I build one Catalyst app for many clients. How do I deploy it into each client's own project and roll out updates to all of them?

Deploy it to each client’s project separately: Catalyst doesn’t push one update to many projects at once, but you can script the deployments with the Catalyst CLI. When each client owns the project in their own Catalyst account, their data and usage bill stay with them.

1. Ask each client to invite you from Settings → Collaborators → Add or Assign, as an Admin for the whole account or as a Project Member of the project.
2. Create the client’s project from your app: export your project with Infrastructure as Code (IaC) from the console or the CLI, and import the ZIP into the client’s account. The ZIP carries the configuration and code, not the data, and the imported project is a new project with its own IDs, so update any IDs your code uses.
3. To ship an update, generate a Catalyst CLI token and run catalyst deploy --project <name_or_id> --org <org_id> --token <token> for each client project, from a script or a Catalyst Pipelines job. This updates each project’s Development environment.
4. Deploy each project from Development to Production in its console, from Settings → Environments → Deployments.

Refer to the CLI Options help page and the IaC Settings help page for details.