Fetch a single Holdout

1 min

GET

https://api.optimizely.com/flags/v1//projects/{project_id}/holdouts/{holdout_id}

Retrieves detailed information about a specific holdout by its unique ID within a project.

What you'll get:

Complete holdout configuration including traffic allocation, status, and settings
Associated experiment rules and their current states
Audience conditions and targeting criteria (if configured)
Metric tracking configuration and current values
Lifecycle timestamps (created, updated, started, ended)
RESTful links for related operations (update, delete, archive, etc.)

Holdout States:

Draft: Holdout is configured but not yet active
Running: Currently excluding traffic from experiments
Concluded: Finished collecting data, results available for analysis

Use Cases:

View complete holdout configuration before making changes
Monitor current status and performance metrics
Access experiment rules affected by this holdout
Retrieve data for analysis and reporting
Verify permissions for management operations via included links

This operation corresponds to the url or fetch_holdout_url property found in holdout list responses.

Path Parameters

project_idintegerrequired
Example
12345
Description
The project identifier
holdout_idintegerrequired
Example
54321
Description
The holdout identifier

Responses

200

Successfully retrieved the holdout with all its configuration details.

Response includes:

Core properties: ID, key, name, description, status, traffic allocation
Lifecycle data: Created/updated timestamps, start/end times (if applicable)
Configuration: Environment, audience conditions, metrics setup
Experiment rules: Associated experiments and their allocation settings
Management links: URLs for update, archive, delete operations (if authorized)
System metadata: URN, project association, archive status

Link availability depends on user permissions:

Missing update_url: Cannot modify this holdout
Missing delete_url: Cannot permanently delete
Missing archive_url/unarchive_url: Cannot change archive status

Status-specific data:

Draft holdouts: Full configuration, no timing data
Running holdouts: Includes start_time, active experiment rules
Concluded holdouts: Includes both start_time and end_time

Holdout
Examples
Concluded holdout with complete lifecycle:
{ "archive_url": "/projects/12345/holdouts/archived", "archived": false, "created_time": "2024-06-28T10:00:00.000Z", "delete_url": "/projects/12345/holdouts/987", "description": "Completed control group study showing 15% incremental impact", "end_time": "2024-08-31T23:59:59.000Z", "environment_key": "production", "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9", "id": 987, "key": "q3_control_group", "metrics": [ { "id": "conversion_rate", "name": "Conversion Rate", "type": "custom" }, { "id": "revenue_per_visitor", "name": "Revenue per Visitor", "type": "custom" } ], "name": "Q3 Marketing Control Group - Concluded", "project_id": 12345, "rules": { "456": { "created_time": "2024-06-15T10:00:00.000Z", "flag_key": "promo_banner", "flag_name": "Promotional Banner", "flag_status": "archived", "rule_key": "summer_promo", "rule_name": "Summer Promotion", "traffic_allocation": 2000, "updated_time": "2024-08-31T23:59:59.000Z" } }, "start_time": "2024-07-01T09:00:00.000Z", "status": "concluded", "traffic_allocation": 1000, "updated_time": "2024-08-31T23:59:59.000Z", "url": "/projects/12345/holdouts/987", "urn": "holdouts.flag.optimizely.com::987" }
Draft holdout ready for configuration:
{ "archive_url": "/projects/12345/holdouts/archived", "archived": false, "created_time": "2024-09-15T10:00:00.000Z", "delete_url": "/projects/12345/holdouts/987", "description": "Control group for Q4 marketing campaigns to measure incremental impact", "environment_key": "production", "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9", "id": 987, "key": "q4_control_group", "metrics": [], "name": "Q4 Marketing Control Group", "project_id": 12345, "rules": {}, "status": "draft", "traffic_allocation": 1000, "update_url": "/projects/12345/holdouts/987", "updated_time": "2024-09-15T10:00:00.000Z", "url": "/projects/12345/holdouts/987", "urn": "holdouts.flag.optimizely.com::987" }
Active holdout with experiment rules:
{ "archived": false, "created_time": "2024-09-15T10:00:00.000Z", "delete_url": "/projects/12345/holdouts/987", "description": "Active control group excluding 10% traffic from all experiments", "environment_key": "production", "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9", "id": 987, "key": "q4_control_group", "metrics": [ { "id": "revenue_impact", "name": "Revenue Impact", "type": "custom" } ], "name": "Q4 Marketing Control Group", "project_id": 12345, "rules": { "456": { "created_time": "2024-09-10T14:30:00.000Z", "flag_key": "new_checkout", "flag_name": "New Checkout Experience", "flag_status": "unarchived", "rule_key": "checkout_experiment", "rule_name": "Checkout Flow Test", "traffic_allocation": 2000, "updated_time": "2024-09-12T11:15:00.000Z" } }, "start_time": "2024-09-16T09:00:00.000Z", "status": "running", "traffic_allocation": 1000, "update_url": "/projects/12345/holdouts/987", "updated_time": "2024-09-16T09:00:00.000Z", "url": "/projects/12345/holdouts/987", "urn": "holdouts.flag.optimizely.com::987" }
Description
Represents a holdout experiment that reserves a portion of traffic to measure the impact of feature flags and experiments.

