diff --git a/examples/EvalExample/Program.cs b/examples/EvalExample/Program.cs
index 225d4b9..41e12c3 100644
--- a/examples/EvalExample/Program.cs
+++ b/examples/EvalExample/Program.cs
@@ -1,6 +1,3 @@
-using System;
-using System.Linq;
-using Braintrust.Sdk;
 using Braintrust.Sdk.Eval;
 using Braintrust.Sdk.Instrumentation.OpenAI;
 using OpenAI;
@@ -10,7 +7,7 @@ namespace Braintrust.Sdk.Examples.EvalExample;
 
 class Program
 {
-    static void Main(string[] args)
+    static async Task Main(string[] args)
     {
         var openAIApiKey = Environment.GetEnvironmentVariable("OPENAI_API_KEY");
         if (string.IsNullOrEmpty(openAIApiKey))
@@ -44,7 +41,7 @@ string GetFoodType(string food)
         }
 
         // Create and run the evaluation
-        var eval = braintrust
+        var eval = await braintrust
             .EvalBuilder<string, string>()
             .Name($"dotnet-eval-x-{DateTimeOffset.UtcNow.ToUnixTimeMilliseconds()}")
             .Cases(
@@ -58,9 +55,9 @@ string GetFoodType(string food)
               Scorer<string, string>.Of("exact_match", (expected, actual) => expected == actual ? 1.0 : 0.0),
               Scorer<string, string>.Of("close_enough_match", (expected, actual) => expected.Trim().ToLowerInvariant() == actual.Trim().ToLowerInvariant() ? 1.0 : 0.0)
             )
-            .Build();
+            .BuildAsync();
 
-        var result = eval.Run();
+        var result = await eval.RunAsync();
         Console.WriteLine($"\n\n{result.CreateReportString()}");
     }
 }
diff --git a/examples/OpenAIInstrumentation/Program.cs b/examples/OpenAIInstrumentation/Program.cs
index b8646b0..b8ffb7b 100644
--- a/examples/OpenAIInstrumentation/Program.cs
+++ b/examples/OpenAIInstrumentation/Program.cs
@@ -31,7 +31,7 @@ static async Task Main(string[] args)
             if (rootActivity != null)
             {
                 await ChatCompletionsExample(instrumentedClient);
-                var url = braintrust.ProjectUri()
+                var url = await braintrust.GetProjectUriAsync()
                     + $"/logs?r={rootActivity.TraceId}&s={rootActivity.SpanId}";
                 Console.WriteLine($"\n\n  Example complete! View your data in Braintrust: {url}\n");
             }
diff --git a/examples/SimpleOpenTelemetry/Program.cs b/examples/SimpleOpenTelemetry/Program.cs
index d65c159..d968db0 100644
--- a/examples/SimpleOpenTelemetry/Program.cs
+++ b/examples/SimpleOpenTelemetry/Program.cs
@@ -1,12 +1,8 @@
-using System;
-using System.Threading;
-using Braintrust.Sdk;
-
 namespace Braintrust.Sdk.Examples.SimpleOpenTelemetry;
 
 class Program
 {
-    static void Main(string[] args)
+    static async Task Main(string[] args)
     {
         var braintrust = Braintrust.Get();
         var activitySource = braintrust.GetActivitySource();
@@ -17,7 +13,7 @@ static void Main(string[] args)
             ArgumentNullException.ThrowIfNull(activity);
             Console.WriteLine("Performing simple operation...");
             activity.SetTag("some boolean attribute", true);
-            url = braintrust.ProjectUri() + $"/logs?r={activity.TraceId}&s={activity.SpanId}";
+            url = await braintrust.GetProjectUriAsync() + $"/logs?r={activity.TraceId}&s={activity.SpanId}";
         }
         Console.WriteLine($"\n\n  Example complete! View your data in Braintrust: {url}");
     }
diff --git a/src/Braintrust.Sdk/Api/ApiException.cs b/src/Braintrust.Sdk/Api/ApiException.cs
new file mode 100644
index 0000000..6edd749
--- /dev/null
+++ b/src/Braintrust.Sdk/Api/ApiException.cs
@@ -0,0 +1,18 @@
+namespace Braintrust.Sdk.Api;
+
+/// <summary>
+/// Exception thrown when an API request fails.
+/// </summary>
+public class ApiException : Exception
+{
+    public int? StatusCode { get; }
+
+    public ApiException(string message) : base(message) { }
+
+    public ApiException(string message, Exception innerException) : base(message, innerException) { }
+
+    public ApiException(int statusCode, string message) : base(message)
+    {
+        StatusCode = statusCode;
+    }
+}
\ No newline at end of file
diff --git a/src/Braintrust.Sdk/Api/BraintrustApiClient.cs b/src/Braintrust.Sdk/Api/BraintrustApiClient.cs
index 5cbe3fe..8931e07 100644
--- a/src/Braintrust.Sdk/Api/BraintrustApiClient.cs
+++ b/src/Braintrust.Sdk/Api/BraintrustApiClient.cs
@@ -1,34 +1,11 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Net.Http.Json;
 using System.Text.Json;
 using System.Text.Json.Serialization;
-using System.Threading;
-using System.Threading.Tasks;
 using Braintrust.Sdk.Config;
 
