GPT-5.5 API (gpt-5.5 / gpt-5.5-pro)

$4 / $24 per million tokens (input / output, effective) — one OpenAI-compatible endpoint at https://api.apimart.ai/v1, no monthly plan required. (observed 2026-09-17)

Get an API key · Live pricing · Model page · ⚡ 60-second quickstart

Why teams call GPT-5.5 (gpt-5.5) through APIMart

• One key, entire catalog. The same https://api.apimart.ai/v1 base URL and Authorization header reach GPT-5.5 (gpt-5.5) and 300+ other image, video and language models — switch the model field, not your client.
• $1 minimum, pay as you go. No subscription and no prepaid plan to size up front: top up from $1 and spend it on calls. There is no free quota to burn through first, so the price in this table is the price you pay.
• The charge comes back in the response. Every call reports the amount billed (cost / credits_cost), so a spend number is read per call instead of guessed at month end.
• Drop-in OpenAI shape. POST /v1/chat/completions with the same request body your client already sends; only base_url and model change.

GPT-5.5 on APIMart is an OpenAI-compatible chat route billed per million tokens, with a -pro variant for the hardest prompts. This repository documents the model ids, the measured token rates, the request shapes (non-streaming, streaming, tool calling, JSON mode) and the outputs of real calls.

Endpoint: POST https://api.apimart.ai/v1/chat/completions (OpenAI-compatible). Streaming is the default — pass stream: false when you want one JSON object back.

The effective column is what you pay after the default group discount; data/model.json is refreshed daily by CI, and the usage block in every response tells you exactly which tokens were billed.

curl -sS https://api.apimart.ai/v1/chat/completions \
  -H "Authorization: Bearer $APIMART_API_KEY" -H 'Content-Type: application/json' \
  -d '{"model":"gpt-5.5","stream":false,"messages":[{"role":"user","content":"Name three retry rules."}]}'

import os, requests

BASE = "https://api.apimart.ai/v1"
HEADERS = {"Authorization": f"Bearer {os.environ['APIMART_API_KEY']}", "Content-Type": "application/json"}

payload = requests.post(f"{BASE}/chat/completions", headers=HEADERS, timeout=120, json={
    "model": "gpt-5.5", "stream": False,
    "messages": [{"role": "user", "content": "Name three retry rules."}],
}).json()
print(payload["choices"][0]["message"]["content"])
print(payload["usage"])

Streaming, tool calling and JSON mode examples are in examples/ (t_curl.sh, python_chat.py).

These rows are actual completions recorded from this route, with the token usage the API returned and the cost computed from the effective rates above.

Full transcripts (including longer answers) are in data/samples.json.

What are the GPT-5.5 API model ids?

gpt-5.5 and gpt-5.5-pro. Calls return a dated snapshot id (for example gpt-5.5-2026-04-24), which is useful to log if you need reproducible outputs.

How is GPT-5.5 billed?

Per million tokens, with separate input, cached-input and output rates — the table above is refreshed from the public pricing payload and the effective column is what you actually pay.

Why do I get an empty body when I call the endpoint?

Because streaming is the default. Pass stream: false for a single JSON response, or parse the SSE data: lines.

Is the request shape the same as OpenAI's?

For chat, streaming, tool calling and JSON mode, yes. Keep the base URL and key in environment variables so you can switch routes without touching business logic.

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Start with $1. Get an API key → check live pricing → open GPT-5.5 (gpt-5.5) in the model library. The first call is three steps: submit, poll task_id, read the charged amount off the response.

Outbound APIMart links are minted through the promo link API; hand-made tracking parameters are rejected by tools/check_links.py in CI.

GPT-5.5 is a third-party model served through APIMart; this repository publishes model ids, measured prices and real call outputs, and does not claim official status. Model names, prices and documentation belong to their respective owners. Endpoint reference: https://docs.apimart.ai/en/api-reference/texts/general/chat-completions.

README.md             model ids, token pricing, verified capabilities, real outputs
data/model.json       token rates for every tier (CI-refreshed)
data/samples.json     recorded completions with usage and computed cost
tools/snapshot.py     refresh pricing from the public payload
tools/check_links.py  attribution guard
examples/             curl and Python clients (streaming, tools, JSON mode)
.github/workflows/    daily price refresh + validation

MIT — see LICENSE.