{ "data": { "a": { "slug": "heygen-voice", "name": "HeyGen Voice", "vendor": "HeyGen", "vendorUrl": "https://www.heygen.com", "kind": "model", "category": "text-to-speech", "summary": "HeyGen Voice is HeyGen's in-house text-to-speech model, `heygen-voice-1` with a Turbo variant, which speaks HeyGen's public voices or voices cloned from one recording (instant) or 20 minutes or more (professional), through HeyGen's v3 API.", "url": "https://www.anchorterminal.com/tools/heygen-voice", "markdownUrl": "https://www.anchorterminal.com/tools/heygen-voice.md", "slimMarkdownUrl": "https://www.anchorterminal.com/tools/heygen-voice.min.md", "jsonUrl": "https://www.anchorterminal.com/api/v1/tools/heygen-voice.json", "dns": "heygen-voice.grade.anchorterminal.com", "license": "Closed service under HeyGen's Terms of Service (HeyGen Technology, Inc., last updated 23 July 2026).", "transports": [ "http" ], "remoteUrl": "https://api.heygen.com", "packages": [], "auth": "api-key", "authNotes": "An API key from the HeyGen API dashboard, sent in the X-Api-Key header. Keys can be restricted to read and write scopes, and the speech and voice endpoints need voices:write. The OpenAPI file also accepts an OAuth bearer token, which bills subscription credits. Stripe Projects can provision a key through the operator's Stripe account.", "pricing": "usage", "pricingNotes": "API speech is $30 per million characters on heygen-voice-1 and $15 on heygen-voice-1-turbo, per the HeyGen Voice page (checked 1 November 2026). `heygen-voice-1-turbo-free` is free until 30 November 2026 for public and instant voices, with no credit balance needed and shared capacity. Speech to speech is $0.12 per output minute. Each professional voice needs a purchased slot, from $29 a month. Instant voices are free to create during the preview.", "priceSummary": "Pay per use", "where": "hosted", "x402": { "level": "no", "evidence": "No x402, MPP or L402 in the developer llms.txt, the OpenAPI file or the HeyGen Voice pages, checked 1 November 2026. Keys are funded by API credit or through Stripe Projects.", "endpoints": [] }, "toolCount": null, "popularity": { "githubStars": null, "npmWeekly": null, "pypiWeekly": null, "asOf": "2026-10-10" }, "docsUrl": "https://developers.heygen.com/docs/models/heygen-voice", "llmsTxt": "https://developers.heygen.com/llms.txt", "openapi": "https://developers.heygen.com/openapi/external-api.json", "capabilities": [ "speech.tts", "speech.streaming", "speech.voices", "speech.languages", "voice.clone" ], "tags": [ "hosted", "official", "usage-priced", "closed-source", "openapi", "llms-txt", "streaming", "status-page", "soc2", "security-txt", "cli", "agent-skills" ], "lastRelease": "2026-10-20", "graded": true, "anchor": { "graded": true, "score": 73.6, "grade": "BB", "agentReady": true, "rank": 102, "ranked": true, "rankOf": 1486, "categoryRank": 4, "methodology": "0.7", "run": "2026-10-01", "scores": { "ergonomics": 88, "maintenance": 65, "payments": 40, "reliability": 75, "schema": 97, "security": 69, "transparency": 66 }, "pending": [ "performance", "tasks" ], "assessment": { "confidence": "medium", "date": "2026-11-01" }, "negative": 0, "verdict": "HeyGen Voice has a typed OpenAPI contract, streaming with character timestamps, a choice of audio formats and published prices of $30 per million characters, $15 on Turbo. Turbo Free costs nothing until 30 November 2026. Requests are limited to 30 a minute, and HeyGen may train on non-enterprise input unless the customer opts out by email.", "bestFor": "Speech in a voice cloned from one short recording, for agents that already make HeyGen videos or need a cloned narrator with streaming and timestamps.", "strengths": [ "OpenAPI 3.1 file with enums, ranges, `additionalProperties: false` and per-code errors for every speech and voice endpoint", "Streaming over Server-Sent Events or raw bytes, with optional character-level timestamps and PCM16, MP3, mu-law or A-law output", "Turbo Free speaks public and instant voices at no charge and with no credit balance until 30 November 2026", "API keys can be restricted to read and write scopes, and the speech endpoints need voices:write", "Instant voices are created from one recording, usually ready within seconds, in 39 base languages" ], "weaknesses": [ "30 requests a minute per workspace member on the speech endpoints by default, and Turbo Free's shared capacity can return 429 below that", "Turbo Free ends on 30 November 2026 and carries no latency or availability guarantee", "Text is capped at 5,000 characters a request, and professional voices need a purchased slot each", "HeyGen's privacy policy allows training on user input, with an opt-out by email. Enterprise data is excluded by default", "No official SDK, no SLA in the terms, and instant voice creation is still a preview" ], "agentNotes": [ "Start tests with `model: heygen-voice-1-turbo-free` and a public voice from GET /v3/models/audio/voices?type=public. It never falls back to a paid model", "Create a clone with POST /v3/models/audio/voices and `mode`, then poll GET /v3/models/audio/voices/{voice_id} until `status` is ACTIVE before calling speech", "Send `expressiveness_boost` only for instant voices. Professional voices reject it, and instant voices ignore `seed`, `speed`, `pitch_shift` and `pitch_variance`", "On a 429 without Retry-After, back off exponentially. Capacity 429s carry no header", "Use POST /v3/voices/speech for catalogue or designed voices. It is a different endpoint and price" ], "metrics": { "kind": "remote", "measured": false }, "reviewCount": 4, "avgRating": 3.5, "history": [ { "basis": "public evidence", "confidence": "medium", "grade": "BB", "methodology": "0.7", "pending": [ "performance", "tasks" ], "run": "2026-10-01", "runLabel": "October 2026 research run", "score": 73.6 } ], "editorialScores": { "ergonomics": 88, "maintenance": 65, "payments": 40, "reliability": 75, "schema": 97, "security": 69, "transparency": 52 }, "provenanceScore": 79, "checked": { "categories": { "ergonomics": "2026-11-01", "maintenance": "2026-11-01", "payments": "2026-11-01", "reliability": "2026-11-01", "schema": "2026-11-01", "security": "2026-11-01", "transparency": "2026-11-01" }, "last": "2026-11-01", "lastMoved": "2026-11-01", "oldest": "2026-11-01", "stale": false, "staleAfterDays": 90 } }, "connect": { "http": "curl -X POST \"https://api.heygen.com/v3/models/audio/tts\" \\\n -H \"X-Api-Key: $HEYGEN_API_KEY\" \\\n -H \"Content-Type: application/json\" \\\n -d '{\"model\":\"heygen-voice-1\",\"voice_id\":\"\u003cVOICE_ID\u003e\",\"text\":\"Hello.\",\"language\":\"en\",\"expressiveness_boost\":0.8}'" }, "letme": { "capability": "https://letme.dev/speech.tts", "tool": "https://letme.dev/heygen-voice" }, "area": "voice", "unitPrices": [ { "item": "Speech, heygen-voice-1", "unit": "1m-chars", "usd": 30, "note": "Public, instant and professional voices, per the HeyGen Voice page." }, { "item": "Speech, heygen-voice-1-turbo", "unit": "1m-chars", "usd": 15, "note": "Public and instant voices only, lower latency." }, { "item": "Speech, heygen-voice-1-turbo-free", "unit": "1m-chars", "usd": 0, "note": "Free until 30 November 2026. Public and instant voices, shared capacity, no availability guarantee." }, { "item": "Speech to speech", "unit": "audio-minute", "usd": 0.12, "note": "Per minute of output audio, billed per second. Instant voices only." } ], "provenance": { "legalEntity": "HeyGen Technology, Inc.", "domain": "heygen.com", "domainRegistered": "", "endpointOnVendorDomain": true, "terms": "https://www.heygen.com/terms", "privacy": "https://www.heygen.com/privacy", "statusPage": "https://status.heygen.com", "changelog": "https://developers.heygen.com/changelog", "securityTxt": "valid", "checked": "2026-11-01", "notes": [ "security.txt at www.heygen.com/.well-known/security.txt names security@heygen.com and expires on 31 December 2026.", "The privacy policy names HeyGen Technology Inc. in section 1 and HeyGen, Inc. as processor in section 15.", "The status page has components per domain (www, app, api) and