Yes, you can create a universal holdout group in GrowthBook. Here's a step-by-step guide on how to do it: 1. Create a Holdout Experiment: Start by creating an experiment, for example, "Global Holdout Q1 2024". Set the coverage to 10% and use a 50/50 split to achieve a 10% holdout test population. You may not want to use conversion windows with a holdout experiment as users are going to get exposed to the holdout experiment as soon as you start testing the feature. You can either use your regular metrics and set Conversion Window Override to Ignore Conversion Windows in your Experiment Analysis settings or use metrics that have no conversion window or use a Lookback Window to only measure the last X days of the holdout. Start the experiment even though it doesn't have any linked features [[source](https://docs.growthbook.io/kb/experiments/holdouts#1-create-a-holdout-experiment)]. 2. Add Holdout Experiment to All Future Features: Create a feature that you want to add to your holdout. Before testing or launching the feature, add the above Holdout Experiment as an experiment rule ABOVE any feature experiment. This will ensure your holdout population never gets the feature until you choose to release it to them. Ensure that the

holdout control

and

holdout feature

group get the same value as one another, and that this value is the same as the default/control behavior for your feature test in the

general population

[[source](https://docs.growthbook.io/kb/experiments/holdouts#2-add-holdout-experiment-to-all-future-features)]. 3. Use Namespaces: You can also use namespaces to create a holdout group. Create a single global namespace and for each experiment rule you create, enable the namespace and select a range like

0 to 0.9

. That means the last 10% of users in that namespace would be excluded from the experiment. Then later for your holdout experiment, you could set the range as

0.9 to 1.0

to run a combined test on the holdout group [[source](https://linen.growthbook.io/t/33879/hi-any-tips-on-how-would-i-go-about-configuring-a-holdback-g)]. 4. Use Inline Experiments: You can use inline experiments to create global holdout groups. Here's a code snippet that shows how to do it:

javascript
// The value will be `true` if in the holdout group, otherwise `false`  
const holdout = gb.run({  
  key: "holdout",  
  variations: [true, false],  
  // 10% of users in the holdout group  
  weights: [0.1, 0.9]  
});  
  
// Only run your main experiment if the user is NOT in the holdout  
if (!holdout.value) {  
  const res = gb.run({  
    key: "my-experiment",  
    variations: ["A", "B"]  
  })  
}

[[source](https://docs.growthbook.io/lib/js#holdout-groups)]

New message text here