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Mike Lewis

49 accepted papers

2026

Towards Unified Multimodal Pretraining

ICML 2026spotlight

Unified multimodal models aim to input and output both vision and language data within a single system. In this work, we explore the design space of Unified Multimodal Pretraining through a controlled, from-scratch study. We find that leveraging a single high-dimensional semantic encoder (e.g. SigLI…

Cited by 0SourceScholar
2025

BTS: Harmonizing Specialized Experts into a Generalist LLM

EMNLP 2025

We present Branch-Train-Stitch (BTS), an efficient and flexible training algorithm for combining independently trained large language model (LLM) experts into a single, capable generalist model. Following Li et al., we start with a single seed language model which is branched into domain-specific (e

Cited by 0SourcePDFScholar
2025

Byte Latent Transformer: Patches Scale Better Than Tokens

ACL 2025long

We introduce the Byte Latent Transformer (BLT), a new byte-level LLM architecture that, for the first time, matches tokenization-based LLM performance at scale with significant improvements in inference efficiency and robustness. BLT encodes bytes into dynamically sized patches, which serve as the p…

2025

Compute Optimal Scaling of Skills: Knowledge vs Reasoning

ACL 2025finding

Scaling laws are a critical component of the LLM development pipeline, most famously as a way to forecast training decisions such as ‘compute-optimally’ trading-off parameter count and dataset size, alongside a more recent growing list of other crucial decisions. In this work, we ask whether compute…

Cited by 0SourcePDFScholar
2025

FlexOLMo: Open Language Models for Flexible Data Use

NeurIPS 2025spotlight

We introduce FlexOLMo, a new class of language models (LMs) that supports (1) distributed training without data sharing, where different model parameters are independently trained on private datasets, and (2) data-flexible inference, where these parameters along with their associated data can be eas…

Cited by 0SourceScholar
2025

Law of the Weakest Link: Cross Capabilities of Large Language Models

ICLR 2025poster

The development and evaluation of Large Language Models (LLMs) have largely focused on individual capabilities. However, this overlooks the intersection of multiple abilities across different types of expertise that are often required for real-world tasks, which we term **cross capabilities**. To sy…

2024

Effective Long-Context Scaling of Foundation Models

NAACL 2024long

We present an effective recipe to train strong long-context LLMs that are capable of utilizing massive context windows of up to 32,000 tokens. Our models are built through continual pretraining from Llama 2 checkpoints with longer text sequences and on a dataset where long texts are upsampled. We pe…

Cited by 231SourcePDFScholar
2024

Efficient Streaming Language Models with Attention Sinks

ICLR 2024poster

Deploying Large Language Models (LLMs) in streaming applications such as multi-round dialogue, where long interactions are expected, is urgently needed but poses two major challenges. Firstly, during the decoding stage, caching previous tokens' Key and Value states (KV) consumes extensive memory. Se…

2024

In-Context Pretraining: Language Modeling Beyond Document Boundaries

ICLR 2024spotlight

Language models are currently trained to predict tokens given document prefixes, enabling them to zero shot long form generation and prompting-style tasks which can be reduced to document completion. We instead present IN-CONTEXT PRETRAINING, a new approach where language models are trained on a seq…

2024

RA-DIT: Retrieval-Augmented Dual Instruction Tuning

ICLR 2024poster

Retrieval-augmented language models (RALMs) improve performance by accessing long-tail and up-to-date knowledge from external data stores, but are challenging to build. Existing approaches require either expensive retrieval-specific modifications to LM pre-training or use post-hoc integration of the…

Cited by 142SourcePDFScholar
2024

REPLUG: Retrieval-Augmented Black-Box Language Models

NAACL 2024long

We introduce REPLUG, a retrieval-augmented language modeling framework that treats the language model (LM) as a black box and augments it with a tuneable retrieval model. Unlike prior retrieval-augmented LMs that train language models with special cross-attention mechanisms to encode the retrieved t…

2024

Self-Alignment with Instruction Backtranslation

ICLR 2024oral

We present a scalable method to build a high quality instruction following language model by automatically labelling human-written text with corresponding instructions. Our approach, named instruction backtranslation, starts with a language model finetuned on a small amount of seed data, and a given…

Cited by 230SourcePDFScholar
2024

Trusting Your Evidence: Hallucinate Less with Context-aware Decoding

NAACL 2024short

Language models (LMs) often struggle to pay enough attention to the input context, and generate texts that are unfaithful or contain hallucinations. To mitigate this issue, we present context-aware decoding (CAD), which follows a contrastive output distribution that amplifies the difference between…

2023

Coder Reviewer Reranking for Code Generation

ICML 2023poster

Sampling diverse programs from a code language model and reranking with model likelihood is a popular method for code generation but it is prone to preferring degenerate solutions. Inspired by collaborative programming, we propose Coder-Reviewer reranking. We augment Coder language models from past…

