save_pretrained 4bits/8bits model
### System Info

I have a BitsAndBytes Quantization 4/8bitsmodels，How to save it? I invoked save_pretrained api，however， I get error：AttributeError: 'str' object has no attribute 'numel'。

### Who can help?

_No response_

### Information

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

### Tasks

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

### Reproduction

   bnb_config = BitsAndBytesConfig()
    bnb_config.load_in_8bit = True
    model = AutoModelForCausalLM.from_pretrained(
        model_path,
        load_in_8bit=True,
        device_map="auto",
        trust_remote_code=True
    ).eval()
    model.save_pretrained("BitsAndBytesQuant8/")

### Expected behavior

saved successfully
cc @younesbelkada and @SunMarc <|||||>hi @jameswu2014 
Thanks for the issue, what is the transformers version you are using? Can you try again with the latest version of `transformers`? Also can you share the full traceback and a reproducible handy snippet? Thanks<|||||>having the same issue, believe because there are string values in the state dicts, that are not really tensors<|||||>Hi @psinger,
I just checked our daily CI and we do have a CI test to check int8 serialization works correctly here: https://github.com/huggingface/transformers/blob/main/tests/bnb/test_mixed_int8.py#L286-L311 and the test is passing.
I believe maybe this PR: https://github.com/huggingface/transformers/pull/24416 fixed your issues, can you try to install transformers from source and use the latest version of `bitsandbytes` ?

```bash
pip uninstall transformers bitsandbytes
pip install git+https://github.com/huggingface/transformers.git
pip install --upgrade bitsandbytes
```<|||||>Thanks, I actually misspoke, my error is:
`AttributeError: 'str' object has no attribute 'device'
`

Installing transformers from source indeed seems to solve it.<|||||>> Hi @psinger, I just checked our daily CI and we do have a CI test to check int8 serialization works correctly here: https://github.com/huggingface/transformers/blob/main/tests/bnb/test_mixed_int8.py#L286-L311 and the test is passing. I believe maybe this PR: #24416 fixed your issues, can you try to install transformers from source and use the latest version of `bitsandbytes` ?
> 
> ```shell
> pip uninstall transformers bitsandbytes
> pip install git+https://github.com/huggingface/transformers.git
> pip install --upgrade bitsandbytes
> ```

Whether 4bits supported? I need  both 4bits and 8bits saved.<|||||>Hi @jameswu2014 
Thanks for the heads up, as stated above, currently 4bit saving is not supported yet, feel free to raise an issue on bitsandbytes repository to request this feature<|||||>Is there a work-around for 4-bit models?  Can I convert the model to something like float16 and then save it?  Or is 4-bit fine-tuning not really usable?  Thanks.