diff --git a/modules/core/shared/src/main/scala/TraceValue.scala b/modules/core/shared/src/main/scala/TraceValue.scala
index c388886c..76a23a2e 100644
--- a/modules/core/shared/src/main/scala/TraceValue.scala
+++ b/modules/core/shared/src/main/scala/TraceValue.scala
@@ -4,6 +4,9 @@
 
 package natchez
 
+import cats.*
+import cats.syntax.all.*
+
 sealed trait TraceValue extends Product with Serializable {
   def value: Any
 }
@@ -13,6 +16,12 @@ object TraceValue {
   case class StringValue(value: String) extends TraceValue
   case class BooleanValue(value: Boolean) extends TraceValue
   case class NumberValue(value: Number) extends TraceValue
+  case class ListValue(value: List[TraceValue]) extends TraceValue
+  case object NoneValue extends TraceValue {
+    override def value: Nothing = throw new IllegalStateException(
+      "Cannot extract value from NoneValue"
+    )
+  }
 
   implicit def viaTraceableValue[A: TraceableValue](a: A): TraceValue =
     TraceableValue[A].toTraceValue(a)
@@ -57,4 +66,10 @@ object TraceableValue {
   implicit val longToTraceValue: TraceableValue[Long] = TraceValue.NumberValue(_)
   implicit val doubleToTraceValue: TraceableValue[Double] = TraceValue.NumberValue(_)
   implicit val floatToTraceValue: TraceableValue[Float] = TraceValue.NumberValue(_)
+
+  implicit def foldableToTraceValue[F[_]: Foldable, A: TraceableValue]: TraceableValue[F[A]] =
+    fa => TraceValue.ListValue(fa.toList.map(TraceableValue[A].toTraceValue))
+
+  implicit def optionalToTraceValue[A: TraceableValue]: TraceableValue[Option[A]] =
+    _.fold[TraceValue](TraceValue.NoneValue)(TraceableValue[A].toTraceValue)
 }
diff --git a/modules/datadog/src/main/scala/DDSpan.scala b/modules/datadog/src/main/scala/DDSpan.scala
index 73e42e91..f3245d06 100644
--- a/modules/datadog/src/main/scala/DDSpan.scala
+++ b/modules/datadog/src/main/scala/DDSpan.scala
@@ -6,6 +6,7 @@ package natchez
 package datadog
 
 import io.{opentracing => ot}
+import cats.Applicative
 import cats.data.Nested
 import cats.effect.{Resource, Sync}
 import cats.effect.Resource.ExitCase
@@ -13,7 +14,7 @@ import cats.syntax.all._
 import io.opentracing.log.Fields
 import io.opentracing.propagation.{Format, TextMapAdapter}
 import io.opentracing.tag.Tags
-import natchez.TraceValue.{BooleanValue, NumberValue, StringValue}
+import natchez.TraceValue._
 import _root_.datadog.trace.api.DDTags
 import natchez.Span.Options
 import natchez.datadog.DDTracer.{addLink, addSpanKind}
@@ -43,9 +44,12 @@ final case class DDSpan[F[_]: Sync](
 
   def put(fields: (String, TraceValue)*): F[Unit] =
     fields.toList.traverse_ {
-      case (str, StringValue(value))  => Sync[F].delay(span.setTag(str, value))
-      case (str, NumberValue(value))  => Sync[F].delay(span.setTag(str, value))
-      case (str, BooleanValue(value)) => Sync[F].delay(span.setTag(str, value))
+      case (str, StringValue(value))  => Sync[F].delay(span.setTag(str, value)).void
+      case (str, NumberValue(value))  => Sync[F].delay(span.setTag(str, value)).void
+      case (str, BooleanValue(value)) => Sync[F].delay(span.setTag(str, value)).void
+      case (str, ListValue(v))        =>
+        Sync[F].delay(span.setTag(str, v.map(_.toString).mkString(", "))).void
+      case (_, NoneValue) => Applicative[F].unit
     }
 