 namespace Braintrust.Sdk.Api;
 
-/// <summary>
-/// Exception thrown when an API request fails.
-/// </summary>
-public class ApiException : Exception
-{
-    public int? StatusCode { get; }
-
-    public ApiException(string message) : base(message) { }
-
-    public ApiException(string message, Exception innerException) : base(message, innerException) { }
-
-    public ApiException(int statusCode, string message) : base(message)
-    {
-        StatusCode = statusCode;
-    }
-}
-
 /// <summary>
 /// Implementation of Braintrust API client.
 /// </summary>
@@ -64,12 +41,11 @@ internal BraintrustApiClient(BraintrustConfig config, HttpClient? httpClient = n
 
     private static HttpClient CreateDefaultHttpClient(BraintrustConfig config)
     {
-        var client = new HttpClient
+        return new HttpClient
         {
             BaseAddress = new Uri(config.ApiUrl),
             Timeout = config.RequestTimeout
         };
-        return client;
     }
 
     private static JsonSerializerOptions CreateJsonOptions()
@@ -82,19 +58,17 @@ private static JsonSerializerOptions CreateJsonOptions()
         };
     }
 
-    public Project GetOrCreateProject(string projectName)
+    public async Task<Project> GetOrCreateProject(string projectName)
     {
         var request = new CreateProjectRequest(projectName);
-        return PostAsync<CreateProjectRequest, Project>("/v1/project", request, default)
-            .ConfigureAwait(false).GetAwaiter().GetResult();
+        return await PostAsync<CreateProjectRequest, Project>("/v1/project", request).ConfigureAwait(false);
     }
 
-    public Project? GetProject(string projectId)
+    public async Task<Project?> GetProject(string projectId)
     {
         try
         {
-            return GetAsync<Project>($"/v1/project/{projectId}", default)
-                .ConfigureAwait(false).GetAwaiter().GetResult();
+            return await GetAsync<Project>($"/v1/project/{projectId}").ConfigureAwait(false);
         }
         catch (ApiException ex) when (ex.StatusCode == 404)
         {
@@ -102,37 +76,37 @@ public Project GetOrCreateProject(string projectName)
         }
     }
 
-    public Experiment GetOrCreateExperiment(CreateExperimentRequest request)
+    public async Task<Experiment> GetOrCreateExperiment(CreateExperimentRequest request)
     {
-        return PostAsync<CreateExperimentRequest, Experiment>("/v1/experiment", request, default)
-            .ConfigureAwait(false).GetAwaiter().GetResult();
+        return await PostAsync<CreateExperimentRequest, Experiment>("/v1/experiment", request)
+            .ConfigureAwait(false);
     }
 
-    public OrganizationAndProjectInfo? GetProjectAndOrgInfo()
+    public async Task<OrganizationAndProjectInfo?> GetProjectAndOrgInfo()
     {
         if (_config.DefaultProjectId != null)
         {
-            return GetProjectAndOrgInfo(_config.DefaultProjectId);
+            return await GetProjectAndOrgInfo(_config.DefaultProjectId).ConfigureAwait(false);
         }
 
         if (_config.DefaultProjectName != null)
         {
-            var project = GetOrCreateProject(_config.DefaultProjectName);
-            return GetProjectAndOrgInfo(project.Id);
+            var project = await GetOrCreateProject(_config.DefaultProjectName).ConfigureAwait(false);
+            return await GetProjectAndOrgInfo(project.Id).ConfigureAwait(false);
         }
 
         return null;
     }
 
-    public OrganizationAndProjectInfo? GetProjectAndOrgInfo(string projectId)
+    public async Task<OrganizationAndProjectInfo?> GetProjectAndOrgInfo(string projectId)
     {
-        var project = GetProject(projectId);
+        var project = await GetProject(projectId).ConfigureAwait(false);
         if (project == null)
         {
             return null;
         }
 
