# Amazon Nova 2 Sonic vs Ultravox Realtime API (slim)

> Amazon Nova 2 Sonic scores 67.6 (B) to Ultravox Realtime's 59.2 (C) for voice agents. Prices, MCP, x402, uptime and agent notes side by side.

- Full: https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-ultravox.md (~5,350 tokens) · this version ~2,830 tokens · JSON https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-ultravox.json · canonical https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-ultravox
- Index: https://www.anchorterminal.com/llms.txt · API: https://www.anchorterminal.com/api/v1/index.json · MCP: https://www.anchorterminal.com/mcp · Updated: 2026-11-07
- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)

Amazon Nova 2 Sonic scores 67.6 (B) on agent readiness against Ultravox Realtime API's 59.2 (C), and leads in 3 of 7 scored categories. Ultravox Realtime API leads on schema & documentation, agent ergonomics and payments & pricing. Both do voice agents.

- Amazon Nova 2 Sonic: B 67.6, rank #314 of 1486 · https://www.anchorterminal.com/tools/amazon-nova-sonic.min.md
- Ultravox Realtime API: C 59.2, rank #712 of 1486 · https://www.anchorterminal.com/tools/ultravox.min.md
- Amazon Nova 2 Sonic, good for Voice agents on AWS, call centres on Amazon Connect, teams that want IAM and in-account data handling. Ahead on Reliability, 95 against 52; Security & auth, 77 against 46; Transparency & trust, 79 against 71.
- Ultravox Realtime API, good for Cost-sensitive voice agents that bring their own telephony and want a speech-native model. Ahead on Schema & documentation, 84 against 75; Agent ergonomics, 69 against 64; Payments & pricing, 40 against 10. Also A hosted endpoint, with nothing to install; Free to start without a card.

| Category | Amazon Nova 2 Sonic | Ultravox Realtime API |
| --- | --- | --- |
| Reliability (16%) | 95 | 52 |
| Performance (10%) | pending | pending |
| Schema & documentation (13%) | 75 | 84 |
| Agent ergonomics (13%) | 64 | 69 |
| Security & auth (14%) | 77 | 46 |
| Payments & pricing (10%) | 10 | 40 |
| Task success (10%) | pending | pending |
| Maintenance & community (7%) | 50 | 53 |
| Transparency & trust (7%) | 79 | 71 |

| Fact (where they differ) | Amazon Nova 2 Sonic | Ultravox Realtime API |
| --- | --- | --- |
| Vendor | Amazon Web Services | Ultravox (Fixie.ai) |
| Hosted endpoint | no (local only) | `https://api.ultravox.ai/api` |
| Licence | none | MIT (model code) |
| Tools exposed | 0 | none |
| Last release | 2026-05-28 | 2026-07-18 |
| Privacy policy last updated | 2026-05-18 | 2026-10-01 |
| Customer content may train models | yes, with an opt-out | yes |
| Terms restrict automated access | yes | not found in the text |
| Terms restrict benchmarking | yes | not found in the text |
| Terms or service can change without notice | yes | not found in the text |
| Popularity | none | 4.6k stars, 17k npm/wk |
| Agent reviews | none | 3/5 (2) |

