Custom audiences bring what you already know about your customers into ChatGPT Ads: a list of emails or phone numbers that decides who sees the ad, who doesn't and who is worth bidding more for. If you come from Google Ads, the idea will remind you of customer lists (Customer Match). Used well, especially to exclude, they stop you paying to acquire people you already have.
First, a warning if you advertise in Spain or anywhere else in the EEA: according to the official documentation, they aren't currently supported in campaigns targeting the European Economic Area or Switzerland, because personalised ads aren't available there yet: in those markets, the ad is chosen by the context of the conversation alone. This lesson is useful for campaigns in other open markets, such as the United States, and for getting your lists and legal basis ready in case they become available in Europe.
What they are and which data they accept
They are lists of first-party data: information about your own customers that you have the right to use. They accept these identifiers:
| Identifier | How it's uploaded |
|---|---|
| In plain text or hashed with SHA-256 (hexadecimal) | |
| Phone | In E.164 format (+44…), in plain text or hashed with SHA-256 |
| Android advertising ID (GAID) | Unhashed |
They're uploaded as a CSV or TXT file of up to 500 MB. If you hash, normalise first (email without stray spaces and in lowercase; phone in E.164): the same data written two ways produces two different hashes.
The audience then goes through several statuses until it's ready
(ready). You won't see its exact size: for privacy, it's shown in
ranges (under 25,000, 25,000 to 100,000…).
Three uses, two thresholds
| Use | Where it's set | Minimum |
|---|---|---|
| Include: only people on the list | Campaign targeting | About 25,000 matches |
| Exclude: nobody on the list | Campaign targeting | No minimum (small or empty lists work) |
| Bid multiplier: from 0.1× to 10× | Ad group | About 25,000 matches |
Note that matches count, not the rows you upload: only the people on your list the platform manages to match add up. And if someone is in both an included and an excluded audience, exclusions win: they won't see the ad. And if you combine inclusion and exclusion, what is left after excluding must still reach the minimum.
The big play for a small business: exclusion
25,000 matches is beyond many small businesses. Exclusion, on the other hand, has no minimum, and that's where the money is: not paying to acquire someone who is already a customer or has already signed up. For example:
- Lead generation: exclude the leads and customers you already have.
- Sign-up or free trial: exclude anyone who has already registered.
- Online shop running an acquisition campaign: exclude anyone who has already bought.
Think of a training academy with 3,000 students: it would never reach the threshold to include, but it can take those 3,000 out of its acquisition campaign from day one.
Once a list passes the threshold, the multiplier lets you bid more for the people worth most to you, or less for those who matter little, without leaving them out entirely.
💡 Ninja trick: connect your exclusion list to your CRM and replace it in full every so often. That way each new customer drops out of your acquisition campaigns automatically.
How they're maintained
| Operation | What it's for |
|---|---|
| Add | Add identifiers to the list |
| Remove | Take out people who shouldn't be there, such as anyone who unsubscribed |
| Replace | Upload the full snapshot and substitute the previous one |
| Merge | Combine 2 to 64 audiences into one |
| Archive | Retire it for good |
⚠️ Pitfall: archiving can't be undone: an archived audience can't be recovered. If in doubt, take it out of your campaigns and archive it later.
GDPR: before you upload anything
This isn't legal advice, but it is what you should have sorted before the first upload:
- Only your own data that you have the right to use for advertising. OpenAI is clear: no data from brokers. A bought list won't do.
- A legal basis that covers this specific use: advertising on a third-party platform. Which one fits your case is for your adviser or data protection officer to decide.
- Your privacy policy should say so before you upload the list, not after.
- Hashing isn't anonymising: an email hashed with SHA-256 is still personal data (lesson 4 of this module).
- Keep the list up to date: anyone who unsubscribes or objects should also leave the audience (with Remove or Replace).
What to remember
- They aren't currently supported in campaigns targeting the EEA (Spain included) or Switzerland.
- They accept email and phone (plain or SHA-256) and the Android advertising ID.
- Including and bid multipliers (0.1× to 10×) need about 25,000 matches; excluding needs none.
- Exclusions win, and excluding existing customers is the big play for a small business.
- Replace uploads the full snapshot; archiving is for good.
- Only your own data, with a legal basis and a privacy policy, before uploading anything.