-        var loginResponse = Login();
+        var loginResponse = await Login().ConfigureAwait(false);
         var orgInfo = loginResponse.OrgInfo.FirstOrDefault(org =>
             string.Equals(org.Id, project.OrgId, StringComparison.OrdinalIgnoreCase));
 
@@ -144,13 +118,13 @@ public Experiment GetOrCreateExperiment(CreateExperimentRequest request)
         return new OrganizationAndProjectInfo(orgInfo, project);
     }
 
-    public OrganizationAndProjectInfo GetOrCreateProjectAndOrgInfo()
+    public async Task<OrganizationAndProjectInfo> GetOrCreateProjectAndOrgInfo()
     {
         Project project;
 
         if (_config.DefaultProjectId != null)
         {
-            var existingProject = GetProject(_config.DefaultProjectId);
+            var existingProject = await GetProject(_config.DefaultProjectId).ConfigureAwait(false);
             if (existingProject == null)
             {
                 throw new ApiException($"Project with ID {_config.DefaultProjectId} not found");
@@ -159,14 +133,14 @@ public OrganizationAndProjectInfo GetOrCreateProjectAndOrgInfo()
         }
         else if (_config.DefaultProjectName != null)
         {
-            project = GetOrCreateProject(_config.DefaultProjectName);
+            project = await GetOrCreateProject(_config.DefaultProjectName).ConfigureAwait(false);
         }
         else
         {
             throw new InvalidOperationException("Either DefaultProjectId or DefaultProjectName must be set in config");
         }
 
-        var loginResponse = Login();
+        var loginResponse = await Login().ConfigureAwait(false);
         var orgInfo = loginResponse.OrgInfo.FirstOrDefault(org =>
             string.Equals(org.Id, project.OrgId, StringComparison.OrdinalIgnoreCase));
 
@@ -178,11 +152,11 @@ public OrganizationAndProjectInfo GetOrCreateProjectAndOrgInfo()
         return new OrganizationAndProjectInfo(orgInfo, project);
     }
 
-    private LoginResponse Login()
+    private async Task<LoginResponse> Login()
     {
         var request = new LoginRequest(_config.ApiKey);
-        return PostAsync<LoginRequest, LoginResponse>("/api/apikey/login", request, default)
-            .ConfigureAwait(false).GetAwaiter().GetResult();
+        return await PostAsync<LoginRequest, LoginResponse>("/api/apikey/login", request)
+            .ConfigureAwait(false);
     }
 
     private async Task<TResponse> GetAsync<TResponse>(string path, CancellationToken cancellationToken = default)
@@ -191,8 +165,8 @@ private async Task<TResponse> GetAsync<TResponse>(string path, CancellationToken
         request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", _config.ApiKey);
         request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
 
-        using var response = await _httpClient.SendAsync(request, cancellationToken);
-        return await HandleResponseAsync<TResponse>(response, cancellationToken);
+        using var response = await _httpClient.SendAsync(request, cancellationToken).ConfigureAwait(false);
+        return await HandleResponseAsync<TResponse>(response, cancellationToken).ConfigureAwait(false);
     }
 
     private async Task<TResponse> PostAsync<TRequest, TResponse>(
@@ -205,15 +179,15 @@ private async Task<TResponse> PostAsync<TRequest, TResponse>(
         request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
         request.Content = JsonContent.Create(body, options: _jsonOptions);
 
-        using var response = await _httpClient.SendAsync(request, cancellationToken);
-        return await HandleResponseAsync<TResponse>(response, cancellationToken);
+        using var response = await _httpClient.SendAsync(request, cancellationToken).ConfigureAwait(false);
+        return await HandleResponseAsync<TResponse>(response, cancellationToken).ConfigureAwait(false);
     }
 
     private async Task<T> HandleResponseAsync<T>(HttpResponseMessage response, CancellationToken cancellationToken)
     {
         if (response.IsSuccessStatusCode)
         {
-            var content = await response.Content.ReadAsStringAsync(cancellationToken);
+            var content = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
             var result = JsonSerializer.Deserialize<T>(content, _jsonOptions);
 
