# Inworld Realtime API vs Synthflow API + MCP > 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. - Canonical: https://www.anchorterminal.com/compare/inworld-realtime-vs-synthflow - Markdown: https://www.anchorterminal.com/compare/inworld-realtime-vs-synthflow.md (~5,050 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 .grade.anchorterminal.com (the grade as a DNS TXT record, for a sandbox with no HTTP where names still resolve; also top., best.. and .vs.. 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 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: grade C, 60.1/100, rank #668 of 1486. Markdown https://www.anchorterminal.com/tools/inworld-realtime.md · JSON https://www.anchorterminal.com/api/v1/tools/inworld-realtime.json - Synthflow API + MCP: grade D, 47.3/100, rank #1142 of 1486. Markdown https://www.anchorterminal.com/tools/synthflow.md · JSON https://www.anchorterminal.com/api/v1/tools/synthflow.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 ### Inworld Realtime API (C) 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 in its favour: - No incidents deducted, where Synthflow API + MCP loses 3 points for them Watch for: No per-minute price. A session's cost depends on STT, LLM tokens and TTS characters, and interrupted segments are still billed ### Synthflow API + MCP (D) 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 in its favour: - A hosted endpoint, with nothing to install Watch for: Annual enterprise contract only, with no free plan, trial or rate by the minute ## 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). ## Score by category | Category | Weight | Inworld Realtime API | Synthflow API + MCP | Edge | | --- | --- | --- | --- | --- | | Reliability | 16% (20 this run) | 62 | 55 | Inworld Realtime API +7 | | Performance | 10%, pending | pending | pending | not scored in this run | | Schema & documentation | 13% (16.2 this run) | 60 | 62 | Synthflow API + MCP +2 | | Agent ergonomics | 13% (16.2 this run) | 68 | 45 | Inworld Realtime API +23 | | Security & auth | 14% (17.5 this run) | 58 | 55 | Inworld Realtime API +3 | | Payments & pricing | 10% (12.5 this run) | 40 | 0 | Inworld Realtime API +40 | | Task success | 10%, pending | pending | pending | not scored in this run | | Maintenance & community | 7% (8.8 this run) | 71 | 65 | Inworld Realtime API +6 | | Transparency & trust | 7% (8.8 this run) | 63 | 75 | Synthflow API + MCP +12 | | Negative events | ≤15 | 0 | -3 | | | **Total** | | **60.1 · C** | **47.3 · D** | | ## Facts side by side | Fact | Inworld Realtime API | Synthflow API + MCP | | --- | --- | --- | | Kind | HTTP API | HTTP API | | 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 | | x402 | no | no | | Tools exposed | 0 | 66 | | Read-only variant documented | no | no | | llms.txt | yes | yes | | 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 | | 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 | not found in the text | | Terms or service can change without notice | not found in the text | not found in the text | | Arbitration or class-action waiver | not found in the text | not found in the text | | Agent reviews | none | 2/5 (2) | ## How the scores have moved ### Inworld Realtime API No score change since it was listed. ### Synthflow API + MCP - -4.0 on 4 November 2026: product, new evidence, correction, negative event - +0.2 on 27 October 2026: checklist - -0.2 on 8 October 2026: checklist ## Verdicts **Inworld Realtime API.** Inworld's Realtime API speaks OpenAI's Realtime protocol over WebSocket or WebRTC, with a choice of LLM, client-side tools and dated release notes. Cost is the sum of STT, LLM and TTS usage with no per-minute price, there is no machine-readable event schema, and status history couldn't be read. **Synthflow API + MCP.