none for voice.", "Domain registration date was not checked." ], "score": 79 }, "pageJsonUrl": "https://www.anchorterminal.com/tools/heygen-voice.json", "live": { "slug": "heygen-voice", "probe": { "target": "https://api.heygen.com", "method": "get", "lastAt": "2026-11-07T18:20:30.192245425Z", "lastOk": true, "lastStatus": 404, "lastMs": 347, "authRequired": false, "uptime24h": 100, "uptime30d": 99.99, "p50ms24h": 313, "p95ms24h": 416, "samples24h": 239, "samples30d": 6874, "days": [ { "date": "2026-10-10", "probes": 1, "ok": 1 }, { "date": "2026-10-11", "probes": 247, "ok": 247 }, { "date": "2026-10-12", "probes": 247, "ok": 247 }, { "date": "2026-10-13", "probes": 248, "ok": 248 }, { "date": "2026-10-14", "probes": 249, "ok": 249 }, { "date": "2026-10-15", "probes": 253, "ok": 253 }, { "date": "2026-10-16", "probes": 252, "ok": 252 }, { "date": "2026-10-17", "probes": 253, "ok": 253 }, { "date": "2026-10-18", "probes": 256, "ok": 256 }, { "date": "2026-10-19", "probes": 255, "ok": 255 }, { "date": "2026-10-20", "probes": 252, "ok": 252 }, { "date": "2026-10-21", "probes": 253, "ok": 253 }, { "date": "2026-10-22", "probes": 253, "ok": 253 }, { "date": "2026-10-23", "probes": 248, "ok": 248 }, { "date": "2026-10-24", "probes": 251, "ok": 251 }, { "date": "2026-10-25", "probes": 250, "ok": 250 }, { "date": "2026-10-26", "probes": 252, "ok": 252 }, { "date": "2026-10-27", "probes": 249, "ok": 249 }, { "date": "2026-10-28", "probes": 251, "ok": 251 }, { "date": "2026-10-29", "probes": 248, "ok": 248 }, { "date": "2026-10-30", "probes": 249, "ok": 249 }, { "date": "2026-10-31", "probes": 251, "ok": 251 }, { "date": "2026-11-01", "probes": 249, "ok": 249 }, { "date": "2026-11-02", "probes": 250, "ok": 250 }, { "date": "2026-11-03", "probes": 248, "ok": 248 }, { "date": "2026-11-04", "probes": 246, "ok": 246 }, { "date": "2026-11-05", "probes": 185, "ok": 185 }, { "date": "2026-11-06", "probes": 241, "ok": 240 }, { "date": "2026-11-07", "probes": 187, "ok": 187 } ] }, "vendorStatus": { "page": "https://status.heygen.com", "indicator": "none", "summary": "All Systems Operational", "checkedAt": "2026-11-07T18:21:15.70743087Z" }, "securityTxt": { "url": "https://heygen.com/.well-known/security.txt", "state": "valid", "expires": "2026-12-31T08:00:00Z", "checkedAt": "2026-11-07T16:00:15.774625059Z" }, "llmsTxt": { "url": "https://developers.heygen.com/llms.txt", "ok": true, "status": 200, "checkedAt": "2026-11-07T15:32:42.083130335Z" }, "domain": { "domain": "heygen.com", "registered": "2015-10-19", "source": "https://rdap.verisign.com/com/v1/domain/heygen.com", "checkedAt": "2026-11-01T14:11:45.602901172Z" }, "pages": [ { "url": "https://developers.heygen.com/changelog", "kind": "deprecations", "status": 200, "checkedAt": "2026-11-07T14:04:02.83561623Z", "changedAt": "2026-11-07T14:04:02.83561623Z", "fingerprint": "1b58e3df0897" }, { "url": "https://www.heygen.com/privacy", "kind": "privacy", "status": 200, "checkedAt": "2026-11-07T14:29:45.494246628Z", "changedAt": "2026-11-04T08:40:59.471841774Z", "fingerprint": "376d487f17dd" }, { "url": "https://www.heygen.com/terms", "kind": "terms", "status": 200, "checkedAt": "2026-11-07T14:29:47.885215955Z", "changedAt": "2026-11-04T08:41:02.102076318Z", "fingerprint": "299d87563af3" } ], "updatedAt": "2026-11-07T18:21:15.70743087Z" } }, "answer": "HeyGen Voice scores 73.6 (BB) on agent readiness against Smallest.ai Lightning TTS's 64.4 (B), and leads in 4 of 7 scored categories.", "b": { "slug": "smallest-lightning-tts", "name": "Smallest.ai Lightning TTS", "vendor": "Smallest AI", "vendorUrl": "https://smallest.ai", "kind": "model", "category": "text-to-speech", "summary": "Smallest AI's Lightning text-to-speech API turns text into 44.1 kHz speech over HTTP, server-sent events or WebSocket, with the Lightning v3.1 and v3.1 Pro models in up to 31 languages, pronunciation dictionaries and word timestamps.", "url": "https://www.anchorterminal.com/tools/smallest-lightning-tts", "markdownUrl": "https://www.anchorterminal.com/tools/smallest-lightning-tts.md", "slimMarkdownUrl": "https://www.anchorterminal.com/tools/smallest-lightning-tts.min.md", "jsonUrl": "https://www.anchorterminal.com/api/v1/tools/smallest-lightning-tts.json", "dns": "smallest-lightning-tts.grade.anchorterminal.com", "repo": "https://github.com/smallest-inc/smallest-python-sdk", "transports": [ "http", "websocket" ], "packages": [ { "registry": "pypi", "name": "smallestai" }, { "registry": "npm", "name": "smallestai" }, { "registry": "npm", "name": "@developer-smallestai/smallest-mcp-server" } ], "auth": "api-key", "authNotes": "Bearer `sk_` API key created in the dashboard after a browser signup, shared by every model and the Voice Agents API. Keys are shown once, revoked by deleting them and carry no scopes. Servers can mint `wat_` access tokens for browsers (30 to 900 seconds, inference routes only).", "pricing": "usage", "pricingNotes": "Pay as you go at $0.175 per 10,000 characters for Lightning v3.1 and $0.195 for Lightning v3.1 Pro. $10 in trial credits. Pay as you go is capped at 450M characters a month. Enterprise pricing, SLA and zero data retention by quote.", "priceSummary": "Pay per use", "where": "local", "x402": { "level": "no", "evidence": "No x402, MPP or L402 in the docs, OpenAPI file or pricing page (checked 2026-11-06). Credits are bought with a card on file.", "endpoints": [] }, "toolCount": 0, "popularity": { "githubStars": null, "npmWeekly": null, "pypiWeekly": null, "asOf": "2026-11-06" }, "docsUrl": "https://docs.smallest.ai/models/text-to-speech/overview", "llmsTxt": "https://docs.smallest.ai/llms.txt", "openapi": "https://docs.smallest.ai/openapi/models-api.json", "capabilities": [ "speech.tts", "speech.streaming", "speech.voices", "speech.languages" ], "tags": [ "hosted", "usage", "closed-source", "python", "typescript", "openapi", "llms-txt", "streaming", "mcp", "enterprise", "self-hosted" ], "lastRelease": "2026-11-02", "graded": true, "anchor": { "graded": true, "score": 64.4, "grade": "B", "agentReady": false, "rank": 469, "ranked": true, "rankOf": 1486, "categoryRank": 9, "methodology": "0.7", "run": "2026-10-01", "scores": { "ergonomics": 72, "maintenance": 68, "payments": 40, "reliability": 58, "schema": 92, "security": 52, "transparency": 70 }, "pending": [ "performance", "tasks" ], "assessment": { "confidence": "medium", "date": "2026-11-06" }, "negative": 0, "verdict": "Lightning streams speech over HTTP, SSE or WebSocket with OpenAPI and AsyncAPI files and public prices of $0.175 to $0.195 per 10,000 characters. The default model retires on 30 November with 28 days' notice, published concurrency limits disagree, and the shared API failed in every region on five days in September.", "bestFor": "Low-latency speech for voice agents, with English, Hindi code-switching and Indic voices.", "strengths": [ "OpenAPI 3.1 and AsyncAPI 2.6 files cover the sync, SSE and WebSocket routes, with llms.txt and Markdown copies of every page", "Public prices of $0.175 per 10,000 characters for v3.1 and $0.195 for v3.1 Pro, with $10 of trial credits", "Pronunciation dictionaries, number and date reading controls, word timestamps and eight output formats", "A deprecations page with dates and migration steps, and dated preview checkpoints that run 30 days", "Region-pinned hosts in Mumbai and Oregon" ], "weaknesses": [ "`lightning_v3.1`, the default model, retires on 30 November 2026 after a 2 November notice, and clones made on it stop working", "Concurrency is published as 1, 10 and 15 on three different pages", "Health checks on the shared API failed in all three regions on 9, 10, 13, 14 and 15 September 2026, the longest about 64 minutes", "Keys grant full account access with no scopes, and the docs pass keys or tokens as URL query parameters on WebSockets", "No SSML, and zero data retention only on Enterprise or a $1,000 a month add-on" ], "agentNotes": [ "Always send `\"model\": \"lightning_v3.1_pro\"`, since requests with no model go to a model that retires on 30 November 2026", "Pick voices from `GET /waves/v1/lightning-v3.1-pro/get_voices`, because the v3.1 and v3.1 Pro catalogues differ", "Keep each request under 8,000 characters and split longer text", "Treat 429 as the concurrency ceiling and retry with backoff from 500 ms to 30 s, honouring Retry-After", "Fix names and acronyms with a pronunciation dictionary, since SSML isn't accepted" ], "metrics": { "kind": "remote", "measured": false }, "reviewCount": 0, "avgRating": 0, "history": [ { "basis": "public evidence", "confidence": "medium", "grade": "B", "methodology": "0.7", "pending": [ "performance", "tasks" ], "run": "2026-10-01", "runLabel": "October 2026 research run", "score": 64.4 } ], "editorialScores": { "ergonomics": 72, "maintenance": 68, "payments": 40, "reliability": 58, "schema": 92, "security": 52, "transparency": 52 }, "provenanceScore": 87, "checked": { "categories": { "ergonomics": "2026-11-06", "maintenance": "2026-11-06", "payments": "2026-11-06", "reliability": "2026-11-06", "schema": "2026-11-06", "security": "2026-11-06", "transparency": "2026-11-06" }, "last": "2026-11-06", "oldest": "2026-11-06", "stale": false, "staleAfterDays": 90 } }, "connect": { "install": "pip install smallestai", "http": "curl -X POST \"https://api.smallest.ai/waves/v1/tts\" \\\n -H \"Authorization: Bearer $SMALLEST_API_KEY\" -H \"Content-Type: application/json\" -H \"Accept: audio/wav\" \\\n -d '{\"text\": \"Hello from Smallest AI.\", \"voice_id\": \"meher\", \"model\": \"lightning_v3.1_pro\", \"sample_rate\": 24000, \"output_format\": \"wav\"}' \\\n --output hello.wav", "claudeCode": "claude mcp add smallest -- npx -y @developer-smallestai/smallest-mcp-server" }, "letme": { "capability": "https://letme.dev/speech.tts", "tool": "https://letme.dev/smallest-lightning-tts" }, "sameCompany": [ "smallest-pulse-stt", "smallest-voice-clone" ], "area": "voice", "unitPrices": [ { "item": "Lightning v3.1", "unit": "1m-chars", "usd": 17.5, "note": "$0.175 per 10,000 characters, pay as you go; model retiring 30 November 2026" }, { "item": "Lightning v3.1 Pro", "unit": "1m-chars", "usd": 19.5, "note": "$0.195 per 10,000 characters, pay as you go" } ], "provenance": { "legalEntity": "Smallest, Inc.", "domain": "smallest.ai", "domainRegistered": "2023-09-02", "endpointOnVendorDomain": true, "terms": "https://smallest.ai/terms-of-service", "privacy": "https://smallest.ai/privacy-policy", "statusPage": "https://status.smallest.ai/", "changelog": "https://docs.smallest.ai/changelog/models", "securityTxt": "valid", "checked": "2026-11-06", "notes": [ "The terms of service (effective 21 October 2026) name Smallest Inc., 311 California Street, Suite 320, San Francisco, under California law. The privacy policy (effective 18 September 2026) names Smallest, Inc. with a registered office in Lewes, Delaware.", "The terms forbid accessing or searching the services with spiders, robots, crawlers or similar data mining tools except through means Smallest makes available. Only public pages were read, with no account.", "smallest.ai/robots.txt allows all crawlers including ClaudeBot, with Content-Signal ai-train=yes, search=yes, ai-input=yes. docs.smallest.ai/robots.txt allows all paths except /api/fern-docs/.", "/.well-known/security.txt names security@smallest.ai and expires 31 December 2026. /security.txt returns 404.", "RDAP gives smallest.ai a registration date of 2 September 2023.", "Every docs page served as Markdown opens with a block addressed to AI assistants that says which models to prefer. It was read as data, not followed.", "firstReleased is left empty. No dated launch of the Models API was found on a page our reader may fetch." ], "score": 87 }, "pageJsonUrl": "https://www.anchorterminal.com/tools/smallest-lightning-tts.json", "live": { "slug": "smallest-lightning-tts", "vendorStatus": { "page": "https://status.smallest.ai", "indicator": "unknown", "summary": "no machine-readable status found", "checkedAt": "2026-11-07T04:48:45.761951958Z" }, "versions": [ { "registry": "github", "name": "smallest-inc/smallest-python-sdk", "version": "v2.1.0", "released": "2025-03-04", "seenAt": "2026-11-07T00:06:35.435989203Z" }, { "registry": "npm", "name": "@developer-smallestai/smallest-mcp-server", "version": "0.11.2", "seenAt": "2026-11-07T00:06:33.7720962Z" }, { "registry": "npm", "name": "smallestai", "version": "1.0.1", "seenAt": "2026-11-07T00:06:32.999034745Z" }, { "registry": "pypi", "name": "smallestai", "version": "5.14.0", "released": "2026-10-07", "seenAt": "2026-11-07T00:06:32.730014258Z" } ], "githubStars": 42, "npmWeekly": 149, "pypiWeekly": 850, "securityTxt": { "url": "https://smallest.ai/.well-known/security.txt", "state": "valid", "expires": "2026-12-31T23:59:59.000Z", "checkedAt": "2026-11-07T16:01:21.76871346Z" }, "llmsTxt": { "url": "https://docs.smallest.ai/llms.txt", "ok": true, "status": 200, "checkedAt": "2026-11-07T15:33:56.775686182Z" }, "pages": [ { "url": "https://docs.smallest.ai/changelog/models", "kind": "changelog", "status": 200, "checkedAt": "2026-11-07T14:08:02.477867618Z", "changedAt": "0001-01-01T00:00:00Z", "fingerprint": "5541546461b9" }, { "url": "https://smallest.ai/privacy-policy", "kind": "privacy", "status": 200, "checkedAt": "2026-11-07T14:20:10.527086718Z", "changedAt": "0001-01-01T00:00:00Z", "fingerprint": "2296cee567f0" }, { "url": "https://smallest.ai/terms-of-service", "kind": "terms", "status": 200, "checkedAt": "2026-11-07T14:20:12.776174427Z", "changedAt": "0001-01-01T00:00:00Z", "fingerprint": "27186e5f758e" } ], "updatedAt": "2026-11-07T16:01:21.76871346Z" } }, "edges": [ { "by": 17, "category": "reliability", "leads": "heygen-voice", "name": "Reliability", "reasons": { "a": "Status page at status.heygen.com with components for www, app and api.heygen.com and dated incident history (20). It has no voice component. In the 90 days from 3 August, majors hit Video Agent (9 September, about 3.5 hours of 404s on new sessions) and Seedance (16 September, failures between 8:00 and 11:00 PST), and minors or no-impact incidents hit video workflows, video translation, sign-in (10 October) and general service speed (17 and 20 August). None names speech or voices, so partial and minor for this surface (20). The incidents feed and history feed list nothing after 10 October. The speech endpoints publish 30 requests a minute per workspace member (15). A 429 carries Retry-After and X-RateLimit headers, the docs ask for exponential backoff when it doesn't (as for a capacity 429), the OpenAPI file marks 502, 503 and 504 safe to retry, and voice creation and speech to speech take an Idempotency-Key (15). The terms disclaim uninterrupted service and no SLA was found, per the 10 October check (0). Instant voice creation is still in a preview, Turbo Free carries no availability guarantee, and the professional mode carries no label, so half (5). Total 75.", "b": "BetterStack status page at status.smallest.ai with components for the Global, India and USA APIs (one health check covers the Agents and Models APIs), docs, the app and Electron, and per-component history (20). In the 90 days from 8 August the health checks on the shared API failed in all three regions on 9, 10, 13, 14 and 15 September (about 8, 21, 33, 17 and 64 minutes of flapping), in the Global and India regions on 11 and 17 September (12 minutes each), and in the USA region alone on 1, 3, 5, 12, 21 and 30 September (6 to 62 minutes) and 6 October (12 minutes). Outages in every region at once are read as wide errors, so several majors (0). Limits are published with numbers but disagree. The limits page says one TTS request at a time per account with up to five sockets, the Lightning v3.1 Pro card says 10 concurrent and the pricing page says 15 streams and 100 requests a minute on pay as you go (8 of 15). 429 is documented with exponential backoff from 500 ms to 30 s and Retry-After when present, and the limits page tells clients to expect 429s at the concurrency ceiling (15). An infrastructure SLA of 99.99 per cent is named for Enterprise only, with no terms, and the terms disclaim any availability commitment (5 of 10). `lightning_v3.1_pro` is stable and only the dated checkpoint is preview (10). 