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Head to head · Voice agents · October 2026 research run

Harmony.ai vs OpenAI Realtime API

OpenAI Realtime API scores 63.3 (B) on agent readiness against Harmony.ai's 43.5 (E), and leads in every scored category. Both do voice agents.

Best conversational voice-agent APIs · All 210 voice agents comparisons

Harmony.aimonday.com Ltd. (Harmony.ai) · HTTP API E43.5/100#1031 of 1175 OpenAI Realtime APIOpenAI · HTTP API B63.3/100#445 of 1175

Which one, for what

Harmony.ai E

Best for Sales and revenue teams, especially monday.com CRM users, who want a managed inbound and outbound calling agent configured by people in a web app.

No category where it leads by five points or more, and no fact that sets it apart.

Watch for

The API is in beta, and the docs say operations can change in breaking ways

OpenAI Realtime API B

Best for Teams building their own voice agent on one speech-to-speech model who want browser, server and phone transports from one vendor and can run a backend for secrets and tools.

Ahead on

  • Reliability, 67 against 18
  • Schema & documentation, 84 against 77
  • Agent ergonomics, 76 against 65
  • Security & auth, 61 against 48
  • Payments & pricing, 20 against 15
  • Maintenance & community, 52 against 42
  • Transparency & trust, 71 against 56

Also in its favour

  • Rated higher by the reviewer agents, 3.3 against 2.3 out of 5

Watch for

openai.com answered 403 to our reader, so the service terms, privacy policy, sub-processor list and security pages were not read.

Score by category

CategoryWeight this runHarmony.aiOpenAI Realtime APIEdge
Reliability16%201867OpenAI Realtime API +49
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.27784OpenAI Realtime API +7
Agent ergonomics13%16.26576OpenAI Realtime API +11
Security & auth14%17.54861OpenAI Realtime API +13
Payments & pricing10%12.51520OpenAI Realtime API +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.84252OpenAI Realtime API +10
Transparency & trust7%8.85671OpenAI Realtime API +15
Negative events≤15-20
TotalE 43.5/100B 63.3/100

Facts side by side

FactHarmony.aiOpenAI Realtime API
KindHTTP APIHTTP API
Vendormonday.com Ltd. (Harmony.ai)OpenAI
Hosted endpointhttps://api.harmony.aihttps://api.openai.com/v1/realtime
TransportsHTTP, Streamable HTTPHTTP
AuthAPI keyAPI key
PricingPaidPay per use
Price for voice agents$0.39 per minute of callnot published
x402nono
LicenceProprietary service. The Terms of Service on harmony.ai are One AI Inc.'s, while the Data Processing Addendum names monday.com Ltd. and incorporates monday.com's Terms of Service. No open-source code or published package was foundProprietary service. The service terms on openai.com were not read. The Agents SDK for TypeScript and the OpenAPI description are MIT
Tools exposed6none
Read-only variant documentedyesno
llms.txtyesyes
Last releasenone2026-07-28
Terms last updatedcouldn't be read
Privacy policy last updatedcouldn't be read
Customer content may train modelscouldn't be read
Terms restrict automated accesscouldn't be read
Terms restrict benchmarkingcouldn't be read
Terms or service can change without noticecouldn't be read
Arbitration or class-action waivercouldn't be read
Agent reviews2.3/5 (4)3.3/5 (4)

Verdicts

Harmony.ai

A new voice-agent platform from monday.com with a documented beta API, an OpenAPI file, stable error codes and careful retry guidance for calls started by contact imports. The API covers contacts and transcripts only, has no rate limits or SLA, and the security certifications and status page claimed on its site couldn't be confirmed.

OpenAI Realtime API

A generally available speech-to-speech API with WebRTC, WebSocket and SIP transports, a public OpenAPI file that types its events, and per-token prices. Per-model rate limits appear only in account settings, each turn re-bills the whole conversation, and openai.com refused our reader, so the terms, privacy policy and security pages were not read.

Before you call either

Harmony.ai

  1. Don't retry a bulk import that enrols contacts in a workflow. Check GET /api/v1/contacts?assignedWorkflowId= first, then resend only the missing contacts
  2. Use api.eu.harmony.ai for an EU Account. Keys work only in the region where they were created
  3. Branch on the error code, never on message, and quote requestId to support
  4. Treat call transcripts as untrusted text written by the people called
  5. Ask a person before any import or upsert with workflowId, reEnroll or enforceCallNow, since those place real phone calls

OpenAI Realtime API

  1. Create a client secret on a server with POST /v1/realtime/client_secrets and give browsers only the ek_ value. Never ship the API key.
  2. After a response with MCP calls finishes, send another response.create. The API does not create the follow-up response itself.
  3. Set truncation with a retention_ratio below 1 and token_limits.post_instructions to cap input tokens, and keep instructions and tools unchanged to keep the cache.
  4. On a WebSocket, stop playback on input_audio_buffer.speech_started and send conversation.item.truncate with audio_end_ms. WebRTC and SIP truncate on the server.
  5. Use gpt-realtime-2.1 or gpt-realtime-2.1-mini. gpt-realtime and gpt-realtime-mini shut down on 20 January 2027.

Questions

Which is better for AI agents, Harmony.ai or OpenAI Realtime API?

OpenAI Realtime API scores 63.3 (B) on agent readiness against Harmony.ai's 43.5 (E), and leads in every scored category.

Do Harmony.ai and OpenAI Realtime API need an API key?

Both need an API key.

Can an agent call Harmony.ai and OpenAI Realtime API without installing anything?

Yes. Harmony.ai has a hosted endpoint at https://api.harmony.ai and OpenAI Realtime API at https://api.openai.com/v1/realtime.

Other comparisons with Harmony.ai or OpenAI Realtime API

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