diff --git a/brave/src/main/java/zipkin2/reporter/brave/AsyncZipkinSpanHandler.java b/brave/src/main/java/zipkin2/reporter/brave/AsyncZipkinSpanHandler.java
index d9402b56..c52d7d20 100644
--- a/brave/src/main/java/zipkin2/reporter/brave/AsyncZipkinSpanHandler.java
+++ b/brave/src/main/java/zipkin2/reporter/brave/AsyncZipkinSpanHandler.java
@@ -21,6 +21,8 @@
 import java.io.Flushable;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
+import zipkin2.reporter.BytesEncoder;
+import zipkin2.reporter.Encoding;
 import zipkin2.reporter.Reporter;
 import zipkin2.reporter.ReporterMetrics;
 import zipkin2.reporter.Sender;
@@ -69,15 +71,18 @@ public Builder toBuilder() {
   /** @since 2.14 */
   public static final class Builder extends ZipkinSpanHandler.Builder {
     final AsyncReporter.Builder delegate;
+    final Encoding encoding;
 
     Builder(AsyncZipkinSpanHandler handler) {
       this.delegate = ((AsyncReporter<MutableSpan>) handler.spanReporter).toBuilder();
+      this.encoding = handler.encoding;
       this.alwaysReportSpans = handler.alwaysReportSpans;
       this.errorTag = handler.errorTag;
     }
 
     Builder(Sender sender) {
       this.delegate = AsyncReporter.newBuilder(sender);
+      this.encoding = sender.encoding();
     }
 
     /**
@@ -151,18 +156,42 @@ public Builder queuedMaxBytes(int queuedMaxBytes) {
       return (Builder) super.alwaysReportSpans(alwaysReportSpans);
     }
 
+    /**
+     * Builds an async span handler that encodes zipkin spans according to the sender's encoding.
+     */
     // AsyncZipkinSpanHandler not SpanHandler, so that Flushable and Closeable are accessible
     public AsyncZipkinSpanHandler build() {
-      return new AsyncZipkinSpanHandler(this);
+      switch (encoding) {
+        case JSON:
+          return build(new JsonV2Encoder(errorTag));
+        default:
+          throw new UnsupportedOperationException(encoding.name());
+      }
+    }
+
+    /**
+     * Builds an async span handler that encodes zipkin spans according to the encoder.
+     *
+     * <p>Note: The input encoder must use the same error tag implementation as configured by
+     * {@link #errorTag(Tag)}.
+     *
+     * @since 3.1
+     */
+    // AsyncZipkinSpanHandler not SpanHandler, so that Flushable and Closeable are accessible
+    public AsyncZipkinSpanHandler build(BytesEncoder<MutableSpan> encoder) {
+      if (encoder == null) throw new NullPointerException("encoder == null");
+      return new AsyncZipkinSpanHandler(delegate.build(encoder), this);
     }
   }
 
   final Reporter<MutableSpan> spanReporter;
+  final Encoding encoding;
   final Tag<Throwable> errorTag; // for toBuilder()
   final boolean alwaysReportSpans;
 
