accuracy depends only on the rankings of outputs. 7/10
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Noam Razin @noamrazin.bsky.social · 20/03/2025
This result builds on a previous paper (ICLR 2024), where we showed that low reward variance leads to vanishing gradients in RLHF. arxiv.org/abs/2310.20703 6/10
arxiv.org
Vanishing Gradients in Reinforcement Finetuning of Language Models
Pretrained language models are commonly aligned with human preferences and downstream tasks via reinforcement finetuning (RFT), which refers to maximizing a (possibly learned) reward function using po...
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Noam Razin @noamrazin.bsky.social · 20/03/2025
We prove and show empirically that regardless of how accurate an RM is, if it induces *low reward variance*, then the RLHF objective suffers from a flat landscape. As a result, even a perfectly accurate RM can underperform less accurate models due to slow optimization. 5/10
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Noam Razin @noamrazin.bsky.social · 20/03/2025
However, recent empirical evidence suggests that accuracy may not be indicative of an LLM's performance after RLHF. So, what makes an RM a good teacher? 4/10
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Noam Razin @noamrazin.bsky.social · 20/03/2025
RMs are primarily evaluated through accuracy, which measures their agreement with human preferences in terms of ranking output pairs. 3/10
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Noam Razin @noamrazin.bsky.social · 20/03/2025
TL;DR: Alongside being accurate, an RM needs to induce sufficient reward variance for efficient optimization. This allows explaining why even perfectly accurate RMs can be poor teachers and highlights limitations of existing RM benchmarks. arxiv.org/abs/2503.15477 Details 👇 2/10
arxiv.org
What Makes a Reward Model a Good Teacher? An Optimization Perspective
The success of Reinforcement Learning from Human Feedback (RLHF) critically depends on the quality of the reward model. While this quality is primarily evaluated through accuracy, it remains unclear w...
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Noam Razin @noamrazin.bsky.social · 20/03/2025
The success of RLHF depends heavily on the quality of the reward model (RM), but how should we measure this quality? 📰 We study what makes a good RM from an optimization perspective. Among other results, we formalize why more accurate RMs are not necessarily better teachers! 🧵
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Noam Razin @noamrazin.bsky.social · 20/03/2025
Had the pleasure of collaborating with Zixuan Wang, Hubert Strauss, Stanley Wei, @jasondeanlee.bsky.social, @profsanjeevarora.bsky.social. This work was supported in part by the #ZuckermanSTEMLeadershipProgram. 📰 Paper: arxiv.org/abs/2503.15477 10/10
arxiv.org
What Makes a Reward Model a Good Teacher? An Optimization Perspective
The success of Reinforcement Learning from Human Feedback (RLHF) critically depends on the quality of the reward model. While this quality is primarily evaluated through accuracy, it remains unclear w...
000
Noam Razin @noamrazin.bsky.social · 20/03/2025
Overall, despite the importance of RMs, the understanding of what makes a good RM is limited. We hope our insights can inspire further research on RM training and evaluation protocols that account for properties beyond accuracy. 9/10
100
Noam Razin @noamrazin.bsky.social · 20/03/2025
We additionally prove that the same RM can induce high reward variance and work well for one LLM, yet induce low reward variance and perform poorly for another. This reveals a fundamental limitation of evaluating RMs in isolation from the LLM they guide. 8/10
100
Noam Razin @noamrazin.bsky.social · 20/03/2025
Intuitively, accuracy and reward variance measure distinct properties of an RM. Reward variance is determined by how well the RM separates outputs that are likely under the LLM being aligned. In contrast, accuracy depends only on the rankings of outputs. 7/10
100
Noam Razin @noamrazin.bsky.social · 20/03/2025
This result builds on a previous paper (ICLR 2024), where we showed that low reward variance leads to vanishing gradients in RLHF. arxiv.org/abs/2310.20703 6/10
arxiv.org
Vanishing Gradients in Reinforcement Finetuning of Language Models
Pretrained language models are commonly aligned with human preferences and downstream tasks via reinforcement finetuning (RFT), which refers to maximizing a (possibly learned) reward function using po...