Holdouts help establish control groups by excluding a percentage of users from seeing any experiments, allowing you to measure the overall impact of your experimentation program against a baseline.
- archivedboolean
  Description
  Whether the holdout is archived. Archived holdouts are hidden from normal views but retain their historical data and configuration.
- audience_conditionsobject[]
  Example
  ["["or",{"audience_id":5340810295},{"audience_id":1234567890}]"]
  Description
  Defines which audiences this holdout applies to. If omitted, the holdout applies to all users. Uses logical operators like 'and', 'or', 'not' to combine multiple audience conditions.
- audience_idsinteger[]
  Example
```
[
  5340810295,
  1234567890
]
```
  Description
  Warning: Deprecated
  DEPRECATED: Use audience_conditions instead. List of audience IDs that this holdout applies to. This field is maintained for backward compatibility.
- created_by_user_emailstring
  Example
  [email protected]
  Description
  Email address of the user who created the holdout.
- created_timestring<date-time>
  Example
  2023-12-15T10:00:00.000Z
  Description
  Timestamp when the holdout was originally created.
  Format
  date-time
- descriptionstring
  Example
  Holdout group to measure the overall impact of our growth experiments throughout the year
  Description
  Optional detailed description explaining the purpose and context of this holdout. Helps team members understand what this holdout is measuring.
  Max Length
  1000
- end_timestring<date-time>
  Example
  2024-12-31T23:59:59.000Z
  Description
  Timestamp when the holdout finished or will finish. Null for holdouts that are still running or have no defined end time.
  Format
  date-time
- environment_keystring
  Example
  production
  Description
  The environment where this holdout is active (e.g., 'production', 'staging'). The holdout only affects traffic in this specific environment.
- environment_namestring
  Example
  Production
  Description
  The human-readable name of the environment where this holdout is active.
- exclude_targeted_deliveriesboolean
  Description
  When true, Targeted Delivery rules are excluded from this holdout, so holdout users are not withheld from them. Targeted Deliveries represent permanent ship decisions rather than active experiments, so there is nothing to measure by withholding them. Applies to global holdouts only; ignored for local holdouts. Can only be changed while the holdout is in draft status. Defaults to false.
  Default
  false
- holdout_results_api_tokenstring
  Example
  SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9
  Description
  API token for accessing holdout results and analytics data. This token is dynamically generated for each API response and provides secure access to holdout-specific results endpoints.
- idintegerrequired
  Example
  12345
  Description
  System-generated unique identifier for the holdout.
- keystringrequired
  Example
  annual_growth_holdout
  Description
  Unique user-defined identifier for the holdout within the project. Must contain only alphanumeric characters, underscores, and hyphens.
  Max Length
  64
  Pattern
  ^[a-zA-Z0-9_\-]+$
- metricsMetric[]
  Description
  List of metrics being tracked and analyzed for this holdout. These metrics help measure the impact of experiments on the control group.
  - aggregatorstring<unique | count | sum | ratio>required
    Description
    The aggregation function for the numerator of the metric. 'unique' measures the number of unique visitors/sessions that include the specified Event. 'count' measures the total number of occurrences of Event for the scope (visitor/session). 'sum' is the sum of the 'field' value
    Allowed
    uniquecountsumratio
  - display_titlestring
    Description
    An optional title for the unique metric configuration. If not provided, the event name will be used.
  - display_unitstring
    Description
    An optional name for the unit of the unique metric configuration.
  - event_idinteger<int64>
    Example
    32334454244