   override def log(fields: (String, TraceValue)*): F[Unit] = {
diff --git a/modules/jaeger/src/main/scala/JaegerSpan.scala b/modules/jaeger/src/main/scala/JaegerSpan.scala
index 83e0578f..f620f7b8 100644
--- a/modules/jaeger/src/main/scala/JaegerSpan.scala
+++ b/modules/jaeger/src/main/scala/JaegerSpan.scala
@@ -6,6 +6,7 @@ package natchez
 package jaeger
 
 import io.{opentracing => ot}
+import cats.Applicative
 import cats.data.Nested
 import cats.effect.Sync
 import cats.effect.Resource
@@ -40,9 +41,11 @@ private[jaeger] final case class JaegerSpan[F[_]: Sync](
 
   override def put(fields: (String, TraceValue)*): F[Unit] =
     fields.toList.traverse_ {
-      case (k, StringValue(v))  => Sync[F].delay(span.setTag(k, v))
-      case (k, NumberValue(v))  => Sync[F].delay(span.setTag(k, v))
-      case (k, BooleanValue(v)) => Sync[F].delay(span.setTag(k, v))
+      case (k, StringValue(v))  => Sync[F].delay(span.setTag(k, v)).void
+      case (k, NumberValue(v))  => Sync[F].delay(span.setTag(k, v)).void
+      case (k, BooleanValue(v)) => Sync[F].delay(span.setTag(k, v)).void
+      case (k, ListValue(v)) => Sync[F].delay(span.setTag(k, v.map(_.toString).mkString(", "))).void
+      case (_, NoneValue)    => Applicative[F].unit
     }
 
   override def attachError(err: Throwable, fields: (String, TraceValue)*): F[Unit] =
diff --git a/modules/lightstep/src/main/scala/LightstepSpan.scala b/modules/lightstep/src/main/scala/LightstepSpan.scala
index 9a8beed1..03282af0 100644
--- a/modules/lightstep/src/main/scala/LightstepSpan.scala
+++ b/modules/lightstep/src/main/scala/LightstepSpan.scala
@@ -5,16 +5,17 @@
 package natchez
 package lightstep
 
+import cats.Applicative
 import cats.effect.{Resource, Sync}
-import cats.syntax.all._
+import cats.syntax.all.*
 import io.opentracing.log.Fields
-import io.{opentracing => ot}
+import io.opentracing as ot
 import io.opentracing.propagation.{Format, TextMapAdapter}
 import io.opentracing.tag.Tags
 import natchez.Span.Options
-import natchez.lightstep.Lightstep._
+import natchez.lightstep.Lightstep.*
 
-import scala.jdk.CollectionConverters._
+import scala.jdk.CollectionConverters.*
 import java.net.URI
 
 private[lightstep] final case class LightstepSpan[F[_]: Sync](
@@ -36,9 +37,11 @@ private[lightstep] final case class LightstepSpan[F[_]: Sync](
 
   override def put(fields: (String, TraceValue)*): F[Unit] =
     fields.toList.traverse_ {
-      case (k, StringValue(v))  => Sync[F].delay(span.setTag(k, v))
-      case (k, NumberValue(v))  => Sync[F].delay(span.setTag(k, v))
-      case (k, BooleanValue(v)) => Sync[F].delay(span.setTag(k, v))
+      case (k, StringValue(v))  => Sync[F].delay(span.setTag(k, v)).void
+      case (k, NumberValue(v))  => Sync[F].delay(span.setTag(k, v)).void
+      case (k, BooleanValue(v)) => Sync[F].delay(span.setTag(k, v)).void
+      case (k, ListValue(v)) => Sync[F].delay(span.setTag(k, v.map(_.toString).mkString(", "))).void
+      case (_, NoneValue)    => Applicative[F].unit
     }
 
   override def attachError(err: Throwable, fields: (String, TraceValue)*): F[Unit] =
diff --git a/modules/log-odin/src/main/scala/LogSpan.scala b/modules/log-odin/src/main/scala/LogSpan.scala
index e37c9b3d..a9e301dd 100644
--- a/modules/log-odin/src/main/scala/LogSpan.scala
+++ b/modules/log-odin/src/main/scala/LogSpan.scala
@@ -123,7 +123,7 @@ private[logodin] final case class LogSpan[F[_]: Sync: Logger](
 
