Every vendor in this category advertises uptime in the same narrow band, all self-reported and none independently audited. Those numbers are not a way to choose between them.
More importantly, they measure the wrong thing. The API responding is not the failure mode you should worry about. The failure mode is your line getting flagged, at which point the API is up, healthy, and delivering nothing.
What actually determines reliability
| Factor | Why it matters more than uptime | What to ask |
|---|---|---|
| Dedicated vs shared line | On a shared pool, another customer's behaviour degrades your delivery | Is a dedicated number available, and at what price? |
| Number replacement time | A line will eventually be flagged. Recovery speed is the real SLA | What happens, how fast, and do I keep the number? |
| Published rate limits | A vendor that throttles you is protecting your line | What are the limits, and do I get a clear 429? |
| Webhook retries | Inbound loss is silent and worse than an outage you can see | Do you retry, how many times, and is ordering preserved? |
| Line warm-up guidance | New lines sending at volume is the classic flag pattern | Do you ramp new lines, or warn me to? |
Reliability is partly your behaviour, not just theirs
A vendor cannot protect a line from a customer who blasts 500 identical messages on day one. Ramp slowly, vary your messages, expect replies, honour opt-outs instantly — the full list.
Testing reliability before you commit
- Kill your webhook endpoint and send yourself a reply. Bring it back up. Did the message arrive? This single test tells you more than any uptime page.
- Send a burst past the rate limit. A clear 429 with a
Retry-Afteris good. Silence, or accepted-then-dropped, is bad. - Send to an Android number. Clean SMS fallback, explicit error, or silent loss? Silent loss is disqualifying.
- Run for two weeks and watch delivery rate. A quiet decline is what account trouble looks like before it becomes an outage.
And regardless of vendor: build the fallback. A tested SMS path turns the worst case from an outage into a degradation. Error handling and retries covers the implementation.
Common questions
- Which iMessage API is most reliable?
- There is no independently verified answer. The factors that actually predict reliability are whether your line is dedicated, whether the vendor publishes rate limits, whether inbound webhooks retry, and how quickly a flagged number is replaced.