diff --git a/CHANGELOG.md b/CHANGELOG.md
index 33cade1b..7f3c52d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+### Version 11.9
+
+* `OkHttpClient` now implements `AsyncClient`
+
 ### Version 10.9
 
 * Configurable to disable streaming mode for Default client by verils (#1182) 
diff --git a/okhttp/pom.xml b/okhttp/pom.xml
index 7f0ab66c..f3b00598 100644
--- a/okhttp/pom.xml
+++ b/okhttp/pom.xml
@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!--
 
-    Copyright 2012-2021 The Feign Authors
+    Copyright 2012-2022 The Feign 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
@@ -54,5 +54,11 @@
       <artifactId>mockwebserver</artifactId>
       <scope>test</scope>
     </dependency>
+
+    <dependency>
+      <groupId>com.google.code.gson</groupId>
+      <artifactId>gson</artifactId>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 </project>
diff --git a/okhttp/src/main/java/feign/okhttp/OkHttpClient.java b/okhttp/src/main/java/feign/okhttp/OkHttpClient.java
index 80c4fe8c..221cf44e 100644
--- a/okhttp/src/main/java/feign/okhttp/OkHttpClient.java
+++ b/okhttp/src/main/java/feign/okhttp/OkHttpClient.java
@@ -19,7 +19,10 @@ import java.io.Reader;
 import java.nio.charset.Charset;
 import java.util.Collection;
 import java.util.Map;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
+import feign.AsyncClient;
 import feign.Client;
 import feign.Request.HttpMethod;
 import feign.Request.ProtocolVersion;
@@ -35,7 +38,7 @@ import static feign.Util.enumForName;
  * GitHub github = Feign.builder().client(new OkHttpClient()).target(GitHub.class,
  * "https://api.github.com");
  */
-public final class OkHttpClient implements Client {
+public final class OkHttpClient implements Client, AsyncClient<Object> {
 
   private final okhttp3.OkHttpClient delegate;
 
@@ -153,9 +156,7 @@ public final class OkHttpClient implements Client {
     };
   }
 
-  @Override
-  public feign.Response execute(feign.Request input, feign.Request.Options options)
-      throws IOException {
+  private okhttp3.OkHttpClient getClient(feign.Request.Options options) {
     okhttp3.OkHttpClient requestScoped;
     if (delegate.connectTimeoutMillis() != options.connectTimeoutMillis()
         || delegate.readTimeoutMillis() != options.readTimeoutMillis()
@@ -168,8 +169,39 @@ public final class OkHttpClient implements Client {
     } else {
       requestScoped = delegate;
     }
+    return requestScoped;
+  }
+
+  @Override
+  public feign.Response execute(feign.Request input, feign.Request.Options options)
+      throws IOException {
+    okhttp3.OkHttpClient requestScoped = getClient(options);
     Request request = toOkHttpRequest(input);
     Response response = requestScoped.newCall(request).execute();
     return toFeignResponse(response, input).toBuilder().request(input).build();
   }
+
+  @Override
+  public CompletableFuture<feign.Response> execute(feign.Request input,
+                                                   feign.Request.Options options,
+                                                   Optional<Object> requestContext) {
+    okhttp3.OkHttpClient requestScoped = getClient(options);
+    Request request = toOkHttpRequest(input);
+    CompletableFuture<feign.Response> responseFuture = new CompletableFuture<>();
+    requestScoped.newCall(request).enqueue(new Callback() {
+      @Override
+      public void onFailure(Call call, IOException e) {
+        responseFuture.completeExceptionally(e);
+      }
+
+      @Override
+      public void onResponse(Call call, okhttp3.Response response)
+          throws IOException {
+        final feign.Response r =
+            toFeignResponse(response, input).toBuilder().request(input).build();
+        responseFuture.complete(r);
+      }
+    });
+    return responseFuture;
+  }
 }
diff --git a/okhttp/src/test/java/feign/okhttp/CustomPojo.java b/okhttp/src/test/java/feign/okhttp/CustomPojo.java
new file mode 100644
index 00000000..f2f846c4
--- /dev/null
+++ b/okhttp/src/test/java/feign/okhttp/CustomPojo.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2012-2022 The Feign 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 feign.okhttp;
+
