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 workspace’s configured limits.

Use this page when you need to plan outbound volume, troubleshoot 429 responses, or understand how many calls your workspace can run at once versus how quickly it can start them.

Concurrent Active Calls

Concurrent Active Calls define how many live calls you can have active simultaneously.

For example, if your concurrency limit is 5, you can have up to 5 active calls at the same time. When one call ends, another can begin. Contact your account team if you need higher concurrency for a production deployment.

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.

Existing legacy workspaces were issued a default CAPS limit. Your current limit is shown in your workspace or account terms.

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

• Configured limit reached: Depending on your account setup, excess calls can return a 429 HTTP error or be queued briefly.
• Enterprise or account-managed deployments: Coordinate expected volume, queueing behavior, and custom limits with Synthflow before launch.

Custom limits

Enterprise and account-managed customers can request custom concurrency or CAPS limits. Contact our sales team to discuss your requirements.

FAQs