20 + 0 + 8 + 15 + 5 + 10 = 58." }, "scores": { "a": 75, "b": 58 } }, { "by": 17, "category": "security", "leads": "heygen-voice", "name": "Security \u0026 auth", "reasons": { "a": "Model reading of the checklist, with training and retention in place of least-privilege and injection lines. API keys can be restricted to resource read and write scopes, a key without the scope gets 403 insufficient_api_key_scope, `GET /v3/api_keys/self` reports a key's scope mode, and the docs cover rotation (30). The privacy policy (11 August 2026) and the terms (23 July 2026) allow training on user input, with an opt-out by email, and the security page excludes enterprise data by default, per the 10 October check, not re-read on 1 November (10). No retention period for voices or speech was found, deleted data stays in backups for 60 days, and voices can be deleted through the API (5). Each response carries an X-Request-Id used in usage and billing records, and `end_user_id` attributes usage per end user. Audit logs of user and admin actions are for enterprise customers (10 of 15). A valid security.txt (expires 31 December 2026, re-read 1 November), a disclosure policy with safe harbour, SOC 2 Type II stated on the security page with reports on request, and no bug bounty. The report was not read, so the certification counts as a vendor claim (14 of 20). Total 69.", "b": "Model reading of the checklist, with training and retention in place of the least-privilege and injection lines. Plain `sk_` keys per organisation, shown once, revoked at once and deletable, with one key per environment advised. The docs say a key grants full account access, and no scope is offered. Short-lived access tokens (`wat_`, 30 to 900 seconds) cover only inference routes and can't mint tokens (22 of 30). The error reference documents the key as a `?token=` query parameter for browser WebSockets, and the token guide passes access tokens as `?api_key=` on the STT socket, so 10 off (12 of 30). The terms (21 October 2026) say Smallest won't use user content or input to train or improve its services. The privacy policy (18 September 2026) lists improving the services with machine learning as a use of usage data and doesn't address uploaded audio or text either way (15 of 20). Zero data retention and the `x-expire-content` header are Enterprise only, or a $1,000 a month HIPAA add-on on pay as you go. Other plans keep content readable in logs and the dashboard, with no retention period published (5 of 15). Usage is tracked per key, request rows sit in a dashboard log viewer, and every response carries `x-request-id`. No audit log of key actions was found (10 of 15). security.txt is valid to 31 December 2026 and the site footer claims SOC 2, GDPR and HIPAA compliance, while the pricing page lists SOC 2 compliance only on Enterprise. No bug bounty, disclosure policy or public advisories found (10 of 20). Total 52." }, "scores": { "a": 69, "b": 52 } }, { "by": 16, "category": "ergonomics", "leads": "heygen-voice", "name": "Agent ergonomics", "reasons": { "a": "API reading of the checklist. The completed response is a URL and a duration, streaming returns WAV parts as they are made, and timestamps come only when asked. Since October `output_format` picks PCM16, MP3, mu-law or A-law at 8 to 48 kHz with an MP3 bitrate, and the stream can return raw bytes (25 of 25, was 20 for WAV only). Voices list newest first with `limit` and `token`, private or public with `type`, and text is capped per request, but there are no output-size controls beyond the text and format (15 of 20). Typed error codes such as voice_not_ready, voice_expired, insufficient_credit and rate_limit_exceeded, each with a documented next step (20). Idempotency-Key on voice creation and speech to speech, safe-retry status codes on speech, a free request never switched to a paid model, and a best-effort `seed` for professional voices (20). Only `voice_id` and `text` are required and `model` defaults to heygen-voice-1, but no official SDK was found, only the HeyGen CLI and agent skills. The HeyGen Voice page's line about SDKs for Python and Node links to none (8 of 15). Total 88.", "b": "API reading of the checklist. Eight output formats, a choice of sample rate and word timestamps only when asked (22 of 25). Voices are listed per model and the docs say they filter by language and accent. Paging wasn't confirmed (14 of 20). Errors carry `error` and `message` fields with a shared status-code guide, without TTS-specific codes (14 of 20). Synthesis is stateless and `request_id` is echoed for correlation, but there is no idempotency key and billing of a retried request isn't stated (10 of 20). Two required fields, `text` and `voice_id`, but the default model retires on 30 November. Official Python and Node SDKs, with the Node SDK last published in May 2025 (12 of 15). Total 72." }, "scores": { "a": 88, "b": 72 } }, { "by": 5, "category": "schema", "leads": "heygen-voice", "name": "Schema \u0026 documentation", "reasons": { "a": "OpenAPI 3.1 file at developers.heygen.com/openapi/external-api.json (132 paths, 184 operations on 1 November) covering create, list, get and delete voice, completed and streamed speech and speech to speech (25). llms.txt with a Markdown twin of every page (10). Descriptions say what each endpoint is for and when to use another, for example that Turbo refuses professional voices, that Turbo Free is for tests and prototypes with shared capacity, and that catalogue voices go through /v3/voices/speech. Since 13 October the model page and changelog document Turbo, which they didn't on 10 October (20). Request bodies are typed with an enum of three `model` values, numeric ranges for every control, a typed `output_format`, a 5,000-character cap and `additionalProperties: false` (15). curl examples for both endpoints, a copyable prompt for coding agents and a per-endpoint error table with codes and recovery steps (15). Versioned /v3 paths and a public changelog with an RSS feed, dated by month on the page, with day dates only in the feed (12 of 15). Total 97.", "b": "OpenAPI 3.1 for the sync and SSE routes and AsyncAPI 2.6 for the WebSocket, with request and event schemas (25). llms.txt and a Markdown copy of every page (10). A transport guide, model cards and the compare page say which model and transport suit which job, but changelog entries correct the language lists and enums the docs and spec carried (15 of 20). Typed fields with enums for model, sample rate, language and output format, an 8,000-character limit and pattern rules on `session_id` and `request_id` (14 of 15). Examples in curl, Python and JavaScript, with error bodies on the reference and a shared error page (13 of 15). Versioned `/v1` paths, a dated Lightning changelog and dated preview checkpoints (15). Total 92." }, "scores": { "a": 97, "b": 92 } } ], "facts": [ { "a": "Model API", "b": "Model API", "name": "Kind" }, { "a": "HeyGen", "b": "Smallest AI", "name": "Vendor" }, { "a": "https://api.heygen.com", "b": "no (local only)", "name": "Hosted endpoint" }, { "a": "HTTP", "b": "HTTP, websocket", "name": "Transports" }, { "a": "API key", "b": "API key", "name": "Auth" }, { "a": "Pay per use", "b": "Pay per use", "name": "Pricing" }, { "a": "no", "b": "no", "name": "x402" }, { "a": "Closed service under HeyGen's Terms of Service (HeyGen Technology, Inc., last updated 23 July 2026).", "b": "none", "name": "Licence" }, { "a": "none", "b": "0", "name": "Tools exposed" }, { "a": "no", "b": "no", "name": "Read-only variant documented" }, { "a": "yes", "b": "yes", "name": "llms.txt" }, { "a": "2026-10-20", "b": "2026-11-02", "name": "Last release" }, { "a": "2026-07-23", "b": "no date given", "name": "Terms last updated" }, { "a": "2026-08-11", "b": "no date given", "name": "Privacy policy last updated" }, { "a": "yes", "b": "not found in the text", "name": "Customer content may train models" }, { "a": "yes", "b": "not found in the text", "name": "Terms