+public class CustomPojo {
+
+  private final String name;
+  private final Integer number;
+
+  CustomPojo(String name, Integer number) {
+    this.name = name;
+    this.number = number;
+  }
+}
diff --git a/okhttp/src/test/java/feign/okhttp/OkHttpClientAsyncTest.java b/okhttp/src/test/java/feign/okhttp/OkHttpClientAsyncTest.java
new file mode 100644
index 00000000..95303213
--- /dev/null
+++ b/okhttp/src/test/java/feign/okhttp/OkHttpClientAsyncTest.java
@@ -0,0 +1,1028 @@
+/*
+ * Copyright 2012-2022 The Feign 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 feign.okhttp;
+
+import static feign.assertj.MockWebServerAssertions.assertThat;
+import static org.assertj.core.data.MapEntry.entry;
+import static org.hamcrest.CoreMatchers.isA;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+import java.io.IOException;
+import java.lang.reflect.Type;
+import java.net.URI;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Date;
+import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+import com.google.gson.Gson;
+import com.google.gson.reflect.TypeToken;
+import org.assertj.core.api.Assertions;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import feign.AsyncClient;
+import feign.AsyncFeign;
+import feign.Body;
+import feign.ChildPojo;
+import feign.Feign;
+import feign.Feign.ResponseMappingDecoder;
+import feign.FeignException;
+import feign.HeaderMap;
+import feign.Headers;
+import feign.Param;
+import feign.PropertyPojo;
+import feign.QueryMap;
+import feign.QueryMapEncoder;
+import feign.Request;
+import feign.Request.HttpMethod;
+import feign.RequestInterceptor;
+import feign.RequestLine;
+import feign.RequestTemplate;
+import feign.Response;
+import feign.ResponseMapper;
+import feign.Target;
+import feign.Target.HardCodedTarget;
+import feign.Util;
+import feign.codec.DecodeException;
+import feign.codec.Decoder;
+import feign.codec.EncodeException;
+import feign.codec.Encoder;
+import feign.codec.ErrorDecoder;
+import feign.codec.StringDecoder;
+import feign.querymap.BeanQueryMapEncoder;
+import feign.querymap.FieldQueryMapEncoder;
+import okhttp3.mockwebserver.MockResponse;
+import okhttp3.mockwebserver.MockWebServer;
+import okio.Buffer;
+
+public class OkHttpClientAsyncTest {
+  @Rule
+  public final ExpectedException thrown = ExpectedException.none();
+  @Rule
+  public final MockWebServer server = new MockWebServer();
+
+  @Test
+  public void iterableQueryParams() throws Exception {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    api.queryParams("user", Arrays.asList("apple", "pear"));
+
+    assertThat(server.takeRequest()).hasPath("/?1=user&2=apple&2=pear");
+  }
+
+  @Test
+  public void postTemplateParamsResolve() throws Exception {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    api.login("netflix", "denominator", "password");
+
+    assertThat(server.takeRequest()).hasBody(
+        "{\"customer_name\": \"netflix\", \"user_name\": \"denominator\", \"password\": \"password\"}");
+  }
+
+  @Test
+  public void responseCoercesToStringBody() throws Throwable {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final Response response = unwrap(api.response());
+    assertTrue(response.body().isRepeatable());
+    assertEquals("foo", Util.toString(response.body().asReader(StandardCharsets.UTF_8)));
+  }
+
+  @Test
+  public void postFormParams() throws Exception {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.form("netflix", "denominator", "password");
+
+    assertThat(server.takeRequest())
+        .hasBody(
+            "{\"customer_name\":\"netflix\",\"user_name\":\"denominator\",\"password\":\"password\"}");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void postBodyParam() throws Exception {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.body(Arrays.asList("netflix", "denominator", "password"));
+
+    assertThat(server.takeRequest())
+        .hasHeaders(entry("Content-Length", Collections.singletonList("32")))
+        .hasBody("[netflix, denominator, password]");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  /**
+   * The type of a parameter value may not be the desired type to encode as. Prefer the interface
+   * type.
