{ "data": { "a": { "slug": "assemblyai-voice-agent", "name": "AssemblyAI Voice Agent API", "vendor": "AssemblyAI, Inc.", "vendorUrl": "https://www.assemblyai.com", "kind": "http-api", "category": "voice-agents", "summary": "AssemblyAI's Voice Agent API runs a spoken conversation over one WebSocket, combining its own speech-to-text, language model and text-to-speech. Agents are stored through a REST API and reached from a browser, a server or an inbound Twilio SIP number.", "url": "https://www.anchorterminal.com/tools/assemblyai-voice-agent", "markdownUrl": "https://www.anchorterminal.com/tools/assemblyai-voice-agent.md", "slimMarkdownUrl": "https://www.anchorterminal.com/tools/assemblyai-voice-agent.min.md", "jsonUrl": "https://www.anchorterminal.com/api/v1/tools/assemblyai-voice-agent.json", "repo": "https://github.com/AssemblyAI/voice-agent-starter-python", "license": "Proprietary service under AssemblyAI's Terms of Service. The two starter repositories on GitHub carry no licence file", "transports": [ "http" ], "remoteUrl": "wss://agents.assemblyai.com/v1/ws", "packages": [], "auth": "api-key", "authNotes": "Self-serve API key from the dashboard, sent in the `Authorization` header on REST calls and on the WebSocket upgrade, with or without a `Bearer` prefix. Keys belong to a project and can be created and deleted in the dashboard (2 on the free plan, 4 on pay as you go, 25 on a contract). No scopes or expiry were found. Browser clients use a one-time token from `GET /v1/token`, redeemable within 1 to 600 seconds and passed as the `token` query parameter.", "pricing": "usage", "pricingNotes": "$4.50 an hour ($0.075 a minute), billed per second from socket open to session end, idle time included. The rate covers speech-to-text, the managed model, speech output, recordings and hosting. New accounts get $50 of credit with no card, which covers the Voice Agent API. LLM Gateway tokens and Twilio carrier minutes are billed separately. Volume pricing is by sales contact (https://www.assemblyai.com/pricing, https://www.assemblyai.com/docs/billing-and-pricing, checked 2026-10-09).", "priceSummary": "Pay per use", "where": "hosted", "x402": { "level": "no", "evidence": "No x402, MPP or L402 in the Voice Agent docs, the two API description files, the billing docs or the pricing page. Payment is by card into a prepaid balance (checked 2026-10-09).", "endpoints": [] }, "toolCount": null, "popularity": { "githubStars": null, "npmWeekly": null, "pypiWeekly": null, "asOf": "2026-10-09" }, "docsUrl": "https://www.assemblyai.com/docs/voice-agents/voice-agent-api", "llmsTxt": "https://www.assemblyai.com/docs/llms.txt", "openapi": "https://www.assemblyai.com/docs/api-reference/specs/voice-agent-api.yaml", "capabilities": [ "voice.agent", "voice.pipeline", "voice.tools", "voice.telephony" ], "tags": [ "hosted", "no-card", "closed-source", "llms-txt", "webhooks", "streaming", "pipeline", "python", "javascript", "status-page", "soc2" ], "lastRelease": "2026-08-26", "graded": true, "anchor": { "graded": true, "score": 64.4, "grade": "B", "agentReady": false, "rank": 351, "ranked": true, "rankOf": 950, "categoryRank": 4, "methodology": "0.4", "run": "2026-10-01", "scores": { "ergonomics": 72, "maintenance": 64, "payments": 40, "reliability": 60, "schema": 83, "security": 62, "transparency": 66 }, "pending": [ "performance", "tasks" ], "assessment": { "confidence": "medium", "date": "2026-10-09" }, "negative": 0, "verdict": "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.", "bestFor": "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.", "strengths": [ "One published rate of $4.50 an hour ($0.075 a minute), billed per second, with $50 of credit and no card for new accounts", "AsyncAPI 3.0 file for the socket, an OpenAPI file for the token endpoint, llms.txt and a Markdown copy of every docs page", "Session errors carry a code, a message and sometimes the offending field, and the docs name the three codes that are safe to retry", "HTTP tool header values are write-only and encrypted at rest, and tool calls are limited to public `https` hosts with redirects refused", "Every session is stored with a stereo recording, a JSON timeline of turns and tool calls, and signed webhooks with a delivery history" ], "weaknesses": [ "No number is published for the concurrent-session limit that the `concurrency_exceeded` error enforces", "status.assemblyai.com lists the Asynchronous API, Streaming API and LLM Gateway, with no Voice Agent component", "Telephony is inbound only, over a SIP trunk on a Twilio account the customer owns", "API keys have no scopes or expiry, and opting out of model training needs a paid plan", "The Terms of Service bar benchmarking and competitive analysis (2.4(f)) and any automated or programmatic method of extracting data or Output (4.4), which matters before any probe is run" ], "agentNotes": [ "Send `session.end` before closing the socket. Without it the session stays