 private[logodin] object LogSpan {
 
-  implicit val EncodeTraceValue: Encoder[TraceValue] =
+  implicit lazy val EncodeTraceValue: Encoder[TraceValue] =
     Encoder.instance {
       case StringValue(s)                       => s.asJson
       case BooleanValue(b)                      => b.asJson
@@ -138,6 +138,8 @@ private[logodin] object LogSpan {
       case NumberValue(n: BigDecimal)           => n.asJson
       case NumberValue(n: BigInt)               => n.asJson
       case NumberValue(n)                       => n.doubleValue.asJson
+      case ListValue(vs)                        => vs.map(EncodeTraceValue(_)).asJson
+      case NoneValue                            => Json.Null
     }
 
   implicit val KeyEncodeCIString: KeyEncoder[CIString] = KeyEncoder[String].contramap(_.toString)
diff --git a/modules/log/shared/src/main/scala/LogSpan.scala b/modules/log/shared/src/main/scala/LogSpan.scala
index 4ff21f88..8375b294 100644
--- a/modules/log/shared/src/main/scala/LogSpan.scala
+++ b/modules/log/shared/src/main/scala/LogSpan.scala
@@ -111,7 +111,7 @@ private[log] final case class LogSpan[F[_]: Sync: Logger: UUIDGen](
 
 private[log] object LogSpan {
 
-  implicit val EncodeTraceValue: Encoder[TraceValue] =
+  implicit lazy val EncodeTraceValue: Encoder[TraceValue] =
     Encoder.instance {
       case StringValue(s)                       => s.asJson
       case BooleanValue(b)                      => b.asJson
@@ -126,6 +126,8 @@ private[log] object LogSpan {
       case NumberValue(n: BigDecimal)           => n.asJson
       case NumberValue(n: BigInt)               => n.asJson
       case NumberValue(n)                       => n.doubleValue.asJson
+      case ListValue(vs)                        => vs.map(EncodeTraceValue(_)).asJson
+      case NoneValue                            => Json.Null
     }
 
   implicit val KeyEncodeCIString: KeyEncoder[CIString] = KeyEncoder[String].contramap(_.toString)
diff --git a/modules/mock/src/main/scala/MockSpan.scala b/modules/mock/src/main/scala/MockSpan.scala
index 5b4745ef..5796d98a 100644
--- a/modules/mock/src/main/scala/MockSpan.scala
+++ b/modules/mock/src/main/scala/MockSpan.scala
@@ -7,13 +7,14 @@ package mock
 
 import scala.jdk.CollectionConverters._
 
+import cats.Applicative
 import cats.effect.{Resource, Sync}
 import cats.syntax.all._
 import io.opentracing.log.Fields
 import io.{opentracing => ot}
 import io.opentracing.propagation.{Format, TextMapAdapter}
 import io.opentracing.tag.Tags
-import natchez.TraceValue.{BooleanValue, NumberValue, StringValue}
+import natchez.TraceValue._
 import java.net.URI
 
 final case class MockSpan[F[_]: Sync](tracer: ot.mock.MockTracer, span: ot.mock.MockSpan)
@@ -32,9 +33,11 @@ final case class MockSpan[F[_]: Sync](tracer: ot.mock.MockTracer, span: ot.mock.
 
   def put(fields: (String, TraceValue)*): F[Unit] =
     fields.toList.traverse_ {
-      case (k, StringValue(v))  => Sync[F].delay(span.setTag(k, v))
-      case (k, NumberValue(v))  => Sync[F].delay(span.setTag(k, v))
-      case (k, BooleanValue(v)) => Sync[F].delay(span.setTag(k, v))
+      case (k, StringValue(v))  => Sync[F].delay(span.setTag(k, v)).void
+      case (k, NumberValue(v))  => Sync[F].delay(span.setTag(k, v)).void
+      case (k, BooleanValue(v)) => Sync[F].delay(span.setTag(k, v)).void
+      case (k, ListValue(v)) => Sync[F].delay(span.setTag(k, v.map(_.toString).mkString(", "))).void
+      case (_, NoneValue)    => Applicative[F].unit
     }
 