+   */
+  @Test
+  public void bodyTypeCorrespondsWithParameterType() throws Exception {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final AtomicReference<Type> encodedType = new AtomicReference<Type>();
+    final TestInterfaceAsync api = newAsyncBuilder().encoder(new Encoder.Default() {
+      @Override
+      public void encode(Object object, Type bodyType, RequestTemplate template) {
+        encodedType.set(bodyType);
+      }
+    }).target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.body(Arrays.asList("netflix", "denominator", "password"));
+
+    server.takeRequest();
+
+    Assertions.assertThat(encodedType.get()).isEqualTo(new TypeToken<List<String>>() {}.getType());
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void singleInterceptor() throws Exception {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().requestInterceptor(new ForwardedForInterceptor())
+            .target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.post();
+
+    assertThat(server.takeRequest())
+        .hasHeaders(entry("X-Forwarded-For", Collections.singletonList("origin.host.com")));
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void multipleInterceptor() throws Exception {
+    server.enqueue(new MockResponse().setBody("foo"));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().requestInterceptor(new ForwardedForInterceptor())
+            .requestInterceptor(new UserAgentInterceptor())
+            .target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.post();
+
+    assertThat(server.takeRequest()).hasHeaders(
+        entry("X-Forwarded-For", Collections.singletonList("origin.host.com")),
+        entry("User-Agent", Collections.singletonList("Feign")));
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void customExpander() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.expand(new Date(1234l));
+
+    assertThat(server.takeRequest()).hasPath("/?date=1234");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void customExpanderListParam() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf =
+        api.expandList(Arrays.asList(new Date(1234l), new Date(12345l)));
+
+    assertThat(server.takeRequest()).hasPath("/?date=1234&date=12345");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void customExpanderNullParam() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.expandList(Arrays.asList(new Date(1234l), null));
+
+    assertThat(server.takeRequest()).hasPath("/?date=1234");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void headerMap() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final Map<String, Object> headerMap = new LinkedHashMap<String, Object>();
+    headerMap.put("Content-Type", "myContent");
+    headerMap.put("Custom-Header", "fooValue");
+    final CompletableFuture<?> cf = api.headerMap(headerMap);
+
+    assertThat(server.takeRequest()).hasHeaders(entry("Content-Type", Arrays.asList("myContent")),
+        entry("Custom-Header", Arrays.asList("fooValue")));
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void headerMapWithHeaderAnnotations() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final Map<String, Object> headerMap = new LinkedHashMap<String, Object>();
+    headerMap.put("Custom-Header", "fooValue");
+    api.headerMapWithHeaderAnnotations(headerMap);
+
+    // header map should be additive for headers provided by annotations
+    assertThat(server.takeRequest()).hasHeaders(entry("Content-Encoding", Arrays.asList("deflate")),
+        entry("Custom-Header", Arrays.asList("fooValue")));
+
+    server.enqueue(new MockResponse());
+    headerMap.put("Content-Encoding", "overrideFromMap");
+
+    final CompletableFuture<?> cf = api.headerMapWithHeaderAnnotations(headerMap);
+
+    /*
+     * @HeaderMap map values no longer override @Header parameters. This caused confusion as it is
+     * valid to have more than one value for a header.
+     */
+    assertThat(server.takeRequest()).hasHeaders(
+        entry("Content-Encoding", Arrays.asList("deflate", "overrideFromMap")),
+        entry("Custom-Header", Arrays.asList("fooValue")));
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void queryMap() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final Map<String, Object> queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("name", "alice");
+    queryMap.put("fooKey", "fooValue");
+    final CompletableFuture<?> cf = api.queryMap(queryMap);
+
+    assertThat(server.takeRequest()).hasPath("/?name=alice&fooKey=fooValue");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void queryMapIterableValuesExpanded() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final Map<String, Object> queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("name", Arrays.asList("Alice", "Bob"));
+    queryMap.put("fooKey", "fooValue");
+    queryMap.put("emptyListKey", new ArrayList<String>());
+    queryMap.put("emptyStringKey", ""); // empty values are ignored.
+    final CompletableFuture<?> cf = api.queryMap(queryMap);
+
+    assertThat(server.takeRequest())
+        .hasPath("/?name=Alice&name=Bob&fooKey=fooValue&emptyStringKey");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void queryMapWithQueryParams() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    server.enqueue(new MockResponse());
+    Map<String, Object> queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("fooKey", "fooValue");
+    api.queryMapWithQueryParams("alice", queryMap);
+    // query map should be expanded after built-in parameters
+    assertThat(server.takeRequest()).hasPath("/?name=alice&fooKey=fooValue");
+
+    server.enqueue(new MockResponse());
+    queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("name", "bob");
+    api.queryMapWithQueryParams("alice", queryMap);
+    // queries are additive
+    assertThat(server.takeRequest()).hasPath("/?name=alice&name=bob");
+
+    server.enqueue(new MockResponse());
+    queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("name", null);
+    api.queryMapWithQueryParams("alice", queryMap);
+    // null value for a query map key removes query parameter
+    assertThat(server.takeRequest()).hasPath("/?name=alice");
+  }
+
+  @Test
