Anonymous-to-Identified Merge

Anonymous-to-identified merge is the step that joins a visitor's pre-login event history to their account identity at the moment they authenticate.

At sign-up or login the client sends both the device identifier and the account identifier in one call, and the backend writes a mapping that resolves the two to a single profile. Tools differ on one decisive point: whether earlier events are rewritten onto the account, or whether the identity applies only from that call forward. Under forward-only merging, acquisition attribution stays stranded on the anonymous profile and every sign-up appears to arrive from direct traffic. Shared devices are the other classic failure, since on a family computer or an in-store kiosk the merge attaches somebody else's browsing to the account, which is why the call should fire on confirmed authentication rather than on a form submission.