Fix Hermes chat template validation error

[danielhanchen]

Replacement for #4183 due to Studio rebasing

Fixes #4150

Summary

Hermes models use ChatML-style templates that don't require the {% if add_generation_prompt %} validation check. This PR adds hermes to the list of models that bypass this check, similar to how mistral and qwen3guard are already handled.

Changes

• Added hermes to the model bypass list in load_correct_tokenizer function in unsloth/tokenizer_utils.py

Root Cause

When loading a Hermes model (or a LoRA adapter trained with Hermes/ChatML template), the fix_chat_template function was raising a RuntimeError because:

1. The ChatML template doesn't have {% if add_generation_prompt %} in a format the auto-fixer expects
2. The auto-fixer _fix_chat_template couldn't patch it automatically
3. This caused the error: "does not have a {% if add_generation_prompt %} for generation purposes"

Testing

The fix follows the existing pattern used for mistral and qwen3guard models, which have similar template structures that don't require this validation.

Diff Stats

 unsloth/tokenizer_utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a RuntimeError encountered when loading Hermes models due to an incompatibility with the fix_chat_template function's validation check. By adding Hermes to an existing bypass list, it ensures that models using ChatML-style templates, which do not require the add_generation_prompt validation, can be loaded correctly, improving the robustness of the tokenizer loading process for various model architectures.

Highlights

• Hermes Model Support: Added "hermes" to the list of models that bypass the {% if add_generation_prompt %} validation check in unsloth/tokenizer_utils.py, resolving a RuntimeError when loading Hermes models.

Changelog

• unsloth/tokenizer_utils.py
  • Added "hermes" to the list of model names that bypass the add_generation_prompt validation.

Activity

• The pull request was created to replace Fix Hermes chat template validation error #4183 due to rebasing issues and fixes [Bug] Hermes Lora chat test bug: does not have a {% if add_generation_prompt %} for generation purposes #4150.
• No human activity (comments, reviews) has occurred yet.

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[gemini-code-assist]

Code Review

This pull request correctly adds hermes to the list of models that bypass the chat template validation, which resolves a RuntimeError. The change is straightforward and aligns with the existing implementation for mistral and qwen3guard. I have one suggestion to improve the code's maintainability by extracting the hardcoded list of model names into a constant.

[gemini-code-assist]

For better readability and maintainability, it's good practice to extract this list of model names into a well-named constant. This makes the code easier to understand and modify in the future. Using a tuple instead of a list is also slightly more performant for this kind of check.

Suggested change

	if any(
	s in str(getattr(tokenizer, "name_or_path", "")).lower()
	for s in ["mistral", "qwen3guard"]
	for s in ["mistral", "qwen3guard", "hermes"]
	):
	MODELS_BYPASSING_CHAT_TEMPLATE_FIX = ("mistral", "qwen3guard", "hermes")
	if any(
	s in str(getattr(tokenizer, "name_or_path", "")).lower()
	for s in MODELS_BYPASSING_CHAT_TEMPLATE_FIX
	):

[mykeehu]

This is a more elegant solution:
#4426
or this:
#4298