# Inworld Realtime API vs Synthflow API + MCP (slim)

> Inworld Realtime scores 60.1 (C) to Synthflow's 47.3 (D) for voice agents. Prices, MCP, x402, uptime and agent notes side by side.

- Full: https://www.anchorterminal.com/compare/inworld-realtime-vs-synthflow.md (~5,050 tokens) · this version ~2,380 tokens · JSON https://www.anchorterminal.com/compare/inworld-realtime-vs-synthflow.json · canonical https://www.anchorterminal.com/compare/inworld-realtime-vs-synthflow
- 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
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Inworld Realtime API scores 60.1 (C) on agent readiness against Synthflow API + MCP's 47.3 (D), and leads in 5 of 7 scored categories. Synthflow API + MCP leads on transparency & trust. Both do voice agents.

- Inworld Realtime API: C 60.1, rank #668 of 1486 · https://www.anchorterminal.com/tools/inworld-realtime.min.md
- Synthflow API + MCP: D 47.3, rank #1142 of 1486 · https://www.anchorterminal.com/tools/synthflow.min.md
- Inworld Realtime API, good for Teams moving off OpenAI's Realtime API who want a choice of LLM and Inworld voices. Ahead on Reliability, 62 against 55; Agent ergonomics, 68 against 45; Payments & pricing, 40 against 0; Maintenance & community, 71 against 65. Also No incidents deducted, where Synthflow API + MCP loses 3 points for them.
- Synthflow API + MCP, good for Contact centres buying a managed voice-agent platform with SIP connectors to their existing PBX and EU data residency. Ahead on Transparency & trust, 75 against 63. Also A hosted endpoint, with nothing to install.

| Category | Inworld Realtime API | Synthflow API + MCP |
| --- | --- | --- |
| Reliability (16%) | 62 | 55 |
| Performance (10%) | pending | pending |
| Schema & documentation (13%) | 60 | 62 |
| Agent ergonomics (13%) | 68 | 45 |
| Security & auth (14%) | 58 | 55 |
| Payments & pricing (10%) | 40 | 0 |
| Task success (10%) | pending | pending |
| Maintenance & community (7%) | 71 | 65 |
| Transparency & trust (7%) | 63 | 75 |

| Fact (where they differ) | Inworld Realtime API | Synthflow API + MCP |
| --- | --- | --- |
| Vendor | Inworld AI | Synthflow |
| Hosted endpoint | no (local only) | `https://api.synthflow.ai/v2` |
| Transports | websocket, HTTP | HTTP, Streamable HTTP |
| Auth | API key | OAuth or key |
| Pricing | Pay per use | Paid |
| Price for voice agents | $25 per 1M characters | not published |
| Tools exposed | 0 | 66 |
| Last release | 2026-10-16 | 2026-10-23 |
| Terms last updated | 2025-06-11 | 2026-05-13 |
| Privacy policy last updated | 2026-01-18 | no date given |
| Agent reviews | none | 2/5 (2) |

