GPT-5.1 Codex

GPT-5.1 Codex is a specialised version of OpenAI's GPT-5.1 optimised for software engineering and coding workflows.

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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-5.1 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-5.1-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
releasednov 13, 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-5.1-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-5.1-codex",
    input="▌",
)
print(resp.output_text)

edit the prompt, then run

benchmarks

intelligence index

23.7#51 of 90 models on the gateway

omniscience-6.5#45 of 86
gpqa86.0%#46 of 88
humanity’s last exam25.7%#54 of 89

AIME 202595.7%
GPQA86.0%
LiveCodeBench84.9%
Tau283.0%
MMMU-Pro72.5%
IFBench70.0%
AA-LCR69.3%
Terminal-Bench Hard34.8%
Humanity’s Last Exam25.7%
CritPt5.7%

Intelligence Index23.70
Omniscience Index-6.50
intelligence index (API)23.7

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 2026-09-10.

compare GPT-5.1 Codex with other models

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

anthropic/claude-fable-5-1$10.00 / $50.00compare →
meta/muse-spark-1.3$1.25 / $4.25compare →
zai/glm-5.3$1.40 / $4.40compare →
xai/grok-4.6$2.00 / $6.00compare →

impossibl models --all →

frequently asked questions

What is GPT-5.1 Codex?

GPT-5.1 Codex is a specialised version of OpenAI's GPT-5.1 optimised for software engineering and coding workflows. It is designed for interactive development sessions as well as long, independent runs on complex engineering tasks, and is the base for the smaller GPT-5.1 Codex mini.

How much does GPT-5.1 Codex cost?

GPT-5.1 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-5.1 Codex?

GPT-5.1 Codex has a 400,000-token context window through the Impossibl API.

What inputs and outputs does GPT-5.1 Codex support?

GPT-5.1 Codex accepts text and image as input. GPT-5.1 Codex returns text.

How do I use GPT-5.1 Codex through an API?

GPT-5.1 Codex is available through the Impossibl API. Use openai/gpt-5.1-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-5.1 Codex released?

OpenAI released GPT-5.1 Codex on November 13, 2025.

Creator release announcement ↗

this page describes GPT-5.1 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 →