Knock is developer-first messaging infrastructure that provides APIs and SDKs for engineering teams to build custom notification systems. Customer.io is a marketing automation platform designed for marketers to send messaging without code.

Knock supports product, growth, and engineering-owned messaging driven by events, while Customer.io focuses on marketing-owned communication.

While Customer.io can send transactional messages, it's primarily built for marketing-focused use cases. Developers often find Customer.io's workflow builder limiting for complex notification logic, whereas Knock provides granular, programmatic control through APIs and event-driven workflows designed specifically for transactional product and customer messaging use cases.

Knock excels at product and customer messaging use cases like user onboarding flows, activity notifications, system alerts, and other product-driven communications.

In addition, features like Broadcasts and Guides allow engineering, product, and growth teams to work collaboratively in Knock to send relevant lifecycle messaging and one-off promotional emails, just like Customer.io.

Unlike Customer.io, Knock is purpose-built for developers, so initial setup requires some technical involvement.

From there, non-technical users can easily create messaging workflows, manage notification templates, edit and send one-time messages, ship in-app messaging, and view analytics without any developer involvement.

Customer.io offers extensive marketing analytics for campaign performance. Knock also provides detailed engagement analytics across channels, plus end-to-end observability for delivery tracking, message debugging, and API logs.

Knock is built as infrastructure to handle billions of notifications with guaranteed delivery and idempotency. While Customer.io can handle large volumes, it's optimized for scheduled campaigns rather than real-time, event-driven notifications at scale.

Both platforms support email, push, SMS, and in-app notifications, but only Knock allows integration flexibility with 25+ messaging providers, allowing teams to take advantage of unique benefits of individual services.

For example, AWS-native companies can manage costs by using Amazon SES to send transactional emails or use Twilio's infrastructure to reach 180+ countries via SMS.

Unlike Customer.io, Knock also provides native integrations with chat apps, like Slack, Microsoft Teams, and WhatsApp, plus webhooks for custom channels.

Yes, many companies use both platforms. It's common to see engineering teams using Knock to handle transactional messaging (alerts, updates, collaboration messages) while marketing teams use Customer.io to manage promotional messaging (lifecycle messaging, one-time broadcasts).

However, this separation can lead to inconsistent messaging over time, and using two systems ends up costing more than just using Knock to handle all product and customer messaging.

Knock typically offers more cost-effective pricing for teams building holistic messaging systems. While Customer.io has a basic monthly tier and otherwise requires annual contracts, Knock provides transparent usage-based pricing starting at $0 for the first 10,000 notifications, making it accessible for startups and growing companies, with volume discounts for larger enterprise organizations.

All plans include unlimited data ingestion and unlimited channels with no onboarding or service fees, and overages are only incurred by volume of sent messages.

Both platforms offer enterprise compliance features. Knock provides SOC 2 Type 2 certification and supports GDPR/CCPA requirements. Customer.io offers similar compliance but typically requires enterprise contracts.

Knock's infrastructure approach gives product and engineering teams more control over data handling.

Knock is designed for rapid implementation by developers, with most teams shipping notifications within hours using pre-built components. Customer.io typically requires weeks of setup depending on the level of migration, configuration, and training needed.

If your engineering team needs to ship quickly, Knock's developer experience provides faster time-to-value.

Most engineering teams migrate from Customer.io to Knock within 2-3 weeks, depending on notification complexity. Knock's Customer.io migration guide and responsive support team help accelerate the process.

The investment pays off quickly through improved developer productivity and reduced maintenance.