             if (result == null)
@@ -225,7 +199,7 @@ private async Task<T> HandleResponseAsync<T>(HttpResponseMessage response, Cance
         }
         else
         {
-            var content = await response.Content.ReadAsStringAsync(cancellationToken);
+            var content = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
             throw new ApiException(
                 (int)response.StatusCode,
                 $"API request failed with status {(int)response.StatusCode}: {content}");
@@ -236,7 +210,7 @@ public void Dispose()
     {
         if (_ownsHttpClient)
         {
-            _httpClient?.Dispose();
+            _httpClient.Dispose();
         }
     }
 }
diff --git a/src/Braintrust.Sdk/Api/IBraintrustApiClient.cs b/src/Braintrust.Sdk/Api/IBraintrustApiClient.cs
index d6f7eec..bb603f2 100644
--- a/src/Braintrust.Sdk/Api/IBraintrustApiClient.cs
+++ b/src/Braintrust.Sdk/Api/IBraintrustApiClient.cs
@@ -8,30 +8,30 @@ public interface IBraintrustApiClient
     /// <summary>
     /// Get or create a project by name.
     /// </summary>
-    Project GetOrCreateProject(string projectName);
+    Task<Project> GetOrCreateProject(string projectName);
 
     /// <summary>
     /// Get a project by ID.
     /// </summary>
-    Project? GetProject(string projectId);
+    Task<Project?> GetProject(string projectId);
 
     /// <summary>
     /// Get or create an experiment.
     /// </summary>
-    Experiment GetOrCreateExperiment(CreateExperimentRequest request);
+    Task<Experiment> GetOrCreateExperiment(CreateExperimentRequest request);
 
     /// <summary>
     /// Get project and organization information using the default project from config.
     /// </summary>
-    OrganizationAndProjectInfo? GetProjectAndOrgInfo();
+    Task<OrganizationAndProjectInfo?> GetProjectAndOrgInfo();
 
     /// <summary>
     /// Get project and organization information for a specific project ID.
     /// </summary>
-    OrganizationAndProjectInfo? GetProjectAndOrgInfo(string projectId);
+    Task<OrganizationAndProjectInfo?> GetProjectAndOrgInfo(string projectId);
 
     /// <summary>
     /// Get or create project and organization information from config.
     /// </summary>
-    OrganizationAndProjectInfo GetOrCreateProjectAndOrgInfo();
+    Task<OrganizationAndProjectInfo> GetOrCreateProjectAndOrgInfo();
 }
diff --git a/src/Braintrust.Sdk/Braintrust.cs b/src/Braintrust.Sdk/Braintrust.cs
index 4920130..69dfde9 100644
--- a/src/Braintrust.Sdk/Braintrust.cs
+++ b/src/Braintrust.Sdk/Braintrust.cs
@@ -1,5 +1,3 @@
-using System;
-using System.Threading;
 using Braintrust.Sdk.Api;
 using Braintrust.Sdk.Config;
 using Microsoft.Extensions.Logging;
@@ -100,16 +98,16 @@ private Braintrust(BraintrustConfig config, IBraintrustApiClient apiClient, Bool
         ApiClient = apiClient ?? throw new ArgumentNullException(nameof(apiClient));
         if (autoManageOpenTelemetry)
         {
-            this._tracer = Trace.BraintrustTracing.CreateTracerProvider(this.Config);
+            _tracer = Trace.BraintrustTracing.CreateTracerProvider(this.Config);
         }
     }
 
     /// <summary>
     /// Get the URI to the configured Braintrust org and project.
     /// </summary>
-    public Uri ProjectUri()
+    public async Task<Uri> GetProjectUriAsync()
     {
-        var orgAndProject = ApiClient.GetOrCreateProjectAndOrgInfo();
+        var orgAndProject = await ApiClient.GetOrCreateProjectAndOrgInfo().ConfigureAwait(false);
         return new Uri($"{Config.AppUrl}/app/{orgAndProject.OrgInfo.Name}/p/{orgAndProject.Project.Name}");
     }
 