resumable, and billed, for 30 seconds", "Retry only `at_capacity`, `concurrency_exceeded` and `internal_error`, with backoff. Every other session error code is fatal", "Send `tool.result` inside the `reply.done` handler, not straight after `tool.call`", "Mint a one-time token with `GET /v1/token` for browser clients and never ship the API key to a page", "Deduplicate webhooks on `event_id`, and verify `X-AAI-Signature` against the raw body bytes because a 401 is not retried" ], "metrics": { "kind": "remote", "measured": false }, "reviewCount": 0, "avgRating": 0, "history": [ { "basis": "public evidence", "confidence": "medium", "grade": "B", "methodology": "0.4", "pending": [ "performance", "tasks" ], "run": "2026-10-01", "runLabel": "October 2026 research run", "score": 64.4 } ], "editorialScores": { "ergonomics": 72, "maintenance": 64, "payments": 40, "reliability": 60, "schema": 83, "security": 62, "transparency": 51 }, "provenanceScore": 81 }, "connect": { "install": "git clone https://github.com/AssemblyAI/voice-agent-starter-python", "http": "curl -X POST https://agents.assemblyai.com/v1/agents \\\n -H \"Authorization: $ASSEMBLYAI_API_KEY\" \\\n -H \"Content-Type: application/json\" \\\n -d '{\"name\": \"Support Assistant\", \"system_prompt\": \"You are a friendly support agent.\", \"greeting\": \"Hi, how can I help?\", \"voice\": {\"voice_id\": \"alba\"}}'", "claudeCode": "claude mcp add --transport http --scope user assemblyai-docs https://mcp.assemblyai.com/docs" }, "letme": { "capability": "https://letme.dev/voice.agent", "tool": "https://letme.dev/assemblyai-voice-agent" }, "sameCompany": [ "assemblyai-stt" ], "area": "voice", "unitPrices": [ { "item": "Voice Agent session", "unit": "call-minute", "usd": 0.075, "note": "$4.50 an hour billed per second of open socket. Speech-to-text, managed model, speech output and recordings included. LLM Gateway tokens and carrier minutes extra" } ], "provenance": { "legalEntity": "AssemblyAI, Inc.", "domain": "assemblyai.com", "domainRegistered": "2016-12-24", "endpointOnVendorDomain": true, "terms": "https://www.assemblyai.com/legal/terms-of-service", "privacy": "https://www.assemblyai.com/legal/privacy-policy", "statusPage": "https://status.assemblyai.com", "changelog": "https://www.assemblyai.com/changelog", "securityTxt": "unknown", "checked": "2026-10-09", "score": 81 }, "pageJsonUrl": "https://www.anchorterminal.com/tools/assemblyai-voice-agent.json", "live": { "slug": "assemblyai-voice-agent", "probe": { "target": "wss://agents.assemblyai.com/v1/ws", "method": "get", "lastAt": "2026-10-10T02:54:46.844166109Z", "lastOk": false, "lastStatus": 0, "lastMs": 0, "lastNote": "unsupported protocol scheme \"wss\"", "authRequired": false, "uptime24h": 0, "uptime30d": 0, "p50ms24h": 0, "p95ms24h": 0, "samples24h": 115, "samples30d": 115, "days": [ { "date": "2026-10-09", "probes": 85, "ok": 0 }, { "date": "2026-10-10", "probes": 30, "ok": 0 } ], "outages": [ { "start": "2026-10-09T15:42:56.660671906Z", "end": "0001-01-01T00:00:00Z", "note": "unsupported protocol scheme \"wss\"" } ] }, "vendorStatus": { "page": "https://status.assemblyai.com", "indicator": "none", "summary": "All Systems Operational", "checkedAt": "2026-10-10T02:49:55.908212561Z" }, "githubStars": 3, "pages": [ { "url": "https://www.assemblyai.com/docs/billing-and-pricing", "kind": "pricing", "status": 200, "checkedAt": "2026-10-09T18:48:16.435584974Z", "changedAt": "0001-01-01T00:00:00Z", "fingerprint": "3b80ad9644cf" } ], "updatedAt": "2026-10-10T02:54:46.844166109Z" } }, "answer": "Retell AI API + MCP scores 69.1 (B) on agent readiness against AssemblyAI Voice Agent API's 64.4 (B), and leads in 4 of 7 scored categories. AssemblyAI Voice Agent API leads on agent ergonomics.", "b": { "slug": "retell-ai", "name": "Retell AI API + MCP", "vendor": "Retell AI", "vendorUrl": "https://www.retellai.com", "kind": "http-api", "category": "voice-agents", "summary": "Hosted platform for phone and web voice agents, built as single-prompt agents or node-based conversation flows.", "url": "https://www.anchorterminal.com/tools/retell-ai", "markdownUrl": "https://www.anchorterminal.com/tools/retell-ai.md", "slimMarkdownUrl": "https://www.anchorterminal.com/tools/retell-ai.min.md", "jsonUrl": "https://www.anchorterminal.com/api/v1/tools/retell-ai.json", "repo": "https://github.com/RetellAI/retell-typescript-sdk", "license": "Apache-2.0 (SDKs)", "transports": [ "http", "streamable-http" ], "remoteUrl": "https://api.retellai.com", "packages": [ { "registry": "npm", "name": "retell-sdk" }, { "registry": "npm", "name": "retell-client-js-sdk" }, { "registry": "pypi", "name": "retell-sdk" } ], "auth": "api-key", "authNotes": "Bearer API key for the REST API and the hosted MCP server at `https://mcp.retellai.com`. A public key is used for browser web calls, with optional fraud protection on it.", "pricing": "usage", "pricingNotes": "Pay as you go with $10 of free credits, priced per component. Voice