Change in Anonymous User ID System at kapa.ai: From anonymous to $device
kapa.ai In the beginning our anonymous users had a distinct id that included "anonymous", but now they have a distinct id with $device - Why is that?
kapa.ai In the beginning our anonymous users had a distinct id that included "anonymous", but now they have a distinct id with $device - Why is that?
The change you’re seeing—from anonymous users having a distinct_id like "anonymous..." to one prefixed with "$device:" (e.g., "$device:anonymous111")—is due to how Mixpanel’s Simplified ID Merge API handles anonymous user identification.
With the Simplified ID Merge API, Mixpanel uses the $device_id property to track anonymous users. When an event is sent with only a $device_id (and no $user_id), Mixpanel automatically sets the distinct_id to "$device:{device_id}". This is a deliberate design to clearly distinguish anonymous device-based IDs from identified user IDs. For example:
```
{ "event": "View Anonymous Page", "properties": { "token": "{{token}}", "$device_id": "anonymous111" } } // Mixpanel sets: "distinct_id": "$device:anonymous111"
LBKSIf you previously used a different ID convention (like just "anonymous...") for anonymous users, the switch to the "$device:" prefix likely coincided with a migration to the Simplified ID Merge API or an update in your implementation to follow Mixpanel’s current best practices. This prefixing helps Mixpanel distinguish between device-based (anonymous) and user-based (identified) IDs, ensuring more accurate identity management and merging behavior [Understanding Simplified ID Merge](https://docs.mixpanel.com/docs/tracking-methods/id-management/migrating-to-simplified-id-merge-system#understanding-simplified-id-merge).
In summary:
Anonymous users now have a distinct_id prefixed with "$device:" because Mixpanel’s Simplified ID Merge API automatically applies this format to all anonymous device IDs for clarity and consistency [Identifying Users (Simplified)](https://docs.mixpanel.com/docs/tracking-methods/id-management/identifying-users-simplified).
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