    Description
    The ID for the Event to select data from. Omitted for global metrics that are not relative to a specific Event, i.e. "overall revenue"
    Format
    int64
  - event_propertiesobject
    - filterobject
      - combine_operatorstring<or | and>
        Allowed
        orand
      - conditionsEventPropertyCondition[]
        namestringrequired
        operatorstring<equal_to | not_equal_to | greater_than | greater_than_or_equal_to | less_than | less_than_or_equal_to | contains | does_not_contain>required
        Allowed
        equal_tonot_equal_togreater_thangreater_than_or_equal_toless_thanless_than_or_equal_tocontainsdoes_not_contain
        typestring<string | number | boolean>required
        Allowed
        stringnumberboolean
        valuestringrequired
  - event_typestring
  - fieldstring<revenue | value>
    Description
    The field to aggregate for the numerator of the metric. Required when 'aggregator' = 'sum', otherwise omitted
    Allowed
    revenuevalue
  - idstring
    Description
    A unique identifier for the metric configuration.
  - metricsSubMetric[]
    - aggregatorstring
    - display_titlestring
    - event_idinteger
    - event_typestring
    - fieldstring
    - rolestring<numerator | denominator>
      Allowed
      numeratordenominator
    - scopestring
  - project_idinteger
    Description
    A unique identifier for the project associated with the metric.
  - scopestring<session | visitor | event>
    Description
    Specifies how Events should be grouped together. Can also be thought of as the denonimator of the metric. 'session' divides by the number of sessions. "Influenced sessions", or sessions that do not contain a decision Event but carry a decision from a previous session are not included in counts for numerator or denominator. 'visitor' divides by the number of visitors. 'event' divides by the total occurrences (impressions) of the specified Event
    Allowed
    sessionvisitorevent
  - visibilitystring<account | experiment | project>
    Description
    The visibility of the metric.
    Allowed
    accountexperimentproject
  - winning_directionstring<increasing | decreasing>required
    Description
    The winning direction of this metric
    Allowed
    increasingdecreasing
- namestringrequired
  Example
  Annual Growth Control Group
  Description
  Human-readable name for the holdout displayed in the UI.
  Max Length
  255
- project_idinteger<int64>
  Example
  98765
  Description
  The unique identifier of the project this holdout belongs to.
  Format
  int64
- projectsobject[]
  Example
```
[
  {
    "id": 123
  }
]
```
  Description
  Project objects returned by cross-project GET endpoints. For global-scope holdouts, lists target project IDs. Empty array for local-scope holdouts. Frontend resolves project names via entity-management API.
  - idinteger<int64>
    Description
    Project ID.
    Format
    int64
- revisioninteger
  Example
  3
  Description
  Revision number that increments with each change to the holdout. Used for tracking modifications and ensuring data consistency.
- rulesobject[]
  Example
```
[
  {
    "flag_key": "my_flag",
    "id": 456,
    "key": "experiment_rule_a",
    "name": "Experiment Rule A",
    "project_id": 123
  }
]
```
  Description
  Enriched rule objects returned by cross-project GET endpoints. For local-scope holdouts, lists target rules with metadata. Empty array for global-scope holdouts.
  - flag_idinteger<int64>
    Description
    ID of the flag containing this rule.
    Format
    int64
  - flag_keystring
    Description
    Key of the flag containing this rule.
  - flag_namestring
    Description
    Name of the flag containing this rule.
  - idinteger<int64>
    Description
    Rule ID.
    Format
    int64
  - keystring
    Description
    Rule key.
  - namestring
    Description
    Rule name.
  - project_idinteger<int64>
    Description
    ID of the project this rule belongs to.
    Format
    int64
- scopestring<global | local>
  Example
  global
  Description
  Defines the scope of the holdout:
  
