You have a launch date, a product manager asking when customers can message you on WhatsApp, and a browser full of tutorials that disagree with each other. Some tell you to host a server. Some tell you to treat WhatsApp like SMS. You need to know which advice is stale before you commit engineering time.
Sinch has published a developer guide to WhatsApp API integration, and its first point clears out a lot of that noise. Meta sunset the On-Premises API in October 2025, so, in the guide's words, "the Cloud API is the only architecture." There is nothing for you to host. The real decision is whose API you call: Meta's directly, or a provider's built on top of it.
The guide's best line is its mental model: "WhatsApp is a conversation platform, not a fire-and-forget pipe." Sinch says teams that bolt webhooks on late end up rebuilding their data model around conversations anyway. If you were planning to send first and think about inbound replies later, that is the warning aimed at you.
Then come the limits, which are Meta's rules rather than Sinch's marketing, and they are the useful part. 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 in which you can reply free-form. Templates are reviewed by Meta, typically in minutes to a few hours, so you should design them before you design the flows. And marketing templates to U.S. numbers have been paused since April 2025, which matters if your first campaign was headed there.
The guide also makes a vendor pitch, and it states it fairly. The Cloud API is free to call. Template operations, compliance, monitoring and fallbacks are, in the guide's phrase, where the engineering months go. That is what a provider like Sinch sells. You can weigh that as a build-versus-buy question rather than a slogan.
Here is the turn. A guide is a company describing itself, so it is worth checking whether the company's own record agrees. The APIs.io catalog lists Sinch with 101 API pages, and the four moving parts the guide describes each map to one. Your account and sender setup sit in the Sinch WhatsApp Accounts API and Senders API. Templates have their own 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 in-chat forms are the WhatsApp Flows API. The shape you would build against matches the shape the guide recommends.
The catalog's numbers add detail. Its agentic access profile counts 550 operations, 299 of them acting and 68 human-in-the-loop. Sinch scores 71.5 on the Kin Score, in the exemplar band, carried by operational transparency at 84.2, discoverability at 81.7 and developer ergonomics at 79.8. Agent Readiness is 55.6. 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 that sits behind a messaging cap.
The catalog also files weaknesses against Sinch. Access clarity is 50.0 and contract governance is 22.0. 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, so ask Sinch how it handles that before you assume it does.
What you take away is practical. Skip any tutorial that mentions hosting. Plan around conversations, not messages: webhooks first, templates before flows, and your tier cap in the schedule. If you buy rather than build, the provider's surface does line up with the guide's advice, but its published record is weakest exactly where your compliance questions will land.
Read the original: https://apis.io/2026/11/03/sinch-says-whatsapp-is-a-conversation-platform-and-its-api-surface-agrees/