+  public void queryMapValueStartingWithBrace() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    server.enqueue(new MockResponse());
+    Map<String, Object> queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("name", "{alice");
+    api.queryMap(queryMap);
+    assertThat(server.takeRequest()).hasPath("/?name=%7Balice");
+
+    server.enqueue(new MockResponse());
+    queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("{name", "alice");
+    api.queryMap(queryMap);
+    assertThat(server.takeRequest()).hasPath("/?%7Bname=alice");
+
+    server.enqueue(new MockResponse());
+    queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("name", "%7Balice");
+    api.queryMapEncoded(queryMap);
+    assertThat(server.takeRequest()).hasPath("/?name=%7Balice");
+
+    server.enqueue(new MockResponse());
+    queryMap = new LinkedHashMap<String, Object>();
+    queryMap.put("%7Bname", "%7Balice");
+    api.queryMapEncoded(queryMap);
+    assertThat(server.takeRequest()).hasPath("/?%7Bname=%7Balice");
+  }
+
+  @Test
+  public void queryMapPojoWithFullParams() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CustomPojo customPojo = new CustomPojo("Name", 3);
+
+    server.enqueue(new MockResponse());
+    final CompletableFuture<?> cf = api.queryMapPojo(customPojo);
+    assertThat(server.takeRequest()).hasQueryParams(Arrays.asList("name=Name", "number=3"));
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void queryMapPojoWithPartialParams() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CustomPojo customPojo = new CustomPojo("Name", null);
+
+    server.enqueue(new MockResponse());
+    final CompletableFuture<?> cf = api.queryMapPojo(customPojo);
+    assertThat(server.takeRequest()).hasPath("/?name=Name");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void queryMapPojoWithEmptyParams() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CustomPojo customPojo = new CustomPojo(null, null);
+
+    server.enqueue(new MockResponse());
+    api.queryMapPojo(customPojo);
+    assertThat(server.takeRequest()).hasPath("/");
+  }
+
+  @Test
+  public void configKeyFormatsAsExpected() throws Exception {
+    assertEquals("TestInterfaceAsync#post()",
+        Feign.configKey(TestInterfaceAsync.class,
+            TestInterfaceAsync.class.getDeclaredMethod("post")));
+    assertEquals("TestInterfaceAsync#uriParam(String,URI,String)",
+        Feign.configKey(TestInterfaceAsync.class,
+            TestInterfaceAsync.class.getDeclaredMethod("uriParam", String.class, URI.class,
+                String.class)));
+  }
+
+  @Test
+  public void configKeyUsesChildType() throws Exception {
+    assertEquals("List#iterator()",
+        Feign.configKey(List.class, Iterable.class.getDeclaredMethod("iterator")));
+  }
+
+  private <T> T unwrap(CompletableFuture<T> cf) throws Throwable {
+    try {
+      return cf.get(1, TimeUnit.SECONDS);
+    } catch (final ExecutionException e) {
+      throw e.getCause();
+    }
+  }
+
+  @Test
+  public void canOverrideErrorDecoder() throws Throwable {
+    server.enqueue(new MockResponse().setResponseCode(400).setBody("foo"));
+    thrown.expect(IllegalArgumentException.class);
+    thrown.expectMessage("bad zone name");
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().errorDecoder(new IllegalArgumentExceptionOn400())
+            .target("http://localhost:" + server.getPort());
+
+    unwrap(api.post());
+  }
+
+  @Test
+  public void overrideTypeSpecificDecoder() throws Throwable {
+    server.enqueue(new MockResponse().setBody("success!"));
+
+    final TestInterfaceAsync api = newAsyncBuilder()
+        .decoder((response, type) -> "fail").target("http://localhost:" + server.getPort());
+
+    assertEquals("fail", unwrap(api.post()));
+  }
+
+  @Test
+  public void doesntRetryAfterResponseIsSent() throws Throwable {
+    server.enqueue(new MockResponse().setBody("success!"));
+    thrown.expect(FeignException.class);
+    thrown.expectMessage("timeout reading POST http://");
+
+    final TestInterfaceAsync api = newAsyncBuilder().decoder((response, type) -> {
+      throw new IOException("timeout");
+    }).target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.post();
+    server.takeRequest();
+    unwrap(cf);
+  }
+
+  @Test
+  public void throwsFeignExceptionIncludingBody() throws Throwable {
+    server.enqueue(new MockResponse().setBody("success!"));
+
+    final TestInterfaceAsync api = newAsyncBuilder().decoder((response, type) -> {
+      throw new IOException("timeout");
+    }).target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.body("Request body");
+    server.takeRequest();
+    try {
+      unwrap(cf);
+    } catch (final FeignException e) {
+      Assertions.assertThat(e.getMessage())
+          .isEqualTo("timeout reading POST http://localhost:" + server.getPort() + "/");
+      Assertions.assertThat(e.contentUTF8()).isEqualTo("Request body");
+      return;
+    }
+    fail();
+  }
+
+  @Test
+  public void throwsFeignExceptionWithoutBody() {
+    server.enqueue(new MockResponse().setBody("success!"));
+
+    final TestInterfaceAsync api = newAsyncBuilder().decoder((response, type) -> {
+      throw new IOException("timeout");
+    }).target("http://localhost:" + server.getPort());
+
+    try {
+      api.noContent();
+    } catch (final FeignException e) {
+      Assertions.assertThat(e.getMessage())
+          .isEqualTo("timeout reading POST http://localhost:" + server.getPort() + "/");
+      Assertions.assertThat(e.contentUTF8()).isEqualTo("");
+    }
+  }
+
+  @SuppressWarnings("deprecation")
+  @Test
+  public void whenReturnTypeIsResponseNoErrorHandling() throws Throwable {
+    final Map<String, Collection<String>> headers = new LinkedHashMap<String, Collection<String>>();
+    headers.put("Location", Arrays.asList("http://bar.com"));
+    final Response response = Response.builder().status(302).reason("Found").headers(headers)
+        .request(Request.create(HttpMethod.GET, "/", Collections.emptyMap(), null, Util.UTF_8))
+        .body(new byte[0]).build();
+
+    final ExecutorService execs = Executors.newSingleThreadExecutor();
+
+    // fake client as Client.Default follows redirects.