  'global': Affects all experiments across the entire project
  
  'local': Affects only specific experiments or flags
  Allowed
  globallocal
- start_timestring<date-time>
  Example
  2024-01-01T00:00:00.000Z
  Description
  Timestamp when the holdout became or will become active. When the holdout starts affecting traffic allocation.
  Format
  date-time
- statusstring<draft | running | concluded>
  Example
  running
  Description
  Current operational status of the holdout:
  
  'draft': Holdout is configured but not yet active
  
  'running': Holdout is currently active and affecting traffic
  
  'concluded': Holdout has finished and is no longer active
  Allowed
  draftrunningconcluded
- traffic_allocationinteger
  Example
  1000
  Description
  Percentage of traffic allocated to this holdout, expressed in basis points (1/100th of a percent). For example: 100 = 1%, 1000 = 10%, 5000 = 50%. The remaining traffic sees experiments normally.
  Minimum
  0
  Maximum
  10000
- updated_timestring<date-time>
  Example
  2024-01-01T10:00:00.000Z
  Description
  Timestamp when the holdout was last modified.
  Format
  date-time
- urlstring
  Example
  /holdouts/12345
  Description
  RESTful link to fetch this holdout's details. For project-scoped endpoints: /projects/{project_id}/holdouts/{holdout_id} For cross-project endpoints: /holdouts/{holdout_id}
- urnstring
  Example
  holdout.flag.optimizely.com::12345
  Description
  Universal Resource Name (URN) for the holdout, used for global identification.

400

Bad Request - Invalid request parameters or malformed holdout ID.

Common causes:

Invalid holdout_id format (must be a positive integer)
Invalid project_id format (must be a positive integer)
Malformed request structure or unsupported query parameters

ProblemDetail
Example
```
{
  "detail": "Holdout ID must be a positive integer",
  "status": 400,
  "title": "Invalid holdout ID",
  "type": "about:blank"
}
```
Description
https://tools.ietf.org/html/rfc7807#section-3.1
- detailstringrequired
  Description
  A human-readable explanation specific to this occurrence of the problem.
- statusintegerrequired
  Description
  The HTTP status code ([RFC7231], Section 6) generated by the origin server for this occurrence of the problem.
- titlestringrequired
  Description
  A short, human-readable summary of the problem type.
- typestringrequired
  Description
  A URI reference [RFC3986] that identifies the problem type. Contains 'about
  ' if unspecified.
- uuidstring
  Description
  Error reference for customer support

401Invalid credentials

403Do not have permission to perform the operation

404

Not Found - The specified holdout does not exist or you don't have access to it.

