Sinch has written a developer guide to WhatsApp API integration, and its first point clears out a lot of stale tutorials: since Meta sunset the On-Premises API in October 2025, “the Cloud API is the only architecture.” There is nothing to host, so the decision is whose API you call, Meta’s directly or a provider’s built on top of it. The guide’s best line is the mental model: “WhatsApp is a conversation platform, not a fire-and-forget pipe.” Teams that bolt webhooks on late, Sinch says, end up rebuilding their data model around conversations anyway.
The limits are the useful part, and they are Meta’s rules rather than Sinch’s marketing. Business-initiated conversations are capped per rolling 24 hours, starting at 1,000 unique customers and scaling to 10,000, 100,000 and unlimited. Every inbound message opens a 24-hour window for free-form replies. Templates are reviewed by Meta, typically minutes to a few hours, so design them before the flows. Marketing templates to U.S. numbers have been paused since April 2025. The vendor part is the build-versus-buy pitch, and Sinch states it fairly: the Cloud API is free to call, while template ops, compliance, monitoring and fallbacks “is where the engineering months go.” That is what a provider like Sinch sells.
The catalog shows that Sinch’s own surface is shaped the way the guide says an integration should be. Sinch on apis.io carries 101 API pages, and the four moving parts each map to one. The account is the Sinch WhatsApp Accounts API and Sinch WhatsApp Senders API; templates are the Sinch WhatsApp Templates API; the send call and the multichannel fallback go through the Sinch Conversation API; inbound replies and receipts arrive through the Sinch Webhooks API; and the in-chat forms are the Sinch WhatsApp Flows API. The agentic access profile counts 550 operations, 299 acting and 68 human-in-the-loop.
Sinch scores 71.5 on the Kin Score, exemplar, carried by operational transparency at 84.2, discoverability at 81.7 and developer ergonomics at 79.8. Agent Readiness is 55.6, and event surface described is lit, which is the measured version of the guide’s insistence that webhooks are the core feature. Idempotency is lit too, which matters for a send call behind a messaging cap. The two weak facets are access clarity at 50.0 and contract governance at 22.0, and on the agent side delegated identity and consent identity are unlit. For a platform whose whole guide is about opt-ins and template approval, consent is the dimension to watch.