Cannot import AutoModelForSeq2SeqLM 
# 🐛 Bug

Has the `AutoModelForSeq2SeqLM` class changed? 

I am trying to run transformer examples, basically the [token-classification](https://github.com/huggingface/transformers/blob/master/examples/token-classification/run_pl.sh) with pytorch-lightning, which calls [AutoModelForSeq2SeqLM](https://github.com/huggingface/transformers/blob/master/examples/lightning_base.py#L18). However, I am getting an import error. See below.

## Information

Model I am using (Bert, XLNet ...):

`bert-base-multilingual-cased`

Language I am using the model on (English, Chinese ...): 

`English`

The problem arises when using:
* [X] the official example scripts: (give details below)
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [X] an official GLUE/SQUaD task: (give the name)
* [ ] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:

```
cd transformers/examples/token-classification
./run_pl.sh
```

```
Traceback (most recent call last):
  File "run_pl_ner.py", line 12, in <module>
    from lightning_base import BaseTransformer, add_generic_args, generic_train
  File "/transformers/examples/lightning_base.py", line 12, in <module>
    from transformers import (
ImportError: cannot import name 'AutoModelForSeq2SeqLM' from 'transformers' (/anaconda3/envs/transformers/lib/python3.8/site-packages/transformers/__init__.py)
```

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## Expected behavior

<!-- A clear and concise description of what you would expect to happen. -->

Reproduce the example.

## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `transformers` version: 2.11.0
- Platform: Linux
- Python version: Python 3.8.3
- PyTorch version (GPU?): 1.5.1
- Tensorflow version (GPU?):
- Using GPU in script?: Yes
- Using distributed or parallel set-up in script?:

I think this is because you don't have installed the library from source (see the [note here](https://github.com/huggingface/transformers/blob/master/examples/README.md#important-note)).

To install from source, follow the steps [here](https://huggingface.co/transformers/installation.html#installing-from-source)<|||||>@sgugger Thanks, it works when installing with the source (through small changes) :) 

Also, as I said, the 2.11.0 version (installed by pip) still has this bug 

```
from transformers import AutoModelForSeq2SeqLM
```

What do you suggest for a stable version of transformers? <|||||>I'm not sure I follow. 2.11.0 is the last stable version, but the examples script on the main branch only works with an installation from source. 

If you want a version of the examples compatible with 2.11.0, you should use their version in the [2.11.0 tagged repo](https://github.com/huggingface/transformers/tree/v2.11.0).<|||||>Same Issue v2.11.0<|||||>Again this is not an issue. The examples in the master repo are on par with the version of transformers on master, so you need an installation from source to run them, which is clearly indicated in the README.

If you want to execute the examples script as they were for v2.11.0, you should use 2.11.0 tagged repo](https://github.com/huggingface/transformers/tree/v2.11.0).

Closing this issue, please reopen if anything I said was unclear.