Possible reasons:

Holdout ID does not exist in the specified project
Project ID does not exist or you don't have access to it
Holdout was permanently deleted
Insufficient permissions to view this holdout

ProblemDetail
Example
```
{
  "detail": "Holdout not found with id '987'",
  "status": 404,
  "title": "Holdout not found",
  "type": "about:blank"
}
```
Description
https://tools.ietf.org/html/rfc7807#section-3.1
- detailstringrequired
  Description
  A human-readable explanation specific to this occurrence of the problem.
- statusintegerrequired
  Description
  The HTTP status code ([RFC7231], Section 6) generated by the origin server for this occurrence of the problem.
- titlestringrequired
  Description
  A short, human-readable summary of the problem type.
- typestringrequired
  Description
  A URI reference [RFC3986] that identifies the problem type. Contains 'about
  ' if unspecified.
- uuidstring
  Description
  Error reference for customer support

curl

curl --request GET \
     --url https://api.optimizely.com/flags/v1//projects/{project_id}/holdouts/{holdout_id} \
     --header 'accept: application/json'

javascript

var myHeaders = new Headers();
myHeaders.append("accept", "application/json");
myHeaders.append("content-type", "application/json");

var requestOptions = {
   method: 'GET',
   headers: myHeaders,
   redirect: 'follow'
};

fetch("https://api.optimizely.com/flags/v1//projects/{project_id}/holdouts/{holdout_id}", requestOptions)
   .then(response => response.text())
   .then(result => console.log(result))
   .catch(error => console.log('error', error));

ruby

require "uri"
require "json"
require "net/http"

url = URI("https://api.optimizely.com/flags/v1//projects/{project_id}/holdouts/{holdout_id}")

https = Net::HTTP.new(url.host, url.port)
https.use_ssl = true

request = Net::HTTP::Get.new(url)
request["accept"] = "application/json"
request["content-type"] = "application/json"

response = https.request(request)
puts response.read_body

python

import requests
import json

url = "https://api.optimizely.com/flags/v1//projects/{project_id}/holdouts/{holdout_id}"

payload = {}
headers = {
   'accept': 'application/json',
   'content-type': 'application/json'
}

response = requests.request("GET", url, headers=headers, data=payload)

print(response.text)

200

// Successfully retrieved the holdout with all its configuration details.
Response includes:

Core properties: ID, key, name, description, status, traffic allocation
Lifecycle data: Created/updated timestamps, start/end times (if applicable)
Configuration: Environment, audience conditions, metrics setup
Experiment rules: Associated experiments and their allocation settings
Management links: URLs for update, archive, delete operations (if authorized)
System metadata: URN, project association, archive status

Link availability depends on user permissions:

Missing update_url: Cannot modify this holdout
Missing delete_url: Cannot permanently delete
Missing archive_url/unarchive_url: Cannot change archive status

Status-specific data:

Draft holdouts: Full configuration, no timing data
Running holdouts: Includes start_time, active experiment rules
Concluded holdouts: Includes both start_time and end_time
{
  "archived": false,
  "audience_conditions": [
    {}
  ],
  "audience_ids": [
    0
  ],
  "created_by_user_email": "[email protected]",
  "created_time": "2023-12-15T10:00:00.000Z",
  "description": "Holdout group to measure the overall impact of our growth experiments throughout the year",
  "end_time": "2024-12-31T23:59:59.000Z",
  "environment_key": "production",
  "environment_name": "Production",
  "exclude_targeted_deliveries": false,
  "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9",
  "id": 12345,
  "key": "annual_growth_holdout",
  "metrics": [
    {
      "aggregator": "",
      "display_title": "",
      "display_unit": "",
      "event_id": 32334454244,
      "event_properties": {
        "filter": {
          "combine_operator": "",
          "conditions": [
            {
              "name": "",
              "operator": "",
              "type": "",
              "value": ""
            }
          ]
        }
      },
      "event_type": "",
      "field": "",
      "id": "",
      "metrics": [
        {
          "aggregator": "",
          "display_title": "",
          "event_id": 0,
          "event_type": "",
          "field": "",
          "role": "",
          "scope": ""
        }
      ],
      "project_id": 0,
      "scope": "",
      "visibility": "",
      "winning_direction": ""
    }
  ],
  "name": "Annual Growth Control Group",
  "project_id": 98765,
  "projects": [
    {
      "id": ""
    }
  ],
  "revision": 3,
  "rules": [
    {
      "flag_id": "",
      "flag_key": "",
      "flag_name": "",
      "id": "",
      "key": "",
      "name": "",
      "project_id": ""
    }
  ],
  "scope": "global",
  "start_time": "2024-01-01T00:00:00.000Z",
  "status": "running",
  "traffic_allocation": 1000,
  "updated_time": "2024-01-01T10:00:00.000Z",
  "url": "/holdouts/12345",
  "urn": "holdout.flag.optimizely.com::12345"
}

