diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/CancelOperationOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/CancelOperationOptions.java
new file mode 100644
index 0000000..a56a8f2
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/CancelOperationOptions.java
@@ -0,0 +1,41 @@
+package io.nexusrpc.client;
+
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+/** CancelOperationOptions is used to specify options for canceling an operation. */
+public class CancelOperationOptions {
+  /** Create a builder for CancelOperationOptions. */
+  public static CancelOperationOptions.Builder newBuilder() {
+    return new CancelOperationOptions.Builder();
+  }
+
+  private final SortedMap<String, String> headers;
+
+  private CancelOperationOptions(SortedMap<String, String> headers) {
+    this.headers = headers;
+  }
+
+  /** Headers. The returned map operates without regard to case. */
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+
+    private Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    /** Get headers to mutate. */
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    public CancelOperationOptions build() {
+      return new CancelOperationOptions(headers);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/ExecuteOperationOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/ExecuteOperationOptions.java
new file mode 100644
index 0000000..69706f9
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/ExecuteOperationOptions.java
@@ -0,0 +1,103 @@
+package io.nexusrpc.client;
+
+import io.nexusrpc.Link;
+import java.time.Duration;
+import java.util.List;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class ExecuteOperationOptions {
+  private final Map<String, String> headers;
+  private final String callbackURL;
+  private final Map<String, String> callbackHeaders;
+  private final String requestId;
+  private final List<Link> inboundLinks;
+  private final Duration timeout;
+
+  public ExecuteOperationOptions(
+      Map<String, String> headers,
+      String callbackURL,
+      Map<String, String> callbackHeaders,
+      String requestId,
+      List<Link> inboundLinks,
+      Duration timeout) {
+    this.headers = headers;
+    this.callbackURL = callbackURL;
+    this.callbackHeaders = callbackHeaders;
+    this.requestId = requestId;
+    this.inboundLinks = inboundLinks;
+    this.timeout = timeout;
+  }
+
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public String getCallbackURL() {
+    return callbackURL;
+  }
+
+  public Map<String, String> getCallbackHeaders() {
+    return callbackHeaders;
+  }
+
+  public String getRequestId() {
+    return requestId;
+  }
+
+  public List<Link> getInboundLinks() {
+    return inboundLinks;
+  }
+
+  public Duration getTimeout() {
+    return timeout;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+    private String callbackURL;
+    private SortedMap<String, String> callbackHeaders;
+    private String requestId;
+    private List<Link> inboundLinks;
+    private Duration timeout;
+
+    public Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+      callbackHeaders = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    public Builder setCallbackURL(String callbackURL) {
+      this.callbackURL = callbackURL;
+      return this;
+    }
+
+    public Map<String, String> getCallbackHeaders() {
+      return callbackHeaders;
+    }
+
+    public Builder setRequestId(String requestId) {
+      this.requestId = requestId;
+      return this;
+    }
+
+    public Builder setInboundLinks(List<Link> inboundLinks) {
+      this.inboundLinks = inboundLinks;
+      return this;
+    }
+
+    public Builder setTimeout(Duration timeout) {
+      this.timeout = timeout;
+      return this;
+    }
+
+    public ExecuteOperationOptions build() {
+      return new ExecuteOperationOptions(
+          headers, callbackURL, callbackHeaders, requestId, inboundLinks, timeout);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/GetOperationInfoOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/GetOperationInfoOptions.java
new file mode 100644
index 0000000..d230195
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/GetOperationInfoOptions.java
@@ -0,0 +1,40 @@
+package io.nexusrpc.client;
+
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class GetOperationInfoOptions {
+  /** Create a builder for CancelOperationOptions. */
+  public static GetOperationInfoOptions.Builder newBuilder() {
+    return new GetOperationInfoOptions.Builder();
+  }
+
+  private final SortedMap<String, String> headers;
+
+  private GetOperationInfoOptions(SortedMap<String, String> headers) {
+    this.headers = headers;
+  }
+
+  /** Headers. The returned map operates without regard to case. */
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+
+    private Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    /** Get headers to mutate. */
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    public GetOperationInfoOptions build() {
+      return new GetOperationInfoOptions(headers);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/GetOperationResultOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/GetOperationResultOptions.java
new file mode 100644
index 0000000..30e913f
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/GetOperationResultOptions.java
@@ -0,0 +1,59 @@
+package io.nexusrpc.client;
+
+import java.time.Duration;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class GetOperationResultOptions {
+  /** Create a builder for GetOperationResultOptions. */
+  public static GetOperationResultOptions.Builder newBuilder() {
+    return new GetOperationResultOptions.Builder();
+  }
+
+  private final Duration timeout;
+  private final SortedMap<String, String> headers;
+
+  private GetOperationResultOptions(Duration timeout, SortedMap<String, String> headers) {
+    this.timeout = timeout;
+    this.headers = headers;
+  }
+
+  /** Headers. The returned map operates without regard to case. */
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public Duration getTimeout() {
+    return timeout;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+    private Duration timeout;
+
+    private Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    /** Get headers to mutate. */
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    /**
+     * Set the timeout for the operation.
