Splitting a segment into two

You could try using Random Bucket numbers! One segment could be < 5000 and the other > 5000. Screenshots below! May not be exactly 50/50 depending on the size of your audience, but certainly faster.

Not sure what you're then doing with the segments, but there is also the A/B testing functionality in campaigns that would randomly split them into variants, or in Canvas there are Experiment Steps or Audience Paths that could both accomplish this. 

What are you trying to do? In canvas or campaign you can split the audience. 

Currently, Braze doesn’t offer a built‐in option in the dashboard to automatically divide an existing segment into two equal parts. However, there are two common approaches you could consider:

1. A/B Testing Campaigns: If your goal is to test messages or campaigns with an even split of your audience, Braze’s A/B testing functionality will automatically allocate your target users into evenly distributed groups when you launch the campaign. This takes care of evenly splitting the segment on the fly.
2. Creating Custom Segments with a Random Attribute: For more persistent segmentation needs, you could add a custom attribute (for example, a flag or a random value such as 0 or 1) to your user profiles during ingestion or via a backend process. With this attribute in place, you can create two segments by filtering on that attribute (e.g., one segment for users with a value of 0 and another for users with a value of 1), effectively dividing your original segment into two even groups.

These methods depend on whether you want a temporary split for a specific campaign (using the A/B testing tool) or a permanent, static division of your audience (using custom attributes).

For further details on segmentation best practices and A/B testing in Braze, please review our official guides:
• Segmentation: https://www.braze.com/docs/user_guide/segmentation/
• A/B Testing: https://www.braze.com/docs/user_guide/message_building_by_channel/a_b_testing/

We hope this helps streamline your workflow!