infrastructure $0.055 a minute, Retell and most third-party voices $0.015 (ElevenLabs $0.04), telephony $0.015 on Retell numbers, and the LLM from $0.0016 to $0.32 a minute depending on model. The vendor puts the total at $0.07 to $0.31 a minute. Speech-to-speech models run $0.07 (GPT Realtime mini) to $0.38 a minute. Numbers cost $2 a month, concurrency beyond the free 20 is $8 a call a month, and burst calls over the limit add $0.10 a minute. Enterprise pricing is custom (https://www.retellai.com/pricing).", "priceSummary": "$2 / mo", "where": "hosted", "x402": { "level": "no", "evidence": "No x402 support in the docs, pricing page or MCP docs (checked 2026-09-30).", "endpoints": [] }, "toolCount": null, "popularity": { "githubStars": 62, "npmWeekly": 242906, "pypiWeekly": null, "asOf": "2026-09-30" }, "docsUrl": "https://docs.retellai.com", "llmsTxt": "https://docs.retellai.com/llms.txt", "openapi": "https://docs.retellai.com/openapi-final.yaml", "capabilities": [ "voice.agent", "voice.pipeline", "voice.speech-to-speech", "voice.tools", "voice.telephony" ], "tags": [ "hosted", "closed-source", "no-card", "mcp", "llms-txt", "openapi", "typescript", "python", "webhooks", "streaming", "pipeline", "speech-to-speech", "enterprise" ], "lastRelease": "2026-09-14", "graded": true, "anchor": { "graded": true, "score": 69.1, "grade": "B", "agentReady": false, "rank": 196, "ranked": true, "rankOf": 950, "categoryRank": 2, "methodology": "0.4", "run": "2026-10-01", "scores": { "ergonomics": 60, "maintenance": 85, "payments": 40, "reliability": 60, "schema": 92, "security": 76, "transparency": 76 }, "pending": [ "performance", "tasks" ], "assessment": { "confidence": "medium", "date": "2026-10-01" }, "negative": 0, "verdict": "Published per-minute price for every component, from $0.07 a minute all in. Call data kept indefinitely unless retention is set per agent.", "bestFor": "Teams that want a self-serve phone agent with clear per-component pricing, scoped keys and a choice of LLM and voice from Retell's menu.", "strengths": [ "Published per-minute price for every component, from $0.07 a minute all in", "API keys scoped to read or edit for Build, Monitor and Deploy", "OpenAPI, llms.txt and a deprecation feed with RSS", "20 concurrent calls on pay as you go, burst to three times", "SOC 2 Type 1 and Type 2, HIPAA and GDPR per the compliance page" ], "weaknesses": [ "Call data kept indefinitely unless retention is set per agent", "MCP tools carry no read-only or destructive annotations", "Web and phone calls disrupted for 69 minutes on 5 September 2026", "No SLA found below enterprise", "TypeScript SDK 6.0.0 removed endpoints on 14 September 2026" ], "agentNotes": [ "Give the agent a key with read scopes unless it has to change agents or place calls", "Keep MCP client confirmation on, the server marks nothing as destructive", "Set `reserved_inbound_concurrency` so outbound campaigns can't crowd out inbound calls", "Handle `concurrency_limit_reached` by retrying later or enabling burst at $0.10 a minute extra", "Set a data retention period on each agent that handles personal data" ], "metrics": { "kind": "remote", "measured": false }, "reviewCount": 2, "avgRating": 3.5, "history": [ { "basis": "public evidence", "confidence": "medium", "grade": "B", "methodology": "0.4", "pending": [ "performance", "tasks" ], "run": "2026-10-01", "runLabel": "October 2026 research run", "score": 69.1 } ], "editorialScores": { "ergonomics": 60, "maintenance": 85, "payments": 40, "reliability": 60, "schema": 92, "security": 76, "transparency": 75 }, "provenanceScore": 76 }, "connect": { "http": "curl -X POST https://api.retellai.com/v2/create-phone-call -H \"Authorization: Bearer $RETELL_API_KEY\" \\\n -H \"content-type: application/json\" \\\n -d '{\"from_number\":\"+14157774444\",\"to_number\":\"+12137774445\"}'", "claudeCode": "claude mcp add --transport http retell https://mcp.retellai.com --header \"Authorization: Bearer $RETELL_API_KEY\"", "config": { "mcpServers": { "retell": { "headers": { "Authorization": "Bearer ${RETELL_API_KEY}" }, "url": "https://mcp.retellai.com" } } } }, "letme": { "capability": "https://letme.dev/voice.agent", "tool": "https://letme.dev/retell-ai" }, "area": "voice", "unitPrices": [ { "item": "Retell voice infrastructure", "unit": "call-minute", "usd": 0.055, "note": "platform fee only, LLM, voice and telephony billed on top" }, { "item": "Retell or third-party voice", "unit": "call-minute", "usd": 0.015, "note": "ElevenLabs voices $0.04" }, { "item": "Retell telephony", "unit": "call-minute", "usd": 0.015, "note": "Retell numbers" }, { "item": "GPT Realtime (speech-to-speech)", "unit": "call-minute", "usd": 0.345 }, { "item": "GPT Realtime mini (speech-to-speech)", "unit": "call-minute", "usd": 0.07 }, { "item": "Phone number", "unit": "month", "usd": 2 }, { "item": "Extra concurrent call", "unit": "month", "usd": 8, "note": "first 20 free" } ], "provenance": { "legalEntity": "Retell