Model comparison
Compare Inworld Realtime TTS-2 and Grok Voice Think Fast 2.0 using the same provider-sourced voice & realtime rubric. No mystery score and no invented benchmark ranking.
Facts checked September 4, 2026
Quick take
Inworld's newest expressive realtime text-to-speech model, designed to remember conversational delivery and speak in more than 100 languages.
This is the speech layer, not a complete agent. Inworld's current zero-data-retention page does not explicitly list TTS-2, so confirm coverage before sending sensitive text or voice data.
SpaceXAI's current realtime speech-to-speech model for sub-second conversational agents with tool access.
The model-specific price is higher than the generic 'starting at' Voice API headline. Use the Think Fast 2.0 row when budgeting.
Compare the published facts
Values use each provider's own published units and limits. A blank means the provider did not publish a directly comparable value in the sources reviewed.
| Voice & realtime | Inworld Realtime TTS-2 | Grok Voice Think Fast 2.0 |
|---|---|---|
| Price basisToken-, character-, or minute-based price for the listed access route. | $25 / 1M chars on demand; volume discounts | $0.08 / audio minute |
| Interaction modeSpeech-to-speech, audio-to-audio, or streamed text-to-speech behavior. | Steerable realtime TTS with prior-audio context | Realtime speech-to-speech with tools |
| Published latencyProvider-published measurement with its stated exclusions; not a Cody test. | Under 200ms median TTFA | Sub-second provider claim |
| LanguagesProvider-documented language coverage or a clear unpublished marker. | 100+ with mid-utterance switching | Exact supported list not published here |
| Tools & controlNative function calling, reasoning, or speech-control features. | Voice direction, design, cloning, non-verbals | Realtime tool use |
| Context or input limitDocumented token or character limit where it is meaningful. | Not published | Not published |
How to choose
Start with the job you need to complete, then validate cost, access, and policy details on your exact provider route.
Inworld advertises zero data retention as an enterprise add-on, but its currently published ZDR support page names only TTS-1.5 Mini and Max. Confirm TTS-2 coverage directly before sending regulated or confidential text.
SpaceXAI says it does not train on API inputs or outputs without explicit permission. Default encrypted retention is 30 days; team-level zero data retention is available with feature tradeoffs.
Provider and API links
Frequently asked questions
Inworld Realtime TTS-2: Inworld's newest expressive realtime text-to-speech model, designed to remember conversational delivery and speak in more than 100 languages. Grok Voice Think Fast 2.0: SpaceXAI's current realtime speech-to-speech model for sub-second conversational agents with tool access.
Consider Inworld Realtime TTS-2 when your priority is Realtime companions and support voices. Consider Grok Voice Think Fast 2.0 when your priority is Realtime voice agents with tools. Test both with your own data and provider route before committing.
No. This comparison aligns provider-published facts for the Voice & realtime category. It does not claim a universal winner or combine incompatible third-party benchmark scores.
