GPT-5.5 Pro
Provider list prices: no platform markup, pay-as-you-go. These are official list prices. Logged-in customers may see effective prices including workspace discounts on /console/pricing.
Use GPT-5.5 Pro in 30 seconds
OpenAI-compatible: swap the base_url, keep your SDK. POST /v1/chat/completions
from openai import OpenAI
client = OpenAI(
base_url="https://synthorai.io/v1",
api_key="sk-syn-...",
)
resp = client.chat.completions.create(
model="gpt-5.5-pro",
messages=[{"role": "user", "content": "Summarize this diff"}],
reasoning_effort="medium",
)
print(resp.choices[0].message.content)import OpenAI from "openai";
const client = new OpenAI({
baseURL: "https://synthorai.io/v1",
apiKey: "sk-syn-...",
});
const resp = await client.chat.completions.create({
model: "gpt-5.5-pro",
messages: [{ role: "user", content: "Summarize this diff" }],
reasoning_effort: "medium",
});
console.log(resp.choices[0].message.content);curl https://synthorai.io/v1/chat/completions \
-H "Authorization: Bearer sk-syn-..." \
-H "Content-Type: application/json" \
-d '{
"model": "gpt-5.5-pro",
"messages": [{"role": "user", "content": "Hello"}],
"reasoning_effort": "medium"
}'package main
import (
"context"
"fmt"
"github.com/openai/openai-go/v3"
"github.com/openai/openai-go/v3/option"
)
func main() {
client := openai.NewClient(
option.WithBaseURL("https://synthorai.io/v1"),
option.WithAPIKey("sk-syn-..."),
)
resp, _ := client.Chat.Completions.New(context.TODO(), openai.ChatCompletionNewParams{
Model: "gpt-5.5-pro",
Messages: []openai.ChatCompletionMessageParamUnion{
openai.UserMessage("Summarize this diff"),
},
ReasoningEffort: openai.ReasoningEffortMedium,
})
fmt.Println(resp.Choices[0].Message.Content)
}import com.openai.client.OpenAIClient;
import com.openai.client.okhttp.OpenAIOkHttpClient;
import com.openai.models.chat.completions.*;
import com.openai.models.ReasoningEffort;
OpenAIClient client = OpenAIOkHttpClient.builder()
.baseUrl("https://synthorai.io/v1")
.apiKey("sk-syn-...")
.build();
ChatCompletion resp = client.chat().completions().create(
ChatCompletionCreateParams.builder()
.model("gpt-5.5-pro")
.addUserMessage("Summarize this diff")
.reasoningEffort(ReasoningEffort.MEDIUM)
.build());
System.out.println(resp.choices().get(0).message().content().orElse(""));About GPT-5.5 Pro
GPT-5.5 Pro is OpenAI's most advanced reasoning model, applying additional compute to GPT-5.5 to produce smarter and more precise responses on the hardest problems.
- It offers a 1,050,000-token context window (vendor spec), 128K max output tokens, image input, and reasoning effort at medium, high, and xhigh, with access to hosted tools such as web search, file search, and code interpreter.
- Because responses can take minutes, OpenAI recommends background mode for long jobs.
- On Synthorai, GPT-5.5 Pro sits behind the same OpenAI-compatible API as the rest of the fleet.
Specs & limits
| Max output (vendor spec) | 128,000 |
| Modalities | text + image → text |
| Features | tools · structured_output · vision · batch · reasoning |
| Notable | Streaming not supported; cached-input pricing discounts do not apply; requests may take minutes (background mode recommended); reasoning effort medium-xhigh. |
FAQ
Is the GPT-5.5 Pro API free to try?
Yes: new accounts get 10 trial calls and up to $1 in free credit, no card required. At $30/M input tokens, that credit alone covers roughly 4 requests of ~8K tokens against GPT-5.5 Pro.
What is GPT-5.5 Pro best at?
Additional compute for smarter, more precise responses, plus web search, file search, and code interpreter and background mode recommended for long jobs. See the About section for the full picture from the vendor's own release notes.
How much does GPT-5.5 Pro cost?
GPT-5.5 Pro costs $30 per million input tokens and $180 per million output tokens on Synthorai. That is the provider's list price, with no platform markup.
Does GPT-5.5 Pro support prompt caching?
GPT-5.5 Pro has no cache-read discount on Synthorai today. Prompt caching still applies to other models on the gateway; see the pricing table for cache-enabled alternatives. Provider caching comparison →
How do I get access to GPT-5.5 Pro?
Point your existing OpenAI SDK at base_url="https://synthorai.io/v1", set model="gpt-5.5-pro", and you're done. One API key covers every model on the gateway.
What is GPT-5.5 Pro's knowledge cutoff?
GPT-5.5 Pro's knowledge cutoff is 2025-12, per the vendor's official documentation (as of 2026-07-09).