2023

Contrastive Decoding: Open-ended Text Generation as Optimization

ACL 2023long

Given a language model (LM), maximum probability is a poor decoding objective for open-ended generation, because it produces short and repetitive text. On the other hand, sampling can often produce incoherent text that drifts from the original topics. We propose contrastive decoding (CD), a reliable…

2023

FActScore: Fine-grained Atomic Evaluation of Factual Precision in Long Form Text Generation

EMNLP 2023long main

Evaluating the factuality of long-form text generated by large language models (LMs) is non-trivial because (1) generations often contain a mixture of supported and unsupported pieces of information, making binary judgments of quality inadequate, and (2) human evaluation is time-consuming and costly…

Cited by 0SourcecodeScholar
2023

In-context Examples Selection for Machine Translation

ACL 2023findings

Large-scale generative models show an impressive ability to perform a wide range of Natural Language Processing (NLP) tasks using in-context learning, where a few examples are used to describe a task to the model. For Machine Translation (MT), these examples are typically randomly sampled from the d…

2023

InCoder: A Generative Model for Code Infilling and Synthesis

ICLR 2023top-25%

Code is seldom written in a single left-to-right pass and is instead repeatedly edited and refined. We introduce InCoder, a unified generative model that can perform program synthesis (via left-to-right generation) as well as editing (via masking and infilling). InCoder is trained to generate code f…

2023

MEGABYTE: Predicting Million-byte Sequences with Multiscale Transformers

NeurIPS 2023poster

Autoregressive transformers are spectacular models for short sequences but scale poorly to long sequences such as high-resolution images, podcasts, code, or books. We proposed Megabyte, a multi-scale decoder architecture that enables end-to-end differentiable modeling of sequences of over one millio…

Cited by 91SourcePDFScholar
2023

Measuring and Narrowing the Compositionality Gap in Language Models

EMNLP 2023long findings

We investigate the ability of language models to perform compositional reasoning tasks where the overall solution depends on correctly composing the answers to sub-problems. We measure how often models can correctly answer all sub-problems but not generate the overall solution, a ratio we call the…

Cited by 0SourcecodeScholar
2023

Nonparametric Masked Language Modeling

ACL 2023findings

Existing language models (LMs) predict tokens with a softmax over a finite vocabulary, which can make it difficult to predict rare tokens or phrases. We introduce NPM, the first nonparametric masked language model that replaces this softmax with a nonparametric distribution over every phrase in a re…

2023

Progressive Prompts: Continual Learning for Language Models

ICLR 2023poster

We introduce Progressive Prompts – a simple and efficient approach for continual learning in language models. Our method allows forward transfer and resists catastrophic forgetting, without relying on data replay or a large number of task-specific parameters. Progressive Prompts learns a new soft pr…

2023

Residual Prompt Tuning: improving prompt tuning with residual reparameterization

ACL 2023findings

Prompt tuning is one of the successful approaches for parameter-efficient tuning of pre-trained language models. Despite being arguably the most parameter-efficient (tuned soft prompts constitute <0.1% of total parameters), it typically performs worse than other efficient tuning methods and is quite…

2023

Retrieval-Augmented Multimodal Language Modeling

ICML 2023poster

Recent multimodal models such as DALL-E and CM3 have achieved remarkable progress in text-to-image and image-to-text generation. However, these models store all their knowledge (e.g., the appearance of the Eiffel Tower) in the model parameters, requiring increasingly larger models and training data…

Cited by 159SourcePDFScholar
2022

8-bit Optimizers via Block-wise Quantization

ICLR 2022spotlight

Stateful optimizers maintain gradient statistics over time, e.g., the exponentially smoothed sum (SGD with momentum) or squared sum (Adam) of past gradient values. This state can be used to accelerate optimization significantly, compared to plain stochastic gradient descent, but uses memory that mig…

2022

DEMix Layers: Disentangling Domains for Modular Language Modeling

NAACL 2022long

We introduce a new domain expert mixture (DEMix) layer that enables conditioning a language model (LM) on the domain of the input text. A DEMix layer includes a collection of expert feedforward networks, each specialized to a domain, that makes the LM modular: experts can be mixed, added, or removed…

2022

GPT3.int8(): 8-bit Matrix Multiplication for Transformers at Scale

NeurIPS 2022accept

Large language models have been widely adopted but require significant GPU memory for inference. We develop a procedure for Int8 matrix multiplication for feed-forward and attention projection layers in transformers, which cut the memory needed for inference by half while retaining full precision pe…

Cited by 1133SourcePDFScholar
2022

HTLM: Hyper-Text Pre-Training and Prompting of Language Models

ICLR 2022poster

We introduce HTLM, a hyper-text language model trained on a large-scale web crawl. Modeling hyper-text has a number of advantages: (1) it is easily gathered at scale, (2) it provides rich document-level and end-task-adjacent supervision (e.g. 'class' and 'id' attributes often encode document categor…

