Every plan has a concurrency limit — the number of calls that can be live at the same time. It is the least glamorous setting in the product and the one that decides whether a batch finishes this afternoon or on Thursday.
The arithmetic
It is simple enough to do in your head.
Wall-clock time ≈ (number of calls × average minutes) ÷ concurrency
Two thousand calls at 4 minutes each is 8,000 call-minutes. At a concurrency of 1, that is 8,000 minutes — five and a half days of continuous dialling. At 5, just over a day. At 20, about seven hours.
Same list, same cost, same agent. The only variable is how many phones ring at once.
Why it is capped at all
Three reasons, and only one of them is commercial.
Your caller ID. A single number placing forty simultaneous calls looks, to a carrier's spam heuristics, exactly like a robocall operation. The consequence is not a warning; it is your number getting flagged, and flagged numbers stop connecting. Concurrency limits protect the asset you are calling from.
Whoever answers. If your agent hands off to a human — a recruiter, a sales rep — then concurrency higher than the number of available humans just produces people on hold.
Capacity. Every live call holds a media connection and a speech pipeline. This is the commercial part, and it is the reason the limit rises with the plan.
Announcements are different, deliberately
One-way announcement calls do not use the conversation concurrency limit. They can be dialled in parallel, because there is no conversation to hold up and no human to hand off to — the message is cached audio and the call ends when it finishes.
This is why a thousand-person alert goes out in minutes while a thousand-person screening batch takes hours. If a job is time-critical and one-way, do not run it as a conversation.
Planning a batch backwards
Start from the deadline, not the list.
- How many calls, and how long is each? Multiply.
- Divide by your concurrency. That is your dialling time.
- Now apply the calling window. If you may only dial between 9 AM and 7 PM, you have ten usable hours a day, not twenty-four — this is the step people forget, and it doubles most estimates.
- Add a retry pass for no-answers, which is typically a third of the list on a first attempt.
Two thousand screening calls at concurrency 5 is about 27 hours of dialling, which inside a ten-hour window is three working days before retries. If someone needs the shortlist on Wednesday, that batch starts Monday morning, not Tuesday night.
When to raise it
Raise concurrency when the arithmetic says you will miss a deadline — not by default. And if you are dialling hard from a single number, consider a second one: spreading volume across two caller IDs is better for deliverability than pushing one number to its limit.
The limit is per workspace and set by your plan. See the plans for the current numbers.