QUICK VERDICT — AUGUST 5, 2026
● AA STS Quality Index: Grok TF 2.0 — 82.9% vs GPT-Realtime-2.1 — 79.1%
● Full Duplex Bench: GPT-Realtime-2.1 slightly ahead per Artificial Analysis
● First audio response: Grok TF 2.0 — 0.70s vs GPT-Realtime — varies (depends on model variant)
● Pricing model: Grok — flat $0.08/min audio. GPT-Realtime — per audio + text token (complex)
● Languages: Grok TF 2.0 — 24. GPT-Realtime-2.1 — broader but less documented noisy-environment performance
● Noisy environments: Grok TF 2.0 — 10× better than v1.0 and leading transcription models
The Artificial Analysis benchmark places Grok Voice Think Fast 2.0 at 82.9% on the Speech-to-Speech Quality Index, above GPT-Realtime-2.1 at 79.1%. GPT-Realtime-2.1 is "slightly ahead on Full Duplex Bench" according to the same analysis — meaning in a live two-way conversation where both parties can speak simultaneously, GPT-Realtime handles turn-taking more naturally. That is a specific but important distinction for customer-facing voice agents: full duplex handling affects how natural interruptions and overlapping speech feel.
The pricing model difference matters for cost modelling. Grok Voice Think Fast 2.0 charges $0.08 per minute of audio — simple, predictable, budget-friendly at volume. GPT-Realtime-2.1 charges separately for audio input tokens, audio output tokens, and text tokens, plus any tool calls made during the conversation. For a standard support call, GPT-Realtime costs typically come out higher per minute than Grok Voice at $0.08 — but the exact difference depends on call length, tool call frequency, and ratio of listening to speaking.
Grok Voice TF 2.0 for: High-volume voice agents where per-minute flat pricing is easier to budget, noisy environment deployments (10× transcription improvement), and teams already in the xAI/SpaceXAI ecosystem. Best overall STS Quality Index score (82.9%).
GPT-Realtime-2.1 for: Applications where full duplex handling — natural interruption and turn overlap — is critical to user experience. Deep OpenAI API ecosystem integration. Broader tool calling ecosystem.
Last updated August 4, 2026. Related: Grok Voice migration guide → · Think Fast 2.0 full launch review →