GENERATED

// Successfully retrieved the holdout with all its configuration details.
Response includes:

Core properties: ID, key, name, description, status, traffic allocation
Lifecycle data: Created/updated timestamps, start/end times (if applicable)
Configuration: Environment, audience conditions, metrics setup
Experiment rules: Associated experiments and their allocation settings
Management links: URLs for update, archive, delete operations (if authorized)
System metadata: URN, project association, archive status

Link availability depends on user permissions:

Missing update_url: Cannot modify this holdout
Missing delete_url: Cannot permanently delete
Missing archive_url/unarchive_url: Cannot change archive status

Status-specific data:

Draft holdouts: Full configuration, no timing data
Running holdouts: Includes start_time, active experiment rules
Concluded holdouts: Includes both start_time and end_time
{
  "archived": false,
  "audience_conditions": [
    {}
  ],
  "audience_ids": [
    0
  ],
  "created_by_user_email": "[email protected]",
  "created_time": "2023-12-15T10:00:00.000Z",
  "description": "Holdout group to measure the overall impact of our growth experiments throughout the year",
  "end_time": "2024-12-31T23:59:59.000Z",
  "environment_key": "production",
  "environment_name": "Production",
  "exclude_targeted_deliveries": false,
  "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9",
  "id": 12345,
  "key": "annual_growth_holdout",
  "metrics": [
    {
      "aggregator": "",
      "display_title": "",
      "display_unit": "",
      "event_id": 32334454244,
      "event_properties": {
        "filter": {
          "combine_operator": "",
          "conditions": [
            {
              "name": "",
              "operator": "",
              "type": "",
              "value": ""
            }
          ]
        }
      },
      "event_type": "",
      "field": "",
      "id": "",
      "metrics": [
        {
          "aggregator": "",
          "display_title": "",
          "event_id": 0,
          "event_type": "",
          "field": "",
          "role": "",
          "scope": ""
        }
      ],
      "project_id": 0,
      "scope": "",
      "visibility": "",
      "winning_direction": ""
    }
  ],
  "name": "Annual Growth Control Group",
  "project_id": 98765,
  "projects": [
    {
      "id": ""
    }
  ],
  "revision": 3,
  "rules": [
    {
      "flag_id": "",
      "flag_key": "",
      "flag_name": "",
      "id": "",
      "key": "",
      "name": "",
      "project_id": ""
    }
  ],
  "scope": "global",
  "start_time": "2024-01-01T00:00:00.000Z",
  "status": "running",
  "traffic_allocation": 1000,
  "updated_time": "2024-01-01T10:00:00.000Z",
  "url": "/holdouts/12345",
  "urn": "holdout.flag.optimizely.com::12345"
}