   def attachError(err: Throwable, fields: (String, TraceValue)*): F[Unit] =
diff --git a/modules/newrelic/src/main/scala/natchez/newrelic/NewrelicSpan.scala b/modules/newrelic/src/main/scala/natchez/newrelic/NewrelicSpan.scala
index 7f1c9fd1..e6f8ba31 100644
--- a/modules/newrelic/src/main/scala/natchez/newrelic/NewrelicSpan.scala
+++ b/modules/newrelic/src/main/scala/natchez/newrelic/NewrelicSpan.scala
@@ -4,6 +4,7 @@
 
 package natchez.newrelic
 
+import cats.Applicative
 import java.net.URI
 import java.util.UUID
 import cats.effect.Ref
@@ -11,7 +12,7 @@ import cats.effect.{Resource, Sync}
 import cats.syntax.all._
 import com.newrelic.telemetry.Attributes
 import com.newrelic.telemetry.spans.{Span, SpanBatch, SpanBatchSender}
-import natchez.TraceValue.{BooleanValue, NumberValue, StringValue}
+import natchez.TraceValue._
 import natchez.newrelic.NewrelicSpan.Headers
 import natchez.{Kernel, TraceValue}
 import org.typelevel.ci._
@@ -45,9 +46,11 @@ private[newrelic] final case class NewrelicSpan[F[_]: Sync](
 
   override def put(fields: (String, TraceValue)*): F[Unit] =
     fields.toList.traverse_ {
-      case (k, StringValue(v))  => attributes.update(att => att.put(k, v))
-      case (k, NumberValue(v))  => attributes.update(att => att.put(k, v))
-      case (k, BooleanValue(v)) => attributes.update(att => att.put(k, v))
+      case (k, StringValue(v))  => attributes.update(att => att.put(k, v)).void
+      case (k, NumberValue(v))  => attributes.update(att => att.put(k, v)).void
+      case (k, BooleanValue(v)) => attributes.update(att => att.put(k, v)).void
+      case (k, ListValue(vs))   => attributes.update(att => att.put(k, vs.mkString(", "))).void
+      case (_, NoneValue)       => Applicative[F].unit
     }
 
   override def attachError(err: Throwable, fields: (String, TraceValue)*): F[Unit] =
diff --git a/modules/opencensus/src/main/scala/OpenCensusSpan.scala b/modules/opencensus/src/main/scala/OpenCensusSpan.scala
index b27c1aba..4f42c3e1 100644
--- a/modules/opencensus/src/main/scala/OpenCensusSpan.scala
+++ b/modules/opencensus/src/main/scala/OpenCensusSpan.scala
@@ -14,7 +14,7 @@ import io.opencensus.trace.{AttributeValue, Sampler, SpanBuilder, Tracer, Tracin
 import io.opencensus.trace.propagation.SpanContextParseException
 import io.opencensus.trace.propagation.TextFormat.Getter
 import natchez.Span.{Options, SpanKind}
-import natchez.TraceValue.{BooleanValue, NumberValue, StringValue}
+import natchez.TraceValue._
 import org.typelevel.ci._
 
 import scala.collection.mutable
@@ -32,24 +32,38 @@ private[opencensus] final case class OpenCensusSpan[F[_]: Sync](
   override protected val spanCreationPolicyOverride: Options.SpanCreationPolicy =
     options.spanCreationPolicy
 
-  private def traceToAttribute(value: TraceValue): AttributeValue = value match {
+  private def traceToAttribute(value: TraceValue): Option[AttributeValue] = value match {
     case StringValue(v) =>
       val safeString = if (v == null) "null" else v
-      AttributeValue.stringAttributeValue(safeString)
+      AttributeValue.stringAttributeValue(safeString).some
     case NumberValue(v) =>
-      AttributeValue.doubleAttributeValue(v.doubleValue())
+      AttributeValue.doubleAttributeValue(v.doubleValue()).some
     case BooleanValue(v) =>
-      AttributeValue.booleanAttributeValue(v)
+      AttributeValue.booleanAttributeValue(v).some
+    case ListValue(v) =>
+      AttributeValue.stringAttributeValue(v.map(_.toString).mkString(", ")).some
+    case NoneValue => None
   }
 