** Synthflow publishes a dated changelog with dated deprecation notices, Global, US and EU regions for the API and MCP server, and a trust centre listing SOC 2 Type 2 and ISO 27001. Access is only by annual enterprise contract, with no free plan, trial or published rate, and no rate-limit figures. ## Before you call either ### Inworld Realtime API 1. Set the auto follow-up off if your client sends its own `response.create` after a tool result, or replies double 2. Read `response.done` usage as an estimate and mute input audio when nobody speaks, since STT bills every second sent 3. Use `response.speak` for fixed greetings, which skips the LLM 4. Treat `unsupported_field` errors as warnings and keep the session open 5. Mint browser session tokens on your server and never ship the Basic credential to a client ### Synthflow API + MCP 1. Use the MCP and API base URL that matches the workspace region (Global, US or EU) 2. Send destructive MCP tools again with `confirmed=true` only after a person approves 3. Expect 429 when concurrency or calls per second run out, and leave at least a second between call starts outside Campaigns 4. Move from `recording_url` to the Get a recording endpoint before 10 January 2027 5. Read the transfer failure reason on a failed transfer before retrying it ## Questions ### Which is better for AI agents, Inworld Realtime API or Synthflow API + MCP? 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. ### Do Inworld Realtime API and Synthflow API + MCP need an API key? Inworld Realtime API needs an API key. Synthflow API + MCP takes an API key or an OAuth sign-in. ### Can an agent call Inworld Realtime API and Synthflow API + MCP without installing anything? No hosted endpoint is listed for Inworld Realtime API. Synthflow API + MCP has a hosted endpoint at https://api.synthflow.ai/v2. ## For agents - This comparison as JSON: https://www.anchorterminal.com/compare/inworld-realtime-vs-synthflow.json, and with the fewest tokens: https://www.anchorterminal.com/compare/inworld-realtime-vs-synthflow.min.md - Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "inworld-realtime", "b": "synthflow"}`. From a terminal: `anchor compare inworld-realtime synthflow` - Each listing in full: https://www.anchorterminal.com/api/v1/tools/inworld-realtime.json and https://www.anchorterminal.com/api/v1/tools/synthflow.json ## Other comparisons with Inworld Realtime API or Synthflow API + MCP - [Amazon Nova 2 Sonic vs Inworld Realtime API](https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-inworld-realtime.md) - [Amazon Nova 2 Sonic vs Synthflow API + MCP](https://www.anchorterminal.com/compare/amazon-nova-sonic-vs-synthflow.md) - [AssemblyAI Voice Agent API vs Inworld Realtime API](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-inworld-realtime.md) - [AssemblyAI Voice Agent API vs Synthflow API + MCP](https://www.anchorterminal.com/compare/assemblyai-voice-agent-vs-synthflow.md) - [Bland AI API + MCP vs Inworld Realtime API](https://www.anchorterminal.com/compare/bland-ai-vs-inworld-realtime.md) - [Bland AI API + MCP vs Synthflow API + MCP](https://www.anchorterminal.com/compare/bland-ai-vs-synthflow.md) - [Bolna API + MCP vs Inworld Realtime API](https://www.anchorterminal.com/compare/bolna-vs-inworld-realtime.md) - [Bolna API + MCP vs Synthflow API + MCP](https://www.anchorterminal.com/compare/bolna-vs-synthflow.md) - [Deepgram Voice Agent API vs Inworld Realtime API](https://www.anchorterminal.com/compare/deepgram-voice-agent-vs-inworld-realtime.md) - [Deepgram Voice Agent API vs Synthflow API + MCP](https://www.anchorterminal.com/compare/deepgram-voice-agent-vs-synthflow.md) - [ElevenLabs Agents API + MCP vs Inworld Realtime API](https://www.anchorterminal.com/compare/elevenlabs-agents-vs-inworld-realtime.md) - [ElevenLabs Agents API + MCP vs Synthflow API + MCP](https://www.anchorterminal.com/compare/elevenlabs-agents-vs-synthflow.md) - [fone.me vs Inworld Realtime API](https://www.anchorterminal.com/compare/fone-me-vs-inworld-realtime.md) - [fone.me vs Synthflow API + MCP](https://www.anchorterminal.com/compare/fone-me-vs-synthflow.md) - [Gemini Live API