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The synthetic panel is a screening aid. AI personas, built from statistics about your audience, rate your subject-line variants before you send anything. Use it to drop weak variants. It is not a prediction, and it never picks a winner. A real A/B test decides.
In published studies, synthetic panels agreed with real respondents about 79% of the time, and they exaggerated differences between segments 2–4×. Treat the scores as a hint about which variants are weak, not as a forecast of your open rate.

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Where to find it

  • Plan page: the Synthetic panel (screening) card at the bottom of a campaign plan. Email 1’s subject is variant V1. Add up to three alternative subjects with Add an alternative subject.
  • Send wizard: on the A/B test step, when the test type is Subject line, the card screens the variations you typed.
Click Run panel. A run takes a few seconds.

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What the personas are built from

The panel only uses aggregate statistics about the audience you picked. It never uses a contact’s details.
  • how many contacts are in each engagement group: opened or clicked in the last 30 days, 31–90 days ago, more than 90 days ago, or never
  • the countries in each engagement group
  • the audience’s most common languages and time zone
  • which mail apps your workspace’s opens come from
  • how many contacts completed a goal or made a purchase recently
  • your recent average open and click rates, and what your real A/B tests found
  • for up to three dropdown or yes/no custom fields, the share of each option among contacts that have a value (for example Plan tier: free 70%, pro 30%)
From this the panel makes between one and eight personas, for example Highly engaged, United Kingdom or Dormant 90+ days, France. Each persona stands for a share of the audience. A country that is less than 3% of the audience is grouped with other countries. If your audience has fewer distinct groups, you get fewer personas. The panel never adds made-up personas. Only dropdown and yes/no custom fields are used, and only as shares of their options. Text, number, date and JSON fields are never used, and neither is any field marked sensitive.

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Reading the results

For each variant you see: If the gap between the top variants is smaller than their spread, the card says so. Treat those variants as equal.

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Then run a real test

Keep the strongest variants and click Create real A/B test. The send wizard opens on the A/B step.

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Cost and limits

  • One run uses one AI text generation from your plan’s allowance. Running the same personas on the same variants again within 7 days shows the saved result and costs nothing.
  • Up to four variants and eight personas per run.
  • You need permission to edit campaigns to run the panel. Anyone who can view the campaign can see the last run.
  • Spark and the MCP server can read the last run with get_synthetic_panel_results. They cannot start a run.