Add new Mintlify documentation site (docs_new/) (#23001)

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docs_new/docs/references/custom_chat_template.mdx

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+---
+title: "Custom Chat Template"
+metatags:
+    description: "SGLang custom chat templates: JSON and Jinja formats for OpenAI-compatible API server. Override tokenizer defaults."
+---
+**NOTE**: There are two chat template systems in SGLang project. This document is about setting a custom chat template for the OpenAI-compatible API server (defined at [conversation.py](https://github.com/sgl-project/sglang/blob/main/python/sglang/srt/conversation.py)). It is NOT related to the chat template used in the SGLang language frontend (defined at [chat_template.py](https://github.com/sgl-project/sglang/blob/main/python/sglang/lang/chat_template.py)).
+
+By default, the server uses the chat template specified in the model tokenizer from Hugging Face.
+It should just work for most official models such as Llama-2/Llama-3.
+
+If needed, you can also override the chat template when launching the server:
+
+```bash Command
+python -m sglang.launch_server \
+  --model-path meta-llama/Llama-2-7b-chat-hf \
+  --port 30000 \
+  --chat-template llama-2
+```
+
+If the chat template you are looking for is missing, you are welcome to contribute it or load it from a file.
+
+## JSON Format
+
+You can load the JSON format, which is defined by `conversation.py`.
+
+```json Config
+{
+  "name": "my_model",
+  "system": "<|im_start|>system",
+  "user": "<|im_start|>user",
+  "assistant": "<|im_start|>assistant",
+  "sep_style": "CHATML",
+  "sep": "<|im_end|>",
+  "stop_str": ["<|im_end|>", "<|im_start|>"]
+}
+```
+
+```bash Command
+python -m sglang.launch_server \
+  --model-path meta-llama/Llama-2-7b-chat-hf \
+  --port 30000 \
+  --chat-template ./my_model_template.json
+```
+
+## Jinja Format
+
+You can also use the [Jinja template format](https://huggingface.co/docs/transformers/main/en/chat_templating) as defined by Hugging Face Transformers.
+
+```bash Command
+python -m sglang.launch_server \
+  --model-path meta-llama/Llama-2-7b-chat-hf \
+  --port 30000 \
+  --chat-template ./my_model_template.jinja
+```