Create experiment arms

Page Summary

Experiment arms are essential components for testing and comparing different campaign strategies within an experiment, with each experiment requiring exactly one control arm based on an existing campaign.
The traffic_split setting in each experiment arm determines the percentage of traffic directed to that arm, and the sum of all traffic splits across all arms must equal 100.
Currently, there is a limit of one treatment arm per experiment, and all experiment arms must be created simultaneously in a single request without using partial failure.
Treatment arms automatically generate in-design campaigns that can be modified to test changes, and these changes must be applied before scheduling the experiment.

Once you've created an experiment, you need to create multiple experiment arms in order to give the experiment more information about what exactly you're testing.

Experiment arms

The ExperimentArm represents one part of the comparison you're performing for the experiment. All experiments must always have exactly one control arm. This arm is an existing campaign that forms the basis against which you compare the other arm.

The other arms are called treatment arms, and in these arms you make changes to the campaign before beginning the experiment.

The ExperimentArm also contains the traffic_split setting. This lets you specify the percentage of traffic that is directed to each arm of the experiment. Each arm must specify a traffic split, and the sum of traffic split values in all arms must add up to 100.

Because of this traffic split restriction, all experiment arms must be created in the same request.

Code example

Java

private String createExperimentArms(
    GoogleAdsClient googleAdsClient, long customerId, long campaignId, String experiment) {
  List<ExperimentArmOperation> operations = new ArrayList<>();
  operations.add(
      ExperimentArmOperation.newBuilder()
          .setCreate(
              // The "control" arm references an already-existing campaign.
              ExperimentArm.newBuilder()
                  .setControl(true)
                  .addCampaigns(ResourceNames.campaign(customerId, campaignId))
                  .setExperiment(experiment)
                  .setName("control arm")
                  .setTrafficSplit(40)
                  .build())
          .build());
  operations.add(
      ExperimentArmOperation.newBuilder()
          .setCreate(
              // The non-"control" arm, also called a "treatment" arm, will automatically
              // generate draft campaigns that you can modify before starting the experiment.
              ExperimentArm.newBuilder()
                  .setControl(false)
                  .setExperiment(experiment)
                  .setName("experiment arm")
                  .setTrafficSplit(60)
                  .build())
          .build());

  try (ExperimentArmServiceClient experimentArmServiceClient =
      googleAdsClient.getLatestVersion().createExperimentArmServiceClient()) {
    // Constructs the mutate request.
    MutateExperimentArmsRequest mutateRequest = MutateExperimentArmsRequest.newBuilder()
        .setCustomerId(Long.toString(customerId))
        .addAllOperations(operations)
        // We want to fetch the draft campaign IDs from the treatment arm, so the easiest way to do
        // that is to have the response return the newly created entities.
        .setResponseContentType(ResponseContentType.MUTABLE_RESOURCE)
        .build();

    // Sends the mutate request.
    MutateExperimentArmsResponse response =
        experimentArmServiceClient.mutateExperimentArms(mutateRequest);

    // Results always return in the order that you specify them in the request. Since we created
    // the treatment arm last, it will be the last result.  If you don't remember which arm is the
    // treatment arm, you can always filter the query in the next section with
    // `experiment_arm.control = false`.
    MutateExperimentArmResult controlArmResult = response.getResults(0);
    MutateExperimentArmResult treatmentArmResult = response.getResults(
        response.getResultsCount() - 1);

    System.out.printf("Created control arm with resource name '%s'%n",
        controlArmResult.getResourceName());
    System.out.printf("Created treatment arm with resource name '%s'%n",
        treatmentArmResult.getResourceName());

    return treatmentArmResult.getExperimentArm().getInDesignCampaigns(0);
  }
}CreateExperiment.java

