Speko + OpenAI Realtime API
OpenAI Realtime eliminates the STT and TTS layers entirely. Speko benchmarks it against Gemini Live and cascaded stacks so you can decide whether the speech-to-speech premium fits your use case and budget.
Last updated: March 2026
What OpenAI Realtime API Does
OpenAI Realtime is a speech-to-speech API that processes audio input and generates audio output in a single model call — eliminating the need for separate STT, LLM, and TTS providers in your voice agent architecture.
Speech-to-Speech, No Cascading
OpenAI Realtime bypasses the traditional STT → LLM → TTS pipeline. Audio goes in, audio comes out — processed by a single multimodal model. This removes transcription errors from cascading between layers and simplifies your integration to one API.
GPT-4o and GPT-4o-mini Models
Realtime is available with GPT-4o for maximum reasoning quality and GPT-4o-mini for reduced cost. Both models support function calling, allowing your voice agent to interact with external systems mid-conversation without leaving the audio loop.
Low Latency S2S from OpenAI
OpenAI Realtime is the lowest-latency speech-to-speech option in OpenAI's lineup. For use cases where GPT-4o quality is required and simplicity matters more than cost, it offers a streamlined path to production without managing multiple vendor integrations.
How Speko Works with OpenAI Realtime
Speko benchmarks OpenAI Realtime against Gemini Live and equivalent cascaded stacks — covering latency, conversation quality, and total cost at scale to give you a complete decision framework.
Realtime vs Gemini Live vs Cascaded
Speko runs structured comparisons between OpenAI GPT-4o Realtime, Gemini 2.0 Flash Live, and a best-in-class cascaded stack. See how they compare on end-to-end latency, conversation quality, and cost per minute under the same test conditions.
Cost Analysis at Your Volume
GPT-4o Realtime at $0.30/min vs Gemini Flash at $0.00165/min vs cascaded at ~$0.015–0.020/min — the cost gap is significant. Speko models total cost at your projected usage including context accumulation over long conversations.
S2S Decision Framework
Speko surfaces a clear recommendation: when OpenAI Realtime is the right architecture for your requirements, and when a cascaded stack saves you money without meaningful quality loss. Based on data, not vendor marketing.
OpenAI Realtime Features Benchmarked by Speko
- GPT-4o Realtime API cost: ~$0.30/min (includes audio input + output tokens)
- GPT-4o-mini Realtime cost: ~$0.084/min (lower cost, reduced reasoning capability)
- End-to-end latency vs equivalent cascaded Deepgram + GPT-4o-mini + Cartesia stacks
- Context token accumulation cost growth over long conversations
- Language and accent support compared to best-in-class cascaded alternatives
Frequently Asked Questions
Is OpenAI Realtime API worth the cost for production voice agents?
The OpenAI Realtime API (GPT-4o) costs approximately $0.30 per minute of audio — roughly 20x more than a comparable cascaded stack using Deepgram + GPT-4o-mini + Cartesia. For latency-critical use cases where the speech-to-speech architecture meaningfully reduces perceived response time and audio fidelity matters, it can be worth it. For high-volume applications, the cost difference is prohibitive. Speko's cost analysis shows the exact break-even point for your projected volume.
How does OpenAI Realtime compare to Gemini Live?
Both are speech-to-speech APIs that eliminate the STT and TTS layers of a cascaded pipeline. The key differences: GPT-4o Realtime at $0.30/min delivers GPT-4o's reasoning quality; Gemini 2.0 Flash Live at approximately $0.00165/min is dramatically cheaper but based on a different model family. For most cost-conscious deployments, Gemini Flash Live wins on price by a wide margin. Speko benchmarks both for latency, conversation quality, and cost so you can make a data-driven choice.
When should I use OpenAI Realtime instead of a cascaded pipeline?
Choose OpenAI Realtime when: (1) minimizing integration complexity matters more than cost — one API call replaces three separate providers; (2) you need GPT-4o-level reasoning in the voice loop; (3) your use case is low-volume enough that the per-minute cost doesn't accumulate painfully. Cascaded pipelines give you more flexibility, lower cost, and the ability to mix best-in-class providers at each layer — at the cost of integration complexity.
What does OpenAI Realtime cost for 1,000 minutes per month?
GPT-4o Realtime at $0.30/min costs $300 for 1,000 minutes. GPT-4o-mini Realtime at approximately $0.084/min costs $84 for 1,000 minutes. A comparable cascaded stack (Deepgram Nova-3 + GPT-4o-mini + Cartesia Sonic-3) runs approximately $15–20 for the same volume. Context tokens in long conversations accumulate additional cost on both Realtime tiers. Speko models cost growth over conversation length so you can forecast accurately.
Find Out If OpenAI Realtime Fits Your Budget
The speech-to-speech premium is real. Run a Speko benchmark to see whether OpenAI Realtime's cost is justified for your use case — or whether a cascaded stack gets you 90% of the quality at 5% of the price.