Stop Sequences

Reviewed by Proof · Updated

Definition

A stop sequence is a string that tells the model to stop writing as soon as it would produce that text.

Key takeaways

  • In the OpenAI format it's the stop field: one string or a short list of strings.
  • When the model's output would include a stop string, generation ends right there.
  • The stop string itself is left out of the reply.
  • When a stop sequence ends the reply, finish_reason is stop.
  • Check Request Parameters to confirm luv13 supports stop for your model.

Why use them

Stop sequences keep replies from running past the part you want. Common uses:

  • One item only. Stop at "\n" to get a single line.
  • Fixed formats. If you've asked for an answer followed by a marker like END, stop at "END".
  • Role play or transcripts. Stop at "User:" so the model doesn't write the other side of the conversation.

They also save output tokens, because the model stops early instead of writing text you'd throw away.

Things to watch

  • Pick strings that won't show up by accident in a good answer.
  • The match is on exact text. "END" won't match "end".
  • Stop sequences are a cutoff, not a format guarantee. If you need structured data, see JSON Mode.

Example

This asks for a list but stops after the first line.

curl https://api.luv13.ai/v1/chat/completions \
  -H "Authorization: Bearer $LUV13_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "luv13/glm-5.3-flash",
    "messages": [{"role": "user", "content": "List three fruits, one per line."}],
    "stop": ["\n"]
  }'