GPT-5.3 Codex

GPT-5.3 Codex is OpenAI's agentic coding model, optimised for autonomous software engineering in Codex and similar environments.

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input · usd / 1m tok

$1.75

output · usd / 1m tok

$14.00

context window

400ktokens

modalities · in → out

pricing

base api ratesusd per 1m tokens

input: $1.75
output: $14.00
cache read: $0.175

providers

Azure OpenAI hosts GPT-5.3 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-5.3-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
releasedfeb 5, 2026
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-5.3-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-5.3-codex",
    input="▌",
)
print(resp.output_text)

edit the prompt, then run

benchmarks

intelligence index

32.5#32 of 90 models on the gateway

omniscience10.9#23 of 86
gpqa91.5%#26 of 88
humanity’s last exam42.5%#19 of 89

GPQA91.5%
Tau286.0%
AA-LCR83.3%
MMMU-Pro78.5%
IFBench75.4%
Terminal-Bench Hard53.0%
Humanity’s Last Exam42.5%
CritPt16.9%

Intelligence Index32.50
Omniscience Index10.87
intelligence index (API)32.5

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-5.3 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 →
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zai/glm-5.3$1.40 / $4.40compare →
xai/grok-4.6$2.00 / $6.00compare →

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frequently asked questions

What is GPT-5.3 Codex?

GPT-5.3 Codex is OpenAI's agentic coding model, optimised for autonomous software engineering in Codex and similar environments. It combines the engineering strengths of GPT-5.2 Codex with the broader reasoning and professional knowledge of GPT-5.2, and supports reasoning effort from low up to xhigh.

How much does GPT-5.3 Codex cost?

GPT-5.3 Codex costs $1.75 per million input tokens and $14.00 per million output tokens through the Impossibl API. Cache reads cost $0.175 per million tokens. All rates are in USD.

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What is the context length of GPT-5.3 Codex?

GPT-5.3 Codex has a 400,000-token context window through the Impossibl API.

What inputs and outputs does GPT-5.3 Codex support?

GPT-5.3 Codex accepts text and image as input. GPT-5.3 Codex returns text.

How do I use GPT-5.3 Codex through an API?

GPT-5.3 Codex is available through the Impossibl API. Use openai/gpt-5.3-codex as the model identifier with /v1/chat/completions. The quickstart explains how to create an API key and send your first request.

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When was GPT-5.3 Codex released?

OpenAI released GPT-5.3 Codex on February 5, 2026.

Creator release announcement ↗

this page describes GPT-5.3 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.

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