+    final TestInterfaceAsync api = AsyncFeign.<Void>asyncBuilder()
+        .client(new AsyncClient.Default<>((request, options) -> response, execs))
+        .target(TestInterfaceAsync.class, "http://localhost:" + server.getPort());
+
+    assertThat(unwrap(api.response()).headers().get("Location"))
+        .contains("http://bar.com");
+
+    execs.shutdown();
+  }
+
+  @Test
+  public void okIfDecodeRootCauseHasNoMessage() throws Throwable {
+    server.enqueue(new MockResponse().setBody("success!"));
+    thrown.expect(DecodeException.class);
+
+    final TestInterfaceAsync api = newAsyncBuilder().decoder((response, type) -> {
+      throw new RuntimeException();
+    }).target("http://localhost:" + server.getPort());
+
+    unwrap(api.post());
+  }
+
+  @Test
+  public void decodingExceptionGetWrappedInDismiss404Mode() throws Throwable {
+    server.enqueue(new MockResponse().setResponseCode(404));
+    thrown.expect(DecodeException.class);
+    thrown.expectCause(isA(NoSuchElementException.class));
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().dismiss404().decoder((response, type) -> {
+          assertEquals(404, response.status());
+          throw new NoSuchElementException();
+        }).target("http://localhost:" + server.getPort());
+
+    unwrap(api.post());
+  }
+
+  @Test
+  public void decodingDoesNotSwallow404ErrorsInDismiss404Mode() throws Throwable {
+    server.enqueue(new MockResponse().setResponseCode(404));
+    thrown.expect(IllegalArgumentException.class);
+
+    final TestInterfaceAsync api = newAsyncBuilder().dismiss404()
+        .errorDecoder(new IllegalArgumentExceptionOn404())
+        .target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<Void> cf = api.queryMap(Collections.<String, Object>emptyMap());
+    server.takeRequest();
+    unwrap(cf);
+  }
+
+  @Test
+  public void okIfEncodeRootCauseHasNoMessage() throws Throwable {
+    server.enqueue(new MockResponse().setBody("success!"));
+    thrown.expect(EncodeException.class);
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().encoder((object, bodyType, template) -> {
+          throw new RuntimeException();
+        }).target("http://localhost:" + server.getPort());
+
+    unwrap(api.body(Arrays.asList("foo")));
+  }
+
+  @Test
+  public void equalsHashCodeAndToStringWork() {
+    final Target<TestInterfaceAsync> t1 =
+        new HardCodedTarget<TestInterfaceAsync>(TestInterfaceAsync.class,
+            "http://localhost:8080");
+    final Target<TestInterfaceAsync> t2 =
+        new HardCodedTarget<TestInterfaceAsync>(TestInterfaceAsync.class,
+            "http://localhost:8888");
+    final Target<OtherTestInterfaceAsync> t3 =
+        new HardCodedTarget<OtherTestInterfaceAsync>(OtherTestInterfaceAsync.class,
+            "http://localhost:8080");
+    final TestInterfaceAsync i1 = newAsyncBuilder().target(t1);
+    final TestInterfaceAsync i2 = newAsyncBuilder().target(t1);
+    final TestInterfaceAsync i3 = newAsyncBuilder().target(t2);
+    final OtherTestInterfaceAsync i4 = newAsyncBuilder().target(t3);
+
+    Assertions.assertThat(i1).isEqualTo(i2).isNotEqualTo(i3).isNotEqualTo(i4);
+
+    Assertions.assertThat(i1.hashCode()).isEqualTo(i2.hashCode()).isNotEqualTo(i3.hashCode())
+        .isNotEqualTo(i4.hashCode());
+
+    Assertions.assertThat(i1.toString()).isEqualTo(i2.toString()).isNotEqualTo(i3.toString())
+        .isNotEqualTo(i4.toString());
+
+    Assertions.assertThat(t1).isNotEqualTo(i1);
+
+    Assertions.assertThat(t1.hashCode()).isEqualTo(i1.hashCode());
+
+    Assertions.assertThat(t1.toString()).isEqualTo(i1.toString());
+  }
+
+  @SuppressWarnings("resource")
+  @Test
+  public void decodeLogicSupportsByteArray() throws Throwable {
+    final byte[] expectedResponse = {12, 34, 56};
+    server.enqueue(new MockResponse().setBody(new Buffer().write(expectedResponse)));
+
+    final OtherTestInterfaceAsync api =
+        newAsyncBuilder().target(new HardCodedTarget<>(
+            OtherTestInterfaceAsync.class,
+            "http://localhost:" + server.getPort()));
+
+    Assertions.assertThat(unwrap(api.binaryResponseBody())).containsExactly(expectedResponse);
+  }
+
+  @Test
