> For a complete page index, fetch https://docs.synthflow.ai/llms.txt. For full documentation content, fetch https://docs.synthflow.ai/llms-full.txt.

# Concurrency

> Understand Synthflow concurrency and CAPS limits, how they differ, and what happens when your workspace exceeds them.

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.

| Account setup                            | Concurrency limit                        |
| ---------------------------------------- | ---------------------------------------- |
| Enterprise or account-managed deployment | Scoped with Synthflow                    |
| Existing legacy workspace                | Shown in your workspace or account terms |

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.

**Legacy plans**: Earlier Pro, Growth, and Agency plans were issued with fixed concurrency limits. These plans are no longer available for new subscriptions and remain supported for existing customers. Your current limit is shown in your workspace or account terms.

## CAPS: Call Attempts Per Second

**CAPS (Call Attempts Per Second)** defines how frequently you can trigger the [Make a Phone Call](/api-reference/platform-api/calls/voice-call) API. It limits how often you can start calls, not how many calls can be active at once.

| Account setup                            | CAPS limit                               |
| ---------------------------------------- | ---------------------------------------- |
| Enterprise or account-managed deployment | Scoped with Synthflow                    |
| Existing legacy workspace                | Shown in your workspace or account terms |

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](https://synthflow.ai/talk-to-sales) 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?

Depending on your account setup, excess calls can return a `429` HTTP error or be queued briefly. Contact your account team if you need predictable handling at higher volume.

#### Can I increase my limits?

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

#### How do subaccounts share limits?

Concurrency is set by your plan, and your accounts and subaccounts share the main account's total. [Contact our sales team](https://synthflow.ai/talk-to-sales) if you need more capacity.

#### How do I avoid hitting CAPS limits when calling a large list?

[Campaigns](/batch-calling) dial within your concurrency limit instead of firing requests at the API, so a campaign is the safest way to work through a long list. Set [`reserved_concurrency`](/batch-calling#control-dialing-speed) to hold back slots for inbound traffic and one-off calls.

If you instead drive calls yourself from GoHighLevel, HubSpot, Zapier, or another automation tool, add a delay or throttle between calls. A 1-second delay between call initiations keeps you 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.