100
Noam Razin @noamrazin.bsky.social · 20/03/2025
We prove and show empirically that regardless of how accurate an RM is, if it induces *low reward variance*, then the RLHF objective suffers from a flat landscape. As a result, even a perfectly accurate RM can underperform less accurate models due to slow optimization. 5/10
100
Noam Razin @noamrazin.bsky.social · 20/03/2025
However, recent empirical evidence suggests that accuracy may not be indicative of an LLM's performance after RLHF. So, what makes an RM a good teacher? 4/10
100
Noam Razin @noamrazin.bsky.social · 20/03/2025
RMs are primarily evaluated through accuracy, which measures their agreement with human preferences in terms of ranking output pairs. 3/10
100
Noam Razin @noamrazin.bsky.social · 20/03/2025
TL;DR: Alongside being accurate, an RM needs to induce sufficient reward variance for efficient optimization. This allows explaining why even perfectly accurate RMs can be poor teachers and highlights limitations of existing RM benchmarks. arxiv.org/abs/2503.15477 Details 👇 2/10
arxiv.org
What Makes a Reward Model a Good Teacher? An Optimization Perspective
The success of Reinforcement Learning from Human Feedback (RLHF) critically depends on the quality of the reward model. While this quality is primarily evaluated through accuracy, it remains unclear w...
100
Noam Razin @noamrazin.bsky.social · 14/12/2024
Paper link: arxiv.org/abs/2410.08847
arxiv.org
Unintentional Unalignment: Likelihood Displacement in Direct Preference Optimization
Direct Preference Optimization (DPO) and its variants are increasingly used for aligning language models with human preferences. Although these methods are designed to teach a model to generate prefer...
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Noam Razin @noamrazin.bsky.social · 14/12/2024
Presenting tomorrow a poster on why DPO often decreases the probability of preferred responses, how that can cause surprising failures in alignment, and what can we do about it. Catch me at these #NeurIPS workshop poster sessions: - M3L 11:15am - ATTRIB 3:00pm - FITML 4:40pm
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Noam Razin @noamrazin.bsky.social · 09/12/2024
I am attending NeurIPS! Feel free to reach out if you want to chat. I will present in the M3L, FITML, and ATTRIB workshops our paper on why DPO often decreases the probability of preferred responses and how that can lead to weird failures in alignment. arxiv.org/abs/2410.08847
arxiv.org
Unintentional Unalignment: Likelihood Displacement in Direct Preference Optimization
Direct Preference Optimization (DPO) and its variants are increasingly used for aligning language models with human preferences. Although these methods are designed to teach a model to generate prefer...
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Noam Razin @noamrazin.bsky.social · 26/11/2024
Catch Sadhika's talk today if you want to learn more about the surprising ways in which aligning language models based on preference data can fail
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Noam Razin @noamrazin.bsky.social · 22/11/2024
True. Though I believe there are several ways you can formalize that even without KL regularization, if you are training on samples from your model and it does not give non-trivial probability to anything with a high reward, then it will necessarily take a long time to increase the reward
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Noam Razin @noamrazin.bsky.social · 22/11/2024
Related to your original Q, another potentially useful perspective is that DPO and explicit reward models are almost identical. So if one of them gets it right, it is likely that the other will as well (and vice-versa)?
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Noam Razin @noamrazin.bsky.social · 22/11/2024
I believe so. We give a demonstration where that leads to a surprising failure when trying to align a model to refuse unsafe prompts. If you filter your data, add SFT regularization or use multiple models to generate responses (which people often do) it can help though
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Noam Razin @noamrazin.bsky.social · 22/11/2024
It is hard to tell for your specific setting without running the experiment, but we have a recent work suggesting that in such cases, where preferences are not sufficiently distinct, DPO may result in unexpected/undesirable behaviors (a bit of shameless advertising :)) arxiv.org/abs/2410.08847
arxiv.org
Unintentional Unalignment: Likelihood Displacement in Direct Preference Optimization
Direct Preference Optimization (DPO) and its variants are increasingly used for aligning language models with human preferences. Although these methods are designed to teach a model to generate prefer...
110
Noam Razin @noamrazin.bsky.social · 20/11/2024
Nadav Cohen and I recently uploaded lecture notes on the theory (and surprising practical applications) of linear neural networks. Hope that it can be useful, especially to those entering the field as it highlights distinctions between DL and "classical" ML theory arxiv.org/abs/2408.13767
arxiv.org
Lecture Notes on Linear Neural Networks: A Tale of Optimization and Generalization in Deep Learning
These notes are based on a lecture delivered by NC on March 2021, as part of an advanced course in Princeton University on the mathematical understanding of deep learning. They present a theory (devel...
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