OASST model is unavailable for Transformer Agent: `'inputs' must have less than 1024 tokens.`
### System Info

- transformers version: 4.29.0
- huggingface_hub version: 0.16.4
- python version: 3.10.6
- OS: Ubuntu 22.04.2 LTS 
* run on Google Colab using [the provided notebook](https://colab.research.google.com/drive/1c7MHD-T1forUPGcC_jlwsIptOzpG3hSj?usp=sharing).
* [my notebook](https://colab.research.google.com/drive/1UBIWVCIXowlUJpp5gwD-Z0hmVlLLCr9I?usp=sharing), copied from the above.

### Who can help?

@sgugger 
`OpenAssistant/oasst-sft-4-pythia-12b-epoch-3.5`, one of the models listed as available in the official notebook, is unusable due to the length of the tokens. When executing `agent.chat()` or `agent.run()` with the model, the following error raised:
```
ValueError: Error 422: {'error': 'Input validation error: `inputs` must have less than 1024 tokens. Given: 1553', 'error_type': 'validation'}
```

I guess that `max_input_length` of the model is `1024` if it follows the model configuration [here](https://github.com/LAION-AI/Open-Assistant/blob/main/oasst-shared/oasst_shared/model_configs.py#L50). Could you check this error? In addition, I would like to hear if you will update to reduce the length of the default prompt for Agent.

### Information

- [X] The official example scripts
- [ ] My own modified scripts

### Tasks

- [X] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

Below is the code for the first three cells of the official code provided in the notebook.

```
transformers_version = "v4.29.0"

print(f"Setting up everything with transformers version {transformers_version}")

!pip install huggingface_hub>=0.14.1 git+https://github.com/huggingface/transformers@$transformers_version -q diffusers accelerate datasets torch soundfile sentencepiece opencv-python openai

import IPython
import soundfile as sf

def play_audio(audio):
    sf.write("speech_converted.wav", audio.numpy(), samplerate=16000)
    return IPython.display.Audio("speech_converted.wav")

from huggingface_hub import notebook_login
notebook_login()
```
```
agent_name = "OpenAssistant (HF Token)"

import getpass

if agent_name == "StarCoder (HF Token)":
    from transformers.tools import HfAgent
    agent = HfAgent("https://api-inference.huggingface.co/models/bigcode/starcoder")
    print("StarCoder is initialized 💪")
elif agent_name == "OpenAssistant (HF Token)":
    from transformers.tools import HfAgent
    agent = HfAgent(url_endpoint="https://api-inference.huggingface.co/models/OpenAssistant/oasst-sft-4-pythia-12b-epoch-3.5")
    print("OpenAssistant is initialized 💪")
if agent_name == "OpenAI (API Key)":
    from transformers.tools import OpenAiAgent
    pswd = getpass.getpass('OpenAI API key:')
    agent = OpenAiAgent(model="text-davinci-003", api_key=pswd)
    print("OpenAI is initialized 💪")
```
```
boat = agent.run("Generate an image of a boat in the water")
boat
```

### Expected behavior

```
==Explanation from the agent==
I will use the following tool: `image_generator` to generate an image.


==Code generated by the agent==
image = image_generator(prompt="a boat in the water")


==Result==
<image.png>
```

as like `bigcode/starcoder` or `text-davinci-003`, but I got
```
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
[<ipython-input-3-4578d52c5ccf>](https://localhost:8080/#) in <cell line: 1>()
----> 1 boat = agent.run("Generate an image of a boat in the water")
      2 boat

1 frames
[/usr/local/lib/python3.10/dist-packages/transformers/tools/agents.py](https://localhost:8080/#) in run(self, task, return_code, remote, **kwargs)
    312         """
    313         prompt = self.format_prompt(task)
--> 314         result = self.generate_one(prompt, stop=["Task:"])
    315         explanation, code = clean_code_for_run(result)
    316 

[/usr/local/lib/python3.10/dist-packages/transformers/tools/agents.py](https://localhost:8080/#) in generate_one(self, prompt, stop)
    486             return self._generate_one(prompt)
    487         elif response.status_code != 200:
--> 488             raise ValueError(f"Error {response.status_code}: {response.json()}")
    489 
    490         result = response.json()[0]["generated_text"]

ValueError: Error 422: {'error': 'Input validation error: `inputs` must have less than 1024 tokens. Given: 1553', 'error_type': 'validation'}
```
Hi there. We temporarily increased the max length for this endpoint when releasing the Agents framework, but it's not back to its normal value. So yes, this one won't work anymore.<|||||>Thank you for the info, @sgugger!

> So yes, this one won't work anymore.

Then other OpenAssisant models may also only work with customizing a prompt. For now, I believe removing that model from the notebook or replacing it with another one would reduce the inconvenience.

May I try to edit the prompt so that other models with less input max length will be available?<|||||>You can definitely try!