Stop Sequences

In depth

Custom strings that tell a model to stop generating as soon as it produces one of them. In the Claude Messages API you pass them as stop_sequences, and when one matches, the response comes back with stop_reason set to "stop_sequence" and the matched string in the stop_sequence field. They let you cut output at a known delimiter, such as a closing XML tag, without paying for tokens you would throw away. Some compatible endpoints ignore the parameter, so check before relying on it.

Primary source: platform.claude.com