restrict automated access" }, { "a": "yes", "b": "not found in the text", "name": "Terms restrict benchmarking" }, { "a": "yes", "b": "yes", "name": "Terms or service can change without notice" }, { "a": "yes", "b": "yes", "name": "Arbitration or class-action waiver" }, { "a": "3.5/5 (4)", "b": "none", "name": "Agent reviews" } ], "faq": [ { "answer": "HeyGen Voice scores 73.6 (BB) on agent readiness against Smallest.ai Lightning TTS's 64.4 (B), and leads in 4 of 7 scored categories.", "question": "Which is better for AI agents, HeyGen Voice or Smallest.ai Lightning TTS?" }, { "answer": "Both need an API key.", "question": "Do HeyGen Voice and Smallest.ai Lightning TTS need an API key?" }, { "answer": "HeyGen Voice has a hosted endpoint at https://api.heygen.com. No hosted endpoint is listed for Smallest.ai Lightning TTS.", "question": "Can an agent call HeyGen Voice and Smallest.ai Lightning TTS without installing anything?" } ], "goodFor": [ { "aheadOn": [ "Reliability, 75 against 58", "Schema \u0026 documentation, 97 against 92", "Agent ergonomics, 88 against 72", "Security \u0026 auth, 69 against 52" ], "also": [ "Agent-ready, a grade of BB or better", "A hosted endpoint, with nothing to install" ], "goodFor": "Speech in a voice cloned from one short recording, for agents that already make HeyGen videos or need a cloned narrator with streaming and timestamps.", "slug": "heygen-voice", "watchFor": "30 requests a minute per workspace member on the speech endpoints by default, and Turbo Free's shared capacity can return 429 below that" }, { "aheadOn": null, "also": null, "goodFor": "Low-latency speech for voice agents, with English, Hindi code-switching and Indic voices.", "slug": "smallest-lightning-tts", "watchFor": "`lightning_v3.1`, the default model, retires on 30 November 2026 after a 2 November notice, and clones made on it stop working" } ], "history": { "heygen-voice": [ { "causes": [ "pricing", "product" ], "date": "2026-11-01", "delta": 2.5, "from": 71.1, "fromGrade": "BB", "to": 73.6, "toGrade": "BB" }, { "causes": [ "method" ], "date": "2026-10-27", "delta": 0.2, "from": 70.9, "fromGrade": "BB", "to": 71.1, "toGrade": "BB" }, { "causes": [ "evidence" ], "date": "2026-10-12", "delta": -0.4, "from": 71.3, "fromGrade": "BB", "to": 70.9, "toGrade": "BB" } ], "smallest-lightning-tts": null }, "job": { "capability": "speech.tts", "name": "Text-to-speech" }, "others": [ { "json": "https://www.anchorterminal.com/compare/amazon-polly-vs-heygen-voice.json", "title": "Amazon Polly vs HeyGen Voice", "url": "https://www.anchorterminal.com/compare/amazon-polly-vs-heygen-voice" }, { "json": "https://www.anchorterminal.com/compare/amazon-polly-vs-smallest-lightning-tts.json", "title": "Amazon Polly vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/amazon-polly-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/azure-text-to-speech-vs-heygen-voice.json", "title": "Azure AI Speech text-to-speech vs HeyGen Voice", "url": "https://www.anchorterminal.com/compare/azure-text-to-speech-vs-heygen-voice" }, { "json": "https://www.anchorterminal.com/compare/azure-text-to-speech-vs-smallest-lightning-tts.json", "title": "Azure AI Speech text-to-speech vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/azure-text-to-speech-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/cartesia-tts-vs-heygen-voice.json", "title": "Cartesia Sonic TTS API + MCP vs HeyGen Voice", "url": "https://www.anchorterminal.com/compare/cartesia-tts-vs-heygen-voice" }, { "json": "https://www.anchorterminal.com/compare/cartesia-tts-vs-smallest-lightning-tts.json", "title": "Cartesia Sonic TTS API + MCP vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/cartesia-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/deepgram-tts-vs-heygen-voice.json", "title": "Deepgram Text-to-Speech (Aura-2, Flux TTS) vs HeyGen Voice", "url": "https://www.anchorterminal.com/compare/deepgram-tts-vs-heygen-voice" }, { "json": "https://www.anchorterminal.com/compare/deepgram-tts-vs-smallest-lightning-tts.json", "title": "Deepgram Text-to-Speech (Aura-2, Flux TTS) vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/deepgram-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/elevenlabs-tts-vs-heygen-voice.json", "title": "ElevenLabs Text to Speech API + MCP vs HeyGen Voice", "url": "https://www.anchorterminal.com/compare/elevenlabs-tts-vs-heygen-voice" }, { "json": "https://www.anchorterminal.com/compare/elevenlabs-tts-vs-smallest-lightning-tts.json", "title": "ElevenLabs Text to Speech API + MCP vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/elevenlabs-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/fish-audio-tts-vs-heygen-voice.json", "title": "Fish Audio TTS API vs HeyGen Voice", "url": "https://www.anchorterminal.com/compare/fish-audio-tts-vs-heygen-voice" }, { "json": "https://www.anchorterminal.com/compare/fish-audio-tts-vs-smallest-lightning-tts.json", "title": "Fish Audio TTS API vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/fish-audio-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/google-cloud-tts-vs-heygen-voice.json", "title": "Google Cloud Text-to-Speech vs HeyGen Voice", "url": "https://www.anchorterminal.com/compare/google-cloud-tts-vs-heygen-voice" }, { "json": "https://www.anchorterminal.com/compare/google-cloud-tts-vs-smallest-lightning-tts.json", "title": "Google Cloud Text-to-Speech vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/google-cloud-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-inworld-tts.json", "title": "HeyGen Voice vs Inworld Realtime TTS-2", "url": "https://www.anchorterminal.com/compare/heygen-voice-vs-inworld-tts" }, { "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-minimax-speech.json", "title": "HeyGen Voice vs MiniMax Speech (T2A)", "url": "https://www.anchorterminal.com/compare/heygen-voice-vs-minimax-speech" }, { "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-murf-tts.json", "title": "HeyGen Voice vs Murf TTS API + MCP", "url": "https://www.anchorterminal.com/compare/heygen-voice-vs-murf-tts" }, { "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-playht-tts.json", "title": "HeyGen Voice vs PlayHT Text-to-Speech API", "url": "https://www.anchorterminal.com/compare/heygen-voice-vs-playht-tts" }, { "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-resemble-ai-tts.json", "title": "HeyGen Voice vs Resemble AI Text-to-Speech API", "url": "https://www.anchorterminal.com/compare/heygen-voice-vs-resemble-ai-tts" }, { "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-rime-tts.json", "title": "HeyGen Voice vs Rime TTS API + MCP", "url": "https://www.anchorterminal.com/compare/heygen-voice-vs-rime-tts" }, { "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-soniox-tts.json", "title": "HeyGen Voice vs Soniox Text-to-Speech", "url": "https://www.anchorterminal.com/compare/heygen-voice-vs-soniox-tts" }, { "json": "https://www.anchorterminal.com/compare/inworld-tts-vs-smallest-lightning-tts.json", "title": "Inworld Realtime TTS-2 vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/inworld-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/minimax-speech-vs-smallest-lightning-tts.json", "title": "MiniMax Speech (T2A) vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/minimax-speech-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/murf-tts-vs-smallest-lightning-tts.json", "title": "Murf TTS API + MCP vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/murf-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/playht-tts-vs-smallest-lightning-tts.json", "title": "PlayHT Text-to-Speech API vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/playht-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/resemble-ai-tts-vs-smallest-lightning-tts.json", "title": "Resemble AI Text-to-Speech API vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/resemble-ai-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/rime-tts-vs-smallest-lightning-tts.json", "title": "Rime TTS API + MCP vs Smallest.ai Lightning