@@ -122,9 +120,9 @@ public Uri ProjectUri()
     /// </summary>
     public void OpenTelemetryEnable(OpenTelemetry.Trace.TracerProviderBuilder tracerProviderBuilder, ILoggingBuilder loggingBuilder, MeterProviderBuilder meterProviderBuilder)
     {
-        if (this._tracer != null)
+        if (_tracer != null)
         {
-            throw new System.InvalidOperationException("cannot call enable for Braintrusts which autoManage Open Telemetry");
+            throw new InvalidOperationException("cannot call enable for Braintrusts which autoManage Open Telemetry");
         }
         Trace.BraintrustTracing.Enable(Config, tracerProviderBuilder, loggingBuilder, meterProviderBuilder);
     }
diff --git a/src/Braintrust.Sdk/Eval/Eval.cs b/src/Braintrust.Sdk/Eval/Eval.cs
index e65cb31..6b7335a 100644
--- a/src/Braintrust.Sdk/Eval/Eval.cs
+++ b/src/Braintrust.Sdk/Eval/Eval.cs
@@ -1,7 +1,4 @@
-using System;
-using System.Collections.Generic;
 using System.Diagnostics;
-using System.Linq;
 using System.Text.Json;
 using Braintrust.Sdk.Api;
 using Braintrust.Sdk.Config;
@@ -33,22 +30,12 @@ public sealed class Eval<TInput, TOutput>
     private readonly Task<TInput, TOutput> _task;
     private readonly IReadOnlyList<Scorer<TInput, TOutput>> _scorers;
 
-    private Eval(Builder builder)
+    private Eval(Builder builder, OrganizationAndProjectInfo orgAndProject)
     {
         _experimentName = builder._experimentName;
         _config = builder._config ?? throw new ArgumentNullException(nameof(builder._config));
         _client = builder._apiClient ?? throw new ArgumentNullException(nameof(builder._apiClient));
-
-        if (builder._projectId == null)
-        {
-            _orgAndProject = _client.GetProjectAndOrgInfo()
-                ?? throw new InvalidOperationException("Unable to retrieve project and org info");
-        }
-        else
-        {
-            _orgAndProject = _client.GetProjectAndOrgInfo(builder._projectId)
-                ?? throw new InvalidOperationException($"Invalid project id: {builder._projectId}");
-        }
+        _orgAndProject = orgAndProject ?? throw new ArgumentNullException(nameof(orgAndProject));
 
         _activitySource = builder._activitySource ?? throw new ArgumentNullException(nameof(builder._activitySource));
         _dataset = builder._dataset ?? throw new ArgumentNullException(nameof(builder._dataset));
@@ -59,14 +46,13 @@ private Eval(Builder builder)
     /// <summary>
     /// Runs the evaluation and returns results.
     /// </summary>
-    public EvalResult Run()
+    public async Task<EvalResult> RunAsync()
     {
-        var experiment = _client.GetOrCreateExperiment(
+        var experiment = await _client.GetOrCreateExperiment(
             new CreateExperimentRequest(
                 _orgAndProject.Project.Id,
-                _experimentName,
-                null,
-                null));
+                _experimentName))
+            .ConfigureAwait(false);
 
         var experimentId = experiment.Id;
 
@@ -212,7 +198,7 @@ public sealed class Builder
         /// <summary>
         /// Build the Eval instance.
         /// </summary>
-        public Eval<TInput, TOutput> Build()
+        public async Task<Eval<TInput, TOutput>> BuildAsync()
         {
             _config ??= BraintrustConfig.FromEnvironment();
             _activitySource ??= BraintrustTracing.GetActivitySource();
@@ -234,7 +220,13 @@ public Eval<TInput, TOutput> Build()
                 throw new InvalidOperationException("Must provide a task");
             }
 
-            return new Eval<TInput, TOutput>(this);
+            OrganizationAndProjectInfo? orgAndProject =
+                _projectId == null
+                    ? await _apiClient.GetProjectAndOrgInfo().ConfigureAwait(false)
+                        ?? throw new InvalidOperationException("Unable to retrieve project and org info")
+                    : await _apiClient.GetProjectAndOrgInfo(_projectId).ConfigureAwait(false)
+                        ?? throw new InvalidOperationException($"Invalid project id: {_projectId}");
+            return new Eval<TInput, TOutput>(this, orgAndProject);
         }
 
         /// <summary>
diff --git a/tests/Braintrust.Sdk.Tests/Api/BraintrustApiClientTest.cs b/tests/Braintrust.Sdk.Tests/Api/BraintrustApiClientTest.cs
index 620cc0a..13209d4 100644
--- a/tests/Braintrust.Sdk.Tests/Api/BraintrustApiClientTest.cs
+++ b/tests/Braintrust.Sdk.Tests/Api/BraintrustApiClientTest.cs
@@ -1,13 +1,8 @@
-using System;
 using System.Net;
-using System.Net.Http;
 using System.Text;
 using System.Text.Json;
-using System.Threading;
-using System.Threading.Tasks;
 using Braintrust.Sdk.Api;
 using Braintrust.Sdk.Config;
-using Xunit;
 
 namespace Braintrust.Sdk.Tests.Api;
 
