Concurrency
Synthflow enforces concurrency and rate limits to maintain system stability and call quality. This page explains how concurrency and CAPS work, how they differ, and what happens when you exceed your plan’s limits.
Concurrent Active Calls
Concurrent Active Calls define how many live calls you can have active simultaneously.
For example, if your concurrency limit is 50, you can have up to 50 active calls at the same time. When one call ends, another can begin.
CAPS — Call Attempts Per Second
CAPS (Call Attempts Per Second) defines how frequently you can trigger the Make a Phone Call API. It limits how often you can start calls, not how many calls can be active at once.
For example, if you have a CAPS limit of 2, you can initiate 2 new outbound calls per second. Sending 10 call requests in 1 second would exceed the limit and some would be rejected or queued.
Understanding the difference
- Concurrency = how many calls you have active — controls the number of simultaneous live calls
- CAPS = how fast you start calls — controls the rate at which you can initiate new calls
Both limits work together to ensure system stability and call quality.
Behavior when limits are exceeded
- Non‑Enterprise tiers: Exceeding the Concurrency or CAPS limit returns a
429HTTP error. Excess calls are not processed. - Enterprise tier: A priority queueing system processes calls exceeding the limit with a brief delay, providing flexibility and scalability.
Scope
These limits apply to outbound calls only. Inbound calls are not affected.
If you use workflows with GoHighLevel, HubSpot, Zapier, or other automation tools, implement a delay or throttle mechanism when batching calls to stay within CAPS limits.
Custom limits
Enterprise customers can request custom concurrency or CAPS limits. Contact our sales team to discuss your requirements.
FAQs
What's the difference between concurrency and CAPS?
Concurrency limits control how many calls can be active at the same time. CAPS limits control how quickly you can start new calls. Both limits work together to ensure system stability and call quality.
What happens when I exceed my concurrency limit?
On Non-Enterprise tiers, you’ll receive a 429 HTTP error and excess calls will not be processed. On Enterprise tier, a priority queueing system will handle calls exceeding the limit with a brief delay.
Do these limits apply to inbound calls?
No. Both concurrency and CAPS limits apply to outbound calls only. Inbound calls are not affected by these restrictions.
Can I increase my limits?
Yes. Enterprise customers can request custom concurrency or CAPS limits. Contact our sales team to discuss your specific requirements and usage patterns.
How do I avoid hitting CAPS limits when batch calling?
If you use workflows with GoHighLevel, HubSpot, Zapier, or other automation tools, implement a delay or throttle mechanism when batching calls. For example, add a 1-second delay between each call initiation to stay within the default CAPS limit.
Can I monitor my current usage?
You can view active call counts in your dashboard analytics. For API-based monitoring, track 429 HTTP error responses which indicate you’ve hit a limit.