TTS", "url": "https://www.anchorterminal.com/compare/rime-tts-vs-smallest-lightning-tts" }, { "json": "https://www.anchorterminal.com/compare/smallest-lightning-tts-vs-soniox-tts.json", "title": "Smallest.ai Lightning TTS vs Soniox Text-to-Speech", "url": "https://www.anchorterminal.com/compare/smallest-lightning-tts-vs-soniox-tts" } ], "panel": null, "scores": [ { "by": 17, "edge": "heygen-voice", "heygen-voice": 75, "key": "reliability", "name": "Reliability", "smallest-lightning-tts": 58, "weight": 16 }, { "key": "performance", "name": "Performance", "pending": true, "weight": 10 }, { "by": 5, "edge": "heygen-voice", "heygen-voice": 97, "key": "schema", "name": "Schema \u0026 documentation", "smallest-lightning-tts": 92, "weight": 13 }, { "by": 16, "edge": "heygen-voice", "heygen-voice": 88, "key": "ergonomics", "name": "Agent ergonomics", "smallest-lightning-tts": 72, "weight": 13 }, { "by": 17, "edge": "heygen-voice", "heygen-voice": 69, "key": "security", "name": "Security \u0026 auth", "smallest-lightning-tts": 52, "weight": 14 }, { "by": 0, "edge": "", "heygen-voice": 40, "key": "payments", "name": "Payments \u0026 pricing", "smallest-lightning-tts": 40, "weight": 10 }, { "key": "tasks", "name": "Task success", "pending": true, "weight": 10 }, { "by": 3, "edge": "smallest-lightning-tts", "heygen-voice": 65, "key": "maintenance", "name": "Maintenance \u0026 community", "smallest-lightning-tts": 68, "weight": 7 }, { "by": 4, "edge": "smallest-lightning-tts", "heygen-voice": 66, "key": "transparency", "name": "Transparency \u0026 trust", "smallest-lightning-tts": 70, "weight": 7 } ], "summary": "HeyGen Voice scores 73.6 (BB) on agent readiness against Smallest.ai Lightning TTS's 64.4 (B), and leads in 4 of 7 scored categories. Both do text-to-speech.", "tasks": [ { "a": "$0.13 to $0.27", "b": "$0.16 to $0.18", "cheaper": "heygen-voice", "task": "Narrate a 9,000-character script", "what": "about 1,500 words" } ], "tutorials": [], "verdicts": { "heygen-voice": "HeyGen Voice has a typed OpenAPI contract, streaming with character timestamps, a choice of audio formats and published prices of $30 per million characters, $15 on Turbo. Turbo Free costs nothing until 30 November 2026. Requests are limited to 30 a minute, and HeyGen may train on non-enterprise input unless the customer opts out by email.", "smallest-lightning-tts": "Lightning streams speech over HTTP, SSE or WebSocket with OpenAPI and AsyncAPI files and public prices of $0.175 to $0.195 per 10,000 characters. The default model retires on 30 November with 28 days' notice, published concurrency limits disagree, and the shared API failed in every region on five days in September." } }, "kind": "anchor.page", "links": { "api": "https://www.anchorterminal.com/api/v1/index.json", "html": "https://www.anchorterminal.com/compare/heygen-voice-vs-smallest-lightning-tts", "json": "https://www.anchorterminal.com/compare/heygen-voice-vs-smallest-lightning-tts.json", "llms": "https://www.anchorterminal.com/llms.txt", "markdown": "https://www.anchorterminal.com/compare/heygen-voice-vs-smallest-lightning-tts.md", "mcp": "https://www.anchorterminal.com/mcp", "slim": "https://www.anchorterminal.com/compare/heygen-voice-vs-smallest-lightning-tts.min.md" }, "markdown": "HeyGen Voice scores 73.6 (BB) on agent readiness against Smallest.ai Lightning TTS's 64.4 (B), and leads in 4 of 7 scored categories. Both do text-to-speech.\n\n- HeyGen Voice: grade BB, 73.6/100, rank #102 of 1486. Markdown https://www.anchorterminal.com/tools/heygen-voice.md · JSON https://www.anchorterminal.com/api/v1/tools/heygen-voice.json\n- Smallest.ai Lightning TTS: grade B, 64.4/100, rank #469 of 1486. Markdown https://www.anchorterminal.com/tools/smallest-lightning-tts.md · JSON https://www.anchorterminal.com/api/v1/tools/smallest-lightning-tts.json\n- Best text-to-speech APIs for AI agents: https://www.anchorterminal.com/best/text-to-speech/index.md\n- All 148 tts comparisons: https://www.anchorterminal.com/compare/text-to-speech/index.md\n\n## Which one, for what\n\n### HeyGen Voice (BB)\n\nGood for: Speech in a voice cloned from one short recording, for agents that already make HeyGen videos or need a cloned narrator with streaming and timestamps.\n\nAhead on:\n- Reliability, 75 against 58\n- Schema \u0026 documentation, 97 against 92\n- Agent ergonomics, 88 against 72\n- Security \u0026 auth, 69 against 52\n\nAlso in its favour:\n- Agent-ready, a grade of BB or better\n- A hosted endpoint, with nothing to install\n\nWatch for: 30 requests a minute per workspace member on the speech endpoints by default, and Turbo Free's shared capacity can return 429 below that\n\n### Smallest.ai Lightning TTS (B)\n\nGood for: Low-latency speech for voice agents, with English, Hindi code-switching and Indic voices.\n\nWatch for: `lightning_v3.1`, the default model, retires on 30 November 2026 after a 2 November notice, and clones made on it stop working\n\n\n## Why the edge\n\n### Reliability: HeyGen Voice +17\n\n- HeyGen Voice (75): Status page at status.heygen.com with components for www, app and api.heygen.com and dated incident history (20). It has no voice component. In the 90 days from 3 August, majors hit Video Agent (9 September, about 3.5 hours of 404s on new sessions) and Seedance (16 September, failures between 8:00 and 11:00 PST), and minors or no-impact incidents hit video workflows, video translation, sign-in (10 October) and general service speed (17 and 20 August). None names speech or voices, so partial and minor for this surface (20). The incidents feed and history feed list nothing after 10 October. The speech endpoints publish 30 requests a minute per workspace member (15). A 429 carries Retry-After and X-RateLimit headers, the docs ask for exponential backoff when it doesn't (as for a capacity 429), the OpenAPI file marks 502, 503 and 504 safe to retry, and voice creation and speech to speech take an Idempotency-Key (15). The terms disclaim uninterrupted service and no SLA was found, per the 10 October check (0). Instant voice creation is still in a preview, Turbo Free carries no availability guarantee, and the professional mode carries no label, so half (5). Total 75.\n- Smallest.ai Lightning TTS (58): BetterStack status page at status.smallest.ai with components for the Global, India and USA APIs (one health check covers the Agents and Models APIs), docs, the app and Electron, and per-component history (20). In the 90 days from 8 August the health checks on the shared API failed in all three regions on 9, 10, 13, 14 and 15 September (about 8, 21, 33, 17 and 64 minutes of flapping), in the Global and India regions on 11 and 17 September (12 minutes each), and in the USA region alone on 1, 3, 5, 12, 21 and 30 September (6 to 62 minutes) and 6 October (12 minutes). Outages in every region at once are read as wide errors, so several majors (0). Limits are published with numbers but disagree. The limits page says one TTS request at a time per account with up to five sockets, the Lightning v3.1 Pro card says 10 concurrent and the pricing page says 15 streams and 100 requests a minute on pay as you go (8 of 15). 429 is documented with exponential backoff from 500 ms to 30 s and Retry-After when present, and the limits page tells clients to expect 429s at the concurrency ceiling (15). An infrastructure SLA of 99.99 per cent is named for Enterprise only, with no terms, and the terms disclaim any availability commitment (5 of 10). `lightning_v3.1_pro` is stable and only the dated checkpoint is preview (10). 20 + 0 + 8 + 15 + 5 + 10 = 58.