+     *
+     * @param timeout the duration to wait for the operation result
+     * @return this builder instance
+     */
+    public Builder setTimeout(Duration timeout) {
+      this.timeout = timeout;
+      return this;
+    }
+
+    public GetOperationResultOptions build() {
+      return new GetOperationResultOptions(timeout, headers);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/GetResultResponse.java b/nexus-sdk/src/main/java/io/nexusrpc/client/GetResultResponse.java
new file mode 100644
index 0000000..6585104
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/GetResultResponse.java
@@ -0,0 +1,45 @@
+package io.nexusrpc.client;
+
+import io.nexusrpc.Link;
+import java.util.List;
+
+public class GetResultResponse<T> {
+  public static GetResultResponse.Builder newBuilder() {
+    return new GetResultResponse.Builder();
+  }
+
+  private final T result;
+  private final List<Link> links;
+
+  private GetResultResponse(T result, List<Link> links) {
+    this.result = result;
+    this.links = links;
+  }
+
+  public T getResult() {
+    return result;
+  }
+
+  public List<Link> getLinks() {
+    return links;
+  }
+
+  public static class Builder<T> {
+    private T result;
+    private List<Link> links;
+
+    public Builder setResult(T result) {
+      this.result = result;
+      return this;
+    }
+
+    public Builder setLinks(List<Link> links) {
+      this.links = links;
+      return this;
+    }
+
+    public GetResultResponse<T> build() {
+      return new GetResultResponse<>(result, links);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/OperationHandle.java b/nexus-sdk/src/main/java/io/nexusrpc/client/OperationHandle.java
new file mode 100644
index 0000000..d7beebd
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/OperationHandle.java
@@ -0,0 +1,132 @@
+package io.nexusrpc.client;
+
+import io.nexusrpc.OperationInfo;
+import io.nexusrpc.client.transport.GetOperationInfoResponse;
+import io.nexusrpc.client.transport.GetOperationResultResponse;
+import io.nexusrpc.client.transport.Transport;
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * OperationHandle represents a handle to an operation that can be used to interact with the
+ * operation.
