GPT Realtime is OpenAI's first general-availability realtime model: a single speech-to-speech model that listens and responds with natural, expressive audio directly, rather than chaining separate transcription and synthesis models.
- Input
- audio text $4/M
- Output
- audio text $16/M
- Audio input
- $32/M
- Audio output
- $64/M
- Cache read
- $0.4/M
- Knowledge cutoff
- 2023-10
Benchmarks
GPT Realtime: 8 published, but no benchmark it shares with enough other models to compare.
Price in context
Where the price sits among 6 comparable models
The bar shows how this model’s price compares with every other model of the same kind on Synthorai. The cheapest and the most expensive are named at each end. These are base rates; batch, region and cache-write discounts are on the pricing page.
Specs & limits
Tokens
| Context window (vendor spec) | 32,000 |
|---|---|
| Max output (vendor spec) | 4,096 |
| Knowledge cutoff | 2023-10 |
Prompt caching
| How it caches | automatic |
|---|---|
| Min prefix | 1,024 |
| Lifetime | 5-10m, up to 1h |
Realtime
| Session | Native speech-to-speech over WebSocket · function calling · 32K context |
|---|
Model
| Modalities | audio + text → audio + text |
|---|
- OpenAI's first general-availability realtime model (snapshot gpt-realtime-2025-08-28): native speech-to-speech with function calling
- 32k context
Use GPT Realtime in 30 seconds
OpenAI Realtime-compatible: connect over WebSocket and stream audio in, audio out. WS /v1/realtime
import asyncio, base64, json, websockets
URL = "wss://synthorai.io/v1/realtime?model=gpt-realtime"
# Send ONLY the Authorization header - the beta protocol is retired.
HEADERS = {"Authorization": "Bearer sk-syn-..."}
async def main():
async with websockets.connect(URL, additional_headers=HEADERS) as ws:
# 1) configure the speech-to-speech session
await ws.send(json.dumps({
"type": "session.update",
"session": {
"type": "realtime",
"output_modalities": ["audio"],
"audio": {"output": {"voice": "alloy"}},
},
}))
# 2) send input audio (base64 PCM16), then request a spoken reply
await ws.send(json.dumps({"type": "input_audio_buffer.append", "audio": pcm16_b64}))
await ws.send(json.dumps({"type": "input_audio_buffer.commit"}))
await ws.send(json.dumps({"type": "response.create"}))
# 3) stream the model's audio (and text) back
async for raw in ws:
ev = json.loads(raw)
if ev["type"] == "response.audio.delta":
play(base64.b64decode(ev["delta"])) # audio out
elif ev["type"] == "response.done":
break
asyncio.run(main())import WebSocket from "ws";
const ws = new WebSocket("wss://synthorai.io/v1/realtime?model=gpt-realtime", {
// Send ONLY the Authorization header — the beta protocol is retired.
headers: { Authorization: "Bearer sk-syn-..." },
});
ws.on("open", () => {
// configure the speech-to-speech session
ws.send(JSON.stringify({ type: "session.update", session: {
type: "realtime", output_modalities: ["audio"], audio: { output: { voice: "alloy" } },
} }));
// send input audio (base64 PCM16), then request a spoken reply
ws.send(JSON.stringify({ type: "input_audio_buffer.append", audio: pcm16Base64 }));
ws.send(JSON.stringify({ type: "input_audio_buffer.commit" }));
ws.send(JSON.stringify({ type: "response.create" }));
});
ws.on("message", (raw) => {
const ev = JSON.parse(raw.toString());
if (ev.type === "response.audio.delta") playAudio(Buffer.from(ev.delta, "base64")); // audio out
else if (ev.type === "response.done") ws.close();
});# Realtime is a WebSocket protocol - use a WS client such as websocat.
# Each line below is one OpenAI Realtime event (JSON) sent to the session.
websocat -H 'Authorization: Bearer sk-syn-...' \
'wss://synthorai.io/v1/realtime?model=gpt-realtime' <<'EOF'
{"type":"session.update","session":{"type":"realtime","output_modalities":["audio"],"audio":{"output":{"voice":"alloy"}}}}
{"type":"input_audio_buffer.append","audio":"<base64-pcm16>"}
{"type":"input_audio_buffer.commit"}
{"type":"response.create"}
EOF
# Responses stream back as response.audio.delta (base64 audio out) … response.donepackage main
import (
"net/http"
"github.com/gorilla/websocket"
)
func main() {
h := http.Header{}
h.Set("Authorization", "Bearer sk-syn-...")