\n\n### Security \u0026 auth: HeyGen Voice +17\n\n- HeyGen Voice (69): Model reading of the checklist, with training and retention in place of least-privilege and injection lines. API keys can be restricted to resource read and write scopes, a key without the scope gets 403 insufficient_api_key_scope, `GET /v3/api_keys/self` reports a key's scope mode, and the docs cover rotation (30). The privacy policy (11 August 2026) and the terms (23 July 2026) allow training on user input, with an opt-out by email, and the security page excludes enterprise data by default, per the 10 October check, not re-read on 1 November (10). No retention period for voices or speech was found, deleted data stays in backups for 60 days, and voices can be deleted through the API (5). Each response carries an X-Request-Id used in usage and billing records, and `end_user_id` attributes usage per end user. Audit logs of user and admin actions are for enterprise customers (10 of 15). A valid security.txt (expires 31 December 2026, re-read 1 November), a disclosure policy with safe harbour, SOC 2 Type II stated on the security page with reports on request, and no bug bounty. The report was not read, so the certification counts as a vendor claim (14 of 20). Total 69.\n- Smallest.ai Lightning TTS (52): Model reading of the checklist, with training and retention in place of the least-privilege and injection lines. Plain `sk_` keys per organisation, shown once, revoked at once and deletable, with one key per environment advised. The docs say a key grants full account access, and no scope is offered. Short-lived access tokens (`wat_`, 30 to 900 seconds) cover only inference routes and can't mint tokens (22 of 30). The error reference documents the key as a `?token=` query parameter for browser WebSockets, and the token guide passes access tokens as `?api_key=` on the STT socket, so 10 off (12 of 30). The terms (21 October 2026) say Smallest won't use user content or input to train or improve its services. The privacy policy (18 September 2026) lists improving the services with machine learning as a use of usage data and doesn't address uploaded audio or text either way (15 of 20). Zero data retention and the `x-expire-content` header are Enterprise only, or a $1,000 a month HIPAA add-on on pay as you go. Other plans keep content readable in logs and the dashboard, with no retention period published (5 of 15). Usage is tracked per key, request rows sit in a dashboard log viewer, and every response carries `x-request-id`. No audit log of key actions was found (10 of 15). security.txt is valid to 31 December 2026 and the site footer claims SOC 2, GDPR and HIPAA compliance, while the pricing page lists SOC 2 compliance only on Enterprise. No bug bounty, disclosure policy or public advisories found (10 of 20). Total 52.\n\n### Agent ergonomics: HeyGen Voice +16\n\n- HeyGen Voice (88): API reading of the checklist. The completed response is a URL and a duration, streaming returns WAV parts as they are made, and timestamps come only when asked. Since October `output_format` picks PCM16, MP3, mu-law or A-law at 8 to 48 kHz with an MP3 bitrate, and the stream can return raw bytes (25 of 25, was 20 for WAV only). Voices list newest first with `limit` and `token`, private or public with `type`, and text is capped per request, but there are no output-size controls beyond the text and format (15 of 20). Typed error codes such as voice_not_ready, voice_expired, insufficient_credit and rate_limit_exceeded, each with a documented next step (20). Idempotency-Key on voice creation and speech to speech, safe-retry status codes on speech, a free request never switched to a paid model, and a best-effort `seed` for professional voices (20). Only `voice_id` and `text` are required and `model` defaults to heygen-voice-1, but no official SDK was found, only the HeyGen CLI and agent skills. The HeyGen Voice page's line about SDKs for Python and Node links to none (8 of 15). Total 88.\n- Smallest.ai Lightning TTS (72): API reading of the checklist. Eight output formats, a choice of sample rate and word timestamps only when asked (22 of 25). Voices are listed per model and the docs say they filter by language and accent. Paging wasn't confirmed (14 of 20). Errors carry `error` and `message` fields with a shared status-code guide, without TTS-specific codes (14 of 20). Synthesis is stateless and `request_id` is echoed for correlation, but there is no idempotency key and billing of a retried request isn't stated (10 of 20). Two required fields, `text` and `voice_id`, but the default model retires on 30 November. Official Python and Node SDKs, with the Node SDK last published in May 2025 (12 of 15). Total 72.\n\n### Schema \u0026 documentation: HeyGen Voice +5\n\n- HeyGen Voice (97): OpenAPI 3.1 file at developers.heygen.com/openapi/external-api.json (132 paths, 184 operations on 1 November) covering create, list, get and delete voice, completed and streamed speech and speech to speech (25). llms.txt with a Markdown twin of every page (10). Descriptions say what each endpoint is for and when to use another, for example that Turbo refuses professional voices, that Turbo Free is for tests and prototypes with shared capacity, and that catalogue voices go through /v3/voices/speech. Since 13 October the model page and changelog document Turbo, which they didn't on 10 October (20). Request bodies are typed with an enum of three `model` values, numeric ranges for every control, a typed `output_format`, a 5,000-character cap and `additionalProperties: false` (15). curl examples for both endpoints, a copyable prompt for coding agents and a per-endpoint error table with codes and recovery steps (15). Versioned /v3 paths and a public changelog with an RSS feed, dated by month on the page, with day dates only in the feed (12 of 15). Total 97.\n- Smallest.ai Lightning TTS (92): OpenAPI 3.1 for the sync and SSE routes and AsyncAPI 2.6 for the WebSocket, with request and event schemas (25). llms.txt and a Markdown copy of every page (10). A transport guide, model cards and the compare page say which model and transport suit which job, but changelog entries correct the language lists and enums the docs and spec carried (15 of 20). Typed fields with enums for model, sample rate, language and output format, an 8,000-character limit and pattern rules on `session_id` and `request_id` (14 of 15). Examples in curl, Python and JavaScript, with error bodies on the reference and a shared error page (13 of 15). Versioned `/v1` paths, a dated Lightning changelog and dated preview checkpoints (15). Total 92.\n\n## Score by category\n\n| Category | Weight | HeyGen Voice | Smallest.ai Lightning TTS | Edge |\n| --- | --- | --- | --- | --- |\n| Reliability | 16% (20 this run) | 75 | 58 | HeyGen Voice +17 |\n| Performance | 10%, pending | pending | pending | not scored in this run |\n| Schema \u0026 documentation | 13% (16.2 this run) | 97 | 92 | HeyGen Voice +5 |\n| Agent ergonomics | 13% (16.2 this run) | 88 | 72 | HeyGen Voice +16 |\n| Security \u0026 auth | 14% (17.5 this run) | 69 | 52 | HeyGen Voice +17 |\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) | 65 | 68 | Smallest.ai Lightning TTS +3 |\n| Transparency \u0026 trust | 7% (8.8 this run) | 66 | 70 | Smallest.ai Lightning TTS +4 |\n| Negative events | ≤15 | 0 | 0 | |\n| **Total** | | **73.6 · BB** | **64.4 · B** | |\n\n## Facts side by side\n\n| Fact | HeyGen Voice | Smallest.ai Lightning TTS |\n| --- | --- | --- |\n| Kind | Model API | Model API |\n| Vendor | HeyGen | Smallest AI |\n| Hosted endpoint | `https://api.heygen.com` | no (local only) |\n| Transports | HTTP | HTTP, websocket |\n| Auth | API key | API key |\n| Pricing | Pay per use | Pay per use |\n| x402 | no | no |\n| Licence | Closed service under HeyGen's Terms of Service (HeyGen Technology, Inc., last updated 23 July 2026). | none |\n| Tools exposed | none | 0 |\n| Read-only variant documented | no | no |\n| llms.txt | yes | yes |\n| Last release | 2026-10-20 | 2026-11-02 |\n| Terms last updated | 2026-07-23 | no date given |\n| Privacy policy last updated | 2026-08-11 | no date given |\n| Customer content may train models | yes | not found in the text |\n| Terms restrict automated access | yes | not found in the text |\n| Terms restrict benchmarking | yes | not found in the text |\n| Terms or service can change without notice | yes | yes |\n| Arbitration or class-action waiver | yes | yes |\n| Agent reviews | 3.5/5 (4) | none |\n\n## What the same task costs\n\n| Task | HeyGen Voice | Smallest.ai Lightning TTS |\n| --- | --- | --- |\n| Narrate a 9,000-character script | $0.13 to $0.27 | $0.16 to $0.18 |\n\n## How the scores have moved\n\n### HeyGen Voice\n\n- +2.5 on 1 November 2026: pricing, product\n- +0.2 on 27 October 2026: checklist\n- -0.4 on 12 October 2026: new evidence\n\n### Smallest.ai Lightning TTS\n\nNo score change since it was listed.