What does "im" in "im_start" and "im_end" stands for?

[2catycm]

Is it "input message" or "instant message"?
It is really confusing

[MansoobeZahra]

Most likely, im = "input message" (not "instant message").
This aligns with OpenAI's ChatML (Chat Markup Language) conventions, where:
im_start = Start of a user or assistant input.
im_end = End of that input.
These tokens help the model parse structured conversations, especially in multi-turn chats.

Why Not "Instant Message"?
Instant message" (IM) is an older term (like in AIM or MSN Messenger), but in this context, it doesn't fit the structured role of these tokens.The tokens are more about demarcating inputs rather than describing real-time messaging.

[Bahtya]

"im" stands for "instruction message" — it comes from the ChatML tokenization format that OpenAI used internally.

The special tokens <|im_start|> and <|im_end|> are ChatML delimiters used to mark the boundaries of messages in a conversation:

<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Hello!<|im_end|>
<|im_start|>assistant
Hi there!<|im_end|>

ChatML was OpenAI's internal markup language for formatting multi-turn conversations before sending them to the model. The im_start/im_end tokens tell the tokenizer where each message role and content begins and ends.

These tokens are primarily relevant when working with the raw tokenized format of older models. If you're using the chat completions API with the messages array, you don't need to deal with them directly — the API handles the formatting internally.