Krun One can decline to answer a question. When it abstains, choice is null and abstain is true:
This answer comes from the context "What is the weather like on Mars?" with three banking intents. None of them applies, the probabilities are almost flat, and confidence is close to 0.
When the model abstains
The model abstains when confidence, the margin between the two best options, is below the threshold configured for that kind of question. Typical reasons:
- None of the options applies. The request is out of scope for your option set.
- Two options are hard to tell apart. The context fits both, or the options overlap.
- The context is too vague to pick an option.
Abstention is decided per question. In a request with several questions, some answers can abstain while others don’t.
Handling abstention
probabilities is still returned when the model abstains, so you can see its best guess. Krun and the SDKs never replace null with that guess: what to do is your decision.
Common fallbacks:
- send the request to a human or a general-purpose flow,
- ask the user a clarifying question,
- pass the request and the best guess to an LLM,
- add a missing option to your option set, if abstentions show a gap.
Abstention status
Every answer includes abstention_status. It tells you how much to trust abstain for that kind of question:
Calibrated
For intent questions with label-only options, the abstention threshold was validated on held-out data at a target of 98% accuracy on the answers the model does not abstain on. On data similar to Krun One’s evaluation data, answers with abstain: false should be correct at about that rate. Your traffic can differ, so monitor it with feedback.
Advisory
Advisory abstention is a hint, not a guarantee. When abstention_status is advisory, abstain: false does not mean the answer was validated to meet an accuracy target. For tool routing in particular, Krun One v0 still picks a tool for a significant share of requests where no tool applies. Keep your own safeguards, such as argument validation, a confirmation step before side effects, or a “none of these” path.
- Tool routing. Abstention was measured on real “no tool applies” requests and does not yet meet the bar for calibrated. See Benchmarks.
- Intents with descriptions. This setup has not been calibrated yet.
The status stays advisory until these setups are recalibrated. It is reported per answer, so a request can mix calibrated and advisory answers.
For intent routing with the strongest abstention guarantee, use label-only options with descriptive ids, like transaction_charged_twice. See Intent routing. 