C#

/// <summary>
/// Creates the experiment arms.
/// </summary>
/// <param name="client">The Google Ads client.</param>
/// <param name="customerId">The customer ID for which the call is made.</param>
/// <param name="baseCampaignId">ID of the campaign for which the control arm is
/// created.</param>
/// <param name="experimentResourceName">Resource name of the experiment.</param>
/// <returns>The control and treatment arms.</returns>
private static (MutateExperimentArmResult, MutateExperimentArmResult)
    CreateExperimentArms(GoogleAdsClient client, long customerId, long baseCampaignId,
        string experimentResourceName)
{
    // Get the ExperimentArmService.
    ExperimentArmServiceClient experimentService = client.GetService(
        Services.V22.ExperimentArmService);

    // Create the control arm. The control arm references an already-existing campaign.
    ExperimentArmOperation controlArmOperation = new ExperimentArmOperation()
    {
        Create = new ExperimentArm()
        {
            Control = true,
            Campaigns = {
                ResourceNames.Campaign(customerId, baseCampaignId)
            },
            Experiment = experimentResourceName,
            Name = "Control Arm",
            TrafficSplit = 40
        }
    };

    // Create the non-control arm. The non-"control" arm, also called a "treatment" arm,
    // will automatically generate draft campaigns that you can modify before starting the
    // experiment.
    ExperimentArmOperation treatmentArmOperation = new ExperimentArmOperation()
    {
        Create = new ExperimentArm()
        {
            Control = false,
            Experiment = experimentResourceName,
            Name = "Experiment Arm",
            TrafficSplit = 60
        }
    };

    // We want to fetch the draft campaign IDs from the treatment arm, so the
    // easiest way to do that is to have the response return the newly created
    // entities.
    MutateExperimentArmsRequest request = new MutateExperimentArmsRequest
    {
        CustomerId = customerId.ToString(),
        Operations = { controlArmOperation, treatmentArmOperation },
        ResponseContentType = ResponseContentType.MutableResource
    };


    MutateExperimentArmsResponse response = experimentService.MutateExperimentArms(
        request
    );

    // Results always return in the order that you specify them in the request.
    // Since we created the treatment arm last, it will be the last result.
    MutateExperimentArmResult controlArm = response.Results.First();
    MutateExperimentArmResult treatmentArm = response.Results.Last();

    Console.WriteLine($"Created control arm with resource name " +
        $"'{controlArm.ResourceName}.");
    Console.WriteLine($"Created treatment arm with resource name" +
      $" '{treatmentArm.ResourceName}'.");
    return (controlArm, treatmentArm);
}
CreateExperiment.cs

PHP

private static function createExperimentArms(
    GoogleAdsClient $googleAdsClient,
    int $customerId,
    int $campaignId,
    string $experimentResourceName
): string {
    $operations = [];
    $experimentArm1 = new ExperimentArm([
        // The "control" arm references an already-existing campaign.
        'control' => true,
        'campaigns' => [ResourceNames::forCampaign($customerId, $campaignId)],
        'experiment' => $experimentResourceName,
        'name' => 'control arm',
        'traffic_split' => 40
    ]);
    $operations[] = new ExperimentArmOperation(['create' => $experimentArm1]);
    $experimentArm2 = new ExperimentArm([
        // The non-"control" arm, also called a "treatment" arm, will automatically
        // generate draft campaigns that you can modify before starting the
        // experiment.
        'control' => false,
        'experiment' => $experimentResourceName,
        'name' => 'experiment arm',
        'traffic_split' => 60
    ]);
    $operations[] = new ExperimentArmOperation(['create' => $experimentArm2]);

    // Issues a request to create the experiment arms.
    $experimentArmServiceClient = $googleAdsClient->getExperimentArmServiceClient();
    $response = $experimentArmServiceClient->mutateExperimentArms(
        MutateExperimentArmsRequest::build($customerId, $operations)
            // We want to fetch the draft campaign IDs from the treatment arm, so the easiest
            // way to do that is to have the response return the newly created entities.
            ->setResponseContentType(ResponseContentType::MUTABLE_RESOURCE)
    );
    // Results always return in the order that you specify them in the request.
    // Since we created the treatment arm last, it will be the last result.
    $controlArmResourceName = $response->getResults()[0]->getResourceName();
    $treatmentArm = $response->getResults()[count($operations) - 1];
    print "Created control arm with resource name '$controlArmResourceName'" . PHP_EOL;
    print "Created treatment arm with resource name '{$treatmentArm->getResourceName()}'"
        . PHP_EOL;

    return $treatmentArm->getExperimentArm()->getInDesignCampaigns()[0];
}CreateExperiment.php