+ */
+public class OperationHandle<T> {
+  private final String operation;
+  private final String service;
+  private final String operationToken;
+  private final Transport transport;
+
+  public OperationHandle(
+      String operation, String service, String operationToken, Transport transport) {
+    this.operation = operation;
+    this.service = service;
+    this.operationToken = operationToken;
+    this.transport = transport;
+  }
+
+  public String getOperation() {
+    return operation;
+  }
+
+  public String getService() {
+    return service;
+  }
+
+  String getOperationToken() {
+    return operationToken;
+  }
+
+  OperationInfo getInfo(GetOperationInfoOptions options) {
+    // TODO: translate options to transport options if necessary
+    return transport
+        .getOperationInfo(
+            operation,
+            service,
+            operationToken,
+            io.nexusrpc.client.transport.GetOperationInfoOptions.newBuilder().build())
+        .getOperationInfo();
+  }
+
+  void cancel(CancelOperationOptions options) {
+    // TODO: translate options to transport options if necessary
+    transport.cancelOperation(
+        operation,
+        service,
+        operationToken,
+        io.nexusrpc.client.transport.CancelOperationOptions.newBuilder().build());
+  }
+
+  T getResult(GetOperationResultOptions options) {
+    // TODO: translate options to transport options if necessary
+    return (T)
+        transport
+            .getOperationResult(
+                operation,
+                service,
+                operationToken,
+                io.nexusrpc.client.transport.GetOperationResultOptions.newBuilder().build())
+            .getResult();
+  }
+
+  GetResultResponse<T> getResultWithDetails(GetOperationResultOptions options) {
+    // TODO: translate options to transport options if necessary
+    GetOperationResultResponse response =
+        transport.getOperationResult(
+            operation,
+            service,
+            operationToken,
+            io.nexusrpc.client.transport.GetOperationResultOptions.newBuilder().build());
+    return GetResultResponse.<T>newBuilder()
+        .setResult(response)
+        .setLinks(response.getLinks())
+        .build();
+  }
+
+  CompletableFuture<OperationInfo> getInfoAsync(GetOperationInfoOptions options) {
+    return transport
+        .getOperationInfoAsync(
+            operation,
+            service,
+            operationToken,
+            io.nexusrpc.client.transport.GetOperationInfoOptions.newBuilder().build())
+        .thenApply(GetOperationInfoResponse::getOperationInfo);
+  }
+
+  CompletableFuture<Void> cancelAsync(CancelOperationOptions options) {
+    return transport
+        .cancelOperationAsync(
+            operation,
+            service,
+            operationToken,
+            io.nexusrpc.client.transport.CancelOperationOptions.newBuilder().build())
+        .thenApply(response -> null);
+  }
+
+  CompletableFuture<T> getResultAsync(GetOperationResultOptions options) {
+    return transport
+        .getOperationResultAsync(
+            operation,
+            service,
+            operationToken,
+            io.nexusrpc.client.transport.GetOperationResultOptions.newBuilder().build())
+        .thenApply(response -> (T) response.getResult());
+  }
+
+  CompletableFuture<GetResultResponse<T>> getResultWithDetailsAsync(
+      GetOperationResultOptions options) {
+    return transport
+        .getOperationResultAsync(
+            operation,
+            service,
+            operationToken,
+            io.nexusrpc.client.transport.GetOperationResultOptions.newBuilder().build())
+        .thenApply(
+            response ->
+                GetResultResponse.<T>newBuilder()
+                    .setResult(response)
+                    .setLinks(response.getLinks())
+                    .build());
+  }
+
+  // TODO Add no arg versions of the above methods that use default options.
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/ServiceClient.java b/nexus-sdk/src/main/java/io/nexusrpc/client/ServiceClient.java
new file mode 100644
index 0000000..2a9140f
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/ServiceClient.java
@@ -0,0 +1,137 @@
+package io.nexusrpc.client;
+
+import io.nexusrpc.client.transport.GetOperationResultResponse;
+import io.nexusrpc.client.transport.StartOperationResponse;
+import io.nexusrpc.client.transport.Transport;
+import java.util.function.BiFunction;
+
+public class ServiceClient<T> {
+  private final String service;
+  private final Transport transport;
+
+  // TODO maybe use the builder pattern for consistency
+  public ServiceClient(String service, Transport transport) {
+    this.service = service;
+    this.transport = transport;
+  }
+
+  /**
+   * Executes an operation on the Nexus service with the provided input. This method is synchronous
+   * and returns the result directly.
+   *
+   * @param operation The operation method to execute, represented as a BiFunction.
+   * @param input The input to the operation.
+   * @return The result of the operation.
+   */
+  <U, R> R executeOperation(BiFunction<T, U, R> operation, U input) {
+    throw new UnsupportedOperationException("Not implemented yet");
+  }
+
+  /**
+   * Executes an operation on the Nexus service with the provided input. This method is synchronous
+   * and returns the result directly.
+   *
+   * @param operation The operation method to execute, represented as a BiFunction.
+   * @param input The input to the operation.
+   * @param options for execute operations
+   * @return The result of the operation.
+   */
+  <U, R> R executeOperation(
+      BiFunction<T, U, R> operation, U input, ExecuteOperationOptions options) {
+    throw new UnsupportedOperationException("Not implemented yet");
+  }
+
+  /**
+   * Starts an operation on the Nexus service with the provided input.