+  private def fieldsToAttributeValues(
+      fields: List[(String, TraceValue)]
+  ): List[(String, AttributeValue)] =
+    fields.nested
+      .map(traceToAttribute)
+      .value
+      .collect { case (key, Some(value)) =>
+        key -> value
+      }
+
   override def put(fields: (String, TraceValue)*): F[Unit] =
-    fields.toList.traverse_ { case (key, value) =>
-      Sync[F].delay(span.putAttribute(key, traceToAttribute(value)))
-    }
+    fieldsToAttributeValues(fields.toList)
+      .traverse_ { case (key, value) =>
+        Sync[F].delay(span.putAttribute(key, value))
+      }
 
   override def log(fields: (String, TraceValue)*): F[Unit] = {
-    val map = fields.map { case (k, v) => k -> traceToAttribute(v) }.toMap.asJava
-    Sync[F].delay(span.addAnnotation("event", map)).void
+    val map = fieldsToAttributeValues(fields.toList).toMap.asJava
+    Sync[F].delay(span.addAnnotation("event", map)).unlessA(map.isEmpty)
   }
 
   override def log(event: String): F[Unit] =
diff --git a/modules/opentelemetry/src/main/scala/natchez/opentelemetry/OpenTelemetrySpan.scala b/modules/opentelemetry/src/main/scala/natchez/opentelemetry/OpenTelemetrySpan.scala
index 59b100da..8800883f 100644
--- a/modules/opentelemetry/src/main/scala/natchez/opentelemetry/OpenTelemetrySpan.scala
+++ b/modules/opentelemetry/src/main/scala/natchez/opentelemetry/OpenTelemetrySpan.scala
@@ -24,7 +24,7 @@ import io.opentelemetry.context.Context
 
 import java.lang
 import io.opentelemetry.api.{OpenTelemetry => OTel}
-import TraceValue.{BooleanValue, NumberValue, StringValue}
+import TraceValue._
 
 import java.net.URI
 import scala.collection.mutable
@@ -66,6 +66,17 @@ private[opentelemetry] final case class OpenTelemetrySpan[F[_]: Sync](
       // and any other Number can fall back to a Double
       case (k, NumberValue(v))  => bldr.put(k, v.doubleValue())
       case (k, BooleanValue(v)) => bldr.put(k, v)
+      case (k, ListValue(vs))   =>
+        // TODO when support for HLists is merged, stop converting to string
+        // see https://opentelemetry.io/blog/2025/complex-attribute-types/#upcoming-support-for-complex-attribute-types-in-opentelemetry
+        val strings: List[String] = vs.collect {
+          case StringValue(v)  => v
+          case BooleanValue(v) => v.toString
+          case NumberValue(v)  => v.toString
+          case ListValue(v)    => v.mkString(", ")
+        }
+        bldr.put(k, strings: _*)
+      case (_, NoneValue) => ()
     }
     bldr.build()
   }
diff --git a/modules/xray/src/main/scala/natchez/xray/XRaySpan.scala b/modules/xray/src/main/scala/natchez/xray/XRaySpan.scala
index b36bff69..62031885 100644
--- a/modules/xray/src/main/scala/natchez/xray/XRaySpan.scala
+++ b/modules/xray/src/main/scala/natchez/xray/XRaySpan.scala
@@ -154,7 +154,7 @@ private[xray] object XRaySpan {
 
   final case class XRayException(id: String, ex: Throwable)
 
-  implicit val EncodeTraceValue: Encoder[TraceValue] =
+  implicit lazy val EncodeTraceValue: Encoder[TraceValue] =
     Encoder.instance {
       case StringValue(s)                       => s.asJson
       case BooleanValue(b)                      => b.asJson
@@ -169,6 +169,8 @@ private[xray] object XRaySpan {
       case NumberValue(n: BigDecimal)           => n.asJson
       case NumberValue(n: BigInt)               => n.asJson
       case NumberValue(n)                       => n.doubleValue.asJson
+      case ListValue(vs)                        => vs.map(EncodeTraceValue(_)).asJson
+      case NoneValue                            => Json.Null
     }
 
   val Header = ci"X-Amzn-Trace-Id"