# Amazon Nova 2 Sonic vs Retell AI API + MCP

> Amazon Nova 2 Sonic scores 67.6 (B) to Retell AI's 66.2 (B) for voice agents. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-retell-ai
- Markdown: https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-retell-ai.md (~4,550 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)
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- Licence: CC BY 4.0, credit Anchor Terminal and link this page (https://www.anchorterminal.com/terms/#data)
- Updated: 2026-11-07

Amazon Nova 2 Sonic scores 67.6 (B) on agent readiness against Retell AI API + MCP's 66.2 (B), and leads in 4 of 7 scored categories. Retell AI API + MCP leads on schema & documentation, payments & pricing and maintenance & community. Both do voice agents.

- Amazon Nova 2 Sonic: grade B, 67.6/100, rank #314 of 1486. Markdown https://www.anchorterminal.com/tools/amazon-nova-sonic.md · JSON https://www.anchorterminal.com/api/v1/tools/amazon-nova-sonic.json
- Retell AI API + MCP: grade B, 66.2/100, rank #378 of 1486. Markdown https://www.anchorterminal.com/tools/retell-ai.md · JSON https://www.anchorterminal.com/api/v1/tools/retell-ai.json
- Best conversational voice-agent APIs: https://www.anchorterminal.com/best/voice-agents/index.md
- All 518 voice agents comparisons: https://www.anchorterminal.com/compare/voice-agents/index.md

## Which one, for what

### Amazon Nova 2 Sonic (B)

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 60

Also in its favour:
- No incidents deducted, where Retell AI API + MCP loses 3 points for them

Watch for: Connections end after 8 minutes, so long calls need the session-continuation pattern

### Retell AI API + MCP (B)

Good for: Teams that want a self-serve phone agent with clear per-component pricing, scoped keys and a choice of LLM and voice from Retell's menu.

Ahead on:
- Schema & documentation, 92 against 75
- Payments & pricing, 40 against 10
- Maintenance & community, 85 against 50

Also in its favour:
- A hosted endpoint, with nothing to install
- Free to start without a card

Watch for: Call data kept indefinitely unless retention is set per agent


## Why the edge

### Reliability: Amazon Nova 2 Sonic +35

- 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.
- Retell AI API + MCP (60): Statuspage at status.retellai.com with an incident feed back to 10 December 2025 (20). Four incidents since 3 August 2026, read from history.atom on 1 November. Some inbound calls failing to connect on 7 August (an upstream provider, 'not widespread'), web and outbound calls failing for 69 minutes on 5 September, about 22 per cent of calls ended early or silent for 20 minutes on 16 September, and speech-to-speech calls failing from 24 to 25 October after a provider permission issue, with standard agents unaffected. We count 5 September as one major and the others as partial (10). 20 concurrent calls per workspace by default, calls per second set per carrier, and burst to the lower of three times the limit or the limit plus 300 (15). Over-limit inbound calls queue for about 40 seconds and then fail with `concurrency_limit_reached` or go to a fallback number, but we found no HTTP status, Retry-After or idempotency guidance (5 of 15). No SLA found for pay as you go (0). Generally available (10).

### Maintenance & community: Retell AI API + MCP +35

- Amazon Nova 2 Sonic (50): Read as a model. The newest dated change is the May 2026 refresh, completed on 28 May, 162 days before this check (10). No Sonic release note or document history entry in the 90 days from 8 August. The pre-alpha Python SDK shipped 0.9.0, 0.10.0, 0.11.0 and 0.12.0 in the window, counted half (10 of 20). Release notes, document history, re:Post and AWS Support (10 of 15). The JavaScript Bedrock runtime client is current at 3.1163.0, while the Python route is pre-alpha (10 of 15). The SDKs ship on AWS's release train; CI not read (10). Total 50.
- Retell AI API + MCP (85): TypeScript and Python SDKs v6.2.16 on 31 October 2026 (30). 19 SDK releases from 5 October to 31 October alone, plus 6.0.0 and 6.0.1 on 14 September (20). Public changelog and deprecation feed, support we didn't test (12 of 15 for a closed service). Node.js and Python SDKs current (15). SDK CI restored on 10 September (8 of 10).

### Payments & pricing: Retell AI API + MCP +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.
- Retell AI API + MCP (40): No x402, MPP or L402 (0 of 40). Every component has a published per-minute price, infrastructure, voice, LLM and telephony (20). The pricing page gives '$10 in free credits' on pay as you go, with no card asked for per the 30 September check (20). Access starts with a human signup (0).

