Text To Speech Updates & Release Notes

Realtime TTS now serves POST /v1/audio/speech in OpenAI's format, so apps built on OpenAI's text-to-speech can switch to Inworld by pointing the SDK at Inworld and choosing an Inworld model and voice — see OpenAI Compatibility.

Works with the OpenAI SDKs

• The official Python and Node.js SDKs work unchanged, including streaming responses.
• Formats: mp3, opus, flac, wav, and pcm, plus server-sent events with stream_format: "sse".
• One base URL: https://api.inworld.ai/v1 also serves the Inworld Router, so one client configuration covers LLM and TTS.

Launched Realtime TTS-2 Flash (inworld-tts-2-flash), the fastest member of the TTS-2 family — see Models:

• Our lowest latency: 20 ms time to first audio (server-side P90 TTFB, excluding network latency) — 5× faster than inworld-tts-2 at 100 ms, making it the best choice for latency-critical real-time agents.
• Our lowest cost: The most cost-efficient model per character, ideal for high-volume workloads.
• Full TTS-2 language coverage: The same 200+ languages and locales as inworld-tts-2, plus instant voice cloning and timestamp alignment.

Steering instructions and Professional Voice Cloning are supported on inworld-tts-2 only — use it when you need directed, contextually aware delivery. Non-verbal tags like [laugh] work on both models.

Steering on inworld-tts-2 follows one rule: a [tag] applies from where you write it until you change it. See the Steering guide.

• [reset]: New reserved tag that ends a styled passage and returns the voice to its own character for the rest of the text. [shouting] We need to leave now! [reset] Do you understand me? shouts only the first sentence.
• Instructions survive pauses: A <break/> no longer clears the active instruction. A pause is a pause and never changes delivery.

Behavior change

An inline [tag] previously affected only the text immediately after it and delivery could revert on its own partway through longer text. A tag now stays in force until you change it. If you relied on an instruction wearing off — for example [shout] Hi. Normal text. expecting the second sentence unstyled — add [reset] where normal delivery should resume. Requests that use no inline tags are unaffected, as are inworld-tts-1.5-max and inworld-tts-1.5-mini.

Launched Realtime TTS-2 (inworld-tts-2), our most powerful and expressive TTS model:

• Natural Language Steering: Direct any voice with bracketed instructions like [say excitedly], [whisper in a hushed style], or free-form directions like [speak as if barely holding back rage]. Covers articulation, intonation, volume, pitch, range, speed, vocal style, and non-verbals ([laugh], [sigh], etc.). See the Steering guide.
• Stronger Multilingual Support: Production-quality synthesis across 15 languages, plus experimental support for 90+ additional languages. See Languages.
• Cross-Lingual Voice Synthesis: Reuse the same voice across multiple languages. For best results, specify the language field.
• Voice Localization: Localize your voice for the most consistent, native-sounding speech in a target language. See Voice Localization.
• Delivery Mode: New deliveryMode field (STABLE, BALANCED, EXPRESSIVE) controls the trade-off between consistency and emotional range.
• Updated Voice Design: Released an updated version of Voice Design with improved generations. See Voice Design.

Launched Inworld TTS 1.5, our newest generation of realtime TTS models featuring:

• Two New Models: Our flagship model inworld-tts-1.5-max is ideal for most use cases, with the best balance of quality and speed. For use cases where latency is the top priority, we also offer inworld-tts-1.5-mini.
• Latency Improvements: Our new TTS-1.5 models achieve P90 latency for first audio chunk delivery under 250ms for our Max model and under 130ms for our Mini model, a 4x improvement compared to TTS-1.
• More Expressive and More Stable: TTS-1.5 is 30% more expressive than prior generations and demonstrates a 40% reduction in word error rates.
• Additional Languages: We've added support for additional languages, including Hindi, Arabic, and Hebrew, bringing total languages supported to 15.

Released an upgraded version of the Inworld TTS models with higher overall quality.

• Speech Quality: Clearer, more natural speech with smoother pacing and more accurate pronunciation.
• Voice Similarity: Cloned voices sound closer to the originals, preserving each voice’s unique style.
• Non-English Languages: More consistent, reliable output across supported non-English languages.
• Inline custom pronunciation: New support for inline IPA, giving you control over exact word pronunciations. See Inline custom pronunciation for details.