GPT-5.5

OpenAI’s GPT-5.5 — flagship model for complex reasoning and professional work.

GPT-5.5 is available through AnyFast via the OpenAI Responses API (/v1/responses). It is OpenAI’s most capable frontier model, designed for the most demanding professional and coding tasks.

Key capabilities

• Responses API — Uses the newer /v1/responses endpoint with input instead of messages
• Advanced reasoning — Supports reasoning effort levels: none, low, medium (default), high, and xhigh
• Verbosity control — Set response verbosity to low, medium, or high
• Streaming — Supports real-time token streaming via SSE
• Tool use — Supports function calling, web search, file search, and computer use

Quick example

cURL

curl https://www.anyfast.ai/v1/responses \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.5",
    "input": [
      { "role": "user", "content": "Explain quantum entanglement in simple terms." }
    ],
    "reasoning": {
      "effort": "high",
      "summary": "auto"
    },
    "text": {
      "format": { "type": "text" },
      "verbosity": "medium"
    },
    "store": true
  }'

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://www.anyfast.ai/v1"
)

response = client.responses.create(
    model="gpt-5.5",
    input=[
        {"role": "user", "content": "Explain quantum entanglement in simple terms."}
    ],
    reasoning={"effort": "high", "summary": "auto"},
    text={"format": {"type": "text"}, "verbosity": "medium"},
    store=True
)

print(response.output[0].content[0].text)

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_API_KEY",
    base_url="https://www.anyfast.ai/v1"
)

stream = client.responses.create(
    model="gpt-5.5",
    input=[
        {"role": "user", "content": "Write a short poem about the sea."}
    ],
    stream=True
)

for event in stream:
    if hasattr(event, 'delta'):
        print(event.delta, end="")

Parameters

Parameter	Type	Required	Description
model	string	Yes	Must be gpt-5.5
input	array	Yes	List of { role, content } objects
stream	boolean	No	Enable SSE streaming. Default: false
temperature	float	No	0–2. Controls randomness. Default: 1
max_output_tokens	integer	No	Maximum output tokens to generate. Minimum: 16
stop	string / array	No	Sequences that stop generation
reasoning	object	No	{ effort, summary } — effort: none / low / medium / high / xhigh
text	object	No	{ format, verbosity } — controls output format and verbosity
tools	array	No	List of tools the model may call
store	boolean	No	Store response for later retrieval. Default: true

API Reference

View the interactive API playground for GPT-5.5.