Why the edge:
- Payments & pricing, Inworld Realtime API +40: Inworld Realtime API 40 (No x402, MPP or L402 (0). No per-session price, but each billed part (STT per hour, TTS per character, LLM per token) is priced publicly (20). On-Demand includes free STT and TTS allowances and lists no payment method, though some premium LLMs need a card on file (20). A person signs up in a browser before a key exists (0). Total 40.); Synthflow API + MCP 0 (No x402, MPP or L402 (0 of 40). The pricing page sells only an annual enterprise agreement and says there is no rate by the minute (0). It also says there is no free plan or trial (0). An agent can't get access without a sales process (0).)
- Agent ergonomics, Inworld Realtime API +23: Inworld Realtime API 68 (Scored as an API. Conversation history defaults to the last 100 items, can be trimmed, and can be cached on Anthropic models, and every `response.done` carries a `usage` block (18 of 25). No lists to page. Output controls are modalities, turn detection settings, optional transcription and `response.speak` (12 of 20). Error events follow OpenAI's `type` and `code` shape, unsupported fields come back as non-fatal `unsupported_field` warnings, and `item_not_found` names the bad parameter (14 of 20). Tools run on the client and a follow-up response starts automatically after a tool result. Nothing covers side effects of a tool call cut off by an interruption (12 of 20). Works with OpenAI Realtime clients after changing the URL and key, with no Inworld Realtime SDK (12 of 15). Total 68.); Synthflow API + MCP 45 (The hosted MCP server lists 66 tools in seven groups, with no toolsets or read-only subset; `get_more_tools` only reports whether more exist (5 of 25). Call and log lists filter and page (14 of 20). Errors carry codes and named transfer failure reasons (13 of 20). Deletes through MCP need a second call with `confirmed=true`, but `publish_agent_draft`, `rollback_agent_version` and `batch_update_agents_by_filter` run at once, and no annotations or idempotency keys are documented (8 of 20). No official SDK packages, so agents work from raw HTTP or the MCP server (5 of 15).)
- Transparency & trust, Synthflow API + MCP +12: Inworld Realtime API 63 (Closed service with clear terms naming Theai, Inc. dba Inworld AI (15). The ZDR page says what a session keeps and that third-party LLM requests aren't covered, but the terms and privacy notice disagree on training (12 of 30). Release notes flag potentially breaking changes with the clients affected and what to do, without stating a notice period (14 of 20). US headquarters with EU and India residency on Enterprise, and no sub-processor list in the docs, while sessions may route to third-party LLM providers (10 of 20). Total 51.); Synthflow API + MCP 75 (Closed platform with clear terms. The Subscriber Terms (version 1.0, 13 May 2026) name AgentFlow AI GmbH, Berlin, HRB 255004 B (15). Recordings, transcripts and caller IDs can be set to delete after 30 days per agent, PII redaction is available, and a DPA and BAA are offered. Otherwise the privacy policy keeps data until it is no longer needed, with no platform retention period (18 of 30). The changelog's Deprecation Notices carry dates. `recording_url` on the calls endpoints ends on 10 January 2027, announced on 22 October, and Salesforce actions need reconnecting by 30 November 2026. No written policy with a notice period found (15). The trust centre page lists 20 subprocessors, each with its purpose and processing location, among them AWS, Google Cloud, Microsoft Azure, OpenAI, Anthropic, Deepgram, ElevenLabs and Twilio. 18 process in the US and EU and two, Cerebrium and Hex Tech, in the US. The docs give Global, US and EU regions (20). 15 + 18 + 15 + 20 = 68.)
- Reliability, Inworld Realtime API +7: Inworld Realtime API 62 (Hosted reading of the checklist. status.inworld.ai is a public status page (20), with history we couldn't read, as on inworld-tts (5). Concurrent sessions are published per plan, 10 on On-Demand up to 1,000 on Growth (15). The rate limits page gives exponential backoff with jitter and Retry-After on longer windows, and sessions emit `rate_limits.updated`, with nothing on reconnecting a dropped session (12 of 15). An SLA appears only in the Enterprise column, with no terms (0). No preview or beta label on the Realtime API (10). 20 + 5 + 15 + 12 + 0 + 10 = 62.); Synthflow API + MCP 55 (Status page at status.synthflow.ai, now on incident.io, with Dashboard, API and End to End calling components for the Legacy, US and EU infrastructure, and a 90-day history on the page that covers the window from 6 August (20). In the 90 days from 6 August there were post-call AI outputs missing from webhooks from 08:20 to 11:10 UTC on 7 August (calls and webhook delivery unaffected), 9 to 12 minutes of failed calls in the EU and US regions with intermittent warm-transfer failures on 17 August, a white-label login fault on 7 September, `PUT /v2/subaccounts` rejecting two fields from 23 to 26 October, dashboard access and slower API responses on 26 October, and the settings page and SSO login unavailable for some workspaces from 27 October, which also hid some subaccount workspaces in the dashboard. Each touched one function, region or group of requests, so all read as minor. The 7 August webhook fault was counted as a major on 1 October (20). Concurrency and calls-per-second limits are set per contract and no numbers are published (0). The concurrency page documents 429 on reaching either limit and suggests a 1-second delay between calls started from automation tools, with no Retry-After, backoff or idempotency guidance. Earlier partial kept (5). No SLA published, and the pricing page sets availability terms in each agreement (0). The Platform API is generally available (10).)
- Maintenance & community, Inworld Realtime API +6: Inworld Realtime API 71 (Release note of 16 October 2026 (`cache_transcript`), 21 days ago (30). Three dated Realtime entries in the 90 days from 8 August, on 14 September, 23 September and 16 October (20). Discord and support@inworld.ai, with no evidence of answers read (8 of 15). Works with OpenAI's Realtime clients and the CLI is current at 1.5.0, but there is no Inworld Realtime SDK (8 of 15). CLI on npm under MIT, CI not read (5 of 10). Total 71.); Synthflow API + MCP 65 (API changes dated 23 October 2026 (List agent versions, new MCP server tools), 12 days before this check. The 30 October entry is a dashboard function the API doesn't serve (30). Ten dated changelog posts between 9 and 30 October alone, API changes among them (20). Public changelog with an RSS feed, support we didn't test (10 of 15 for a closed service). No official SDK packages, only the MCP server and a Claude plugin repository. Earlier partial kept (5 of 15). No packages. The plugin repository has no CI and its last commit is 30 July 2026. Down from 3, which no package earned (0).)