@@ -15,7 +10,6 @@ public class BraintrustApiClientTest : IDisposable
 {
     private readonly TestHttpMessageHandler _handler;
     private readonly HttpClient _httpClient;
-    private readonly BraintrustConfig _config;
     private readonly BraintrustApiClient _apiClient;
 
     public BraintrustApiClientTest()
@@ -26,29 +20,29 @@ public BraintrustApiClientTest()
             BaseAddress = new Uri("https://test-api.example.com")
         };
 
-        _config = BraintrustConfig.Of(
+        var config = BraintrustConfig.Of(
             "BRAINTRUST_API_KEY", "test-api-key",
             "BRAINTRUST_API_URL", "https://test-api.example.com",
             "BRAINTRUST_DEFAULT_PROJECT_NAME", "test-project"
         );
 
-        _apiClient = new BraintrustApiClient(_config, _httpClient);
+        _apiClient = new BraintrustApiClient(config, _httpClient);
     }
 
     public void Dispose()
     {
-        _apiClient?.Dispose();
-        _httpClient?.Dispose();
-        _handler?.Dispose();
+        _apiClient.Dispose();
+        _httpClient.Dispose();
+        _handler.Dispose();
     }
 
     [Fact]
-    public void GetOrCreateProject_CreatesProject()
+    public async Task GetOrCreateProject_CreatesProject()
     {
         var expectedProject = new Project("proj-123", "test-project", "org-456");
         _handler.SetResponse(HttpStatusCode.OK, expectedProject);
 
-        var result = _apiClient.GetOrCreateProject("test-project");
+        var result = await _apiClient.GetOrCreateProject("test-project");
 
         Assert.NotNull(result);
         Assert.Equal("proj-123", result.Id);
@@ -62,37 +56,37 @@ public void GetOrCreateProject_CreatesProject()
     }
 
     [Fact]
-    public void GetProject_ReturnsProject()
+    public async Task GetProject_ReturnsProject()
     {
         var expectedProject = new Project("proj-123", "test-project", "org-456");
         _handler.SetResponse(HttpStatusCode.OK, expectedProject);
 
-        var result = _apiClient.GetProject("proj-123");
+        var result = await _apiClient.GetProject("proj-123");
 
         Assert.NotNull(result);
-        Assert.Equal("proj-123", result!.Id);
+        Assert.Equal("proj-123", result.Id);
         Assert.Equal(HttpMethod.Get, _handler.LastRequest?.Method);
         Assert.Equal("/v1/project/proj-123", _handler.LastRequest?.RequestUri?.AbsolutePath);
     }
 
     [Fact]
-    public void GetProject_ReturnsNull_When404()
+    public async Task GetProject_ReturnsNull_When404()
     {
         _handler.SetResponse(HttpStatusCode.NotFound, "Not found");
 
-        var result = _apiClient.GetProject("missing-project");
+        var result = await _apiClient.GetProject("missing-project");
 
         Assert.Null(result);
     }
 
     [Fact]
-    public void GetOrCreateExperiment_CreatesExperiment()
+    public async Task GetOrCreateExperiment_CreatesExperiment()
     {
         var expectedExperiment = new Experiment("exp-123", "proj-456", "test-experiment");
         _handler.SetResponse(HttpStatusCode.OK, expectedExperiment);
 
         var request = new CreateExperimentRequest("proj-456", "test-experiment", "Test description");
-        var result = _apiClient.GetOrCreateExperiment(request);
+        var result = await _apiClient.GetOrCreateExperiment(request);
 
         Assert.NotNull(result);
         Assert.Equal("exp-123", result.Id);
@@ -103,21 +97,18 @@ public void GetOrCreateExperiment_CreatesExperiment()
     }
 
     [Fact]
-    public void GetOrCreateProjectAndOrgInfo_ReturnsInfo()
+    public async Task GetOrCreateProjectAndOrgInfo_ReturnsInfo()
     {
         // Setup: First call creates/gets project, second call is login
         var project = new Project("proj-123", "test-project", "org-456");
-        var loginResponse = new LoginResponse(new System.Collections.Generic.List<OrganizationInfo>
-        {
-            new OrganizationInfo("org-456", "Test Org")
-        });
+        var loginResponse = new LoginResponse([new OrganizationInfo("org-456", "Test Org")]);
 