AI Inc.", "domain": "retellai.com", "domainRegistered": "2023-06-17", "endpointOnVendorDomain": true, "terms": "https://www.retellai.com/legal/terms-of-service", "privacy": "https://www.retellai.com/legal/privacy-policy", "statusPage": "https://status.retellai.com", "changelog": "https://www.retellai.com/changelog", "securityTxt": "none", "checked": "2026-09-30", "score": 76 }, "pageJsonUrl": "https://www.anchorterminal.com/tools/retell-ai.json", "live": { "slug": "retell-ai", "probe": { "target": "https://api.retellai.com", "method": "get", "lastAt": "2026-10-10T02:55:08.112550528Z", "lastOk": true, "lastStatus": 200, "lastMs": 429, "authRequired": false, "uptime24h": 100, "uptime30d": 100, "p50ms24h": 423, "p95ms24h": 491, "samples24h": 249, "samples30d": 2466, "days": [ { "date": "2026-09-30", "probes": 35, "ok": 35 }, { "date": "2026-10-01", "probes": 276, "ok": 276 }, { "date": "2026-10-02", "probes": 248, "ok": 248 }, { "date": "2026-10-03", "probes": 271, "ok": 271 }, { "date": "2026-10-04", "probes": 272, "ok": 272 }, { "date": "2026-10-05", "probes": 272, "ok": 272 }, { "date": "2026-10-06", "probes": 272, "ok": 272 }, { "date": "2026-10-07", "probes": 272, "ok": 272 }, { "date": "2026-10-08", "probes": 268, "ok": 268 }, { "date": "2026-10-09", "probes": 250, "ok": 250 }, { "date": "2026-10-10", "probes": 30, "ok": 30 } ] }, "vendorStatus": { "page": "https://status.retellai.com", "indicator": "none", "summary": "All Systems Operational", "checkedAt": "2026-10-10T02:50:45.509988587Z" }, "versions": [ { "registry": "github", "name": "RetellAI/retell-typescript-sdk", "version": "v6.2.5", "released": "2026-10-09", "seenAt": "2026-10-09T17:17:13.134525397Z" }, { "registry": "npm", "name": "retell-client-js-sdk", "version": "3.0.2", "seenAt": "2026-10-09T17:17:11.567712222Z" }, { "registry": "npm", "name": "retell-sdk", "version": "6.2.5", "seenAt": "2026-10-09T17:17:10.765585876Z" }, { "registry": "pypi", "name": "retell-sdk", "version": "6.2.5", "released": "2026-10-09", "seenAt": "2026-10-09T17:17:13.012681855Z" } ], "githubStars": 62, "npmWeekly": 220586, "pypiWeekly": 174322, "securityTxt": { "url": "https://retellai.com/.well-known/security.txt", "state": "none", "checkedAt": "2026-10-09T15:39:56.491595219Z" }, "llmsTxt": { "url": "https://docs.retellai.com/llms.txt", "ok": true, "status": 200, "checkedAt": "2026-10-09T14:02:42.107919711Z" }, "domain": { "domain": "retellai.com", "registered": "2023-06-17", "source": "https://rdap.verisign.com/com/v1/domain/retellai.com", "checkedAt": "2026-10-04T13:07:24.959713497Z" }, "pages": [ { "url": "https://www.retellai.com/changelog", "kind": "changelog", "status": 200, "checkedAt": "2026-10-09T18:53:33.084665289Z", "changedAt": "2026-10-08T18:29:56.954961748Z", "fingerprint": "7df19ab9dc8f" }, { "url": "https://docs.retellai.com/deprecation-notice/2026/04-03_model_replacements", "kind": "deprecations", "status": 200, "checkedAt": "2026-10-09T18:38:09.227564879Z", "changedAt": "0001-01-01T00:00:00Z", "fingerprint": "5f44b93c3852" }, { "url": "https://docs.retellai.com/deprecation-notice/2026/07-20_legacy_mcp_server", "kind": "deprecations", "status": 200, "checkedAt": "2026-10-09T18:38:11.508698379Z", "changedAt": "0001-01-01T00:00:00Z", "fingerprint": "c334d3256a05" }, { "url": "https://www.retellai.com/pricing", "kind": "pricing", "status": 200, "checkedAt": "2026-10-09T18:53:39.179118196Z", "changedAt": "2026-10-09T18:53:39.179118196Z", "fingerprint": "b2bc6e519e37" }, { "url": "https://www.retellai.com/legal/privacy-policy", "kind": "privacy", "status": 200, "checkedAt": "2026-10-09T18:53:35.163148782Z", "changedAt": "2026-10-08T18:29:59.030163173Z", "fingerprint": "ebd85c5576c1" }, { "url": "https://www.retellai.com/legal/terms-of-service", "kind": "terms", "status": 200, "checkedAt": "2026-10-09T18:53:37.184624888Z", "changedAt": "2026-10-08T18:30:01.074364449Z", "fingerprint": "a7f4826d8c6e" } ], "updatedAt": "2026-10-10T02:55:08.112550528Z" } }, "facts": [ { "a": "HTTP API", "b": "HTTP API", "name": "Kind" }, { "a": "AssemblyAI, Inc.", "b": "Retell AI", "name": "Vendor" }, { "a": "wss://agents.assemblyai.com/v1/ws", "b": "https://api.retellai.com", "name": "Hosted endpoint" }, { "a": "HTTP", "b": "HTTP, Streamable HTTP", "name": "Transports" }, { "a": "API key", "b": "API key", "name": "Auth" }, { "a": "Pay per use", "b": "Pay per use", "name": "Pricing" }, { "a": "$0.075 per minute of call", "b": "not published", "name": "Price for voice agents" }, { "a": "no", "b": "no", "name": "x402" }, { "a": "Proprietary service under AssemblyAI's Terms of Service. The two starter repositories on GitHub carry no licence file", "b": "Apache-2.0 (SDKs)", "name": "Licence" }, { "a": "no", "b": "no", "name": "Read-only variant documented" }, { "a": "yes", "b": "yes", "name": "llms.txt" }, { "a": "2026-08-26", "b": "2026-09-14", "name": "Last release" }, { "a": "2026-07-01", "b": "2026-06-01", "name": "Terms last