Decision models give AI agents a way to evaluate defined outcomes without generating an answer as text.
The basic interface is straightforward. An application supplies a state, a question, and the possible answers. The model assigns probabilities to those answers, which the application can then use for classification, tool selection, routing, severity assessment, or other decisions.
That sounds simple, but the mathematics has consequences across the entire agent system.
A binary decision produces a probability that can be compared against a threshold. A categorical decision distributes probability mass across the supplied alternatives. An ordinal decision produces a distribution over ordered levels, from which an expected score can be calculated. These are different output contracts, and each requires different handling by the application.
There are also important limitations. Softmax normalization does not guarantee that probabilities are calibrated. A high probability does not establish that a prediction is correct. Changing the available options changes the decision problem, and omitting the correct answer can force probability mass onto incorrect alternatives. Even when the prediction is reasonable, the appropriate action depends on error costs, thresholds, permissions, and escalation policies.
I put together a technical handbook on Decision Models for AI Agents, using Drex 2.0 and Drex Max to work through the mathematics and engineering in detail.
Drex 2.0 provides a useful implementation reference through its released model weights and runtime. The handbook examines how candidate answers are represented, how hidden-state readouts are used in pointer-head scoring, how logits become probabilities, and how question execution can reuse shared state.
Drex Max extends the typed decision interface to images. That introduces another set of problems around image preprocessing, context limits, visual ambiguity, and incomplete evidence. The handbook keeps its documented behavior separate from internal architectural details that have not been publicly established.
The material works through everything from first principles => binary, categorical, and ordinal decisions, probability distributions, expected risk, cost-sensitive thresholds, abstention, pointer-head mathematics, temperature scaling, shared-state inference, multimodal inputs, calibration, evaluation, and production failure modes.
The explanations include worked mathematical examples, with Drex-specific implementation details grounded in Nace AI's official code and documentation.
Sharing the handbook here 👇