HeyGen Voice vs Smallest.ai Lightning TTS

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.

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.

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.

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.

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.

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.

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.

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.