Voice Orchestration Weakens STT Lock-in

The real leverage in voice agents is moving up from speech accuracy to traffic control. Retell AI and Vapi sit above the speech stack, where the developer chooses the transcriber, model, and voice provider for each agent, or plugs in their own provider keys, so the orchestration layer owns the workflow even when AssemblyAI supplies some of the underlying transcription minutes. That makes the voice agent platform, not the STT API, the day to day control point.1 2 3 4 5

• Vapi explicitly supports many STT providers, including AssemblyAI, Deepgram, Google, OpenAI, Speechmatics, and others, and lets the developer set the transcriber on each assistant. In practice, that means swapping providers is a config change, not a rewrite of the whole call flow.4 5
• These orchestration platforms also let customers bring their own provider credentials. That changes the relationship with speech vendors from a direct product dependency into a metered input inside a larger voice workflow, which weakens vendor lock in and gives platforms more pricing leverage.5 6
• The comparable model is cloud infrastructure abstraction. Deepgram and AssemblyAI sell the speech engine itself, while Retell AI and Vapi package telephony, prompt logic, turn taking, testing, monitoring, and routing into one system. Revenue pools can therefore shift toward the layer that manages the full live call experience.1 2 3 7

Going forward, standalone transcription vendors will need to win either by being clearly better on latency, accuracy, or price, or by bundling into fuller voice stacks of their own. As speech models get easier to swap, the strongest position moves toward whoever controls the live call loop and decides where each audio stream gets sent.1 3 4 8