GPT-5 Codex

GPT-5 Codex is a version of OpenAI's GPT-5 optimised for agentic coding in Codex or similar environments.

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input · usd / 1m tok

$1.25

output · usd / 1m tok

$10.00

context window

400ktokens

modalities · in → out

pricing

base api ratesusd per 1m tokens

input: $1.25
output: $10.00
cache read: $0.125

providers

Azure OpenAI hosts GPT-5 Codex. Impossibl routes your request intelligently and handles failover automatically when a provider is down.

Azure OpenAI

specifications

takes text and image in, gives text outopenai/gpt-5-codex

creatorOpenAI
model typeText generation
context window400,000 tokens
maximum outputnot published
input
takes text and image in, gives text out
outputtext
tool callingnot verified
releasedsep 15, 2025
endpoint/v1/chat/completions

unknown means the public catalog does not establish that fact. a model's documented capabilities can differ from what a particular api supports. see the model documentation for integration details.

try it · your prompt, this model, live

# responses API
import os
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["IMPOSSIBL_API_KEY"],
    base_url="https://api.impossibl.com/v1",
)

resp = client.responses.create(
    model="openai/gpt-5-codex",
    input="▌",
)
print(resp.output_text)

edit the prompt, then run

# responses API
import os
from openai import OpenAI

client = OpenAI(
    api_key=os.environ["IMPOSSIBL_API_KEY"],
    base_url="https://api.impossibl.com/v1",
)

resp = client.responses.create(
    model="openai/gpt-5-codex",
    input="▌",
)
print(resp.output_text)

edit the prompt, then run

benchmarks

intelligence index

24.9#63 of 108 models on the gateway

omniscience-7.5#44 of 84
gpqa83.7%#48 of 80
humanity’s last exam27.8%#50 of 87

AIME 202598.7%
Tau286.8%
LiveCodeBench84.0%
GPQA83.7%
IFBench74.1%
MMMU-Pro73.8%
AA-LCR71.7%
Terminal-Bench Hard37.9%
Humanity’s Last Exam27.8%
CritPt5.1%

Intelligence Index24.88
Omniscience Index-7.53
intelligence index (API)24.9

view source ↗all source data and breakdowns (json) ↗

each configuration is listed separately; these evaluations describe the tested model configuration, and performance and costs can differ on impossibl. unmeasured scores are omitted and api values keep their source units. last checked 2026-10-14.

compare GPT-5 Codex with other models

frontier labs and open weights, best-ranked firstusd / 1m tok · in / out

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frequently asked questions

What is GPT-5 Codex?

GPT-5 Codex is a version of OpenAI's GPT-5 optimised for agentic coding in Codex or similar environments. It shares GPT-5's text and image input and reasoning, but is tuned for autonomous, tool-driven software engineering and is available only through the Responses API.

How much does GPT-5 Codex cost?

GPT-5 Codex costs $1.25 per million input tokens and $10.00 per million output tokens through the Impossibl API. Cache reads cost $0.125 per million tokens. All rates are in USD.

view the pricing table ↑

What is the context length of GPT-5 Codex?

GPT-5 Codex has a 400,000-token context window through the Impossibl API.

What inputs and outputs does GPT-5 Codex support?

GPT-5 Codex accepts text and image as input. GPT-5 Codex returns text.

How do I use GPT-5 Codex through an API?

GPT-5 Codex is available through the Impossibl API. Use openai/gpt-5-codex as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request.

follow the api quickstart →

When was GPT-5 Codex released?

OpenAI released GPT-5 Codex on September 15, 2025.

Creator release announcement ↗

this page describes GPT-5 Codex as listed by the impossibl public api. prices and availability come from that catalog, refreshed here every five minutes. this is an impossibl offering, not a comparison of independent hosting-provider quotes. model descriptions and release dates, where available, use the creator sources linked under the answers above.

view the source catalog ↗model as markdown ↗report a correction →