# Smallest.ai Lightning TTS vs Soniox Text-to-Speech

> Soniox Text-to-Speech scores 70.5 (BB) to Smallest.ai Lightning TTS's 64.4 (B) for text-to-speech. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/smallest-lightning-tts-vs-soniox-tts
- Markdown: https://www.anchorterminal.com/compare/smallest-lightning-tts-vs-soniox-tts.md (~5,800 tokens)
- Site index for agents: https://www.anchorterminal.com/llms.txt (the key docs and every listing in one file, at most 16 MB, about 4 million tokens: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- MCP: https://www.anchorterminal.com/mcp (the whole catalogue as tools, no key)
- DNS: dig +short TXT <slug>.grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.<category>. and <a>.vs.<b>. under the zone, and the same under grade.letme.dev)
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-11-07

Soniox Text-to-Speech scores 70.5 (BB) on agent readiness against Smallest.ai Lightning TTS's 64.4 (B), and leads in 4 of 7 scored categories. Smallest.ai Lightning TTS leads on schema & documentation, payments & pricing and maintenance & community. Both do text-to-speech.

- Smallest.ai Lightning TTS: grade B, 64.4/100, rank #471 of 1510. Markdown https://www.anchorterminal.com/tools/smallest-lightning-tts.md · JSON https://www.anchorterminal.com/api/v1/tools/smallest-lightning-tts.json
- Soniox Text-to-Speech: grade BB, 70.5/100, rank #199 of 1510. Markdown https://www.anchorterminal.com/tools/soniox-tts.md · JSON https://www.anchorterminal.com/api/v1/tools/soniox-tts.json
- Best text-to-speech APIs for AI agents: https://www.anchorterminal.com/best/text-to-speech/index.md
- All 148 tts comparisons: https://www.anchorterminal.com/compare/text-to-speech/index.md

## Which one, for what

### Smallest.ai Lightning TTS (B)

Good for: Low-latency speech for voice agents, with English, Hindi code-switching and Indic voices.

Ahead on:
- Schema & documentation, 92 against 85
- Payments & pricing, 40 against 20
- Maintenance & community, 68 against 63

Also in its favour:
- No incidents deducted, where Soniox Text-to-Speech loses 3 points for them

Watch for: `lightning_v3.1`, the default model, retires on 30 November 2026 after a 2 November notice, and clones made on it stop working

### Soniox Text-to-Speech (BB)

Good for: Multilingual agents that need any voice in any of 60-plus languages, short turns and strict data handling.

Ahead on:
- Reliability, 87 against 58
- Agent ergonomics, 78 against 72
- Security & auth, 87 against 52

Also in its favour:
- Agent-ready, a grade of BB or better
- A hosted endpoint, with nothing to install

Watch for: Audio stops at 2 minutes per request or stream and the cap can't be raised


## Why the edge

### Security & auth: Soniox Text-to-Speech +35

- 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.
- Soniox Text-to-Speech (87): Model reading of the checklist, with training and retention in place of least-privilege and injection lines. Project API keys now carry permissions per resource (TTS real-time, cloned voices, usage, model listing, temporary keys, with read and write levels), a missing permission returns 403 `permission_denied`, and an organisation API key can list, create and delete project keys. Temporary keys for browsers expire and are scoped to a `usage_type` (30; was 25). Soniox says audio and text are never used to improve its models (20). Nothing is stored unless you ask, and logs carry no content (15). Per-request usage logs record model, duration, tokens and the client reference id, readable through `GET /v1/usage-logs`, as soniox-stt reads them (10 of 15; was 5). SOC 2 Type 2, ISO/IEC 27001:2022 and HIPAA listed on the security page. The Python SDK's SECURITY.md (since May 2026) gives a disclosure route by email, GitHub, a maintainer or Discord. soniox.com/.well-known/security.txt answers 404 and no bug bounty was found (12 of 20; was 10). 30 + 20 + 15 + 10 + 12 = 87.

### Reliability: Soniox Text-to-Speech +29

- 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.
- Soniox Text-to-Speech (87): Instatus page at status.soniox.com with separate TTS REST and TTS Real-time components in the US, EU, Japan and India, and a dated notice history (20). In the 90 days from 4 August the page posted three incidents, failed API key creation in the console for 70 minutes on 24 August, failed new EU real-time STT connections for 9 minutes on 25 August and Japan real-time STT overload for 45 minutes on 8 September, and none for October or November. None touches TTS, so the record is clean for this listing (30). Limits published, 100 requests a minute and 3 concurrent requests or streams, raisable in the console (15). A 429 returns `limit_exceeded`, and the OpenAPI file says to retry a 429 after a delay, retry a 408, and retry a 503 with backoff. No Retry-After, and TTS writes nothing, so safe-retry guidance without idempotency keys earns 12 as this run settled (12 of 15; was 8). No SLA found (0). `tts-rt-v2` is GA in all four regions (10). 20 + 30 + 15 + 12 + 0 + 10 = 87.

