diff --git a/crates/switchyard-nemo-relay-plugin/README.md b/crates/switchyard-nemo-relay-plugin/README.md
index d1359096a..782ac774f 100644
--- a/crates/switchyard-nemo-relay-plugin/README.md
+++ b/crates/switchyard-nemo-relay-plugin/README.md
@@ -110,6 +110,19 @@ attributes. `target_model` comes from the configured Switchyard target set,
 rather than arbitrary caller input, keeping the metric cardinality bounded by
 the deployment.
 
+Every non-metric mark sets `data_schema.name` to the mark name and
+`data_schema.version` to `1`. Consumers should tolerate unknown fields and
+values. Removing or renaming fields, changing their type, or changing their
+meaning requires a new schema version.
+
+| Mark | Data fields |
+| --- | --- |
+| `switchyard.routing.requested` | `algorithm` |
+| `switchyard.routing.llm_call` | `call_index`, `selected_model`, `call_role`, `outcome`, `latency_ms` |
+| `switchyard.routing.overhead` | `latency_ms` |
+| `switchyard.routing.decision` | `algorithm`, `selected_model` |
+| `switchyard.routing.error` | `failure_kind`; optional `category`, `phase`, `upstream_status`, and `target` |
+
 ## Failure policy
 
 `switchyard-llm-client` owns provider retry and route-candidate fallback
diff --git a/crates/switchyard-nemo-relay-plugin/src/runtime.rs b/crates/switchyard-nemo-relay-plugin/src/runtime.rs
index 7b5a12fb9..136ec2a88 100644
--- a/crates/switchyard-nemo-relay-plugin/src/runtime.rs
+++ b/crates/switchyard-nemo-relay-plugin/src/runtime.rs
@@ -7,8 +7,8 @@ use std::sync::{Arc, Mutex};
 use futures_util::{Stream, StreamExt};
 use http::StatusCode;
 use nemo_relay_plugin::{
-    Json, LlmRequest as RelayRequest, LogSeverity, MetricKind, MetricMeasurement, MetricValueType,
-    PluginRuntime,
+    DataSchema, Json, LlmRequest as RelayRequest, LogSeverity, MetricKind, MetricMeasurement,
+    MetricValueType, PluginRuntime,
 };
 use serde_json::{Map, json};
 use switchyard_llm_client::{LlmCallObservation, RunObservation, RunObserver};
@@ -22,6 +22,8 @@ use switchyard_translation::{TranslationEngine, encode_stream_with_extensions};
 use crate::config::SwitchyardConfig;
 use crate::translation;
 
+const ROUTING_MARK_SCHEMA_VERSION: &str = "1";
+
 #[derive(Debug)]
 pub(crate) struct RoutingMark {
     pub(crate) name: String,
@@ -30,6 +32,15 @@ pub(crate) struct RoutingMark {
     pub(crate) severity: Option<LogSeverity>,
 }
 
+impl RoutingMark {
+    fn data_schema(&self) -> DataSchema {
+        DataSchema {
+            name: self.name.clone(),
+            version: ROUTING_MARK_SCHEMA_VERSION.into(),
+        }
+    }
+}
+
 #[derive(Debug)]
 pub(crate) struct RoutingMetric {
     pub(crate) name: String,
@@ -324,15 +335,18 @@ pub(crate) fn emit_events(runtime: &PluginRuntime, events: Vec<RoutingEvent>) {
 
 pub(crate) fn emit_event(runtime: &PluginRuntime, event: RoutingEvent) {
     let result = match event {
-        RoutingEvent::Mark(mark) => runtime
-            .emit_mark_with_options(
-                &mark.name,
-                Some(&mark.data),
-                Some(&mark.metadata),
-                None,
-                mark.severity,
-            )
-            .map_err(|error| ("routing mark", mark.name, error)),
+        RoutingEvent::Mark(mark) => {
+            let data_schema = mark.data_schema();
+            runtime
+                .emit_mark_with_options(
+                    &mark.name,
+                    Some(&mark.data),
+                    Some(&mark.metadata),
+                    Some(&data_schema),
+                    mark.severity,
+                )
+                .map_err(|error| ("routing mark", mark.name, error))
+        }
         RoutingEvent::Metric(metric) => runtime
             .emit_metric(&metric.name, metric.measurements, Some(&metric.metadata))
             .map_err(|error| ("routing metric", metric.name, error)),
@@ -980,6 +994,8 @@ mod tests {
         assert_eq!(mark.data["target"], "weak");
         assert_eq!(mark.data["upstream_status"], Json::Null);
         assert_eq!(mark.severity, Some(LogSeverity::Error));
+        assert_eq!(mark.data_schema().name, "switchyard.routing.error");
+        assert_eq!(mark.data_schema().version, "1");
         assert!(!mark.data.to_string().contains(secret));
     }