+   *
+   * @param operation The operation method to start, represented as a BiFunction.
+   * @param input The input to the operation.
+   */
+  <U, R> StartOperationResult<R> startOperation(BiFunction<T, U, R> operation, U input) {
+    throw new UnsupportedOperationException("Not implemented yet");
+  }
+
+  /**
+   * Starts an operation on the Nexus service with the provided input.
+   *
+   * @param operation The operation method to start, represented as a BiFunction.
+   * @param input The input to the operation.
+   * @param options for start operations
+   */
+  <U, R> StartOperationResult<R> startOperation(
+      BiFunction<T, U, R> operation, U input, StartOperationOptions options) {
+    throw new UnsupportedOperationException("Not implemented yet");
+  }
+
+  /**
+   * Starts an operation on the Nexus service with the provided input.
+   *
+   * @param operation The operation name to start.
+   * @param input The input to the operation.
+   * @param options for start operations
+   */
+  <U, R> StartOperationResult<R> startOperation(
+      String operation, U input, StartOperationOptions options) {
+    // TODO translate options to transport options
+    StartOperationResponse response =
+        transport.startOperation(
+            operation,
+            service,
+            io.nexusrpc.client.transport.StartOperationOptions.newBuilder().build());
+    // TODO handle response and convert to StartOperationResult<R>
+    return new StartOperationResult<>();
+  }
+
+  /**
+   * Execute an operation on the Nexus service with the provided input.
+   *
+   * @param operation The operation name to start.
+   * @param input The input to the operation.
+   * @param options for start operations
+   */
+  <U, R> StartOperationResult<R> executeOperation(
+      String operation, U input, ExecuteOperationOptions options) {
+    // TODO translate options to transport options
+    StartOperationResponse response =
+        transport.startOperation(
+            operation,
+            service,
+            io.nexusrpc.client.transport.StartOperationOptions.newBuilder().build());
+    if (response.getSyncResult() != null) {
+      // If the operation is synchronous, return the result directly
+      return new StartOperationResult<>();
+    }
+    // TODO handle response and convert to GetOperationResultOptions<R>
+    GetOperationResultResponse result =
+        transport.getOperationResult(
+            operation,
+            service,
+            response.getAsyncOperationToken(),
+            io.nexusrpc.client.transport.GetOperationResultOptions.newBuilder().build());
+    return new StartOperationResult<>();
+  }
+
+  /**
+   * Gets a handle to an asynchronous operation.
+   *
+   * <p>Note: This does not perform validation that the token is valid.
+   *
+   * @param operation name of the operation.
+   * @param token operation token.
+   */
+  OperationHandle<Object> newHandle(String operation, String token) {
+    return new OperationHandle<>(operation, service, token, transport);
+  }
+
+  /**
+   * Gets a handle to an asynchronous operation.
+   *
+   * <p>Note: This does not perform validation that the token is valid.
+   *
+   * @param operation operation method.
+   * @param token operation token.
