Hi there, Hope you're doing well. I understand that enabling more than 10 concurrent calls requires purchasing additional lines. However, I was wondering—if I have a single Twilio number and I'm paying for hundreds of concurrent lines, is there a limit to how many calls that number can handle at once? Would the bottleneck come from Twilio itself, or is it solely dependent on VAPI and the number of concurrent lines I have available there? Hope that makes sense—looking forward to your insights! Best, Matteo

Hi Matteo! 👋 I understand you're curious about concurrent call limits when using a single Twilio number with Vapi. I don't have the exact concurrent call limit for a single Twilio number, but I can definitely help explain how the limits work between both platforms. According to the information I found, the bottleneck could potentially come from both Twilio and Vapi: For Vapi's side: - Vapi has a default concurrent request limit of 10 simultaneous calls (combining both inbound and outbound) [according to Vapi's documentation](https://docs.vapi.ai/billing/billing-limits) - This limit is applied at the account level, not at the phone number level, so importing a number from Twilio doesn't change this limit - You can increase this by purchasing additional concurrent lines through the Vapi dashboard, as you mentioned For Twilio's side: - Twilio does have concurrent call limits that depend on the type of number you have (local, mobile, toll-free) and your service plan - The specific limits vary based on these factors, and Twilio's documentation would have the exact numbers for your specific number type and plan When using both services together, both limits would apply. So even if you purchase hundreds of concurrent lines on Vapi, you might still be limited by Twilio's concurrent call limits for your specific number type and plan. Is there anything else you'd like to know about how Vapi and Twilio work together? Sources: - [Vapi's documentation](https://docs.vapi.ai/billing/billing-limits) - [Discord thread about concurrent call limits](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1324731877235359816) - [Discord thread about Vapi's concurrency limits](https://discord.com/channels/1211482211119796234/1211483291191083018/threads/1343465716686520393)

Hey Matt, You are correct about VAPI's concurrent call handling and how it works. But for Twilio's, we cannot comment on anything. You have to check with the Twilio team regarding your phone numbers rate limitation or concurrent calls limitations.

Twilio has its own set of limitations in regards to these, mainly, the number of calls you are allowed to initiated per second (aka CPS). As far as I can recall, their limit is 1 CPS per customer account. Now, even if you increase the number of concurrent calls, it won't always matter. Here's the math to explain. Let's assume you generate a call every second. Let's say that your answer rate is around 30% (which is huge for auto dialing). That means , every 3 seconds, you connect 1 call. Let's say the average call length is 60 seconds. So, in one minute, you'll connect 20 calls, which will achieve a top concurrency of 20 calls after a minute. At the minute mark calls will start disconnecting, and the cycle begins again. If your answer rate drops below 30%, your concurrency will drop. If your call length drops, same. In other words, more channels aren't always the answer. If you'd like, DM me and we'll go over your use case and I'll see if I can recommend you a more "workable" solution path to your requirements.