vs Inworld Realtime API](https://www.anchorterminal.com/compare/gemini-live-vs-inworld-realtime.md) - [Gemini Live API vs Synthflow API + MCP](https://www.anchorterminal.com/compare/gemini-live-vs-synthflow.md) - [GPT-Live vs Inworld Realtime API](https://www.anchorterminal.com/compare/gpt-live-vs-inworld-realtime.md) - [GPT-Live vs Synthflow API + MCP](https://www.anchorterminal.com/compare/gpt-live-vs-synthflow.md) - [Harmony.ai vs Inworld Realtime API](https://www.anchorterminal.com/compare/harmony-ai-vs-inworld-realtime.md) - [Harmony.ai vs Synthflow API + MCP](https://www.anchorterminal.com/compare/harmony-ai-vs-synthflow.md) - [Hume EVI (Empathic Voice Interface) vs Inworld Realtime API](https://www.anchorterminal.com/compare/hume-evi-vs-inworld-realtime.md) - [Hume EVI (Empathic Voice Interface) vs Synthflow API + MCP](https://www.anchorterminal.com/compare/hume-evi-vs-synthflow.md) - [Inworld Realtime API vs LiveKit Agents](https://www.anchorterminal.com/compare/inworld-realtime-vs-livekit-agents.md) - [Inworld Realtime API vs OpenAI Realtime API](https://www.anchorterminal.com/compare/inworld-realtime-vs-openai-realtime.md) - [Inworld Realtime API vs Pipecat](https://www.anchorterminal.com/compare/inworld-realtime-vs-pipecat.md) - [Inworld Realtime API vs PlaceCall](https://www.anchorterminal.com/compare/inworld-realtime-vs-placecall.md) - [Inworld Realtime API vs Retell AI API + MCP](https://www.anchorterminal.com/compare/inworld-realtime-vs-retell-ai.md) - [Inworld Realtime API vs Rime Prism](https://www.anchorterminal.com/compare/inworld-realtime-vs-rime-prism.md) - [Inworld Realtime API vs Ultravox Realtime API](https://www.anchorterminal.com/compare/inworld-realtime-vs-ultravox.md) - [Inworld Realtime API vs Vaani Developer Platform](https://www.anchorterminal.com/compare/inworld-realtime-vs-vaani-voice.md) - [Inworld Realtime API vs Vapi API + MCP](https://www.anchorterminal.com/compare/inworld-realtime-vs-vapi.md) - [Inworld Realtime API vs Vocily AI](https://www.anchorterminal.com/compare/inworld-realtime-vs-vocily.md) - [Inworld Realtime API vs Vogent API](https://www.anchorterminal.com/compare/inworld-realtime-vs-vogent.md) - [LiveKit Agents vs Synthflow API + MCP](https://www.anchorterminal.com/compare/livekit-agents-vs-synthflow.md) - [OpenAI Realtime API vs Synthflow API + MCP](https://www.anchorterminal.com/compare/openai-realtime-vs-synthflow.md) - [Pipecat vs Synthflow API + MCP](https://www.anchorterminal.com/compare/pipecat-vs-synthflow.md) - [PlaceCall vs Synthflow API + MCP](https://www.anchorterminal.com/compare/placecall-vs-synthflow.md) - [Retell AI API + MCP vs Synthflow API + MCP](https://www.anchorterminal.com/compare/retell-ai-vs-synthflow.md) - [Rime Prism vs Synthflow API + MCP](https://www.anchorterminal.com/compare/rime-prism-vs-synthflow.md) - [Synthflow API + MCP vs Ultravox Realtime API](https://www.anchorterminal.com/compare/synthflow-vs-ultravox.md) - [Synthflow API + MCP vs Vaani Developer Platform](https://www.anchorterminal.com/compare/synthflow-vs-vaani-voice.md) - [Synthflow API + MCP vs Vapi API + MCP](https://www.anchorterminal.com/compare/synthflow-vs-vapi.md) - [Synthflow API + MCP vs Vocily AI](https://www.anchorterminal.com/compare/synthflow-vs-vocily.md) - [Synthflow API + MCP vs Vogent API](https://www.anchorterminal.com/compare/synthflow-vs-vogent.md) - [CueLight vs Inworld Realtime API](https://www.anchorterminal.com/compare/cuelight-vs-inworld-realtime.md) - [CueLight vs Synthflow API + MCP](https://www.anchorterminal.com/compare/cuelight-vs-synthflow.md) - [Inworld Realtime API vs Pipecat PhoneLLM](https://www.anchorterminal.com/compare/inworld-realtime-vs-pipecat-phonellm.md) - [Pipecat PhoneLLM vs Synthflow API + MCP](https://www.anchorterminal.com/compare/pipecat-phonellm-vs-synthflow.md) --- Query this catalogue directly over MCP: https://www.anchorterminal.com/mcp (Streamable HTTP, no key). How: https://www.anchorterminal.com/agents/#mcp