Python

def create_experiment_arms(
    client: GoogleAdsClient,
    customer_id: str,
    base_campaign_id: str,
    experiment: str,
) -> str:
    """Creates a control and treatment experiment arms.

    Args:
        client: an initialized GoogleAdsClient instance.
        customer_id: a client customer ID.
        base_campaign_id: the campaign ID to associate with the control arm of
          the experiment.
        experiment: the resource name for an experiment.

    Returns:
        the resource name for the new treatment experiment arm.
    """
    operations: List[ExperimentArmOperation] = []

    campaign_service: CampaignServiceClient = client.get_service(
        "CampaignService"
    )

    # The "control" arm references an already-existing campaign.
    operation_1: ExperimentArmOperation = client.get_type(
        "ExperimentArmOperation"
    )
    exa_1: ExperimentArm = operation_1.create
    exa_1.control = True
    exa_1.campaigns.append(
        campaign_service.campaign_path(customer_id, base_campaign_id)
    )
    exa_1.experiment = experiment
    exa_1.name = "control arm"
    exa_1.traffic_split = 40
    operations.append(operation_1)

    # The non-"control" arm, also called a "treatment" arm, will automatically
    # generate draft campaigns that you can modify before starting the
    # experiment.
    operation_2: ExperimentArmOperation = client.get_type(
        "ExperimentArmOperation"
    )
    exa_2: ExperimentArm = operation_2.create
    exa_2.control = False
    exa_2.experiment = experiment
    exa_2.name = "experiment arm"
    exa_2.traffic_split = 60
    operations.append(operation_2)

    experiment_arm_service: ExperimentArmServiceClient = client.get_service(
        "ExperimentArmService"
    )
    request: MutateExperimentArmsRequest = client.get_type(
        "MutateExperimentArmsRequest"
    )
    request.customer_id = customer_id
    request.operations = operations
    # We want to fetch the draft campaign IDs from the treatment arm, so the
    # easiest way to do that is to have the response return the newly created
    # entities.
    request.response_content_type = (
        client.enums.ResponseContentTypeEnum.MUTABLE_RESOURCE
    )
    response: MutateExperimentArmsResponse = (
        experiment_arm_service.mutate_experiment_arms(request=request)
    )

    # Results always return in the order that you specify them in the request.
    # Since we created the treatment arm second, it will be the second result.
    control_arm_result: Any = response.results[0]
    treatment_arm_result: Any = response.results[1]

    print(
        f"Created control arm with resource name {control_arm_result.resource_name}"
    )
    print(
        f"Created treatment arm with resource name {treatment_arm_result.resource_name}"
    )

    return treatment_arm_result.experiment_arm.in_design_campaigns[0]create_experiment.py

Ruby

def create_experiment_arms(client, customer_id, base_campaign_id, experiment)
  operations = []
  operations << client.operation.create_resource.experiment_arm do |ea|
    # The "control" arm references an already-existing campaign.
    ea.control = true
    ea.campaigns << client.path.campaign(customer_id, base_campaign_id)
    ea.experiment = experiment
    ea.name = 'control arm'
    ea.traffic_split = 40
  end
  operations << client.operation.create_resource.experiment_arm do |ea|
    # The non-"control" arm, also called a "treatment" arm, will automatically
    # generate draft campaigns that you can modify before starting the
    # experiment.
    ea.control = false
    ea.experiment = experiment
    ea.name = 'experiment arm'
    ea.traffic_split = 60
  end

  response = client.service.experiment_arm.mutate_experiment_arms(
    customer_id: customer_id,
    operations: operations,
    # We want to fetch the draft campaign IDs from the treatment arm, so the
    # easiest way to do that is to have the response return the newly created
    # entities.
    response_content_type: :MUTABLE_RESOURCE,
  )