         _handler.SetResponses(
             (HttpStatusCode.OK, project),
             (HttpStatusCode.OK, loginResponse)
         );
 
-        var result = _apiClient.GetOrCreateProjectAndOrgInfo();
+        var result = await _apiClient.GetOrCreateProjectAndOrgInfo();
 
         Assert.NotNull(result);
         Assert.Equal("proj-123", result.Project.Id);
@@ -126,11 +117,11 @@ public void GetOrCreateProjectAndOrgInfo_ReturnsInfo()
     }
 
     [Fact]
-    public void ApiException_ThrownOn_HttpError()
+    public async Task ApiException_ThrownOn_HttpError()
     {
         _handler.SetResponse(HttpStatusCode.BadRequest, "Bad request");
 
-        var exception = Assert.Throws<ApiException>(() =>
+        var exception = await Assert.ThrowsAsync<ApiException>(() =>
             _apiClient.GetProject("test"));
 
         Assert.Equal(400, exception.StatusCode);
diff --git a/tests/Braintrust.Sdk.Tests/Eval/EvalTest.cs b/tests/Braintrust.Sdk.Tests/Eval/EvalTest.cs
index a2fec6e..9ff95b2 100644
--- a/tests/Braintrust.Sdk.Tests/Eval/EvalTest.cs
+++ b/tests/Braintrust.Sdk.Tests/Eval/EvalTest.cs
@@ -1,10 +1,6 @@
-using System;
 using System.Diagnostics;
-using System.Linq;
-using Braintrust.Sdk.Api;
 using Braintrust.Sdk.Config;
 using Braintrust.Sdk.Eval;
-using Xunit;
 
 namespace Braintrust.Sdk.Tests.Eval;
 
@@ -33,7 +29,7 @@ public void Dispose()
     }
 
     [Fact]
-    public void BasicEvalBuildsAndRuns()
+    public async Task BasicEvalBuildsAndRuns()
     {
         // Arrange
         var config = BraintrustConfig.Of(
@@ -52,7 +48,7 @@ public void BasicEvalBuildsAndRuns()
         };
 
         // Act
-        var eval = Eval<string, string>.NewBuilder()
+        var eval = await Eval<string, string>.NewBuilder()
             .Name("test-eval")
             .Config(config)
             .ApiClient(mockClient)
@@ -62,9 +58,9 @@ public void BasicEvalBuildsAndRuns()
                 Scorer<string, string>.Of("fruit_scorer", (expected, actual) => expected == "fruit" && actual == "fruit" ? 1.0 : 0.0),
                 Scorer<string, string>.Of("vegetable_scorer", (expected, actual) => expected == "vegetable" && actual == "vegetable" ? 1.0 : 0.0)
             )
-            .Build();
+            .BuildAsync();
 
-        var result = eval.Run();
+        var result = await eval.RunAsync();
 
         // Assert
         Assert.NotNull(result);
@@ -74,51 +70,51 @@ public void BasicEvalBuildsAndRuns()
     }
 
     [Fact]
-    public void EvalRequiresAtLeastOneScorer()
+    public async Task EvalRequiresAtLeastOneScorer()
     {
         var config = BraintrustConfig.Of("BRAINTRUST_API_KEY", "test-key");
         var mockClient = new MockBraintrustApiClient();
 
-        Assert.Throws<InvalidOperationException>(() =>
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
             Eval<string, string>.NewBuilder()
                 .Name("test-eval")
                 .Config(config)
                 .ApiClient(mockClient)
                 .Cases(DatasetCase<string, string>.Of("input", "expected"))
                 .TaskFunction(x => x)
-                .Build());
+                .BuildAsync());
     }
 
     [Fact]
-    public void EvalRequiresDataset()
+    public async Task EvalRequiresDataset()
     {
         var config = BraintrustConfig.Of("BRAINTRUST_API_KEY", "test-key");
         var mockClient = new MockBraintrustApiClient();
 
-        Assert.Throws<InvalidOperationException>(() =>
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
             Eval<string, string>.NewBuilder()
                 .Name("test-eval")
                 .Config(config)
                 .ApiClient(mockClient)
                 .TaskFunction(x => x)
                 .Scorers(Scorer<string, string>.Of("test", (_, _) => 1.0))
-                .Build());
+                .BuildAsync());
     }
 
