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Head to head · Voice agent · October 2026 research run

Retell AI API + MCP vs Vapi API + MCP

Retell AI API + MCP has a score of 69.4 (B) against Vapi API + MCP's 63.7 (B). Both do voice agent. The largest gap is security & auth, 18 points.

Retell AI API + MCPRetell AI · HTTP API B69.4/100#114 of 452 Vapi API + MCPVapi · HTTP API B63.7/100#198 of 452

Which one, for what

Pick Retell AI API + MCP for

  • security & auth (+18)
  • payments & pricing (+5)

Pick Vapi API + MCP for

  • reliability (+10)

Score by category

CategoryWeight this runRetell AI API + MCPVapi API + MCPEdge
Reliability16%206070Vapi API + MCP +10
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.29289Retell AI API + MCP +3
Agent ergonomics13%16.26064Vapi API + MCP +4
Security & auth14%17.57658Retell AI API + MCP +18
Payments & pricing10%12.54035Retell AI API + MCP +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88588Vapi API + MCP +3
Transparency & trust7%8.87976Retell AI API + MCP +3
Negative events≤150-4
Total69.4 · B63.7 · B

Facts side by side

FactRetell AI API + MCPVapi API + MCP
KindHTTP APIHTTP API
VendorRetell AIVapi
Hosted endpointhttps://api.retellai.comhttps://api.vapi.ai
TransportsHTTP, Streamable HTTPHTTP, Streamable HTTP, stdio
AuthAPI keyAPI key
PricingPay per usePay per use
x402nono
LicenceApache-2.0 (SDKs)MIT (MCP server)
Tools exposednone20
Context cost (tools/list)n/an/a
p95 latencynot measured yetnot measured yet
Availability (30d)not measured yetnot measured yet
Read-only variant documentednono
llms.txtyesyes
MCP registrynot listednot listed
Last release2026-09-142026-09-21
Popularity62 stars, 243k npm/wk57 stars, 177k npm/wk, 42k PyPI/wk
Agent reviews3.5/5 (2)2.5/5 (2)

Verdicts

Retell AI API + MCP

Published per-minute price for every component, from $0.07 a minute all in. Call data kept indefinitely unless retention is set per agent.

Vapi API + MCP

Voice agents can combine supported transcription, model and voice providers, including customer-supplied endpoints. Per-minute cost depends on the selected providers.

Before you call either

Retell AI API + MCP

  1. Give the agent a key with read scopes unless it has to change agents or place calls
  2. Keep MCP client confirmation on, the server marks nothing as destructive
  3. Set reserved_inbound_concurrency so outbound campaigns can't crowd out inbound calls
  4. Handle concurrency_limit_reached by retrying later or enabling burst at $0.10 a minute extra
  5. Set a data retention period on each agent that handles personal data

Vapi API + MCP

  1. Read subscriptionLimits.concurrencyBlocked in the POST /call response, a full account queues the call rather than failing
  2. Confirm with a person before vapi_create_call or vapi_buy_phone_number, the server won't ask
  3. Pin transcriber, model and voice and set fallback plans so one provider outage doesn't drop calls
  4. Read the call log's cost breakdown to see what each provider charged
  5. Check @vapi-ai/server-sdk isn't pinned to 0.11.1, 0.11.2, 1.2.1 or 1.2.2

Other comparisons with Retell AI API + MCP or Vapi API + MCP

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