-  AsyncZipkinSpanHandler(Builder builder) {
-    this.spanReporter = builder.delegate.build(new JsonV2Encoder(builder.errorTag));
+  AsyncZipkinSpanHandler(AsyncReporter<MutableSpan> spanReporter, Builder builder) {
+    this.spanReporter = spanReporter;
+    this.encoding = builder.encoding;
     this.errorTag = builder.errorTag;
     this.alwaysReportSpans = builder.alwaysReportSpans;
   }
diff --git a/brave/src/test/java/zipkin2/reporter/brave/AsyncZipkinSpanHandlerTest.java b/brave/src/test/java/zipkin2/reporter/brave/AsyncZipkinSpanHandlerTest.java
new file mode 100644
index 00000000..575ee58c
--- /dev/null
+++ b/brave/src/test/java/zipkin2/reporter/brave/AsyncZipkinSpanHandlerTest.java
@@ -0,0 +1,53 @@
+/*
+ * Copyright 2016-2024 The OpenZipkin Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package zipkin2.reporter.brave;
+
+import brave.handler.MutableSpan;
+import org.junit.jupiter.api.Test;
+import zipkin2.reporter.BytesEncoder;
+import zipkin2.reporter.Encoding;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class AsyncZipkinSpanHandlerTest {
+  @Test void build_protoNotYetSupported() {
+    FakeSender sender = FakeSender.create().encoding(Encoding.PROTO3);
+    AsyncZipkinSpanHandler.Builder builder = AsyncZipkinSpanHandler.newBuilder(sender);
+    assertThrows(UnsupportedOperationException.class, builder::build);
+  }
+
+  /** Ready for custom format such as OTLP or Stackdriver. */
+  @Test void build_customProtoEncoder() {
+    FakeSender sender = FakeSender.create().encoding(Encoding.PROTO3);
+    AsyncZipkinSpanHandler.Builder builder = AsyncZipkinSpanHandler.newBuilder(sender);
+    BytesEncoder<MutableSpan> protoEncoder = new BytesEncoder<>() {
+      @Override public Encoding encoding() {
+        return Encoding.PROTO3;
+      }
+
+      @Override public int sizeInBytes(MutableSpan input) {
+        return 0;
+      }
+
+      @Override public byte[] encode(MutableSpan input) {
+        return new byte[0];
+      }
+    };
+
+    try (AsyncZipkinSpanHandler spanReporter = builder.build(protoEncoder)) {
+      assertThat(spanReporter).isNotNull();
+    }
+  }
+}
diff --git a/brave/src/test/java/zipkin2/reporter/brave/FakeSender.java b/brave/src/test/java/zipkin2/reporter/brave/FakeSender.java
new file mode 100644
index 00000000..5d071c32
--- /dev/null
+++ b/brave/src/test/java/zipkin2/reporter/brave/FakeSender.java
@@ -0,0 +1,96 @@
+/*
+ * Copyright 2016-2024 The OpenZipkin Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License
+ * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+ * or implied. See the License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package zipkin2.reporter.brave;
+
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.stream.Collectors;
+import zipkin2.Span;
+import zipkin2.codec.BytesDecoder;
+import zipkin2.codec.SpanBytesDecoder;
+import zipkin2.reporter.BytesEncoder;
+import zipkin2.reporter.BytesMessageEncoder;
+import zipkin2.reporter.Call;
+import zipkin2.reporter.ClosedSenderException;
+import zipkin2.reporter.Encoding;
+import zipkin2.reporter.Sender;
+import zipkin2.reporter.SpanBytesEncoder;
+
+public final class FakeSender extends Sender {
+
+  public static FakeSender create() {
+    return new FakeSender(Encoding.JSON, Integer.MAX_VALUE,
+      BytesMessageEncoder.forEncoding(Encoding.JSON), SpanBytesEncoder.JSON_V2,
+      SpanBytesDecoder.JSON_V2, spans -> {
+    });
+  }
+
+  final Encoding encoding;
+  final int messageMaxBytes;
+  final BytesMessageEncoder messageEncoder;
+  final BytesEncoder<Span> encoder;
+  final BytesDecoder<Span> decoder;
+  final Consumer<List<Span>> onSpans;
+
+  FakeSender(Encoding encoding, int messageMaxBytes, BytesMessageEncoder messageEncoder,
+    BytesEncoder<Span> encoder, BytesDecoder<Span> decoder, Consumer<List<Span>> onSpans) {
+    this.encoding = encoding;
+    this.messageMaxBytes = messageMaxBytes;
+    this.messageEncoder = messageEncoder;
+    this.encoder = encoder;
+    this.decoder = decoder;
+    this.onSpans = onSpans;
+  }
+
+  FakeSender encoding(Encoding encoding) {
+    return new FakeSender(encoding, messageMaxBytes, messageEncoder, // invalid but not needed, yet
+      encoder, // invalid but not needed, yet
+      decoder, // invalid but not needed, yet
+      onSpans);
+  }
+
+  @Override public Encoding encoding() {
+    return encoding;
+  }
+
+  @Override public int messageMaxBytes() {
+    return messageMaxBytes;
+  }
+
+  @Override public int messageSizeInBytes(List<byte[]> encodedSpans) {
+    return encoding.listSizeInBytes(encodedSpans);
+  }
+
+  @Override public int messageSizeInBytes(int encodedSizeInBytes) {
+    return encoding.listSizeInBytes(encodedSizeInBytes);
+  }
+
+  /** close is typically called from a different thread */
+  volatile boolean closeCalled;
+
+  @Override public Call<Void> sendSpans(List<byte[]> encodedSpans) {
+    if (closeCalled) throw new ClosedSenderException();
+    List<Span> decoded = encodedSpans.stream().map(decoder::decodeOne).collect(Collectors.toList());
+    onSpans.accept(decoded);
+    return Call.create(null);
+  }
+
+  @Override public void close() {
+    closeCalled = true;
+  }
+
+  @Override public String toString() {
+    return "FakeSender";
+  }
+}