// Send ONLY the Authorization header — the beta protocol is retired.
c, _, err := websocket.DefaultDialer.Dial("wss://synthorai.io/v1/realtime?model=gpt-realtime", h)
if err != nil {
panic(err)
}
defer c.Close()
// configure the speech-to-speech session, send audio, request a spoken reply
c.WriteJSON(map[string]any{"type": "session.update", "session": map[string]any{
"type": "realtime", "output_modalities": []string{"audio"},
"audio": map[string]any{"output": map[string]any{"voice": "alloy"}}}})
c.WriteJSON(map[string]any{"type": "input_audio_buffer.append", "audio": pcm16B64})
c.WriteJSON(map[string]any{"type": "input_audio_buffer.commit"})
c.WriteJSON(map[string]any{"type": "response.create"})
for {
var ev struct {
Type string `json:"type"`
Delta string `json:"delta"`
}
if err := c.ReadJSON(&ev); err != nil {
return
}
if ev.Type == "response.audio.delta" {
playAudio(ev.Delta) // base64 audio out
} else if ev.Type == "response.done" {
return
}
}
}import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.WebSocket;
import java.util.concurrent.CompletionStage;
// JDK built-in WebSocket — no extra dependency needed.
WebSocket ws = HttpClient.newHttpClient().newWebSocketBuilder()
.header("Authorization", "Bearer sk-syn-...")
// Send ONLY the Authorization header — the beta protocol is retired.
.buildAsync(URI.create("wss://synthorai.io/v1/realtime?model=gpt-realtime"), new WebSocket.Listener() {
public CompletionStage<?> onText(WebSocket w, CharSequence data, boolean last) {
// handle response.audio.delta (base64 audio out) / response.done here
w.request(1);
return null;
}
}).join();
// configure the session, send input audio, then request a spoken reply
ws.sendText("{\"type\":\"session.update\",\"session\":{\"type\":\"realtime\",\"output_modalities\":[\"audio\"],\"audio\":{\"output\":{\"voice\":\"alloy\"}}}}", true);
ws.sendText("{\"type\":\"input_audio_buffer.append\",\"audio\":\"<base64-pcm16>\"}", true);
ws.sendText("{\"type\":\"input_audio_buffer.commit\"}", true);
ws.sendText("{\"type\":\"response.create\"}", true);About GPT Realtime
- It carries a 32K-token context window with 4,096 max output tokens, supports function calling for voice-agent workflows, and takes audio or text input with audio and text output; audio and text are billed at separate per-token rates, with discounted cached input.
- Sessions can be driven over WebRTC for browser and mobile clients, over WebSocket when a server already holds the audio stream, or over SIP for telephony agents, with server-side voice activity detection chunking speech and truncating unplayed audio when a caller interrupts.
- The model page also lists image input alongside text and audio, and voices are chosen per session from OpenAI's published set, with the caveat that a voice cannot be changed once a session has emitted audio.
- It has no reasoning-effort control (that arrives with the 2.1 generation), and its knowledge cutoff is October 2023.
- OpenAI has since announced its deprecation, with shutdown scheduled for January 2027 and GPT Realtime 2.1 named as the migration target, so new voice work belongs on 2.1 while existing integrations still have a runway.
- It remains available as the original GA snapshot of the realtime family.
- Synthorai serves GPT Realtime over the OpenAI-compatible /v1/realtime WebSocket endpoint, so official Realtime SDK clients connect unchanged.
FAQ
Is the GPT Realtime API free to try?
GPT Realtime is currently in invited beta: access is application-based rather than open signup. Apply from the Synthorai console; once approved, standard pay-as-you-go pricing applies with no subscription.
What is GPT Realtime best at?
Speech-to-speech in one model, no transcription chain; expressive natural audio with function calling; original GA snapshot of the realtime family. See the About section for the full picture from the vendor's own release notes.
How much does GPT Realtime cost?
GPT Realtime costs $4 per million input tokens and $16 per million output tokens on Synthorai. That is the provider's list price, with no platform markup. Cached input tokens bill at $0.4/M.
How do I connect to the GPT Realtime API?
GPT Realtime is a speech-to-speech model: connect over WebSocket to wss://synthorai.io/v1/realtime?model=gpt-realtime with the OpenAI Realtime SDK (or a raw WebSocket) and stream audio in, audio out. It is not a POST /v1/audio/transcriptions file upload. Authenticate with your sk-syn key, sending only the Authorization header (the beta protocol is retired).
How do I get access to GPT Realtime?
GPT Realtime is in invited beta: request access from the Synthorai console. Once approved it works like every other model: point your OpenAI SDK at base_url="https://synthorai.io/v1" and set model="gpt-realtime".
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Every value on this page is transcribed from the vendor's own documentation, linked above, and carries the date it was checked. Prices are compared across the catalogue; specification values that vendors define differently are shown with the difference stated rather than charted. Nothing here is measured by us, and nothing is scored.