     [Fact]
-    public void EvalRequiresTask()
+    public async Task EvalRequiresTask()
     {
         var config = BraintrustConfig.Of("BRAINTRUST_API_KEY", "test-key");
         var mockClient = new MockBraintrustApiClient();
 
-        Assert.Throws<InvalidOperationException>(() =>
+        await Assert.ThrowsAsync<InvalidOperationException>(() =>
             Eval<string, string>.NewBuilder()
                 .Name("test-eval")
                 .Config(config)
                 .ApiClient(mockClient)
                 .Cases(DatasetCase<string, string>.Of("input", "expected"))
                 .Scorers(Scorer<string, string>.Of("test", (_, _) => 1.0))
-                .Build());
+                .BuildAsync());
     }
 
     [Fact]
@@ -171,43 +167,4 @@ public void DatasetOfCreatesInMemoryDataset()
         Assert.Equal("input2", case2.Input);
         Assert.Null(case3);
     }
-}
-
-/// <summary>
-/// Mock API client for testing that doesn't make real HTTP calls.
-/// </summary>
-internal class MockBraintrustApiClient : IBraintrustApiClient
-{
-    private readonly OrganizationInfo _orgInfo = new OrganizationInfo("test-org-id", "test-org");
-    private readonly Project _project = new Project("test-project-id", "test-project", "test-org-id", null, null);
-
-    public Project GetOrCreateProject(string projectName)
-    {
-        return _project;
-    }
-
-    public Project? GetProject(string projectId)
-    {
-        return _project;
-    }
-
-    public Experiment GetOrCreateExperiment(CreateExperimentRequest request)
-    {
-        return new Experiment("test-experiment-id", request.ProjectId, request.Name, request.Description, null, null);
-    }
-
-    public OrganizationAndProjectInfo? GetProjectAndOrgInfo()
-    {
-        return new OrganizationAndProjectInfo(_orgInfo, _project);
-    }
-
-    public OrganizationAndProjectInfo? GetProjectAndOrgInfo(string projectId)
-    {
-        return new OrganizationAndProjectInfo(_orgInfo, _project);
-    }
-
-    public OrganizationAndProjectInfo GetOrCreateProjectAndOrgInfo()
-    {
-        return new OrganizationAndProjectInfo(_orgInfo, _project);
-    }
-}
+}
\ No newline at end of file
diff --git a/tests/Braintrust.Sdk.Tests/Eval/MockBraintrustApiClient.cs b/tests/Braintrust.Sdk.Tests/Eval/MockBraintrustApiClient.cs
new file mode 100644
index 0000000..75ff5cf
--- /dev/null
+++ b/tests/Braintrust.Sdk.Tests/Eval/MockBraintrustApiClient.cs
@@ -0,0 +1,42 @@
+using Braintrust.Sdk.Api;
+
+namespace Braintrust.Sdk.Tests.Eval;
+
+/// <summary>
+/// Mock API client for testing that doesn't make real HTTP calls.
+/// </summary>
+internal class MockBraintrustApiClient : IBraintrustApiClient
+{
+    private readonly OrganizationInfo _orgInfo = new OrganizationInfo("test-org-id", "test-org");
+    private readonly Project _project = new Project("test-project-id", "test-project", "test-org-id");
+
+    public Task<Project> GetOrCreateProject(string projectName)
+    {
+        return Task.FromResult(_project);
+    }
+
+    public Task<Project?> GetProject(string projectId)
+    {
+        return Task.FromResult<Project?>(_project);
+    }
+
+    public Task<Experiment> GetOrCreateExperiment(CreateExperimentRequest request)
+    {
+        return Task.FromResult(new Experiment("test-experiment-id", request.ProjectId, request.Name, request.Description));
+    }
+
+    public Task<OrganizationAndProjectInfo?> GetProjectAndOrgInfo()
+    {
+        return Task.FromResult<OrganizationAndProjectInfo?>(new OrganizationAndProjectInfo(_orgInfo, _project));
+    }
+
+    public Task<OrganizationAndProjectInfo?> GetProjectAndOrgInfo(string projectId)
+    {
+        return Task.FromResult<OrganizationAndProjectInfo?>(new OrganizationAndProjectInfo(_orgInfo, _project));
+    }
+
+    public Task<OrganizationAndProjectInfo> GetOrCreateProjectAndOrgInfo()
+    {
+        return Task.FromResult(new OrganizationAndProjectInfo(_orgInfo, _project));
+    }
+}
\ No newline at end of file