+   */
+  <U, R> OperationHandle<R> newHandle(BiFunction<T, U, R> operation, String token) {
+    throw new UnsupportedOperationException("Not implemented yet");
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/StartOperationOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/StartOperationOptions.java
new file mode 100644
index 0000000..18d0ee6
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/StartOperationOptions.java
@@ -0,0 +1,93 @@
+package io.nexusrpc.client;
+
+import io.nexusrpc.Link;
+import java.util.List;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class StartOperationOptions {
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  private final Map<String, String> headers;
+  private final String callbackURL;
+  private final Map<String, String> callbackHeaders;
+  private final String requestId;
+  private final List<Link> inboundLinks;
+
+  private StartOperationOptions(
+      Map<String, String> headers,
+      String callbackURL,
+      Map<String, String> callbackHeaders,
+      String requestId,
+      List<Link> inboundLinks) {
+    this.headers = headers;
+    this.callbackURL = callbackURL;
+    this.callbackHeaders = callbackHeaders;
+    this.requestId = requestId;
+    this.inboundLinks = inboundLinks;
+  }
+
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public String getCallbackURL() {
+    return callbackURL;
+  }
+
+  public Map<String, String> getCallbackHeaders() {
+    return callbackHeaders;
+  }
+
+  public String getRequestId() {
+    return requestId;
+  }
+
+  public List<Link> getInboundLinks() {
+    return inboundLinks;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+    private String callbackURL;
+    private SortedMap<String, String> callbackHeaders;
+    private String requestId;
+    private List<Link> inboundLinks;
+
+    public Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+      callbackHeaders = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    public Builder setCallbackURL(String callbackURL) {
+      this.callbackURL = callbackURL;
+      return this;
+    }
+
+    public Map<String, String> getCallbackHeaders() {
+      return callbackHeaders;
+    }
+
+    public Builder setRequestId(String requestId) {
+      this.requestId = requestId;
+      return this;
+    }
+
+    public Builder setInboundLinks(List<Link> inboundLinks) {
+      this.inboundLinks = inboundLinks;
+      return this;
+    }
+
+    public StartOperationOptions build() {
+      return new StartOperationOptions(
+          headers, callbackURL, callbackHeaders, requestId, inboundLinks);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/StartOperationResult.java b/nexus-sdk/src/main/java/io/nexusrpc/client/StartOperationResult.java
new file mode 100644
index 0000000..5a4a76e
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/StartOperationResult.java
@@ -0,0 +1,21 @@
+package io.nexusrpc.client;
+
+import io.nexusrpc.Link;
+import java.util.List;
+import org.jspecify.annotations.Nullable;
+
+// TODO this can also be an interface with two implementations: one for synchronous and one for
+// asynchronous operations.
+public class StartOperationResult<T> {
+  @Nullable T getResult() {
+    return null;
+  }
+
+  @Nullable OperationHandle<T> getPendingOperationHandle() {
+    return null;
+  }
+
+  List<Link> getLinks() {
+    return null;
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/CancelOperationOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/CancelOperationOptions.java
new file mode 100644
index 0000000..cd94779
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/CancelOperationOptions.java
@@ -0,0 +1,40 @@
+package io.nexusrpc.client.transport;
+
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class CancelOperationOptions {
+  /** Create a builder for CancelOperationOptions. */
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  private final SortedMap<String, String> headers;
+
+  private CancelOperationOptions(SortedMap<String, String> headers) {
+    this.headers = headers;
+  }
+
+  /** Headers. The returned map operates without regard to case. */
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+
+    private Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    /** Get headers to mutate. */
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    public CancelOperationOptions build() {
+      return new CancelOperationOptions(headers);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/CancelOperationResponse.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/CancelOperationResponse.java
new file mode 100644
index 0000000..c35a944
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/CancelOperationResponse.java
@@ -0,0 +1,3 @@
+package io.nexusrpc.client.transport;
+
+public class CancelOperationResponse {}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationInfoOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationInfoOptions.java
new file mode 100644
index 0000000..9837b10
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationInfoOptions.java
@@ -0,0 +1,40 @@
+package io.nexusrpc.client.transport;
+
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class GetOperationInfoOptions {
+  /** Create a builder for GetOperationInfoOptions. */
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  private final SortedMap<String, String> headers;
+
+  private GetOperationInfoOptions(SortedMap<String, String> headers) {
+    this.headers = headers;
+  }
+
+  /** Headers. The returned map operates without regard to case. */
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+
+    private Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    /** Get headers to mutate. */
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    public GetOperationInfoOptions build() {
+      return new GetOperationInfoOptions(headers);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationInfoResponse.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationInfoResponse.java
new file mode 100644
index 0000000..717ec23
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationInfoResponse.java
@@ -0,0 +1,35 @@
+package io.nexusrpc.client.transport;
+
+import io.nexusrpc.OperationInfo;
+
+public class GetOperationInfoResponse {
+  /** Create a builder for GetOperationInfoResponse. */
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  private final OperationInfo operationInfo;
+
+  private GetOperationInfoResponse(OperationInfo operationInfo) {
+    this.operationInfo = operationInfo;
+  }
+
+  public OperationInfo getOperationInfo() {
+    return operationInfo;
+  }
+
+  public static class Builder {
+    private OperationInfo operationInfo;
+
+    private Builder() {}
+
+    public Builder setOperationInfo(OperationInfo operationInfo) {
+      this.operationInfo = operationInfo;
+      return this;
+    }
+
+    public GetOperationInfoResponse build() {
+      return new GetOperationInfoResponse(operationInfo);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationResultOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationResultOptions.java
new file mode 100644
index 0000000..46bd70d
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationResultOptions.java
@@ -0,0 +1,59 @@
+package io.nexusrpc.client.transport;
+
+import java.time.Duration;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class GetOperationResultOptions {
+  /** Create a builder for GetOperationResultOptions. */
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  private final Duration timeout;
+  private final SortedMap<String, String> headers;
+
+  private GetOperationResultOptions(Duration timeout, SortedMap<String, String> headers) {
+    this.timeout = timeout;
+    this.headers = headers;
+  }
+
+  /** Headers. The returned map operates without regard to case. */
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public Duration getTimeout() {
+    return timeout;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+    private Duration timeout;
+
+    private Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    /** Get headers to mutate. */
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    /**
+     * Set the timeout for the operation.
