Chat template
The small piece of formatting that wraps a conversation before the model reads it, marking who said what.
A language model does not see a conversation the way you do. It sees one long block of text. The chat template is the formatting that turns your messages, the assistant’s replies and the system instructions into that block, using special markers so the model can tell the three apart. Every model family has its own template, and using the wrong one makes a good model behave badly.
Because the template touches every single message, it is also a soft spot. Anything an attacker manages to add there is silently appended to every conversation from then on, survives restarts, and is invisible to whatever app is calling the model. That is exactly what the NemoClaw flaw allowed in August 2026.