<!--Copyright 2021 The HuggingFace Team. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
specific language governing permissions and limitations under the License.
-->

# T5v1.1

## Overview

T5v1.1 was released in the [google-research/text-to-text-transfer-transformer](https://github.com/google-research/text-to-text-transfer-transformer/blob/main/released_checkpoints.md#t511)
repository by Colin Raffel et al. It's an improved version of the original T5 model.

One can directly plug in the weights of T5v1.1 into a T5 model, like so:

```python
from transformers import T5ForConditionalGeneration

model = T5ForConditionalGeneration.from_pretrained("google/t5-v1_1-base")
```

T5 Version 1.1 includes the following improvements compared to the original T5 model:

- GEGLU activation in the feed-forward hidden layer, rather than ReLU. See [this paper](https://arxiv.org/abs/2002.05202).

- Dropout was turned off in pre-training (quality win). Dropout should be re-enabled during fine-tuning.

- Pre-trained on C4 only without mixing in the downstream tasks.

- No parameter sharing between the embedding and classifier layer.

- "xl" and "xxl" replace "3B" and "11B". The model shapes are a bit different - larger `d_model` and smaller
  `num_heads` and `d_ff`.

Note: T5 Version 1.1 was only pre-trained on [C4](https://huggingface.co/datasets/c4) excluding any supervised
training. Therefore, this model has to be fine-tuned before it is useable on a downstream task, unlike the original T5
model. Since t5v1.1 was pre-trained unsupervisedly, there's no real advantage to using a task prefix during single-task
fine-tuning. If you are doing multi-task fine-tuning, you should use a prefix.

Google has released the following variants:

- [google/t5-v1_1-small](https://huggingface.co/google/t5-v1_1-small)

- [google/t5-v1_1-base](https://huggingface.co/google/t5-v1_1-base)

- [google/t5-v1_1-large](https://huggingface.co/google/t5-v1_1-large)

- [google/t5-v1_1-xl](https://huggingface.co/google/t5-v1_1-xl)

- [google/t5-v1_1-xxl](https://huggingface.co/google/t5-v1_1-xxl).

One can refer to [T5's documentation page](t5) for all tips, code examples and notebooks.

This model was contributed by [patrickvonplaten](https://huggingface.co/patrickvonplaten). The original code can be
found [here](https://github.com/google-research/text-to-text-transfer-transformer/blob/main/released_checkpoints.md#t511).
