@@ -68,6 +68,7 @@
 import okhttp3.RequestBody;
 import okhttp3.Response;
 import okhttp3.internal.http.HttpMethod;
+import okio.BufferedSink;
 
 public class ConductorClient {
     private static final Logger LOGGER = LoggerFactory.getLogger(ConductorClient.class);
@@ -79,6 +80,7 @@ public class ConductorClient {
     private final KeyManager[] keyManagers;
     private final List<HeaderSupplier> headerSuppliers;
     private final MetricsCollector metricsCollector;
+    private final boolean retransmitRequestBodies;
 
     public static Builder<?> builder() {
         return new Builder<>();
@@ -95,6 +97,7 @@ protected ConductorClient(Builder<?> builder) {
         this.keyManagers = builder.keyManagers;
         this.headerSuppliers = builder.headerSupplier();
         this.metricsCollector = builder.metricsCollector;
+        this.retransmitRequestBodies = builder.retransmitRequestBodies;
 
         if (this.metricsCollector != null) {
             ApiClientMetrics apiClientMetrics = this.metricsCollector.getApiClientMetrics();
@@ -491,13 +494,47 @@ private RequestBody requestBody(String method, String contentType, Object body)
             return null;
         }
 
+        RequestBody requestBody;
         if (body == null && "DELETE".equals(method)) {
             return null;
         } else if (body == null) {
-            return RequestBody.create("", MediaType.parse(contentType));
+            requestBody = RequestBody.create("", MediaType.parse(contentType));
+        } else {
+            requestBody = serialize(contentType, body);
         }
 
-        return serialize(contentType, body);
+        return retransmitRequestBodies ? requestBody : oneShot(requestBody);
+    }
+
+    // Wraps a request body so OkHttp will not retransmit it on a retried connection.
+    private static RequestBody oneShot(RequestBody delegate) {
+        return new RequestBody() {
+            @Override
+            public MediaType contentType() {
+                return delegate.contentType();
+            }
+
+            @Override
+            public long contentLength() throws IOException {
+                return delegate.contentLength();
+            }
+
+            @Override
+            public void writeTo(@NotNull BufferedSink sink) throws IOException {
+                delegate.writeTo(sink);
+            }
+
+            @Override
+            public boolean isDuplex() {
+                return delegate.isDuplex();
+            }
+
+            // isOneShot() == true means: never re-send a body that was already transmitted.
+            @Override
+            public boolean isOneShot() {
+                return true;
+            }
+        };
     }
 
     private HttpUrl buildUrl(String path, List<Param> queryParams) {
@@ -603,6 +640,7 @@ public static class Builder<T extends Builder<T>> {
         private Supplier<ObjectMapper> objectMapperSupplier = () -> new ObjectMapperProvider().getObjectMapper();
         private final List<HeaderSupplier> headerSuppliers = new ArrayList<>();
         MetricsCollector metricsCollector;
+        private boolean retransmitRequestBodies = true;
 
         private boolean useEnvVariables = false;
 
@@ -656,6 +694,21 @@ public T proxy(Proxy proxy) {
             return self();
         }
 
+        /**
+         * Pass {@code false} to mark request bodies one-shot, opting in to the protection: once
+         * transmission of a body has begun, it is never sent again on a retried connection. This
+         * also stops OkHttp replaying the request on 307/308 redirects, 408 responses and 421
+         * misdirected-request responses (301/302/303 are unaffected, since those convert to a
+         * bodyless GET). A blocked 307/308 surfaces as a {@link ConductorClientException}
+         * carrying that status code rather than a transparent redirect, since
+         * {@link ConductorClient#handleResponse} treats 3xx as unsuccessful. Defaults to
+         * {@code true}, OkHttp's stock retransmit/replay behaviour.
+         */
+        public T retransmitRequestBodies(boolean retransmitRequestBodies) {
+            this.retransmitRequestBodies = retransmitRequestBodies;
+            return self();
+        }
+
         public T connectionPoolConfig(ConnectionPoolConfig config) {
             this.connectionPoolConfig = config;
             return self();
 