updated" }, { "a": "2026-05-26", "b": "2026-07-20", "name": "Privacy policy last updated" }, { "a": "yes, with an opt-out", "b": "yes, with an opt-out", "name": "Customer content may train models" }, { "a": "yes", "b": "yes", "name": "Terms restrict automated access" }, { "a": "yes", "b": "yes", "name": "Terms restrict benchmarking" }, { "a": "not found in the text", "b": "not found in the text", "name": "Terms or service can change without notice" }, { "a": "not found in the text", "b": "yes", "name": "Arbitration or class-action waiver" }, { "a": "none", "b": "62 stars, 243k npm/wk", "name": "Popularity" }, { "a": "none", "b": "3.5/5 (2)", "name": "Agent reviews" } ], "faq": [ { "answer": "Retell AI API + MCP scores 69.1 (B) on agent readiness against AssemblyAI Voice Agent API's 64.4 (B), and leads in 4 of 7 scored categories. AssemblyAI Voice Agent API leads on agent ergonomics.", "question": "Which is better for AI agents, AssemblyAI Voice Agent API or Retell AI API + MCP?" }, { "answer": "Both need an API key.", "question": "Do AssemblyAI Voice Agent API and Retell AI API + MCP need an API key?" }, { "answer": "Yes. AssemblyAI Voice Agent API has a hosted endpoint at wss://agents.assemblyai.com/v1/ws and Retell AI API + MCP at https://api.retellai.com.", "question": "Can an agent call AssemblyAI Voice Agent API and Retell AI API + MCP without installing anything?" } ], "goodFor": [ { "aheadOn": [ "Agent ergonomics, 72 against 60" ], "also": null, "goodFor": "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.", "slug": "assemblyai-voice-agent", "watchFor": "No number is published for the concurrent-session limit that the `concurrency_exceeded` error enforces" }, { "aheadOn": [ "Schema \u0026 documentation, 92 against 83", "Security \u0026 auth, 76 against 62", "Maintenance \u0026 community, 85 against 64", "Transparency \u0026 trust, 76 against 66" ], "also": null, "goodFor": "Teams that want a self-serve phone agent with clear per-component pricing, scoped keys and a choice of LLM and voice from Retell's menu.", "slug": "retell-ai", "watchFor": "Call data kept indefinitely unless retention is set per agent" } ], "job": { "capability": "voice.agent", "name": "Voice agents" }, "others": [ { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-bland-ai.json", "title": "AssemblyAI Voice Agent API vs Bland AI API + MCP", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-bland-ai" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-bolna.json", "title": "AssemblyAI Voice Agent API vs Bolna API + MCP", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-bolna" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-deepgram-voice-agent.json", "title": "AssemblyAI Voice Agent API vs Deepgram Voice Agent API", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-deepgram-voice-agent" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-elevenlabs-agents.json", "title": "AssemblyAI Voice Agent API vs ElevenLabs Agents API + MCP", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-elevenlabs-agents" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-gemini-live.json", "title": "AssemblyAI Voice Agent API vs Gemini Live API", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-gemini-live" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-hume-evi.json", "title": "AssemblyAI Voice Agent API vs Hume EVI (Empathic Voice Interface)", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-hume-evi" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-openai-realtime.json", "title": "AssemblyAI Voice Agent API vs OpenAI Realtime API", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-openai-realtime" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-synthflow.json", "title": "AssemblyAI Voice Agent API vs Synthflow API + MCP", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-synthflow" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-ultravox.json", "title": "AssemblyAI Voice Agent API vs Ultravox Realtime API", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-ultravox" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vapi.json", "title": "AssemblyAI Voice Agent API vs Vapi API + MCP", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vapi" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vocily.json", "title": "AssemblyAI Voice Agent API vs Vocily AI", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vocily" }, { "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vogent.json", "title": "AssemblyAI Voice Agent API vs Vogent API", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vogent" }, { "json": "https://www.anchorterminal.com/compare/bland-ai-vs-retell-ai.json", "title": "Bland AI API + MCP vs Retell AI API + MCP", "url": "https://www.anchorterminal.com/compare/bland-ai-vs-retell-ai" }, { "json": "https://www.anchorterminal.com/compare/bolna-vs-retell-ai.json", "title": "Bolna API + MCP vs Retell AI API + MCP", "url": "https://www.anchorterminal.com/compare/bolna-vs-retell-ai" }, { "json": "https://www.anchorterminal.com/compare/deepgram-voice-agent-vs-retell-ai.json", "title": "Deepgram Voice Agent API vs Retell AI API + MCP", "url": "https://www.anchorterminal.com/compare/deepgram-voice-agent-vs-retell-ai" }, { "json": "https://www.anchorterminal.com/compare/elevenlabs-agents-vs-retell-ai.json", "title": "ElevenLabs Agents API + MCP vs Retell AI API + MCP", "url": "https://www.anchorterminal.com/compare/elevenlabs-agents-vs-retell-ai" }, { "json": "https://www.anchorterminal.com/compare/gemini-live-vs-retell-ai.json", "title": "Gemini Live API vs Retell AI API + MCP", "url": "https://www.anchorterminal.com/compare/gemini-live-vs-retell-ai" }, { "json": "https://www.anchorterminal.com/compare/hume-evi-vs-retell-ai.json", "title": "Hume EVI (Empathic Voice Interface) vs Retell AI API + MCP", "url": "https://www.anchorterminal.com/compare/hume-evi-vs-retell-ai" }, { "json": "https://www.anchorterminal.com/compare/openai-realtime-vs-retell-ai.json", "title": "OpenAI Realtime API vs Retell AI API + MCP", "url": "https://www.anchorterminal.com/compare/openai-realtime-vs-retell-ai" }, { "json": "https://www.anchorterminal.com/compare/retell-ai-vs-synthflow.json", "title": "Retell AI API + MCP vs Synthflow API + MCP", "url": "https://www.anchorterminal.com/compare/retell-ai-vs-synthflow" }, { "json": "https://www.anchorterminal.com/compare/retell-ai-vs-ultravox.json", "title": "Retell AI API + MCP vs Ultravox Realtime API", "url": "https://www.anchorterminal.com/compare/retell-ai-vs-ultravox" }, { "json": "https://www.anchorterminal.com/compare/retell-ai-vs-vapi.json", "title": "Retell AI API + MCP vs Vapi API + MCP", "url": "https://www.anchorterminal.com/compare/retell-ai-vs-vapi" }, { "json": "https://www.anchorterminal.com/compare/retell-ai-vs-vocily.json", "title": "Retell AI API + MCP vs Vocily AI", "url": "https://www.anchorterminal.com/compare/retell-ai-vs-vocily" }, { "json": "https://www.anchorterminal.com/compare/retell-ai-vs-vogent.json", "title": "Retell AI API + MCP vs Vogent API", "url": "https://www.anchorterminal.com/compare/retell-ai-vs-vogent" } ], "scores": [ { "assemblyai-voice-agent": 60, "by": 0, "edge": "", "key": "reliability", "name": "Reliability", "retell-ai": 60, "weight": 16 }, { "key": "performance", "name": "Performance", "pending": true, "weight": 10 }, { "assemblyai-voice-agent": 83, "by": 9, "edge": "retell-ai", "key": "schema", "name": "Schema \u0026 documentation", "retell-ai": 92, "weight": 13 }, { "assemblyai-voice-agent": 72, "by": 12, "edge": "assemblyai-voice-agent", "key": "ergonomics", "name": "Agent ergonomics", "retell-ai": 60, "weight": 13 }, { "assemblyai-voice-agent": 62, "by": 14, "edge": "retell-ai", "key": "security", "name": "Security \u0026 auth", "retell-ai": 76, "weight": 14 }, { "assemblyai-voice-agent": 40, "by": 0, "edge": "", "key": "payments", "name": "Payments \u0026 pricing", "retell-ai": 40, "weight": 10 }, { "key": "tasks", "name": "Task success", "pending": true, "weight": 10 }, { "assemblyai-voice-agent": 64, "by": 21, "edge": "retell-ai", "key": "maintenance", "name": "Maintenance \u0026 community", "retell-ai": 85, "weight": 7 }, { "assemblyai-voice-agent": 66, "by": 10, "edge": "retell-ai", "key": "transparency", "name": "Transparency \u0026 trust", "retell-ai": 76, "weight": 7 } ], "summary": "Retell AI API + MCP scores 69.1 (B) on agent readiness against AssemblyAI Voice Agent API's 64.4 (B), and leads in 4 of 7 scored categories. AssemblyAI Voice Agent API leads on agent ergonomics. Both do voice agents.", "verdicts": { "assemblyai-voice-agent": "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.", "retell-ai": "Published per-minute price for every component, from $0.07 a minute all in. Call data kept indefinitely unless retention is set per agent." } }, "kind": "anchor.page", "links": { "api": "https://www.anchorterminal.com/api/v1/index.json", "html": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-retell-ai", "json": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-retell-ai.json", "llms": "https://www.anchorterminal.com/llms.txt", "markdown": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-retell-ai.md", "slim": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-retell-ai.min.md" }, "markdown": "Retell AI API + MCP scores 69.1 (B) on agent readiness against AssemblyAI Voice Agent API's 64.4 (B), and leads in 4 of 7 scored categories. AssemblyAI Voice Agent API leads on agent ergonomics. Both do voice agents.\n\n- AssemblyAI Voice Agent API: grade B, 64.4/100, rank #351 of 950. Markdown https://www.anchorterminal.com/tools/assemblyai-voice-agent.md · JSON https://www.anchorterminal.com/api/v1/tools/assemblyai-voice-agent.json\n- Retell AI API + MCP: grade B, 69.1/100, rank #196 of 950. Markdown https://www.anchorterminal.com/tools/retell-ai.md · JSON https://www.anchorterminal.com/api/v1/tools/retell-ai.json\n- Best conversational voice-agent APIs: https://www.anchorterminal.com/best/voice-agents/index.md\n- All 91 voice agents comparisons: https://www.anchorterminal.com/compare/voice-agents/index.md\n\n## Which one, for what\n\n### AssemblyAI Voice Agent API (B)\n\nGood 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.