Cited by 84SourcePDFScholar
2022

Improving Passage Retrieval with Zero-Shot Question Generation

EMNLP 2022main

We propose a simple and effective re-ranking method for improving passage retrieval in open question answering. The re-ranker re-scores retrieved passages with a zero-shot question generation model, which uses a pre-trained language model to compute the probability of the input question conditioned…

2022

Noisy Channel Language Model Prompting for Few-Shot Text Classification

ACL 2022long

We introduce a noisy channel approach for language model prompting in few-shot text classification. Instead of computing the likelihood of the label given the input (referred as direct models), channel models compute the conditional probability of the input given the label, and are thereby required…

2022

Question Answering Infused Pre-training of General-Purpose Contextualized Representations

ACL 2022findings

We propose a pre-training objective based on question answering (QA) for learning general-purpose contextual representations, motivated by the intuition that the representation of a phrase in a passage should encode all questions that the phrase can answer in context. To this end, we train a bi-enco…

2022

Rethinking the Role of Demonstrations: What Makes In-Context Learning Work?

EMNLP 2022main

Large language models (LMs) are able to in-context learn—perform a new task via inference alone by conditioning on a few input-label pairs (demonstrations) and making predictions for new inputs. However, there has been little understanding of how the model learns and which aspects of the demonstrati…

2022

Sparse Distillation: Speeding Up Text Classification by Using Bigger Student Models

NAACL 2022long

Distilling state-of-the-art transformer models into lightweight student models is an effective way to reduce computation cost at inference time. The student models are typically compact transformers with fewer parameters, while expensive operations such as self-attention persist. Therefore, the impr…

2022

Train Short, Test Long: Attention with Linear Biases Enables Input Length Extrapolation

ICLR 2022poster

Since the introduction of the transformer model by Vaswani et al. (2017), a fundamental question has yet to be answered: how does a model achieve extrapolation at inference time for sequences that are longer than it saw during training? We first show that extrapolation can be enabled by simply chang…

2022

Tricks for Training Sparse Translation Models

NAACL 2022long

Multi-task learning with an unbalanced data distribution skews model learning towards high resource tasks, especially when model capacity is fixed and fully shared across all tasks. Sparse scaling architectures, such as BASELayers, provide flexible mechanisms for different tasks to have a variable n…

Cited by 30SourcePDFScholar
2021

BASE Layers: Simplifying Training of Large, Sparse Models

ICML 2021spotlight

We introduce a new balanced assignment of experts (BASE) layer for large language models that greatly simplifies existing high capacity sparse layers. Sparse layers can dramatically improve the efficiency of training and inference by routing each token to specialized expert modules that contain only…

2021

Joint Verification and Reranking for Open Fact Checking Over Tables

ACL 2021long

Structured information is an important knowledge source for automatic verification of factual claims. Nevertheless, the majority of existing research into this task has focused on textual data, and the few recent inquiries into structured data have been for the closed-domain setting where appropriat…

Cited by 29SourcePDFScholar
2021

Nearest Neighbor Machine Translation

ICLR 2021poster

We introduce $k$-nearest-neighbor machine translation ($k$NN-MT), which predicts tokens with a nearest-neighbor classifier over a large datastore of cached examples, using representations from a neural translation model for similarity search. This approach requires no additional training and scales…

2020

Generalization through Memorization: Nearest Neighbor Language Models

ICLR 2020poster

We introduce $k$NN-LMs, which extend a pre-trained neural language model (LM) by linearly interpolating it with a $k$-nearest neighbors ($k$NN) model. The nearest neighbors are computed according to distance in the pre-trained LM embedding space, and can be drawn from any text collection, including…

Cited by 952SourcecodeScholar
2020

Pre-training via Paraphrasing

NeurIPS 2020poster

We introduce MARGE, a pre-trained sequence-to-sequence model learned with an unsupervised multi-lingual multi-document paraphrasing objective. MARGE provides an alternative to the dominant masked language modeling paradigm, where we self-supervise the \emph{reconstruction} of target text by \emph{re…

Cited by 171SourcePDFScholar
2020

Retrieval-Augmented Generation for Knowledge-Intensive NLP Tasks

NeurIPS 2020poster

Large pre-trained language models have been shown to store factual knowledge in their parameters, and achieve state-of-the-art results when fine-tuned on downstream NLP tasks. However, their ability to access and precisely manipulate knowledge is still limited, and hence on knowledge-intensive tasks…

2019

Hierarchical Decision Making by Generating and Following Natural Language Instructions

NeurIPS 2019poster

We explore using latent natural language instructions as an expressive and compositional representation of complex actions for hierarchical decision making. Rather than directly selecting micro-actions, our agent first generates a latent plan in natural language, which is then executed by a separate…