+  public void encodeLogicSupportsByteArray() throws Exception {
+    final byte[] expectedRequest = {12, 34, 56};
+    server.enqueue(new MockResponse());
+
+    final OtherTestInterfaceAsync api =
+        newAsyncBuilder().encoder(new Encoder.Default()).target(new HardCodedTarget<>(
+            OtherTestInterfaceAsync.class,
+            "http://localhost:" + server.getPort()));
+
+    final CompletableFuture<?> cf = api.binaryRequestBody(expectedRequest);
+
+    assertThat(server.takeRequest()).hasBody(expectedRequest);
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void encodedQueryParam() throws Exception {
+    server.enqueue(new MockResponse());
+
+    final TestInterfaceAsync api =
+        newAsyncBuilder().target("http://localhost:" + server.getPort());
+
+    final CompletableFuture<?> cf = api.encodedQueryParam("5.2FSi+");
+
+    assertThat(server.takeRequest()).hasPath("/?trim=5.2FSi%2B");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  private void checkCFCompletedSoon(CompletableFuture<?> cf) {
+    try {
+      unwrap(cf);
+    } catch (final RuntimeException e) {
+      throw e;
+    } catch (final Throwable t) {
+      throw new RuntimeException(t);
+    }
+  }
+
+  @Test
+  public void responseMapperIsAppliedBeforeDelegate() throws IOException {
+    final ResponseMappingDecoder decoder =
+        new ResponseMappingDecoder(upperCaseResponseMapper(), new StringDecoder());
+    final String output = (String) decoder.decode(responseWithText("response"), String.class);
+
+    Assertions.assertThat(output).isEqualTo("RESPONSE");
+  }
+
+  private static TestInterfaceAsyncBuilder newAsyncBuilder() {
+    return new TestInterfaceAsyncBuilder();
+  }
+
+  private ResponseMapper upperCaseResponseMapper() {
+    return new ResponseMapper() {
+      @SuppressWarnings("deprecation")
+      @Override
+      public Response map(Response response, Type type) {
+        try {
+          return response.toBuilder()
+              .body(Util.toString(response.body().asReader()).toUpperCase().getBytes())
+              .build();
+        } catch (final IOException e) {
+          throw new RuntimeException(e);
+        }
+      }
+    };
+  }
+
+  @SuppressWarnings("deprecation")
+  private Response responseWithText(String text) {
+    return Response.builder().body(text, Util.UTF_8).status(200)
+        .request(Request.create(HttpMethod.GET, "/api", Collections.emptyMap(), null, Util.UTF_8))
+        .headers(new HashMap<>()).build();
+  }
+
+  @Test
+  public void mapAndDecodeExecutesMapFunction() throws Throwable {
+    server.enqueue(new MockResponse().setBody("response!"));
+
+    final TestInterfaceAsync api =
+        AsyncFeign.asyncBuilder().mapAndDecode(upperCaseResponseMapper(), new StringDecoder())
+            .target(TestInterfaceAsync.class, "http://localhost:" + server.getPort());
+
+    assertEquals("RESPONSE!", unwrap(api.post()));
+  }
+
+  @Test
+  public void beanQueryMapEncoderWithPrivateGetterIgnored() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().queryMapEndcoder(new BeanQueryMapEncoder())
+            .target("http://localhost:" + server.getPort());
+
+    final PropertyPojo.ChildPojoClass propertyPojo = new PropertyPojo.ChildPojoClass();
+    propertyPojo.setPrivateGetterProperty("privateGetterProperty");
+    propertyPojo.setName("Name");
+    propertyPojo.setNumber(1);
+
+    server.enqueue(new MockResponse());
+    final CompletableFuture<?> cf = api.queryMapPropertyPojo(propertyPojo);
+    assertThat(server.takeRequest()).hasQueryParams(Arrays.asList("name=Name", "number=1"));
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void queryMap_with_child_pojo() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().queryMapEndcoder(new FieldQueryMapEncoder())
+            .target("http://localhost:" + server.getPort());
+
+    final ChildPojo childPojo = new ChildPojo();
+    childPojo.setChildPrivateProperty("first");
+    childPojo.setParentProtectedProperty("second");
+    childPojo.setParentPublicProperty("third");
+
+    server.enqueue(new MockResponse());
+    final CompletableFuture<?> cf = api.queryMapPropertyInheritence(childPojo);
+    assertThat(server.takeRequest()).hasQueryParams("parentPublicProperty=third",