+     *
+     * @param timeout the duration to wait for the operation result
+     * @return this builder instance
+     */
+    public Builder setTimeout(Duration timeout) {
+      this.timeout = timeout;
+      return this;
+    }
+
+    public GetOperationResultOptions build() {
+      return new GetOperationResultOptions(timeout, headers);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationResultResponse.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationResultResponse.java
new file mode 100644
index 0000000..77f3ce0
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/GetOperationResultResponse.java
@@ -0,0 +1,45 @@
+package io.nexusrpc.client.transport;
+
+import io.nexusrpc.Link;
+import java.util.List;
+
+public class GetOperationResultResponse {
+  public static GetOperationResultResponse.Builder newBuilder() {
+    return new GetOperationResultResponse.Builder();
+  }
+
+  private final Object result;
+  private final List<Link> links;
+
+  private GetOperationResultResponse(Object result, List<Link> links) {
+    this.result = result;
+    this.links = links;
+  }
+
+  public Object getResult() {
+    return result;
+  }
+
+  public List<Link> getLinks() {
+    return links;
+  }
+
+  public static class Builder {
+    private Object result;
+    private List<Link> links;
+
+    public GetOperationResultResponse.Builder setResult(Object result) {
+      this.result = result;
+      return this;
+    }
+
+    public GetOperationResultResponse.Builder setLinks(List<Link> links) {
+      this.links = links;
+      return this;
+    }
+
+    public GetOperationResultResponse build() {
+      return new GetOperationResultResponse(result, links);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/StartOperationOptions.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/StartOperationOptions.java
new file mode 100644
index 0000000..e177cc0
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/StartOperationOptions.java
@@ -0,0 +1,94 @@
+package io.nexusrpc.client.transport;
+
+import io.nexusrpc.Link;
+import java.util.List;
+import java.util.Map;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+public class StartOperationOptions {
+  /** Create a builder for StartOperationOptions. */
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  private final Map<String, String> headers;
+  private final String callbackURL;
+  private final Map<String, String> callbackHeaders;
+  private final String requestId;
+  private final List<Link> inboundLinks;
+
+  private StartOperationOptions(
+      Map<String, String> headers,
+      String callbackURL,
+      Map<String, String> callbackHeaders,
+      String requestId,
+      List<Link> inboundLinks) {
+    this.headers = headers;
+    this.callbackURL = callbackURL;
+    this.callbackHeaders = callbackHeaders;
+    this.requestId = requestId;
+    this.inboundLinks = inboundLinks;
+  }
+
+  public Map<String, String> getHeaders() {
+    return headers;
+  }
+
+  public String getCallbackURL() {
+    return callbackURL;
+  }
+
+  public Map<String, String> getCallbackHeaders() {
+    return callbackHeaders;
+  }
+
+  public String getRequestId() {
+    return requestId;
+  }
+
+  public List<Link> getInboundLinks() {
+    return inboundLinks;
+  }
+
+  public static class Builder {
+    private final SortedMap<String, String> headers;
+    private String callbackURL;
+    private SortedMap<String, String> callbackHeaders;
+    private String requestId;
+    private List<Link> inboundLinks;
+
+    public Builder() {
+      headers = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+      callbackHeaders = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
+    }
+
+    public Map<String, String> getHeaders() {
+      return headers;
+    }
+
+    public Builder setCallbackURL(String callbackURL) {
+      this.callbackURL = callbackURL;
+      return this;
+    }
+
+    public Map<String, String> getCallbackHeaders() {
+      return callbackHeaders;
+    }
