# Hugging Face Transformers v2.1.1 — Release & Upgrade Intelligence
- **Product:** Hugging Face Transformers (https://huggingface.co)
- **Version:** v2.1.1
- **Released:** Oct 11, 2019
- **Impact Score:** 7/10
- **Breaking Changes:** Source flagged
- **Canonical Analysis:** https://changelogs.us/transformers/updates/v2.1.1/

## Executive Summary (TL;DR)
Hugging Face Transformers v2.1.1. Source highlight: New model architectures: CTRL, DistilGPT-2

## Breaking Changes & Deprecations
- Breaking changes - The two methods `add_special_tokens_single_sequence` and `add_special_tokens_sequence_pair` have been removed. They have been replaced by the single method `build_inputs_with_special_tokens ` which has a more comprehensible name and manages both sequence singletons and pairs.

## New Features
- CTRL (from Salesforce) released with the paper CTRL: A Conditional Transformer Language Model for Controllable Generation, by Nitish Shirish Keskar, Bryan McCann, Lav R. Varshney, Caiming Xiong, Richard Socher. This model has been added to the library by @keskarnitish with the help of @thomwolf.

## Improvements
- `run_lm_finetuning.py` has been improved  with the help of @dennymarcels, @jinoobaek-qz and @LysandreJik
- `run_glue.py` has been improved with  the help of @brian41005

## Bug Fixes
- GLUE Processors have been refactored to handle inputs for all tasks coming from the `tensorflow_datasets`. This work has been done by @agrinh and @philipp-eisen.
- The padding_idx is now correctly initialized to 1 in randomly initialized RoBERTa models. @ikuyamada
- The documentation CSS has been adapted to work on older browsers. @TimYagan
- An addition concerning the management of hidden states has been added to the README by @BramVanroy.
- Integration of TF 2.0 models with other Keras modules @thomwolf
- Past values can be opted-out @thomwolf

## Upgrade Command
```bash
python -m pip install 'transformers==2.1.1'
```