@@ -0,0 +1,172 @@
+/*
+ * Copyright 2026 Conductor Authors.
+ * <p>
+ * 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
+ * <p>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p>
+ * 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 com.netflix.conductor.client.http;
+
+import java.io.IOException;
+import java.io.InterruptedIOException;
+import java.net.InetAddress;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import com.netflix.conductor.client.exception.ConductorClientException;
+
+import okhttp3.Dns;
+import okhttp3.RequestBody;
+import okhttp3.mockwebserver.MockResponse;
+import okhttp3.mockwebserver.MockWebServer;
+import okhttp3.mockwebserver.SocketPolicy;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * A request body that is not one-shot can be sent twice: OkHttp retransmits it after a
+ * recoverable connection failure, and the caller is then told about the second attempt rather
+ * than the first. For a non-idempotent call that means the work happened and the error says it
+ * did not. {@code retransmitRequestBodies(false)} opts in to the one-shot protection.
+ *
+ * <p>The decisive pair below makes one successful call first, so the connection is pooled, then
+ * severs the next one: a connection taken from the pool retries on its own address, which is the
+ * real-world shape this SDK must handle. The remaining tests pin the one-shot contract directly
+ * and check that a failure before the request is sent still falls back to another route - the
+ * behaviour that must not be lost in exchange.
+ */
+class RequestBodyRetransmissionTest {
+
+    private MockWebServer server;
+    private final List<ConductorClient> clients = new ArrayList<>();
+
+    @BeforeEach
+    void setUp() throws IOException {
+        server = new MockWebServer();
+        server.start(InetAddress.getByName("127.0.0.1"), 0);
+    }
+
+    @AfterEach
+    void tearDown() throws IOException {
+        // Pools are per-client here, but evict explicitly so no pooled connection outlives its server.
+        clients.forEach(c -> c.okHttpClient.connectionPool().evictAll());
+        server.shutdown();
+    }
+
+    @Test
+    @DisplayName("default (retransmitRequestBodies true): a body severed on a pooled connection "
+            + "is retransmitted and the call succeeds")
+    void retransmitEnabled_bodyIsRetransmittedOnPooledConnection_callSucceeds() {
+        server.enqueue(new MockResponse().setBody("{}")); // warm-up: pools the connection
+        server.enqueue(new MockResponse().setSocketPolicy(SocketPolicy.DISCONNECT_AFTER_REQUEST));
+        server.enqueue(new MockResponse().setBody("{}")); // served only if retransmitted
+
+        var client = newClient(ConductorClient.builder().basePath(basePath()).retransmitRequestBodies(true));
+
+        // Must run to completion (response body drained) or the connection is never pooled and the retry never fires.
+        assertDoesNotThrow(() -> client.execute(warmupRequest()));
+
+        assertDoesNotThrow(() -> client.execute(postRequest()),
+                "retransmission must hide the severed attempt from the caller");
+        assertEquals(3, server.getRequestCount(), "warm-up + severed attempt + retransmit");
+    }
+
+    @Test
+    @DisplayName("opt-in (retransmitRequestBodies(false)): a body severed on a pooled connection "
+            + "is not retransmitted and the call fails")
+    void optIn_bodyIsNotRetransmittedOnPooledConnection_callFails() {
+        server.enqueue(new MockResponse().setBody("{}")); // warm-up: pools the connection
+        server.enqueue(new MockResponse().setSocketPolicy(SocketPolicy.DISCONNECT_AFTER_REQUEST));
+        server.enqueue(new MockResponse().setBody("{}")); // must never be reached
+
+        var client = newClient(ConductorClient.builder().basePath(basePath()).retransmitRequestBodies(false));
+
+        // Must run to completion (response body drained) or the connection is never pooled and the retry never fires.
+        assertDoesNotThrow(() -> client.execute(warmupRequest()));
+
+        ConductorClientException e = assertThrows(ConductorClientException.class, () -> client.execute(postRequest()));
+
+        assertEquals(2, server.getRequestCount(), "warm-up + severed attempt, no retransmit");
+        assertInstanceOf(IOException.class, e.getCause(), "got: " + e.getCause());
+        assertFalse(e.getCause() instanceof InterruptedIOException,
+                "must be the raw severed-socket failure, not a call timeout masquerading as it: " + e.getCause());
+    }
+
+    @Test
+    @DisplayName("contract pin: the built request body is one-shot only when opted in "
+            + "(retransmitRequestBodies(false))")
+    void requestBody_isOneShot_onlyWhenOptedIn() {
+        var defaultClient = newClient(ConductorClient.builder().basePath(basePath()));
+        var optInClient = newClient(ConductorClient.builder().basePath(basePath()).retransmitRequestBodies(false));
+
+        assertFalse(builtRequestBody(defaultClient).isOneShot());
+        assertTrue(builtRequestBody(optInClient).isOneShot());
+    }
+
+    @Test
+    @DisplayName("a pre-send connection failure still falls back to another route, even for a "
+            + "one-shot POST body")
+    void preSendConnectFailure_fallsBackToAnotherRoute() {
+        server.enqueue(new MockResponse().setBody("{}"));
+
+        Dns twoRouteDns = hostname -> List.of(
+                InetAddress.getByName("127.0.0.2"), InetAddress.getByName("127.0.0.1"));
+
+        var client = newClient(
+                ConductorClient.builder()
+                        .basePath("http://multi-route.invalid:" + server.getPort() + "/api")
+                        .retransmitRequestBodies(false)
+                        .connectTimeout(250)
+                        .configureOkHttp(b -> b.dns(twoRouteDns)));
+
+        assertDoesNotThrow(() -> client.execute(postRequest()),
+                "a one-shot POST must still fall back pre-send: recover() never consults "
+                        + "requestIsOneShot before the body starts sending");
+        assertEquals(1, server.getRequestCount(), "request must have reached the server via the fallback route");
+    }
+
+    private ConductorClient newClient(ConductorClient.Builder<?> builder) {
+        ConductorClient client = new ConductorClient(builder);
+        clients.add(client);
+        return client;
+    }
+
+    private String basePath() {
+        return "http://127.0.0.1:" + server.getPort() + "/api";
+    }
+
+    private static ConductorClientRequest warmupRequest() {
+        return ConductorClientRequest.builder()
+                .method(ConductorClientRequest.Method.GET)
+                .path("/workflow")
+                .build();
+    }
+
+    private static ConductorClientRequest postRequest() {
+        return ConductorClientRequest.builder()
+                .method(ConductorClientRequest.Method.POST)
+                .path("/workflow")
+                .body("{\"name\":\"test\"}")
+                .build();
+    }
+
+    private static RequestBody builtRequestBody(ConductorClient client) {
+        return client.buildRequest("POST", "/workflow", List.of(), List.of(), Map.of(), "{\"name\":\"test\"}").body();
+    }
+}