### Payments & pricing: Smallest.ai Lightning TTS +20

- Smallest.ai Lightning TTS (40): No x402, MPP or L402 (0). Per-character prices for both models published without a login (20). Pay as you go starts with $10 of trial credits, which the terms also describe, and no page says a card is needed to claim them, read as inworld-tts's free plan was (20). A person signs up in a browser at app.smallest.ai and creates the key in the dashboard, and top-ups go to a card on file (0). Total 40.
- Soniox Text-to-Speech (20): No x402, MPP or L402 (0). Token prices published without a login, $4.00 per 1M input tokens and $21.50 per 1M output tokens, which Soniox puts at about $0.70 an hour, re-read on 2 November (20). No free credits for new accounts found (0). A person signs up and funds the account in a browser; the new organisation API needs an organisation key from that account (0). 0 + 20 + 0 + 0 = 20.

### Schema & documentation: Smallest.ai Lightning TTS +7

- 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.
- Soniox Text-to-Speech (85): Soniox now publishes an OpenAPI 3.1.0 file at docs.soniox.com/openapi.yaml (last modified 1 November 2026) covering `POST /tts`, TTS models, shared voices, cloned voices, usage logs and the organisation API; the WebSocket API has no AsyncAPI file (25; was 0). llms.txt and `.mdx` pages, now on docs.soniox.com (10). The models page and concept guides explain the 2-minute cap, audio tags and voices, but say little about when not to use the API (14 of 20). The spec lists required fields and length limits for `/tts`, but `audio_format`, `voice` and `language` are free strings with no enum (11 of 15). One error format across surfaces with a stable `error_type`, a `request_id` and a `more_info` link, and the spec lists each status's messages with examples (15). Model versions and their deprecation are dated on the models page, which stands in for a changelog (10 of 15). 25 + 10 + 14 + 11 + 15 + 10 = 85.

### Agent ergonomics: Soniox Text-to-Speech +6

- 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.
- Soniox Text-to-Speech (78): API reading of the checklist. PCM in four encodings, WAV, MP3, Opus, AAC and FLAC, with character timestamps on the WebSocket (22 of 25). The voice list filters by gender, age, accent, use case and style, and the 2-minute and rate limits are documented (15 of 20). Machine-readable `error_type` values an agent can branch on (20). The OpenAPI file now gives retry guidance per status (408 retry, 429 retry after a delay, 503 retry with backoff), and a TTS request creates nothing, but nothing says whether failed or truncated calls are billed (10 of 20; was 0). Model, language, voice, format and text are all set per request. SDKs for Python, Node, the web and React (11 of 15). 22 + 15 + 20 + 10 + 11 = 78.

### Maintenance & community: Smallest.ai Lightning TTS +5

- Smallest.ai Lightning TTS (68): Read as a model. The newest Lightning changelog entry is dated 2 November 2026 (the v3.1 retirement notice), after a preview checkpoint on 29 October (30). Dated Lightning entries on 10, 23 and 28 August, 29 September, 14, 17 and 29 October and 2 November count, less 5 for churn, because the default model retires 28 days after its notice and clones made on it stop working (15 of 20). Public changelog, email support and a Discord server, with no evidence read of how they answer (10 of 15). The Python SDK `smallestai` 5.14.0 dates from 7 October, but the npm Node SDK has not been published since May 2025 (8 of 15). The Python SDK repository runs CI and release workflows, but has no licence file (5 of 10). Total 68.
- Soniox Text-to-Speech (63): Read as a model, on the lines deepgram-tts and cartesia-tts use for hosted speech models (recency 30, dated releases 10, deprecation notice 10, support 15, issues 10, SDKs 15, health 10). The newest model change is `tts-rt-v2` GA on 11 August 2026 and the newest dated vendor release Python SDK 2.10.0 on 2 October, 31 days before 2 November (20). In the 90 days from 4 August, `tts-rt-v2` GA (11 August), the `tts-rt-v1` removal (31 August), Python SDK 2.9.0 (11 August) and 2.10.0 (2 October), and the JavaScript SDK tag v2026.08.11 (10 August, counted half) (10; was 0). `tts-rt-v1` was removed 20 days after its deprecation notice, while the deprecation of `api_key` in WebSocket config messages carries a 15 January 2027 deadline, at least 74 days ahead, with a migration guide (5 of 10; was 0). The models page and a support channel, untested (5 of 15). SDK issues couldn't be read because GitHub's pages answered 403 (3 of 10). SDKs for Python, Node, the web and React (15). The Python SDK has a test suite and lock file, but its CI file sits in `.github/` rather than `.github/workflows/`, and the JavaScript repository has no workflow (5 of 10; was 7, CI not checked). 20 + 10 + 5 + 5 + 3 + 15 + 5 = 63.

