Transitioning from adapter-transformers


adapters is fully compatible to adapter-transformers in terms of model weights, meaning you can load any adapter trained with any version of adapter-transformers to the new library without degradation.

The new adapters library is the successor to the adapter-transformers library. It differs essentially in that adapters is now a stand-alone package, i.e., the package is disentangled from the transformers package from Hugging Face and is no longer a drop-in replacement.

This results in some breaking changes. To transition your code from adapter-transformers to adapters you need to consider the following changes:

Package and Namespace

To use the library you need to install transformers and adapters in the same environment (unlike adapter-transformers which contained transformers and could not be installed in the same environment).

Run the following to install both (installing adapters will automatically trigger the installation of a compatible transformers version):

pip install adapters

This also changes the namespace to adapters. For all imports of adapter classes change the import from transformers to adapters. This mainly affects the following classes:

  • AdapterModel classes, e.g. AutoAdapterModel (see AdapterModels )

  • Adapter configurations e.g. PrefixTuningConfig (see Configurations )

  • Adapter composition blocks, e.g. Stack (see Composition Blocks )

  • The AdapterTrainer class

Model Initialisation

The Hugging Face model classes, such as BertModel, cannot be used directly with adapters. They must first be initialised for adding adapters:

from transformers import AutoModel
import adapters

model = AutoModel.from_pretrained("bert-base-uncased")
adapters.init(model) # prepare model for use with adapters

The necessary change is the call of the adapters.init() method. Note that no additional initialisation is required to use the AdapterModel classes such as the BertAdapterModel’. These classes are provided by the adapters library and are already prepared for using adapters in training and inference.

Bottleneck Configuration Names

The adapters library supports the configuration of adapters using config strings. Compared to the adapter-transformers library, we have changed some of the strings to make them more consistent and intuitive:

  • houlsby -> double_seq_bn

  • pfeiffer -> seq_bn

  • parallel-> par_seq_bn

  • houlsby+inv -> double_seq_bn_inv

  • pfeiffer+inv-> seq_bn_inv

For a complete list of config strings and classes see here. We strongly recommend using the new config strings, but we will continue to support the old config strings for the time being to make the transition easier. Note that with the config strings the corresponding adapter config classes have changed, e.g. PfeifferConfig -> SeqBnConfig.

Another consequence of this that the AdapterConfig class is now not only for the bottleneck adapters anymore, but the base class of all the configurations (previously AdapterConfigBase). Hence, the function this class serves has changed. However, you can still load adapter configs with:

adapter_config = AdapterConfig.load("lora")

Features that are not supported by adapters

Compared to adapter-transformers, there are a few features that are no longer supported by the adapters library:

  • Using transformers pipelines with adapters.

  • Using invertible adapters in the Hugging Face model classes. To use invertible adapters you must use the AdapterModel class.

  • Loading model and adapter checkpoints saved with save_pretrained using Hugging Face classes. This is only supported by the AdapterModel classes.

What has remained the same

  • The new library is fully backwards compatible in terms of adapter weights, i.e. you can load all adapter modules trained with adapter-transformers.

  • The functionality for adding, activating, and training adapters has not changed, except for the renaming of some adapter configs. You still add and activate adapters as follows:

# add adapter to the model
model.add_adapter("adapter_name", config="lora")
# activate adapter
# freeze model weights and activate adapter

Where can I still find adapter-transformers?

The codebase of adapter-transformers has moved to for archival purposes.

The full documentation of the old library is now hosted at