diff --git a/libdd-data-pipeline/src/otlp/metrics.rs b/libdd-data-pipeline/src/otlp/metrics.rs
index 2fb67b0b9b..36dd5421d5 100644
--- a/libdd-data-pipeline/src/otlp/metrics.rs
+++ b/libdd-data-pipeline/src/otlp/metrics.rs
@@ -181,6 +181,11 @@ fn build_attributes(
             push(k, v);
         }
     }
+    for tag in &group.additional_metric_tags {
+        if let Some((k, v)) = tag.split_once(':') {
+            push(k, v);
+        }
+    }
     if !otel_trace_semantics_enabled {
         push("datadog.operation.name", &group.name);
         push("datadog.span.type", &group.r#type);
@@ -580,6 +585,38 @@ mod tests {
         assert_eq!(ok_s + err_s, ns_to_s(combined_ns));
     }
 
+    #[test]
+    fn emits_additional_metric_tags_as_attributes() {
+        let g = group_with_exact(&[1_000_000_000], &[], |g| {
+            g.additional_metric_tags = vec![
+                "custom.primary:a".into(),
+                "region:us-east".into(),
+                // Only the first `:` is a delimiter; the value keeps any embedded `:`.
+                "endpoint:https://host:8080".into(),
+            ];
+        });
+        let req = map_stats_to_otlp_metrics(&buckets(vec![g.clone()]), &resource(), false).unwrap();
+        let a = points(&req)[0]["attributes"].as_array().unwrap();
+        assert_eq!(str_at(a, "custom.primary"), Some("a"));
+        assert_eq!(str_at(a, "region"), Some("us-east"));
+        assert_eq!(str_at(a, "endpoint"), Some("https://host:8080"));
+
+        // Additional metric tags are user/tracer-defined (not Datadog-internal), so unlike
+        // `datadog.*` attributes they still pass through in OTel-semantics mode.
+        let req = map_stats_to_otlp_metrics(&buckets(vec![g]), &resource(), true).unwrap();
+        let a = points(&req)[0]["attributes"].as_array().unwrap();
+        assert_eq!(str_at(a, "custom.primary"), Some("a"));
+
+        // Malformed (no `:`) or empty-value entries are skipped rather than emitted verbatim.
+        let g = group_with_exact(&[1_000_000_000], &[], |g| {
+            g.additional_metric_tags = vec!["malformed".into(), "empty:".into()];
+        });
+        let req = map_stats_to_otlp_metrics(&buckets(vec![g]), &resource(), false).unwrap();
+        let a = points(&req)[0]["attributes"].as_array().unwrap();
+        assert!(!a.iter().any(|kv| kv["key"] == "malformed"));
+        assert!(!a.iter().any(|kv| kv["key"] == "empty"));
+    }
+
     #[test]
     fn test_grpc_status_code_to_name() {
         assert_eq!(grpc_status_code_to_name("0"), Some("OK"));