+        "parentProtectedProperty=second",
+        "childPrivateProperty=first");
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void beanQueryMapEncoderWithNullValueIgnored() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().queryMapEndcoder(new BeanQueryMapEncoder())
+            .target("http://localhost:" + server.getPort());
+
+    final PropertyPojo.ChildPojoClass propertyPojo = new PropertyPojo.ChildPojoClass();
+    propertyPojo.setName(null);
+    propertyPojo.setNumber(1);
+
+    server.enqueue(new MockResponse());
+    final CompletableFuture<?> cf = api.queryMapPropertyPojo(propertyPojo);
+
+    assertThat(server.takeRequest()).hasQueryParams("number=1");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  @Test
+  public void beanQueryMapEncoderWithEmptyParams() throws Exception {
+    final TestInterfaceAsync api =
+        newAsyncBuilder().queryMapEndcoder(new BeanQueryMapEncoder())
+            .target("http://localhost:" + server.getPort());
+
+    final PropertyPojo.ChildPojoClass propertyPojo = new PropertyPojo.ChildPojoClass();
+
+    server.enqueue(new MockResponse());
+    final CompletableFuture<?> cf = api.queryMapPropertyPojo(propertyPojo);
+    assertThat(server.takeRequest()).hasQueryParams("/");
+
+    checkCFCompletedSoon(cf);
+  }
+
+  public interface TestInterfaceAsync {
+
+    @RequestLine("POST /")
+    CompletableFuture<Response> response();
+
+    @RequestLine("POST /")
+    CompletableFuture<String> post() throws TestInterfaceException;
+
+    @RequestLine("POST /")
+    @Body("%7B\"customer_name\": \"{customer_name}\", \"user_name\": \"{user_name}\", \"password\": \"{password}\"%7D")
+    CompletableFuture<Void> login(@Param("customer_name") String customer,
+                                  @Param("user_name") String user,
+                                  @Param("password") String password);
+
+    @RequestLine("POST /")
+    CompletableFuture<Void> body(List<String> contents);
+
+    @RequestLine("POST /")
+    CompletableFuture<String> body(String content);
+
+    @RequestLine("POST /")
+    CompletableFuture<String> noContent();
+
+    @RequestLine("POST /")
+    @Headers("Content-Encoding: gzip")
+    CompletableFuture<Void> gzipBody(List<String> contents);
+
+    @RequestLine("POST /")
+    @Headers("Content-Encoding: deflate")
+    CompletableFuture<Void> deflateBody(List<String> contents);
+
+    @RequestLine("POST /")
+    CompletableFuture<Void> form(@Param("customer_name") String customer,
+                                 @Param("user_name") String user,
+                                 @Param("password") String password);
+
+    @RequestLine("GET /{1}/{2}")
+    CompletableFuture<Response> uriParam(@Param("1") String one,
+                                         URI endpoint,
+                                         @Param("2") String two);
+
+    @RequestLine("GET /?1={1}&2={2}")
+    CompletableFuture<Response> queryParams(@Param("1") String one,
+                                            @Param("2") Iterable<String> twos);
+
+    @RequestLine("POST /?date={date}")
+    CompletableFuture<Void> expand(@Param(value = "date", expander = DateToMillis.class) Date date);
+
+    @RequestLine("GET /?date={date}")
+    CompletableFuture<Void> expandList(@Param(value = "date",
+        expander = DateToMillis.class) List<Date> dates);
+
+    @RequestLine("GET /?date={date}")
+    CompletableFuture<Void> expandArray(@Param(value = "date",
+        expander = DateToMillis.class) Date[] dates);
+
+    @RequestLine("GET /")
+    CompletableFuture<Void> headerMap(@HeaderMap Map<String, Object> headerMap);
+
+    @RequestLine("GET /")
+    @Headers("Content-Encoding: deflate")
+    CompletableFuture<Void> headerMapWithHeaderAnnotations(@HeaderMap Map<String, Object> headerMap);
+
+    @RequestLine("GET /")
+    CompletableFuture<Void> queryMap(@QueryMap Map<String, Object> queryMap);
+
+    @RequestLine("GET /")
+    CompletableFuture<Void> queryMapEncoded(@QueryMap(encoded = true) Map<String, Object> queryMap);
+
+    @RequestLine("GET /?name={name}")
+    CompletableFuture<Void> queryMapWithQueryParams(@Param("name") String name,
