---
library_name: transformers
---

# Multimodal Pretraining Tokenizer

This repository is configured as a pretraining tokenizer.

Tokenizer-level behavior:

- BOS is disabled: `bos_token = None`, `bos_token_id = None`.
- EOS/EOD is `</s>` with token id `2`.
- `generation_config.json` uses `eos_token_id = 2`.
- Plain tokenization does not automatically add BOS or EOS, even with `add_special_tokens=True`.
- The pretraining chat template appends `</s>` after assistant content.
- `chat_template.jinja` is present and is the template file Transformers prioritizes over the JSON `chat_template`.

`<|im_end|>` remains in the vocabulary as token id `11`, but it is not the EOS/EOD token for this pretraining tokenizer.

## Raw Tokenization

```python
from transformers import AutoTokenizer

tok = AutoTokenizer.from_pretrained("sanjeevnv/multimodal-pretraining", use_fast=True)

tok.encode("Hello World", add_special_tokens=False)
# [22177, 5325]

tok.encode("Hello World", add_special_tokens=True)
# [22177, 5325]

tok.convert_ids_to_tokens([22177, 5325])
# ["Hello", "ĠWorld"]
```

To include EOD/EOS in raw text, include `</s>` explicitly:

```python
tok.encode("Hello World</s>", add_special_tokens=True)
# [22177, 5325, 2]

tok.convert_ids_to_tokens([22177, 5325, 2])
# ["Hello", "ĠWorld", "</s>"]
```

## Messages Template

For messages-style formatting, use `apply_chat_template`. The current template is a pretraining question/answer format, not a ChatML post-training format.

```python
messages = [
    {"role": "system", "content": "You are concise."},
    {"role": "user", "content": "Hello World"},
    {"role": "assistant", "content": "Hi."},
]

rendered = tok.apply_chat_template(messages, tokenize=False)
print(rendered)
```

Rendered text:

```text
You are concise.
question: Hello World
answer: Hi.</s>
```

Tokenized output:

```python
ids = tok.apply_chat_template(messages, tokenize=True)
ids
# [4568, 1584, 104335, 1626, 23653, 1058, 45383, 5325, 1010, 24613, 1058, 24665, 1046, 2]

tok.convert_ids_to_tokens(ids)
# ["You", "Ġare", "Ġconcise", ".Ċ", "question", ":", "ĠHello", "ĠWorld", "Ċ", "answer", ":", "ĠHi", ".", "</s>"]
```

With `return_assistant_tokens_mask=True`, the assistant content and `</s>` are marked as assistant tokens:

```python
encoded = tok.apply_chat_template(
    messages,
    tokenize=True,
    return_dict=True,
    return_assistant_tokens_mask=True,
)

encoded["assistant_masks"]
# [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1]
```