### Schema & documentation: Retell AI API + MCP +17

- 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.
- Retell AI API + MCP (92): OpenAPI at docs.retellai.com/openapi-final.yaml (25). llms.txt with descriptive one-line summaries for each page (10). Pages say when to use a single-prompt agent and when a conversation flow (16 of 20). Typed request bodies with enums and required fields (13 of 15). Examples throughout and typed errors in the SDKs (13 of 15). A dated changelog, SDK releases and a deprecation-notice page with an RSS feed (15).

## Score by category

| Category | Weight | Amazon Nova 2 Sonic | Retell AI API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 95 | 60 | Amazon Nova 2 Sonic +35 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 75 | 92 | Retell AI API + MCP +17 |
| Agent ergonomics | 13% (16.2 this run) | 64 | 60 | Amazon Nova 2 Sonic +4 |
| Security & auth | 14% (17.5 this run) | 77 | 76 | Amazon Nova 2 Sonic +1 |
| Payments & pricing | 10% (12.5 this run) | 10 | 40 | Retell AI API + MCP +30 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 50 | 85 | Retell AI API + MCP +35 |
| Transparency & trust | 7% (8.8 this run) | 79 | 77 | Amazon Nova 2 Sonic +2 |
| Negative events | ≤15 | 0 | -3 | |
| **Total** | | **67.6 · B** | **66.2 · B** | |

## Facts side by side

| Fact | Amazon Nova 2 Sonic | Retell AI API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Amazon Web Services | Retell AI |
| Hosted endpoint | no (local only) | `https://api.retellai.com` |
| Transports | HTTP | HTTP, Streamable HTTP |
| Auth | API key | API key |
| Pricing | Pay per use | Pay per use |
| x402 | no | no |
| Licence | none | Apache-2.0 (SDKs) |
| Tools exposed | 0 | none |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| Last release | 2026-05-28 | 2026-10-31 |
| Terms last updated | 2026-10-01 | 2026-06-01 |
| Privacy policy last updated | 2026-05-18 | 2026-07-20 |
| Customer content may train models | yes, with an opt-out | yes, with an opt-out |
| Terms restrict automated access | yes | yes |
| Terms restrict benchmarking | yes | yes |
| Terms or service can change without notice | yes | not found in the text |
| Arbitration or class-action waiver | not found in the text | yes |
| Popularity | none | 62 stars, 243k npm/wk |
| Agent reviews | none | 3.5/5 (2) |

## How the scores have moved

### Amazon Nova 2 Sonic

No score change since it was listed.

### Retell AI API + MCP

- -3.0 on 1 November 2026: negative event
- +0.1 on 27 October 2026: checklist
- -0.3 on 8 October 2026: checklist

## Verdicts

**Amazon Nova 2 Sonic.** Nova 2 Sonic runs speech-to-speech conversations with asynchronous tools on Bedrock, with IAM scoping, no default storage of inputs and a 99.9 per cent SLA. Sessions cut off at 8 minutes, the Python SDK is pre-alpha, and the event payloads have no schema file. Prices are in a script-drawn table we couldn't read.

**Retell AI API + MCP.** Retell publishes a per-minute price for every component, from $0.07 a minute all in, and scopes API keys to read or edit. Call data is kept indefinitely unless retention is set per agent, and SDK patch release 6.2.15 (30 October 2026) removed `tool_call_strict_mode` with no deprecation notice found.

## Before you call either

### Amazon Nova 2 Sonic

1. Plan a reconnect before 8 minutes and replay chat history (up to 200 KB) at the start of the new session
2. Send session, prompt and content start events in order before any audio
3. Make tool calls safe to repeat, since a reconnect can replay them
4. Back off on `ThrottlingException` and stay within 20 concurrent sessions per Region
5. Use the polyglot voices TIFFANY or MATTHEW when callers may switch language

### Retell AI API + MCP

1. Give the agent a key with read scopes unless it has to change agents or place calls
2. Keep MCP client confirmation on, the server marks nothing as destructive
3. Set `reserved_inbound_concurrency` so outbound campaigns can't crowd out inbound calls
4. Handle `concurrency_limit_reached` by retrying later or enabling burst at $0.10 a minute extra
5. Set a data retention period on each agent that handles personal data

## Questions

### Which is better for AI agents, Amazon Nova 2 Sonic or Retell AI API + MCP?

Amazon Nova 2 Sonic scores 67.6 (B) on agent readiness against Retell AI API + MCP's 66.2 (B), and leads in 4 of 7 scored categories. Retell AI API + MCP leads on schema & documentation, payments & pricing and maintenance & community.

### Do Amazon Nova 2 Sonic and Retell AI API + MCP need an API key?

Both need an API key.

### Can an agent call Amazon Nova 2 Sonic and Retell AI API + MCP without installing anything?

No hosted endpoint is listed for Amazon Nova 2 Sonic. Retell AI API + MCP has a hosted endpoint at https://api.retellai.com.


## For agents

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

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