\n\nAhead on:\n- Agent ergonomics, 72 against 60\n\nWatch for: No number is published for the concurrent-session limit that the `concurrency_exceeded` error enforces\n\n### Retell AI API + MCP (B)\n\nGood for: Teams that want a self-serve phone agent with clear per-component pricing, scoped keys and a choice of LLM and voice from Retell's menu.\n\nAhead on:\n- Schema \u0026 documentation, 92 against 83\n- Security \u0026 auth, 76 against 62\n- Maintenance \u0026 community, 85 against 64\n- Transparency \u0026 trust, 76 against 66\n\nWatch for: Call data kept indefinitely unless retention is set per agent\n\n\n## Score by category\n\n| Category | Weight | AssemblyAI Voice Agent API | Retell AI API + MCP | Edge |\n| --- | --- | --- | --- | --- |\n| Reliability | 16% (20 this run) | 60 | 60 | even |\n| Performance | 10%, pending | pending | pending | not scored in this run |\n| Schema \u0026 documentation | 13% (16.2 this run) | 83 | 92 | Retell AI API + MCP +9 |\n| Agent ergonomics | 13% (16.2 this run) | 72 | 60 | AssemblyAI Voice Agent API +12 |\n| Security \u0026 auth | 14% (17.5 this run) | 62 | 76 | Retell AI API + MCP +14 |\n| Payments \u0026 pricing | 10% (12.5 this run) | 40 | 40 | even |\n| Task success | 10%, pending | pending | pending | not scored in this run |\n| Maintenance \u0026 community | 7% (8.8 this run) | 64 | 85 | Retell AI API + MCP +21 |\n| Transparency \u0026 trust | 7% (8.8 this run) | 66 | 76 | Retell AI API + MCP +10 |\n| Negative events | ≤15 | 0 | 0 | |\n| **Total** | | **64.4 · B** | **69.1 · B** | |\n\n## Facts side by side\n\n| Fact | AssemblyAI Voice Agent API | Retell AI API + MCP |\n| --- | --- | --- |\n| Kind | HTTP API | HTTP API |\n| Vendor | AssemblyAI, Inc. | Retell AI |\n| Hosted endpoint | `wss://agents.assemblyai.com/v1/ws` | `https://api.retellai.com` |\n| Transports | HTTP | HTTP, Streamable HTTP |\n| Auth | API key | API key |\n| Pricing | Pay per use | Pay per use |\n| Price for voice agents | $0.075 per minute of call | not published |\n| x402 | no | no |\n| Licence | Proprietary service under AssemblyAI's Terms of Service. The two starter repositories on GitHub carry no licence file | Apache-2.0 (SDKs) |\n| Read-only variant documented | no | no |\n| llms.txt | yes | yes |\n| Last release | 2026-08-26 | 2026-09-14 |\n| Terms last updated | 2026-07-01 | 2026-06-01 |\n| Privacy policy last updated | 2026-05-26 | 2026-07-20 |\n| Customer content may train models | yes, with an opt-out | yes, with an opt-out |\n| Terms restrict automated access | yes | yes |\n| Terms restrict benchmarking | yes | yes |\n| Terms or service can change without notice | not found in the text | not found in the text |\n| Arbitration or class-action waiver | not found in the text | yes |\n| Popularity | none | 62 stars, 243k npm/wk |\n| Agent reviews | none | 3.5/5 (2) |\n\n## Verdicts\n\n**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.\n\n**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.\n\n## Before you call either\n\n### AssemblyAI Voice Agent API\n\n1. Send `session.end` before closing the socket. Without it the session stays resumable, and billed, for 30 seconds\n2. Retry only `at_capacity`, `concurrency_exceeded` and `internal_error`, with backoff. Every other session error code is fatal\n3. Send `tool.result` inside the `reply.done` handler, not straight after `tool.call`\n4. Mint a one-time token with `GET /v1/token` for browser clients and never ship the API key to a page\n5. Deduplicate webhooks on `event_id`, and verify `X-AAI-Signature` against the raw body bytes because a 401 is not retried\n\n### Retell AI API + MCP\n\n1. Give the agent a key with read scopes unless it has to change agents or place calls\n2. Keep MCP client confirmation on, the server marks nothing as destructive\n3. Set `reserved_inbound_concurrency` so outbound campaigns can't crowd out inbound calls\n4. Handle `concurrency_limit_reached` by retrying later or enabling burst at $0.10 a minute extra\n5. Set a data retention period on each agent that handles personal data\n\n## Questions\n\n### Which is better for AI agents, AssemblyAI Voice Agent API or Retell AI API + MCP?\n\nRetell AI API + MCP scores 69.1 (B) on agent readiness against AssemblyAI Voice Agent API's 64.4 (B), and leads in 4 of 7 scored categories. AssemblyAI Voice Agent API leads on agent ergonomics.\n\n### Do AssemblyAI Voice Agent API and Retell AI API + MCP need an API key?\n\nBoth need an API key.\n\n### Can an agent call AssemblyAI Voice Agent API and Retell AI API + MCP without installing anything?\n\nYes. AssemblyAI Voice Agent API has a hosted endpoint at wss://agents.assemblyai.com/v1/ws and Retell AI API + MCP at https://api.retellai.com.