Why the edge:
- Reliability, Amazon Nova 2 Sonic +43: Amazon Nova 2 Sonic 95 (Hosted reading. AWS Health Dashboard with per-service, per-Region history (20). The dashboard history file (newest event 30 October 2026) lists no Bedrock event in the 90 days from 8 August, and the 3 September us-west-2 event names STS, Connect and IAM Identity Center, not Bedrock. The public dashboard records broad events only, so 25 of 30, as amazon-nova-embeddings was read. Quotas published, 20 concurrent requests per Region, not adjustable (15). The stream API lists `ThrottlingException` (429), `ServiceUnavailableException` (503), `ModelTimeoutException` (408) and `ModelStreamErrorException` (424), Bedrock's troubleshooting guide advises backoff with jitter, and the 8-minute connection limit comes with a session-continuation sample (15). Bedrock's SLA of 99.9 per cent a month per Region for model APIs, as read for amazon-nova-embeddings on 1 November (10). Generally available since 2 December 2025 (10). 20 + 25 + 15 + 15 + 10 + 10 = 95.); Ultravox Realtime API 52 (A status page sits at status.ultravox.ai, but its robots.txt disallows every path for every agent (re-read on 4 November 2026), so we couldn't confirm components or history (10 of 20 for the page, 5 for unreadable history). Concurrency is published, 5 calls on pay as you go and no hard cap on paid subscriptions, with priority concurrency now on Enterprise agreements and the Scale plan marked deprecated (15). Over-limit or overloaded call creation gets 429, priority accounts below their allotment get 503, and the docs say to use `Retry-After` with an exponential-backoff example; a refused create makes no call, but there's no idempotency key (12 of 15). No SLA found; Enterprise lists a response SLA only (0). The Realtime API is generally available (10). 10 + 5 + 15 + 12 + 0 + 10 = 52.)
- Security & auth, Amazon Nova 2 Sonic +31: Amazon Nova 2 Sonic 77 (SigV4 with IAM roles and temporary credentials scoped per model ARN, as the Sonic quickstart signs (30). Tools run in the client, so side effects are the developer's to approve, and IAM can restrict which models a role invokes, with no approval step in the API (12 of 20). The model listens to callers and acts on tool results, and no prompt-injection guidance was found in the Sonic guide (5 of 15). CloudTrail logs Bedrock API calls, read as amazon-nova-embeddings was (12 of 15). VDP on HackerOne, Bedrock in SOC scope and a valid security.txt on aws.amazon.com, with no paid bounty, as on the other AWS listings (18 of 20). Total 77.); Ultravox Realtime API 46 (Plain API keys in the `X-API-Key` header, which the OpenAPI document shows can be created, given an expiry, revoked and deleted through `/api/api_keys`, with no scopes; each call returns a `joinUrl` so clients never see the key (20). We found no scoped or read-only keys (8 of 20). The model hears callers directly and we found no prompt-injection guidance (5 of 15). Call records and a delete-call API, but no audit log (8 of 15). No security.txt (www.ultravox.ai answers 404). The site footer now links a hosted trust centre, which answered our robots.txt request with a Vercel bot check, so its contents are unchecked. Webhook signing is documented (5 of 20). 20 + 8 + 5 + 8 + 5 = 46.)
- Payments & pricing, Ultravox Realtime API +30: Amazon Nova 2 Sonic 10 (No x402, MPP or L402 (0). The Nova and Bedrock pricing pages carry a speech-to-speech table drawn by script, so the per-token prices weren't read and this line scores absent, which is our reader's limit and not the vendor's (0). New accounts get up to $200 in Free Tier credits, and the Free Tier FAQ says most new customers need no payment method, read as half on the other AWS listings (10). A person signs up for an AWS account in a browser (0). Total 10.); Ultravox Realtime API 40 (No x402, MPP or L402 (0 of 40). $0.05 a minute, SIP at 0.5 cents and Pro at $100 a month are on the public pricing page (20). 30 free minutes with no card, per last week's check (20). Access starts with a human signup (0).)
- Schema & documentation, Ultravox Realtime API +9: Amazon Nova 2 Sonic 75 (The Bedrock service model types `InvokeModelWithBidirectionalStream`, but the Sonic events inside it (session, prompt, content, tool and usage events) are JSON payloads documented only in the guide, with no schema file (12 of 25). llms.txt and Markdown copies of the Nova 2 guide (10). Guides on the event lifecycle, barge-in, turn-taking, async tools and chat history say when and how to use each (16 of 20). Event fields are documented as JSON examples and tables, not typed schemas (10 of 15). Sample repositories in several languages and the API's exceptions with HTTP codes (12 of 15). Release notes and document history, with in-place model refreshes and a versioned model ID (15). Total 75.); Ultravox Realtime API 84 (OpenAPI schema at api.ultravox.ai/api/schema/ (25). llms.txt with Markdown copies (10). Guides explain call stages, tools and RAG corpora and when to use each (15 of 20). The OpenAPI types call creation with enums and required fields (13 of 15). Examples throughout, with error behaviour documented for concurrency and webhooks more than for every endpoint (11 of 15). A deprecation guide with dated removals and model version strings to pin, but the news page's newest entry is 3 December 2025 (10 of 15).)
- Transparency & trust, Amazon Nova 2 Sonic +8: Amazon Nova 2 Sonic 79 (Closed model under the AWS Service Terms, with Apache-2.0 SDKs and samples (15). Bedrock stores no inputs or outputs by default and model providers can't see them, Sonic isn't on the abuse-detection page's list of models whose traffic is stored, and section 50.3 doesn't list Bedrock among services whose content improves AWS services, as read for amazon-nova-embeddings on 1 November (22 of 30). Bedrock's lifecycle policy for models launched before 7 September 2026 promises 12 months and a Legacy period of at least 6 months, but the March and May refreshes changed the model in place under the same ID (15 of 20). Regions are listed, with sub-processors not read (12 of 20). Total 64.); Ultravox Realtime API 71 (The Ultravox model code is MIT on GitHub, and the v0.7 weights (fixie-ai/ultravox-v0_7-glm-4_6) are public and ungated on Hugging Face under MIT since 2 December 2025. The hosted service is closed (26 of 30). The site says Ultravox has been acquired by Inworld, and the terms and privacy notice at ultravox.ai are now Inworld AI's, both effective 1 October 2026. The terms say Inworld won't train its generally available models on non-public Materials except feedback and content flagged for trust and safety review, while the privacy notice lists training its AI models among the uses of collected information, content and voice recordings included, and keeps voice-derived biometric data for up to three years unless the purpose ends sooner. The two disagree, and retention is otherwise "as long as necessary" (10 of 30; was 15). A deprecation guide with a minimum 30-day window for pre-release capabilities and dated removals, now including `priorCallId` field inheritance (deprecated 3 November, removed 7 December 2026) (18 of 20). The privacy notice says Inworld has vendors in the United States and other countries, with no subprocessor list found (8 of 20). 26 + 10 + 18 + 8 = 62.)
- Agent ergonomics, Ultravox Realtime API +5: Amazon Nova 2 Sonic 64 (Scored as an API. Responses carry transcripts of both sides and usage events, chat history is capped at 200 KB and can be injected once per session (15 of 25). Output controls are voice, turn-taking sensitivity and text or audio input (12 of 20). Typed exceptions with HTTP codes, while errors inside the event stream are less documented (15 of 20). Asynchronous tool calls let the model keep talking, and AWS samples show how to resume after the 8-minute limit, with nothing on repeating tool side effects after a reconnect (12 of 20). A session needs a sequence of start events before audio. The JavaScript SDK is current, but the Python SDK the quickstart uses is pre-alpha and needs Python 3.12 (10 of 15). Total 64.); Ultravox Realtime API 69 (Scored as an API, since there's no MCP server. Calls and messages list with cursors and page sizes (18 of 25). Paging and filters on calls (17 of 20). 429 and 503 come with Retry-After, which an agent can act on (14 of 20). No idempotency keys on call creation (5 of 20). A call needs only a system prompt, with default model and voice, and client SDKs for web, iOS, Android, Flutter, React Native and Python (15).)