+                                                    @QueryMap Map<String, Object> queryMap);
+
+    @RequestLine("GET /?trim={trim}")
+    CompletableFuture<Void> encodedQueryParam(@Param(value = "trim", encoded = true) String trim);
+
+    @RequestLine("GET /")
+    CompletableFuture<Void> queryMapPojo(@QueryMap CustomPojo object);
+
+    @RequestLine("GET /")
+    CompletableFuture<Void> queryMapPropertyPojo(@QueryMap PropertyPojo object);
+
+    @RequestLine("GET /")
+    CompletableFuture<Void> queryMapPropertyInheritence(@QueryMap ChildPojo object);
+
+    class DateToMillis implements Param.Expander {
+
+      @Override
+      public String expand(Object value) {
+        return String.valueOf(((Date) value).getTime());
+      }
+    }
+  }
+
+  class TestInterfaceException extends Exception {
+    private static final long serialVersionUID = 1L;
+
+    TestInterfaceException(String message) {
+      super(message);
+    }
+  }
+
+  public interface OtherTestInterfaceAsync {
+
+    @RequestLine("POST /")
+    CompletableFuture<String> post();
+
+    @RequestLine("POST /")
+    CompletableFuture<byte[]> binaryResponseBody();
+
+    @RequestLine("POST /")
+    CompletableFuture<Void> binaryRequestBody(byte[] contents);
+  }
+
+  static class ForwardedForInterceptor implements RequestInterceptor {
+
+    @Override
+    public void apply(RequestTemplate template) {
+      template.header("X-Forwarded-For", "origin.host.com");
+    }
+  }
+
+  static class UserAgentInterceptor implements RequestInterceptor {
+
+    @Override
+    public void apply(RequestTemplate template) {
+      template.header("User-Agent", "Feign");
+    }
+  }
+
+  static class IllegalArgumentExceptionOn400 extends ErrorDecoder.Default {
+
+    @Override
+    public Exception decode(String methodKey, Response response) {
+      if (response.status() == 400) {
+        return new IllegalArgumentException("bad zone name");
+      }
+      return super.decode(methodKey, response);
+    }
+  }
+
+  static class IllegalArgumentExceptionOn404 extends ErrorDecoder.Default {
+
+    @Override
+    public Exception decode(String methodKey, Response response) {
+      if (response.status() == 404) {
+        return new IllegalArgumentException("bad zone name");
+      }
+      return super.decode(methodKey, response);
+    }
+  }
+
+  static final class TestInterfaceAsyncBuilder {
+
+    private final AsyncFeign.AsyncBuilder<Object> delegate =
+        AsyncFeign.asyncBuilder()
+            .client(new OkHttpClient())
+            .decoder(new Decoder.Default()).encoder((object, bodyType, template) -> {
+              if (object instanceof Map) {
+                template.body(new Gson().toJson(object));
+              } else {
+                template.body(object.toString());
+              }
+            });
+
+    TestInterfaceAsyncBuilder requestInterceptor(RequestInterceptor requestInterceptor) {
+      delegate.requestInterceptor(requestInterceptor);
+      return this;
+    }
+
+    TestInterfaceAsyncBuilder encoder(Encoder encoder) {
+      delegate.encoder(encoder);
+      return this;
+    }
+
+    TestInterfaceAsyncBuilder decoder(Decoder decoder) {
+      delegate.decoder(decoder);
+      return this;
+    }
+
+    TestInterfaceAsyncBuilder errorDecoder(ErrorDecoder errorDecoder) {
+      delegate.errorDecoder(errorDecoder);
+      return this;
+    }
+
+    TestInterfaceAsyncBuilder dismiss404() {
+      delegate.dismiss404();
+      return this;
+    }
+
+    TestInterfaceAsyncBuilder queryMapEndcoder(QueryMapEncoder queryMapEncoder) {
+      delegate.queryMapEncoder(queryMapEncoder);
+      return this;
+    }
+
+    TestInterfaceAsync target(String url) {
+      return delegate.target(TestInterfaceAsync.class, url);
+    }
+
+    <T> T target(Target<T> target) {
+      return delegate.target(target);
+    }
+  }
+
+  static final class ExtendedCF<T> extends CompletableFuture<T> {
+
+  }
+}
diff --git a/src/docs/overview-mindmap.iuml b/src/docs/overview-mindmap.iuml
index cc703dc2..43ada70f 100644
--- a/src/docs/overview-mindmap.iuml
+++ b/src/docs/overview-mindmap.iuml
@@ -11,6 +11,7 @@
 ** async clients
 *** java.net.URL
 *** Apache HC5
+*** OkHttp
 ** contracts
 *** Feign
 *** JAX-RS