  # Results always return in the order that you specify them in the request.
  # Since we created the treatment arm last, it will be the last result.
  control_arm_result = response.results.first
  treatment_arm_result = response.results.last

  puts "Created control arm with resource name #{control_arm_result.resource_name}."
  puts "Created treatment arm with resource name #{treatment_arm_result.resource_name}."

  treatment_arm_result.experiment_arm.in_design_campaigns.first
endcreate_experiment.rb

Perl

sub create_experiment_arms {
  my ($api_client, $customer_id, $base_campaign_id, $experiment) = @_;

  my $operations = [];
  push @$operations,
    Google::Ads::GoogleAds::V22::Services::ExperimentArmService::ExperimentArmOperation
    ->new({
      create => Google::Ads::GoogleAds::V22::Resources::ExperimentArm->new({
          # The "control" arm references an already-existing campaign.
          control   => "true",
          campaigns => [
            Google::Ads::GoogleAds::V22::Utils::ResourceNames::campaign(
              $customer_id, $base_campaign_id
            )
          ],
          experiment   => $experiment,
          name         => "control arm",
          trafficSplit => 40
        })});

  push @$operations,
    Google::Ads::GoogleAds::V22::Services::ExperimentArmService::ExperimentArmOperation
    ->new({
      create => Google::Ads::GoogleAds::V22::Resources::ExperimentArm->new({
          # The non-"control" arm, also called a "treatment" arm, will automatically
          # generate draft campaigns that you can modify before starting the
          # experiment.
          control      => "false",
          experiment   => $experiment,
          name         => "experiment arm",
          trafficSplit => 60
        })});

  my $response = $api_client->ExperimentArmService()->mutate({
    customerId => $customer_id,
    operations => $operations,
    # We want to fetch the draft campaign IDs from the treatment arm, so the
    # easiest way to do that is to have the response return the newly created
    # entities.
    responseContentType => MUTABLE_RESOURCE
  });

  # Results always return in the order that you specify them in the request.
  # Since we created the treatment arm last, it will be the last result.
  my $control_arm_result   = $response->{results}[0];
  my $treatment_arm_result = $response->{results}[1];

  printf "Created control arm with resource name '%s'.\n",
    $control_arm_result->{resourceName};
  printf "Created treatment arm with resource name '%s'.\n",
    $treatment_arm_result->{resourceName};
  return $treatment_arm_result->{experimentArm}{inDesignCampaigns}[0];
}create_experiment.pl

A few key points about the example above:

The name of each arm must be unique within the Experiment.
The traffic_split must add up to 100 across all arms.
Exactly one arm must have control set to true; all other arms must have it set to false.

Only the control arm specifies a campaigns array, which holds only one campaign.

Treatment arms

Once you've created all the experiment arms, the treatment arms—the arms where control is set to false—automatically populate their in_design_campaigns field. You can retrieve the field from the API response by setting the response content type to MUTABLE_RESOURCE like in the code example. You can also fetch it through a GoogleAdsService query:

SELECT experiment_arm.in_design_campaigns
FROM experiment_arm
WHERE experiment_arm.resource_name = "TREATMENT_ARM_RESOURCE_NAME"

In-design campaigns

You can treat these in-design campaigns as regular campaigns. Make whatever changes you want to test in your experiment to these campaigns; the control campaign won't be affected. Once you schedule the experiment, these changes are materialized into a real campaign that can serve ads.

These in-design campaigns are technically draft campaigns. If you want to find them in GoogleAdsService, add the include_drafts=true parameter to the query.

At least one change must be made to the in-design campaign before you can schedule the experiment.

Create experiments

Experiment operations

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Last updated 2025-12-03 UTC.