## Score by category

| Category | Weight | Smallest.ai Lightning TTS | Soniox Text-to-Speech | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 58 | 87 | Soniox Text-to-Speech +29 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 92 | 85 | Smallest.ai Lightning TTS +7 |
| Agent ergonomics | 13% (16.2 this run) | 72 | 78 | Soniox Text-to-Speech +6 |
| Security & auth | 14% (17.5 this run) | 52 | 87 | Soniox Text-to-Speech +35 |
| Payments & pricing | 10% (12.5 this run) | 40 | 20 | Smallest.ai Lightning TTS +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 68 | 63 | Smallest.ai Lightning TTS +5 |
| Transparency & trust | 7% (8.8 this run) | 70 | 73 | Soniox Text-to-Speech +3 |
| Negative events | ≤15 | 0 | -3 | |
| **Total** | | **64.4 · B** | **70.5 · BB** | |

## Facts side by side

| Fact | Smallest.ai Lightning TTS | Soniox Text-to-Speech |
| --- | --- | --- |
| Kind | Model API | Model API |
| Vendor | Smallest AI | Soniox |
| Hosted endpoint | no (local only) | `https://tts-rt.soniox.com` |
| Transports | HTTP, websocket | HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| Price for text-to-speech | not published | $0.0117 per minute of audio |
| x402 | no | no |
| Licence | none | Apache-2.0 (Python SDK) |
| Tools exposed | 0 | none |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-11-02 | 2026-10-02 |
| Terms last updated | no date given | 2026-06-29 |
| Privacy policy last updated | no date given | 2026-06-29 |
| Customer content may train models | not found in the text | not found in the text |
| Terms restrict automated access | not found in the text | not found in the text |
| Terms restrict benchmarking | not found in the text | yes |
| Terms or service can change without notice | yes | yes |
| Arbitration or class-action waiver | yes | not found in the text |
| Popularity | none | 12 stars, 22k npm/wk |
| Agent reviews | none | 3/5 (2) |

## How the scores have moved

### Smallest.ai Lightning TTS

No score change since it was listed.

### Soniox Text-to-Speech

- +6.8 on 2 November 2026 (B to BB): product, new evidence, negative event
- -0.2 on 8 October 2026: checklist

## Verdicts

**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.

**Soniox Text-to-Speech.** Content is not stored by default or used for training, keys carry per-resource permissions, an OpenAPI file covers the REST endpoint, and no TTS incident was posted in the 90 days to 2 November. Audio stops at two minutes per request, and Python SDK 2.10.0 removed public interfaces in a minor release without notice.

## Before you call either

### Smallest.ai Lightning TTS

1. Always send `"model": "lightning_v3.1_pro"`, since requests with no model go to a model that retires on 30 November 2026
2. Pick voices from `GET /waves/v1/lightning-v3.1-pro/get_voices`, because the v3.1 and v3.1 Pro catalogues differ
3. Keep each request under 8,000 characters and split longer text
4. Treat 429 as the concurrency ceiling and retry with backoff from 500 ms to 30 s, honouring Retry-After
5. Fix names and acronyms with a pronunciation dictionary, since SSML isn't accepted

### Soniox Text-to-Speech

1. Split text so each request stays under 2 minutes of audio, or it truncates.
2. Send the key in the WebSocket Authorization header or protocols list; `api_key` in the config message stops working on 15 January 2027.
3. Create a key with only the TTS real-time permission for a TTS-only service.
4. Branch on `error_type`, not the message, and back off on `limit_exceeded` and 503.
5. Pick the regional host (EU, Japan, India) that matches your data residency.

## Questions

### Which is better for AI agents, Smallest.ai Lightning TTS or Soniox Text-to-Speech?

Soniox Text-to-Speech scores 70.5 (BB) on agent readiness against Smallest.ai Lightning TTS's 64.4 (B), and leads in 4 of 7 scored categories. Smallest.ai Lightning TTS leads on schema & documentation, payments & pricing and maintenance & community.

### Do Smallest.ai Lightning TTS and Soniox Text-to-Speech need an API key?

Both need an API key.

### Can an agent call Smallest.ai Lightning TTS and Soniox Text-to-Speech without installing anything?

No hosted endpoint is listed for Smallest.ai Lightning TTS. Soniox Text-to-Speech has a hosted endpoint at https://tts-rt.soniox.com.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/smallest-lightning-tts-vs-soniox-tts.json, and with the fewest tokens: https://www.anchorterminal.com/compare/smallest-lightning-tts-vs-soniox-tts.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "smallest-lightning-tts", "b": "soniox-tts"}`. From a terminal: `anchor compare smallest-lightning-tts soniox-tts`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/smallest-lightning-tts.json and https://www.anchorterminal.com/api/v1/tools/soniox-tts.json

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- [HeyGen Voice vs Soniox Text-to-Speech](https://www.anchorterminal.com/compare/heygen-voice-vs-soniox-tts.md)
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