GPT-Realtime-2 Ships: Your Voice Eval Harness Just Became Obsolete
The Shift
OpenAI collapsed the canonical ASR→LLM→TTS pipeline into a single speech-to-speech model with GPT-5-class reasoning, 128K context (up from 32K), and tunable reasoning effort from minimal to high. The cascade was debuggable because each stage had a metric: WER for ASR, task accuracy for LLM, MOS for TTS. A speech-to-speech model does not expose those seams. When the system mishandles a proper noun, the logs will not tell you whether it heard wrong or reasoned wrong.
The Numbers That Matter
| Dimension | Realtime-1.5 | Realtime-2 | Gemini 3.1 Flash Live |
|---|---|---|---|
| Big Bench Audio | ~81% | 96.6% | 96.6% (tie) |
| Instruction retention (APR) | 36.7% | 70.8% | Not disclosed |
| Context | 32K | 128K | — |
| TTFA | — | 1.12s (min) – 2.33s (high) | — |
| Pricing ($/hr) | $1.15 / $4.61 | $1.15 / $4.61 | — |
The instruction retention doubling (36.7%→70.8%) is the production-critical number. Instruction drift across turns is where real voice agents fail, and a 2x improvement there matters more than another point on BBA. Enterprise A/B results are landing: Glean reports +42.9% helpfulness, Genspark +26% effective conversation rate. Both are self-reported with no disclosed methodology, so treat them as directional.
Median latency improvements are easy to demo. The tail is what users remember. Measure p95 TTFA under barge-in, not median on clean single-turn prompts.
What This Means for the Eval Harness
Three concrete changes follow:
- Reasoning effort is a new hyperparameter. A 2x TTFA swing (1.12s→2.33s) means defaulting to 'low' wastes quality on tool-heavy agents and 'high' burns latency on routing. Map effort tiers per intent and measure the Pareto.
- S2S-native metrics replace WER. Turn-taking, interruption handling, instruction retention, and tool-call correctness are the dimensions that matter. Big Bench Audio and Scale's Audio MultiChallenge are the instruments, but both are saturating, so build domain-specific hard sets (healthcare terms, proper nouns, code-switching).
- Observability requires a parallel transcript. Running Realtime-Whisper alongside for logging, redaction, and compliance is the cheapest fix. The alternative is debugging voice regressions with audio files and vibes.
Gemini 3.1 Flash Live ties on the headline benchmark. On published scores alone there is no reason to pick between them. The thing those scores don't tell you is how either model handles your accent distribution, your domain vocabulary, or your interruption patterns. Run the bake-off on your traffic and weight the slices that correspond to revenue-critical calls. If the two land within noise, pricing and latency tails decide it.
Companion signals: Realtime-Translate (70 input → 13 output languages) and Realtime-Whisper at $0.017/min ($1.02/hr) are now first-class streaming primitives. Vimeo demoed fully live dubbing with no pre-loaded captions. Batch Whisper + NMT localization pipelines are under pressure.
What to do
Stand up a shadow-mode A/B: pipe 5-10% of production voice traffic to GPT-Realtime-2 alongside current stack; log TTFA, tool-call accuracy, and task completion
Rebuild voice eval harness around S2S metrics (interruption handling, instruction retention, tool-call correctness) plus domain-specific hard set
Evaluate Gemini 3.1 Flash Live in parallel — do not single-vendor on voice
Map reasoning_effort per intent class: 'low' for routing/chit-chat, 'medium'/'high' for tool-heavy agents