Act probability

Act probability is the value Laya returns at action.act_probability on every answer. It comes from a small act/escalate head that sits beside the option scorer and is intended to say whether the system should act on the answer automatically or escalate it.

How it is computed

The act head is a two-layer MLP. Its input is the pooled [CLS] representation of the question-plus-state sequence, concatenated with four summary features of the option distribution:

• the top-1 probability
• the margin between the top-1 and top-2 probabilities
• the normalised entropy of the distribution
• the option count k divided by 255

A softmax over the head's outputs gives act_probability, rounded to four decimals.

Current status: do not gate on it

The model card is explicit: action.act_probability carries no usable signal yet (issue #185). It reads about 1.0 for almost every input, and on 396 labelled decisions its raw logits ran against correctness, with an AUROC of 0.30. The confidence field reached an AUROC of 0.77 on the same items.

So in production:

• gate abstention and escalation on confidence, after fitting temperature scaling on your own data
• log act_probability if you like, so you can evaluate future checkpoints, but do not route on it
• if you want an explicit "should a human look at this?" signal, ask it as a noul question, as the needs_human and needs_review ids in the typed-decisions workflows do

The field exists in the response for schema stability, so client code written today will keep working if a later checkpoint trains the head into something informative. Laya Studio returns it unchanged from the model. The act/escalate routing guide covers threshold design with confidence in detail.