concluded_holdout

// Concluded holdout with complete lifecycle
{
  "archive_url": "/projects/12345/holdouts/archived",
  "archived": false,
  "created_time": "2024-06-28T10:00:00.000Z",
  "delete_url": "/projects/12345/holdouts/987",
  "description": "Completed control group study showing 15% incremental impact",
  "end_time": "2024-08-31T23:59:59.000Z",
  "environment_key": "production",
  "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9",
  "id": 987,
  "key": "q3_control_group",
  "metrics": [
    {
      "id": "conversion_rate",
      "name": "Conversion Rate",
      "type": "custom"
    },
    {
      "id": "revenue_per_visitor",
      "name": "Revenue per Visitor",
      "type": "custom"
    }
  ],
  "name": "Q3 Marketing Control Group - Concluded",
  "project_id": 12345,
  "rules": {
    "456": {
      "created_time": "2024-06-15T10:00:00.000Z",
      "flag_key": "promo_banner",
      "flag_name": "Promotional Banner",
      "flag_status": "archived",
      "rule_key": "summer_promo",
      "rule_name": "Summer Promotion",
      "traffic_allocation": 2000,
      "updated_time": "2024-08-31T23:59:59.000Z"
    }
  },
  "start_time": "2024-07-01T09:00:00.000Z",
  "status": "concluded",
  "traffic_allocation": 1000,
  "updated_time": "2024-08-31T23:59:59.000Z",
  "url": "/projects/12345/holdouts/987",
  "urn": "holdouts.flag.optimizely.com::987"
}

draft_holdout

// Draft holdout ready for configuration
{
  "archive_url": "/projects/12345/holdouts/archived",
  "archived": false,
  "created_time": "2024-09-15T10:00:00.000Z",
  "delete_url": "/projects/12345/holdouts/987",
  "description": "Control group for Q4 marketing campaigns to measure incremental impact",
  "environment_key": "production",
  "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9",
  "id": 987,
  "key": "q4_control_group",
  "metrics": [],
  "name": "Q4 Marketing Control Group",
  "project_id": 12345,
  "rules": {},
  "status": "draft",
  "traffic_allocation": 1000,
  "update_url": "/projects/12345/holdouts/987",
  "updated_time": "2024-09-15T10:00:00.000Z",
  "url": "/projects/12345/holdouts/987",
  "urn": "holdouts.flag.optimizely.com::987"
}

running_holdout

// Active holdout with experiment rules
{
  "archived": false,
  "created_time": "2024-09-15T10:00:00.000Z",
  "delete_url": "/projects/12345/holdouts/987",
  "description": "Active control group excluding 10% traffic from all experiments",
  "environment_key": "production",
  "holdout_results_api_token": "SampleToken.eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9",
  "id": 987,
  "key": "q4_control_group",
  "metrics": [
    {
      "id": "revenue_impact",
      "name": "Revenue Impact",
      "type": "custom"
    }
  ],
  "name": "Q4 Marketing Control Group",
  "project_id": 12345,
  "rules": {
    "456": {
      "created_time": "2024-09-10T14:30:00.000Z",
      "flag_key": "new_checkout",
      "flag_name": "New Checkout Experience",
      "flag_status": "unarchived",
      "rule_key": "checkout_experiment",
      "rule_name": "Checkout Flow Test",
      "traffic_allocation": 2000,
      "updated_time": "2024-09-12T11:15:00.000Z"
    }
  },
  "start_time": "2024-09-16T09:00:00.000Z",
  "status": "running",
  "traffic_allocation": 1000,
  "update_url": "/projects/12345/holdouts/987",
  "updated_time": "2024-09-16T09:00:00.000Z",
  "url": "/projects/12345/holdouts/987",
  "urn": "holdouts.flag.optimizely.com::987"
}

400

// Bad Request - Invalid request parameters or malformed holdout ID.
Common causes:

Invalid holdout_id format (must be a positive integer)
Invalid project_id format (must be a positive integer)
Malformed request structure or unsupported query parameters
{
  "detail": "",
  "status": 0,
  "title": "",
  "type": "",
  "uuid": ""
}

401

// Invalid credentials

403

// Do not have permission to perform the operation

404

// Not Found - The specified holdout does not exist or you don't have access to it.
Possible reasons:

Holdout ID does not exist in the specified project
Project ID does not exist or you don't have access to it
Holdout was permanently deleted
Insufficient permissions to view this holdout
{
  "detail": "",
  "status": 0,
  "title": "",
  "type": "",
  "uuid": ""
}