Inworld AI

Best for Voiced realtime NPC dialogue

Can you ship it?

Yes, free tier Pricing table lists a commercial license on every plan, including free On-Demand Source

Price

On-Demand free (pay as you go, TTS from $25 per 1M chars). Creator $25/mo

Works with

REST, WebSocket, WebRTC APIs; Node.js and Python SDKs

Inworld now offers voices, speech-to-text, a model router and realtime speech-to-speech that you wire into NPCs over REST, WebSocket or WebRTC. It lists Unreal and Unity as targets, but the catch is that integration goes through APIs with Node.js and Python SDKs rather than a dedicated engine plugin, and costs scale with every character spoken.