Throughput is the number of messages a gateway or route can accept and deliver per second (TPS); it decides how long a large campaign takes to leave and is shaped by carrier limits and pacing.
Every link in the chain has a ceiling: your API rate limit, the gateway's queue, the route's agreed rate with the operator, the operator's own capacity. A campaign of one million messages at 200 per minute takes about three and a half days; at 50 per second, under six hours. Pacing is often chosen below the maximum on purpose, so that replies and clicks land at a rate your team can handle.
Throughput is not delivery: a fast route that drops messages is worse than a slower one that delivers.
At SMSMeteor: the API accepts 50 requests per second per key and batches of 1,000 messages per API request; campaigns can be paced per minute or spread over hours, and the estimate shows the expected duration before you send.