GPT-5.5

Text & chatNewAvailable
by OpenAIModel ID: gpt-5-5

OpenAI's current flagship chat model (released April 2026). Strongest general reasoning, coding and tool use in the GPT-5 line, with vision input and a large context window.

Price ยท 1M in / out
US$6.00 / US$36.00
Context
400,000 tokens
Max. output
128,000 tokens
Input โ†’ output
Text + Image โ†’ Text
Developer
OpenAI
Updated
September 23, 2026
01

Playground

Try GPT-5.5

Chat

US$6.00/1M in
Try GPT-5.5

Send a message. The answer arrives in full once the model is done (no streaming).

System prompt
Max. answer length (tokens)

This run

at most US$0.0369 ยท 3.69 credits reserved

Billed by the tokens actually used; the unused part of the reservation is refunded.

For accounts without a purchase: runs above 2 credits need a top-up.

New here?

10 free credits (US$0.10) when you sign up with Google

Usable 24 hours after sign-up, up to 5 runs per day and at most 2 credits per run. Other sign-in methods start without credits.

02

About GPT-5.5

TL;DRAs of September 23, 2026

GPT-5.5 is a model by OpenAI in the Text & chat category. On Railwail, GPT-5.5 costs US$6.00 per 1M input tokens and US$36.00 per 1M output tokens. The context window holds 400,000 tokens, and one response can be up to 128,000 tokens long.

GPT-5.5 is the top model in OpenAI's GPT-5 series as of mid-2026. It handles long multi-step reasoning, agentic tool use and code generation, accepts text and image input, and is the default choice when you want OpenAI's best quality rather than a cheaper mini/nano variant. Use the dated snapshot gpt-5.5-2026-04-23 if you need a pinned version.
03

Pricing

Prices in US dollars. Usage is charged from prepaid credits.
InputUS$6.00 / 1M tokens
OutputUS$36.00 / 1M tokens
Input (prompts over 272,000 tokens)US$12.00 / 1M tokens
Output (prompts over 272,000 tokens)US$54.00 / 1M tokens
  • Billed by the tokens each request actually uses.
  • 1 credit = US$0.01

Cost calculator

Price calculator

/ req.
/ req.

Total

US$2.40

240 credits

Per request

US$0.024 ยท 2.4 credits

Each request is rounded up to 0.01 credits.

04

API

Call GPT-5.5 with your Railwail API key. Use this model ID in the request:
curl https://railwail.com/api/v1/chat/completions \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5-5",
    "messages": [
      {
        "role": "user",
        "content": "Explain what a vector database is in two sentences."
      }
    ],
    "max_tokens": 1024
  }'
Set your key as RAILWAIL_API_KEYCreate API key
05

Specifications

Model ID
gpt-5-5
Developer
OpenAI
Category
Text & chat
Input
Text, Image
Output
Text
Context window
400,000 tokens
Max. output
128,000 tokens
Billing
By usage (tokens or GPU time)
Catalog entry updated
September 23, 2026

Input parameters

Inputs and settings from the model's input schema. The example in the API section shows which of them the API accepts.

  • promptrequired

    User message

    Type: Text
    Default: โ€“
    Allowed values: up to 32,000 characters
  • stream
    Type: Yes/no
    Default: false
    Allowed values: โ€“
  • max_tokens
    Type: Integer
    Default: 4096
    Allowed values: 1 to 128,000
  • system_prompt

    Optional system instruction

    Type: Text
    Default: โ€“
    Allowed values: up to 8,000 characters

Tags

  • openai
  • gpt-5
  • flagship
  • reasoning
  • vision
  • tools
06

Use cases

07

Frequently asked questions

What is GPT-5.5?

GPT-5.5 is a model by OpenAI in the Text & chat category. On Railwail you can call it with an API key through the Railwail API.

How much does GPT-5.5 cost on Railwail?

On Railwail, GPT-5.5 costs US$6.00 per 1M input tokens and US$36.00 per 1M output tokens. You are charged for what each request actually uses. Usage is paid from prepaid credits; 1 credit equals US$0.01.

What is the context window of GPT-5.5?

The context window of GPT-5.5 holds 400,000 tokens. One response can be up to 128,000 tokens long.

How fast is GPT-5.5?

There are not enough measured runs of GPT-5.5 on Railwail yet to state a run time. It depends on the input, the settings and the load at the provider.

Is GPT-5.5 better than Claude Fable 5.1?

That depends on the task. GPT-5.5 (OpenAI) and Claude Fable 5.1 (Anthropic) are both models in the Text & chat category. The comparison page shows their prices and specifications side by side.

Compare GPT-5.5 and Claude Fable 5.1

Can GPT-5.5 process images?

Yes. GPT-5.5 accepts images as input in addition to text.

How do I use GPT-5.5 through the API?

Create a Railwail API key and send your request with the model ID gpt-5-5. Code examples for curl, Python and JavaScript are in the API section of this page.

08

Comparable models

All in this category
  • Anthropic's model for the most demanding reasoning and long-horizon agentic work. 1M-token context window, up to 128K output tokens, adaptive thinking that is always on.

    US$12.00/1M in

    100 % more expensive per unit

    Compare GPT-5.5 vs. Claude Fable 5.1
  • The most capable model of Anthropic's Opus 4 series. State of the art on long-horizon agentic work, coding and knowledge tasks, with a 1M-token context window at standard pricing.

    US$6.00/1M in

    Same price per unit

    Compare GPT-5.5 vs. Claude Opus 4.8
  • Anthropic's current Opus model for long-running agentic coding and knowledge work. 1M-token context window, up to 128K output tokens, adaptive thinking that is always on.

    US$4.80/1M in

    20 % cheaper per unit

    Compare GPT-5.5 vs. Claude Opus 5.5

Use GPT-5.5 via the API

One API key for every model on Railwail. Usage is charged from prepaid credits, 1 credit = US$0.01.