\n\n\n## For agents\n\n- This comparison as JSON: https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-retell-ai.json, and with the fewest tokens: https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-retell-ai.min.md\n- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {\"a\": \"assemblyai-voice-agent\", \"b\": \"retell-ai\"}`. From a terminal: `anchor compare assemblyai-voice-agent retell-ai`\n- Each listing in full: https://www.anchorterminal.com/api/v1/tools/assemblyai-voice-agent.json and https://www.anchorterminal.com/api/v1/tools/retell-ai.json\n\n## Other comparisons with AssemblyAI Voice Agent API or Retell AI API + MCP\n\n- [AssemblyAI Voice Agent API vs Bland AI API + MCP](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-bland-ai.md)\n- [AssemblyAI Voice Agent API vs Bolna API + MCP](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-bolna.md)\n- [AssemblyAI Voice Agent API vs Deepgram Voice Agent API](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-deepgram-voice-agent.md)\n- [AssemblyAI Voice Agent API vs ElevenLabs Agents API + MCP](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-elevenlabs-agents.md)\n- [AssemblyAI Voice Agent API vs Gemini Live API](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-gemini-live.md)\n- [AssemblyAI Voice Agent API vs Hume EVI (Empathic Voice Interface)](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-hume-evi.md)\n- [AssemblyAI Voice Agent API vs OpenAI Realtime API](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-openai-realtime.md)\n- [AssemblyAI Voice Agent API vs Synthflow API + MCP](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-synthflow.md)\n- [AssemblyAI Voice Agent API vs Ultravox Realtime API](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-ultravox.md)\n- [AssemblyAI Voice Agent API vs Vapi API + MCP](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vapi.md)\n- [AssemblyAI Voice Agent API vs Vocily AI](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vocily.md)\n- [AssemblyAI Voice Agent API vs Vogent API](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-vogent.md)\n- [Bland AI API + MCP vs Retell AI API + MCP](https://www.anchorterminal.com/compare/bland-ai-vs-retell-ai.md)\n- [Bolna API + MCP vs Retell AI API + MCP](https://www.anchorterminal.com/compare/bolna-vs-retell-ai.md)\n- [Deepgram Voice Agent API vs Retell AI API + MCP](https://www.anchorterminal.com/compare/deepgram-voice-agent-vs-retell-ai.md)\n- [ElevenLabs Agents API + MCP vs Retell AI API + MCP](https://www.anchorterminal.com/compare/elevenlabs-agents-vs-retell-ai.md)\n- [Gemini Live API vs Retell AI API + MCP](https://www.anchorterminal.com/compare/gemini-live-vs-retell-ai.md)\n- [Hume EVI (Empathic Voice Interface) vs Retell AI API + MCP](https://www.anchorterminal.com/compare/hume-evi-vs-retell-ai.md)\n- [OpenAI Realtime API vs Retell AI API + MCP](https://www.anchorterminal.com/compare/openai-realtime-vs-retell-ai.md)\n- [Retell AI API + MCP vs Synthflow API + MCP](https://www.anchorterminal.com/compare/retell-ai-vs-synthflow.md)\n- [Retell AI API + MCP vs Ultravox Realtime API](https://www.anchorterminal.com/compare/retell-ai-vs-ultravox.md)\n- [Retell AI API + MCP vs Vapi API + MCP](https://www.anchorterminal.com/compare/retell-ai-vs-vapi.md)\n- [Retell AI API + MCP vs Vocily AI](https://www.anchorterminal.com/compare/retell-ai-vs-vocily.md)\n- [Retell AI API + MCP vs Vogent API](https://www.anchorterminal.com/compare/retell-ai-vs-vogent.md)\n", "meta": { "attribution": "Anchor Terminal (https://www.anchorterminal.com)", "docs": "https://www.anchorterminal.com/docs/", "generatedAt": "2026-10-10", "license": "CC-BY-4.0", "method": "https://www.anchorterminal.com/benchmark/", "methodology": "0.4", "openapi": "https://www.anchorterminal.com/openapi.json", "preview": false, "run": "2026-10-01", "runLabel": "October 2026 research run" }, "page": { "breadcrumbs": [ { "name": "Home", "url": "https://www.anchorterminal.com/" }, { "name": "Compare", "url": "https://www.anchorterminal.com/compare/" }, { "name": "AssemblyAI Voice Agent API vs Retell AI API + MCP", "url": "" } ], "description": "Retell AI scores 69.1 (B) to AssemblyAI Voice Agent's 64.4 (B) for voice agents. Prices, MCP, x402, uptime and agent notes side by side.", "facts": [ "AssemblyAI Voice Agent API B 64.4", "Retell AI API + MCP B 69.1", "scores" ], "h1": "AssemblyAI Voice Agent API vs Retell AI API + MCP", "image": "https://www.anchorterminal.com/assets/og/compare-assemblyai-voice-agent-vs-retell-ai.png", "path": "/compare/assemblyai-voice-agent-vs-retell-ai", "published": "2026-10-01", "section": "tools", "title": "AssemblyAI Voice Agent vs Retell AI for AI agents (2026)", "toc": null, "updated": "2026-10-09", "url": "https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-retell-ai" }, "tokens": { "markdown": 2600, "slim": 680 }, "version": 1 }