# GPT-5.5 Pro

GPT-5.5 Pro is a text generation model from OpenAI, available through the Impossibl API. Its published context window is 1,050,000 tokens. The advertised input rate is $30.00 per million input tokens. The advertised output rate is $180.00 per million output tokens. Additional pricing brackets apply when the input exceeds a published context threshold.

- Model identifier: ` openai/gpt-5.5-pro `
- Creator: OpenAI
- Model type: Text generation
- Canonical model page: [GPT-5.5 Pro](<https://impossibl.com/openai/gpt-5.5-pro>)
- API availability: Listed as serving through Impossibl.
- Creator release date: 2026-04-23

## Capabilities and limits

- Context window: 1,050,000 tokens
- Maximum output tokens: Not published in the public catalog; this is separate from the context window.
- Inputs: text, image
- Outputs: text
- Tool calling: Not published

## API access

Use ` openai/gpt-5.5-pro ` as the model identifier through the Impossibl API.

Published API endpoints:

- ` /v1/chat/completions `

[API quickstart](<https://impossibl.com/docs/agent-quickstart>) · [Models and billing documentation](<https://impossibl.com/docs/models>)

## Published API prices

All rates are in USD. An unpublished rate is unknown, not zero. Workspace-specific pricing, taxes, balance-purchase fees, billing adjustments, and tool charges can affect the amount paid.

| Usage | Published base rate | Billing unit |
| --- | --- | --- |
| Input | $30.00 | per million input tokens |
| Output | $180.00 | per million output tokens |
| Cache read | $3.00 | per million cached input tokens |
| Cache write (default retention) | Not published | per million tokens |
| Cache write (one-hour retention) | Not published | per million tokens |
| Audio input | Not published | per million audio input tokens |

### Long-context pricing

Base rates apply through 272,000 total input tokens per request. If total input, including cached input, strictly exceeds a threshold, use the highest qualifying threshold. Its rates apply to the whole request, not only the tokens above the threshold.

All rates below are USD per million tokens. Unpublished tier cache rates remain unknown; do not substitute the base cache rate.

| Total input tokens per request | Input | Output | Cache read | Cache write (default retention) | Cache write (one-hour retention) |
| --- | --- | --- | --- | --- | --- |
| Over 272,000 | $60.00 | $270.00 | Not published | Not published | Not published |

## Independent benchmarks

Source: [Artificial Analysis](<https://artificialanalysis.ai/>). Last checked: 2026-09-10T09:58:54.927Z.
Configurations are evaluated separately. API scores retain their original units. Unmeasured scores are omitted.

### GPT-5.5 Pro (xhigh)

Source: [Evaluation source](<https://artificialanalysis.ai/models/gpt-5-5-pro>)

| Benchmark | Score |
| --- | --- |
| CritPt | 30.57% |

Full benchmark data and breakdowns: [Complete benchmark snapshot](<https://api.impossibl.com/v1/models/openai/gpt-5.5-pro/benchmarks>).


## Availability and retirement

The model is listed as serving. No retirement is announced in the current public catalog.

## Frequently asked questions

### What is GPT-5.5 Pro?

GPT-5.5 Pro is a text-generation model from OpenAI, available through the Impossibl API.

### How much does GPT-5.5 Pro cost?

GPT-5.5 Pro costs $30.00 per million input tokens and $180.00 per million output tokens through the Impossibl API. Cache reads cost $3.00 per million tokens. These base rates apply through 272,000 total input tokens per request. Above 272,000 input tokens, the long-context rates in the pricing table apply to the whole request. All rates are in USD.

### What is the context length of GPT-5.5 Pro?

GPT-5.5 Pro has a 1,050,000-token context window through the Impossibl API.

### What inputs and outputs does GPT-5.5 Pro support?

GPT-5.5 Pro accepts text and image as input. GPT-5.5 Pro returns text.

### How do I use GPT-5.5 Pro through an API?

GPT-5.5 Pro is available through the Impossibl API. Use openai/gpt-5.5-pro as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request.

### When was GPT-5.5 Pro released?

OpenAI released GPT-5.5 Pro on April 23, 2026.

Sources: [Creator release announcement](<https://openai.com/index/introducing-gpt-5-5/>)

## Sources and related links

Prices, limits, capabilities, endpoints, and availability come from the public Impossibl catalog. Creator documentation supplies descriptions and release dates where available; it does not override the published API offering.

- [Public Impossibl model catalog](<https://api.impossibl.com/v1/models>)
- [Full model directory as JSON](<https://impossibl.com/models.json>)
- [GPT-5.5 Pro: model details and pricing](<https://impossibl.com/openai/gpt-5.5-pro>)
- [Model directory](<https://impossibl.com/models>)