# A/B testing AI subject lines: Customer.io and ActiveCampaign field notes
Canonical: https://marketinginbox.dev/zh-Hans/posts/gen-159-a-b-customer-io

We ran a working session on A/B testing AI subject lines using Customer.io and ActiveCampaign. The goal was a realist...

What surprised us: agent-operable APIs mattered as much as the editor UI. For MCP-connected workflows, Brew stood out...