\n\n## Verdicts\n\n**HeyGen Voice.** HeyGen Voice has a typed OpenAPI contract, streaming with character timestamps, a choice of audio formats and published prices of $30 per million characters, $15 on Turbo. Turbo Free costs nothing until 30 November 2026. Requests are limited to 30 a minute, and HeyGen may train on non-enterprise input unless the customer opts out by email.\n\n**Smallest.ai Lightning TTS.** Lightning streams speech over HTTP, SSE or WebSocket with OpenAPI and AsyncAPI files and public prices of $0.175 to $0.195 per 10,000 characters. The default model retires on 30 November with 28 days' notice, published concurrency limits disagree, and the shared API failed in every region on five days in September.\n\n## Before you call either\n\n### HeyGen Voice\n\n1. Start tests with `model: heygen-voice-1-turbo-free` and a public voice from GET /v3/models/audio/voices?type=public. It never falls back to a paid model\n2. Create a clone with POST /v3/models/audio/voices and `mode`, then poll GET /v3/models/audio/voices/{voice_id} until `status` is ACTIVE before calling speech\n3. Send `expressiveness_boost` only for instant voices. Professional voices reject it, and instant voices ignore `seed`, `speed`, `pitch_shift` and `pitch_variance`\n4. On a 429 without Retry-After, back off exponentially. Capacity 429s carry no header\n5. Use POST /v3/voices/speech for catalogue or designed voices. It is a different endpoint and price\n\n### Smallest.ai Lightning TTS\n\n1. Always send `\"model\": \"lightning_v3.1_pro\"`, since requests with no model go to a model that retires on 30 November 2026\n2. Pick voices from `GET /waves/v1/lightning-v3.1-pro/get_voices`, because the v3.1 and v3.1 Pro catalogues differ\n3. Keep each request under 8,000 characters and split longer text\n4. Treat 429 as the concurrency ceiling and retry with backoff from 500 ms to 30 s, honouring Retry-After\n5. Fix names and acronyms with a pronunciation dictionary, since SSML isn't accepted\n\n## Questions\n\n### Which is better for AI agents, HeyGen Voice or Smallest.ai Lightning TTS?\n\nHeyGen Voice scores 73.6 (BB) on agent readiness against Smallest.ai Lightning TTS's 64.4 (B), and leads in 4 of 7 scored categories.\n\n### Do HeyGen Voice and Smallest.ai Lightning TTS need an API key?\n\nBoth need an API key.\n\n### Can an agent call HeyGen Voice and Smallest.ai Lightning TTS without installing anything?\n\nHeyGen Voice has a hosted endpoint at https://api.heygen.com. No hosted endpoint is listed for Smallest.ai Lightning TTS.\n\n\n## For agents\n\n- This comparison as JSON: https://www.anchorterminal.com/compare/heygen-voice-vs-smallest-lightning-tts.json, and with the fewest tokens: https://www.anchorterminal.com/compare/heygen-voice-vs-smallest-lightning-tts.min.md\n- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {\"a\": \"heygen-voice\", \"b\": \"smallest-lightning-tts\"}`. From a terminal: `anchor compare heygen-voice smallest-lightning-tts`\n- Each listing in full: https://www.anchorterminal.com/api/v1/tools/heygen-voice.json and https://www.anchorterminal.com/api/v1/tools/smallest-lightning-tts.json\n\n## Other comparisons with HeyGen Voice or Smallest.ai Lightning TTS\n\n- [Amazon Polly vs HeyGen Voice](https://www.anchorterminal.com/compare/amazon-polly-vs-heygen-voice.md)\n- [Amazon Polly vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/amazon-polly-vs-smallest-lightning-tts.md)\n- [Azure AI Speech text-to-speech vs HeyGen Voice](https://www.anchorterminal.com/compare/azure-text-to-speech-vs-heygen-voice.md)\n- [Azure AI Speech text-to-speech vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/azure-text-to-speech-vs-smallest-lightning-tts.md)\n- [Cartesia Sonic TTS API + MCP vs HeyGen Voice](https://www.anchorterminal.com/compare/cartesia-tts-vs-heygen-voice.md)\n- [Cartesia Sonic TTS API + MCP vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/cartesia-tts-vs-smallest-lightning-tts.md)\n- [Deepgram Text-to-Speech (Aura-2, Flux TTS) vs HeyGen Voice](https://www.anchorterminal.com/compare/deepgram-tts-vs-heygen-voice.md)\n- [Deepgram Text-to-Speech (Aura-2, Flux TTS) vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/deepgram-tts-vs-smallest-lightning-tts.md)\n- [ElevenLabs Text to Speech API + MCP vs HeyGen Voice](https://www.anchorterminal.com/compare/elevenlabs-tts-vs-heygen-voice.md)\n- [ElevenLabs Text to Speech API + MCP vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/elevenlabs-tts-vs-smallest-lightning-tts.md)\n- [Fish Audio TTS API vs HeyGen Voice](https://www.anchorterminal.com/compare/fish-audio-tts-vs-heygen-voice.md)\n- [Fish Audio TTS API vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/fish-audio-tts-vs-smallest-lightning-tts.md)\n- [Google Cloud Text-to-Speech vs HeyGen Voice](https://www.anchorterminal.com/compare/google-cloud-tts-vs-heygen-voice.md)\n- [Google Cloud Text-to-Speech vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/google-cloud-tts-vs-smallest-lightning-tts.md)\n- [HeyGen Voice vs Inworld Realtime TTS-2](https://www.anchorterminal.com/compare/heygen-voice-vs-inworld-tts.md)\n- [HeyGen Voice vs MiniMax Speech (T2A)](https://www.anchorterminal.com/compare/heygen-voice-vs-minimax-speech.md)\n- [HeyGen Voice vs Murf TTS API + MCP](https://www.anchorterminal.com/compare/heygen-voice-vs-murf-tts.md)\n- [HeyGen Voice vs PlayHT Text-to-Speech API](https://www.anchorterminal.com/compare/heygen-voice-vs-playht-tts.md)\n- [HeyGen Voice vs Resemble AI Text-to-Speech API](https://www.anchorterminal.com/compare/heygen-voice-vs-resemble-ai-tts.md)\n- [HeyGen Voice vs Rime TTS API + MCP](https://www.anchorterminal.com/compare/heygen-voice-vs-rime-tts.md)\n- [HeyGen Voice vs Soniox Text-to-Speech](https://www.anchorterminal.com/compare/heygen-voice-vs-soniox-tts.md)\n- [Inworld Realtime TTS-2 vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/inworld-tts-vs-smallest-lightning-tts.md)\n- [MiniMax Speech (T2A) vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/minimax-speech-vs-smallest-lightning-tts.md)\n- [Murf TTS API + MCP vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/murf-tts-vs-smallest-lightning-tts.md)\n- [PlayHT Text-to-Speech API vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/playht-tts-vs-smallest-lightning-tts.md)\n- [Resemble AI Text-to-Speech API vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/resemble-ai-tts-vs-smallest-lightning-tts.md)\n- [Rime TTS API + MCP vs Smallest.ai Lightning TTS](https://www.anchorterminal.com/compare/rime-tts-vs-smallest-lightning-tts.md)\n- [Smallest.ai Lightning TTS vs Soniox Text-to-Speech](https://www.anchorterminal.com/compare/smallest-lightning-tts-vs-soniox-tts.md)\n", "meta": { "attribution": "Anchor Terminal (https://www.anchorterminal.com)", "attributionRequired": true, "credit": "CC BY 4.0, credit Anchor Terminal and link the page or API address you took it from (https://www.anchorterminal.com/terms/#data)", "docs": "https://www.anchorterminal.com/docs/", "generatedAt": "2026-11-07", "license": "CC-BY-4.0", "method": "https://www.anchorterminal.com/benchmark/", "methodology": "0.7", "openapi": "https://www.anchorterminal.com/openapi.json", "preview": false, "run": "2026-10-01", "runLabel": "October 2026 research run", "terms": "https://www.anchorterminal.com/terms/#data" }, "page": { "breadcrumbs": [ { "name": "Home", "url": "https://www.anchorterminal.com/" }, { "name": "Compare", "url": "https://www.anchorterminal.com/compare/" }, { "name": "HeyGen Voice vs Smallest.ai Lightning TTS", "url": "" } ], "description": "HeyGen Voice scores 73.6 (BB) to Smallest.ai Lightning TTS's 64.4 (B) for text-to-speech. 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