diff --git a/crates/protocol/src/decision.rs b/crates/protocol/src/decision.rs
new file mode 100644
index 000000000..7d1ea28a8
--- /dev/null
+++ b/crates/protocol/src/decision.rs
@@ -0,0 +1,136 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+//! Provider-neutral decision questions and answers, separate from LLM messages.
+//!
+//! Enums use snake-case `type` tags and a `data` payload in serialized form.
+//! Fields are public; providers and callers are responsible for valid values.
+
+use std::collections::BTreeMap;
+
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+
+use crate::{ModelId, Usage};
+
+/// Answer probability on a `[0, 1]` scale.
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(transparent)]
+pub struct Probability(pub f64);
+
+/// Position in the request's rubric, including fractional positions.
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(transparent)]
+pub struct ScoreValue(pub f64);
+
+/// Provider confidence; its scale and meaning are provider-specific.
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(transparent)]
+pub struct ProviderConfidence(pub f64);
+
+/// Shared context evaluated against independent, named questions.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct DecisionRequest {
+    /// Optional until a target is selected.
+    pub model: Option<ModelId>,
+    /// Conversation, application state, or other material to evaluate.
+    pub context: Value,
+    /// Independent questions keyed by their IDs.
+    pub questions: BTreeMap<String, DecisionQuestion>,
+}
+
+/// Instructions and the expected answer shape for one question.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct DecisionQuestion {
+    /// Structured or textual instructions shared with the provider.
+    pub instructions: Value,
+    /// Expected answer shape.
+    pub kind: DecisionKind,
+}
+
+/// The answer shape and any options or ordered rubric levels.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", content = "data", rename_all = "snake_case")]
+pub enum DecisionKind {
+    /// A Boolean judgment or probability of true.
+    Boolean {
+        /// Meaning of a true answer, when needed.
+        true_description: Option<Value>,
+        /// Meaning of a false answer, when needed.
+        false_description: Option<Value>,
+    },
+    /// Select one of the declared options.
+    Choice {
+        /// Nonempty options with unique IDs, preserving caller order.
+        options: Vec<ChoiceOption>,
+    },
+    /// A position on an ordered rubric, not an arbitrary numeric measurement.
+    Score {
+        /// At least two levels, ordered low to high and indexed from zero.
+        levels: Vec<Value>,
+    },
+}
+
+/// An identified choice with an optional structured description.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct ChoiceOption {
+    /// Stable identifier used by choice answers and distributions.
+    pub id: String,
+    /// Meaning of this option, when its ID alone is insufficient.
+    pub description: Option<Value>,
+}
+
+/// Answers keyed by the matching request's question IDs.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct DecisionResponse {
+    /// Provider-reported response identifier.
+    pub id: Option<String>,
+    /// Provider-reported model identifier.
+    pub model: Option<ModelId>,
+    /// Typed answers corresponding to the request's questions.
+    pub answers: BTreeMap<String, DecisionAnswer>,
+    /// Available token counts; absent counts remain unknown.
+    #[serde(default)]
+    pub usage: Usage,
+}
+
+/// An answer and separate, optional provider confidence.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct DecisionAnswer {
+    /// The estimate for the matching question.
+    pub value: DecisionValue,
+    /// Provider-specific confidence, distinct from answer probabilities.
+    pub provider_confidence: Option<ProviderConfidence>,
+}
+
+/// A typed estimate; missing distributions remain unknown.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", content = "data", rename_all = "snake_case")]
+pub enum DecisionValue {
+    /// A Boolean judgment or probability, without an implicit threshold.
+    Boolean(BooleanEstimate),
+    /// One selected option with an optional complete distribution.
+    Choice {
+        /// Must name an option in the matching question.
+        selected: String,
+        /// Maps every declared option ID to its probability when available.
+        probabilities: Option<BTreeMap<String, Probability>>,
+    },
+    /// A fractional position in the matching request's rubric.
+    Score {
+        /// Must lie in `0..=N-1` for the request's N levels.
+        value: ScoreValue,
+        /// Follows the request's level order. Retain that request to interpret it.
+        probabilities: Option<Vec<Probability>>,
+    },
+}
+
+/// Preserves Boolean-only answers without inventing probability or certainty.
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type", content = "data", rename_all = "snake_case")]
+pub enum BooleanEstimate {
+    /// A Boolean judgment with no probability supplied.
+    Value(bool),
+    /// Probability of true; algorithms choose their own thresholds.
+    ProbabilityTrue(Probability),
+}
diff --git a/crates/protocol/src/lib.rs b/crates/protocol/src/lib.rs
index 0d76b4d17..b32dc6c43 100644
--- a/crates/protocol/src/lib.rs
+++ b/crates/protocol/src/lib.rs
@@ -7,6 +7,7 @@
 pub mod category;
 pub mod client;
 pub mod codex_namespaces;
+pub mod decision;
 pub mod envelope;
 pub mod format;
 pub mod llm;
@@ -16,6 +17,7 @@ pub mod stream;
 
 pub use category::*;
 pub use client::*;
+pub use decision::*;
 pub use envelope::*;
 pub use format::*;
 pub use llm::*;