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Head to head · Voice agents · October 2026 research run

AssemblyAI Voice Agent API vs Vocily AI

AssemblyAI Voice Agent API scores 64.4 (B) on agent readiness against Vocily AI's 53.8 (D), and leads in 4 of 7 scored categories. Vocily AI leads on schema & documentation and agent ergonomics. Both do voice agents.

Best conversational voice-agent APIs · All 91 voice agents comparisons

AssemblyAI Voice Agent APIAssemblyAI, Inc. · HTTP API B64.4/100#351 of 950 Vocily AIVocily AI Private Limited · HTTP API D53.8/100#701 of 950

Which one, for what

AssemblyAI Voice Agent API B

Good for A developer who wants one managed pipeline at a flat rate and is content with AssemblyAI's own speech models and voices, with an optional model of their own.

Ahead on

  • Reliability, 60 against 40
  • Security & auth, 62 against 46
  • Transparency & trust, 66 against 47

Also in its favour

  • Free to start without a card
  • No incidents deducted, where Vocily AI loses 5 points for them

Watch for

No number is published for the concurrent-session limit that the concurrency_exceeded error enforces

Vocily AI D

Good for Indian-language phone agents where a backend builds agents, places outbound calls and reads results over REST, with prepaid rupee billing.

Ahead on

  • Schema & documentation, 90 against 83
  • Agent ergonomics, 84 against 72

Watch for

No status page, incident history or SLA was found

Score by category

CategoryWeight this runAssemblyAI Voice Agent APIVocily AIEdge
Reliability16%206040AssemblyAI Voice Agent API +20
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28390Vocily AI +7
Agent ergonomics13%16.27284Vocily AI +12
Security & auth14%17.56246AssemblyAI Voice Agent API +16
Payments & pricing10%12.54040even
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86461AssemblyAI Voice Agent API +3
Transparency & trust7%8.86647AssemblyAI Voice Agent API +19
Negative events≤150-5
Total64.4 · B53.8 · D

Facts side by side

FactAssemblyAI Voice Agent APIVocily AI
KindHTTP APIHTTP API
VendorAssemblyAI, Inc.Vocily AI Private Limited
Hosted endpointwss://agents.assemblyai.com/v1/wshttps://api.vocily.ai
TransportsHTTPHTTP
AuthAPI keyAPI key
PricingPay per usePay per use
Price for voice agents$0.075 per minute of callnot published
x402nono
LicenceProprietary service under AssemblyAI's Terms of Service. The two starter repositories on GitHub carry no licence fileProprietary service under Vocily's terms of service. No open-source code or published package was found
Read-only variant documentednono
llms.txtyesyes
Last release2026-08-262026-09-30
Terms last updated2026-07-012026-06-10
Privacy policy last updated2026-05-262026-09-03
Customer content may train modelsyes, with an opt-outnot found in the text
Terms restrict automated accessyesnot found in the text
Terms restrict benchmarkingyesnot found in the text
Terms or service can change without noticenot found in the textnot found in the text
Arbitration or class-action waivernot found in the textnot found in the text

Verdicts

AssemblyAI Voice Agent API

One $0.075 a minute rate covers speech-to-text, the managed model, speech output, recordings and hosting, and the socket has an AsyncAPI file, typed error codes and a 30-second resume window. No concurrent-session limit is published, the status page has no Voice Agent component, and phone calls are inbound only through a Twilio trunk the customer owns.

Vocily AI

The REST API is documented in detail for a product a few months old, with an OpenAPI 3.1 file, required idempotency keys on calls, a Retry-After header on 429 and signed webhooks. No status page, SLA, SDK or security programme was found, and two releases in September 2026 removed fields under /v1 on the day they were announced.

Before you call either

AssemblyAI Voice Agent API

  1. Send session.end before closing the socket. Without it the session stays resumable, and billed, for 30 seconds
  2. Retry only at_capacity, concurrency_exceeded and internal_error, with backoff. Every other session error code is fatal
  3. Send tool.result inside the reply.done handler, not straight after tool.call
  4. Mint a one-time token with GET /v1/token for browser clients and never ship the API key to a page
  5. Deduplicate webhooks on event_id, and verify X-AAI-Signature against the raw body bytes because a 401 is not retried

Vocily AI

  1. Send a fresh UUID in Idempotency-Key on every POST /v1/calls. The API refuses the request without it
  2. Pass a from_number the workspace holds. The shared Test Number returns 403 from the API
  3. Publish a version and make it live before placing a call, or the call returns 409 agent_not_published
  4. Branch on detail.code, falling back to the top-level code. A 429 body is flat, so read Retry-After
  5. Read currency on every call and chat record. Costs are in rupees or dollars depending on the organisation

Questions

Which is better for AI agents, AssemblyAI Voice Agent API or Vocily AI?

AssemblyAI Voice Agent API scores 64.4 (B) on agent readiness against Vocily AI's 53.8 (D), and leads in 4 of 7 scored categories. Vocily AI leads on schema & documentation and agent ergonomics.

Do AssemblyAI Voice Agent API and Vocily AI need an API key?

Both need an API key.

Can an agent call AssemblyAI Voice Agent API and Vocily AI without installing anything?

Yes. AssemblyAI Voice Agent API has a hosted endpoint at wss://agents.assemblyai.com/v1/ws and Vocily AI at https://api.vocily.ai.

Other comparisons with AssemblyAI Voice Agent API or Vocily AI

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