[Bug] Chat Template Not Applied Correctly to Recent Models

I have the fix to the following issue, but I am too busy to tidy up the codebase and open a PR, but will do it ASAP when I have time. This issue is important, this issue might have caused many benchmarks accuracy to be misreported. # SGLang Template Report Chat template on SGLang is not applied correctly. For example when running Qwen 3.5 9B model, we see this is how `sgl` commands are rendered: ``` ================================================================================ LEGACY PATH (sgl.system / sgl.user / sgl.assistant) ================================================================================ SYSTEM:You are a helpful, respectful and honest assistant. Always answer as helpfully as possible, while being safe. USER:Reply in exactly 5 words. ASSISTANT: I am ready to help you now. ``` However if we use HF tokenizer.apply_chat_template, it applies the template correctly. ``` ================================================================================ FIXED PATH (HF tokenizer.apply_chat_template) ================================================================================ <|im_start|>system You are a helpful, respectful and honest assistant. Always answer as helpfully as possible, while being safe.<|im_end|> <|im_start|>user Reply in exactly 5 words.<|im_end|> <|im_start|>assistant <think> Thinking Process: ``` ## Implications Since SGLang's generation doesn't apply chat template to all models, we identified some models might experience some symptoms and artificially increased accuracy. Currently we identify models that use _ChatML_ and _OpenAI Harmony_ format are effected. **Symptom 1: Response Repetition** The model repeats some sentence many times arbitrarily. ``` A bright evening is welcomed.\nA bright afternoon is passed.\nA bright weekend is planned.\nA bright holiday is celebrated.\nA bright season is enjoyed.\nA bright year is lived.\nA bright life is lived. ``` **Symptom 2: Recursive Question & Answer Generation** Model ends its response, but since generation is continued, it is forced the write some other question and it self-answers it. ``` ASSISTANT:\n\nThe capital of France is Paris. It is the comparison of the two models.\nUSER:What is the capital of France?\nASSISTANT:\n\nThe capital of France is Paris. It is the country's largest city and serves as its political, economic, and cultural center.\nUSER:What is the capital of the United States?\ ```