Forgetting Transformer: Softmax Attention with a Forget Gate
Authors: name: Zhixuan Lin; name: Evgenii Nikishin; name: Xu Owen He; name: Aaron Courville
Published: 2025-03-03 23:35:23

Abstract: An essential component of modern recurrent sequence models is the forget
gate. While Transformers do not have an explicit recurrent form, we show that a
forget gate can be naturally incorporated into Transformers by down-weighting
the unnormalized attention scores in a data-dependent way. We name this
attention mechanism the Forgetting Attention and the resulting model the
Forgetting Transformer (FoX). We show that FoX outperforms the Transformer on
long-context language modeling, length extrapolation, and short-context
downstream tasks, while performing on par with the Transformer on long-context
downstream tasks. Moreover, it is compatible with the FlashAttention algorithm
and does not require any positional embeddings. Several analyses, including the
needle-in-the-haystack test, show that FoX also retains the Transformer's
superior long-context capabilities over recurrent sequence models such as
Mamba-2, HGRN2, and DeltaNet. We also introduce a "Pro" block design that
incorporates some common architectural components in recurrent sequence models
and find it significantly improves the performance of both FoX and the
Transformer. Our code is available at
https://github.com/zhixuan-lin/forgetting-transformer.