+
+    public Builder setRequestId(String requestId) {
+      this.requestId = requestId;
+      return this;
+    }
+
+    public Builder setInboundLinks(List<Link> inboundLinks) {
+      this.inboundLinks = inboundLinks;
+      return this;
+    }
+
+    public StartOperationOptions build() {
+      return new StartOperationOptions(
+          headers, callbackURL, callbackHeaders, requestId, inboundLinks);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/StartOperationResponse.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/StartOperationResponse.java
new file mode 100644
index 0000000..634e553
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/StartOperationResponse.java
@@ -0,0 +1,57 @@
+package io.nexusrpc.client.transport;
+
+import io.nexusrpc.Link;
+import java.util.List;
+
+public class StartOperationResponse {
+  public static Builder newBuilder() {
+    return new Builder();
+  }
+
+  private final Object syncResult;
+  private final List<Link> links;
+  private final String asyncOperationToken;
+
+  private StartOperationResponse(Object syncResult, String asyncOperationToken, List<Link> links) {
+    this.syncResult = syncResult;
+    this.asyncOperationToken = asyncOperationToken;
+    this.links = links;
+  }
+
+  public Object getSyncResult() {
+    return syncResult;
+  }
+
+  public String getAsyncOperationToken() {
+    return asyncOperationToken;
+  }
+
+  public List<Link> getLinks() {
+    return links;
+  }
+
+  public static class Builder {
+    private Object syncResult;
+    private String asyncOperationToken;
+    private List<Link> links;
+
+    public Builder setResult(Object syncResult) {
+      this.syncResult = syncResult;
+      return this;
+    }
+
+    public Builder setAsyncOperationToken(String asyncOperationToken) {
+      this.asyncOperationToken = asyncOperationToken;
+      return this;
+    }
+
+    public Builder setLinks(List<Link> links) {
+      this.links = links;
+      return this;
+    }
+
+    public StartOperationResponse build() {
+      return new StartOperationResponse(syncResult, asyncOperationToken, links);
+    }
+  }
+}
diff --git a/nexus-sdk/src/main/java/io/nexusrpc/client/transport/Transport.java b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/Transport.java
new file mode 100644
index 0000000..1f245a6
--- /dev/null
+++ b/nexus-sdk/src/main/java/io/nexusrpc/client/transport/Transport.java
@@ -0,0 +1,50 @@
+package io.nexusrpc.client.transport;
+
+import java.util.concurrent.CompletableFuture;
+
+public interface Transport {
+  StartOperationResponse startOperation(
+      String operationName, String serviceName, StartOperationOptions options);
+
+  GetOperationResultResponse getOperationResult(
+      String operationName,
+      String serviceName,
+      String operationToken,
+      GetOperationResultOptions options);
+
+  GetOperationInfoResponse getOperationInfo(
+      String operationName,
+      String serviceName,
+      String operationToken,
+      GetOperationInfoOptions options);
+
+  CancelOperationResponse cancelOperation(
+      String operationName,
+      String serviceName,
+      String operationToken,
+      CancelOperationOptions options);
+
+  CompletableFuture<StartOperationResponse> startOperationAsync(
+      String operationName,
+      String serviceName,
+      String operationToken,
+      StartOperationOptions options);
+
+  CompletableFuture<GetOperationResultResponse> getOperationResultAsync(
+      String operationName,
+      String serviceName,
+      String operationToken,
+      GetOperationResultOptions options);
+
+  CompletableFuture<GetOperationInfoResponse> getOperationInfoAsync(
+      String operationName,
+      String serviceName,
+      String operationToken,
+      GetOperationInfoOptions options);
+
+  CompletableFuture<CancelOperationResponse> cancelOperationAsync(
+      String operationName,
+      String serviceName,
+      String operationToken,
+      CancelOperationOptions options);
+}