Full guide: What is a System One extraction model? Extraction models explained
In a Clairic response, a text field returns the matched text as its value plus a span of [start, end]. In the Workers AI model page’s invoice example, the invoice number comes back with the span [8, 16]. A list field returns an array of values in input order, with their spans.
Spans matter for two reasons. The value cannot be a paraphrase or an invention, because it is a slice of what you sent. And you can highlight the source in a review screen, or check it in code, without searching the text again.
Only text and list answers carry spans. Numbers, dates and durations can be computed rather than copied. A total that adds two figures from an email, for example, appears nowhere in the email.
Decision models have no spans: they return one of the options you listed. The extraction model entry and the extraction model guide cover the rest of the answer shape.