GPT-4.1

Name: GPT-4.1
Brand: OpenAI
SKU: gpt-4-1
Price: 2.4 USD
Availability: InStock

Text & chatNewAvailable

by OpenAIgpt-4-1

OpenAI's newest flagship model. Improved reasoning, instruction following, and coding over GPT-4o.

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Price · 1M in / out: US$2.40 / US$9.60
Context: 1,000,000 tokens
Max. output: 32,768 tokens
Input → output: Text → Text
Developer: OpenAI
Updated: September 23, 2026

Playground

Try GPT-4.1

Chat

US$2.40/1M in

Send a message. The answer arrives in full once the model is done (no streaming).

System prompt

Max. answer length (tokens)

⌘/Ctrl + Enter

This run

at most US$0.0099 · 0.99 credits reserved

Billed by the tokens actually used; the unused part of the reservation is refunded.

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10 free credits (US$0.10) when you sign up with Google

Usable 24 hours after sign-up, up to 5 runs per day and at most 2 credits per run. Other sign-in methods start without credits. Enough for 10 runs of this model.

About GPT-4.1

TL;DRAs of September 23, 2026

GPT-4.1 is a model by OpenAI in the Text & chat category. On Railwail, GPT-4.1 costs US$2.40 per 1M input tokens and US$9.60 per 1M output tokens. The context window holds 1,000,000 tokens, and one response can be up to 32,768 tokens long.

Background

About OpenAI

Founded 2015 · San Francisco, USA

OpenAI was founded in 2015 as a non-profit research lab by Sam Altman, Elon Musk, Greg Brockman, Ilya Sutskever, Wojciech Zaremba and John Schulman. In 2019 it transitioned into a capped-profit company to raise capital from Microsoft, which has invested over $13 billion. OpenAI is the publisher of the GPT series papers (GPT-1 in 2018, GPT-2 in 2019, GPT-3 in 2020, GPT-4 Technical Report in 2023), the InstructGPT paper that introduced RLHF for instruction following, and the GPT-4o System Card. Major products include ChatGPT (launched November 2022, with over 200M weekly active users), the OpenAI API, the o-series reasoning models, Sora for text-to-video and DALL-E for image generation. GPT-4.1 was released in April 2025 as an API-only model family (4.1, 4.1 mini and 4.1 nano) optimised for developers, with major improvements over GPT-4o on coding, instruction following and long-context tasks. The 2025 reported valuation exceeded $300 billion.

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Architecture

Decoder-only Transformer (developer-focused flagship)

GPT-4.1 launched in April 2025 as an API-only successor to GPT-4o aimed primarily at developers and agentic workloads. It is a decoder-only Transformer trained on an updated multi-trillion-token mixture of text, code and image-text pairs, with a knowledge cutoff of June 2024. The model family ships in three sizes (4.1, 4.1 mini, 4.1 nano) sharing the same training recipe but distilled to different capability/latency points. The headline change versus GPT-4o is a 1,047,576-token context window (~1M tokens), validated with new long-context evaluations such as OpenAI's MRCR (Multi-Round Coreference Resolution) and Graphwalks benchmarks. Post-training emphasised coding (SWE-bench Verified moved to 54.6% from 33% on GPT-4o), instruction following on edge-case formats, and reliable behaviour in long agent loops. OpenAI used reinforcement learning against verifiable rewards and large-scale synthetic data generation to push these axes. The model deprecates GPT-4.5 Preview from the API and is positioned as the production workhorse for ChatGPT Enterprise and Team deployments. Vision input is supported in all three sizes, function calling and Structured Outputs are first-class, and pricing is roughly 26% cheaper than GPT-4o at launch.

Parameters: Undisclosed (estimated multi-hundred billion parameters dense)
Context: 1,047,576 tokens

Capabilities

1,047,576 token context window (~1M tokens)
Major coding improvement: 54.6% on SWE-bench Verified at launch
Strong instruction following on edge-case formats and negative constraints
Reliable behaviour over long agent loops
Vision input across all three model sizes (4.1, mini, nano)
Function calling, parallel tool calls and Structured Outputs
Knowledge cutoff June 2024 (later than GPT-4o)
About 26% cheaper than GPT-4o at launch
Diff-style file editing and applied-diff coding workflows
Improved multilingual non-English benchmark performance
Best for: coding agents, IDE copilots, large-document analysis, production assistants.

Training & license

Pretrained on a multi-trillion-token web-scale mixture of text, code repositories, books, licensed datasets and image-text pairs. Knowledge cutoff is June 2024. Post-training combined supervised fine-tuning, RLHF and reinforcement learning against verifiable rewards (especially for code).

License: Proprietary commercial license via OpenAI API and Azure OpenAI Service. Not available through the ChatGPT consumer product.

Safety testing: Evaluated under OpenAI's Preparedness Framework v2 across CBRN, cyber, persuasion and autonomy axes. External red-teamers and OpenAI's Safety Advisory Group reviewed before launch.

Known limitations

API-only, no ChatGPT consumer access initially
1M context window is supported but quality degrades on cross-document recall vs nominal capacity
Higher cost than GPT-4o mini for cost-sensitive use cases
Still hallucinates citations and exact quotes
No native audio I/O (use GPT-4o for voice)

Research papers

Pricing

Prices in US dollars. Usage is charged from prepaid credits.

Input	US$2.40 / 1M tokens
Output	US$9.60 / 1M tokens

Billed by the tokens each request actually uses.
1 credit = US$0.01

Cost calculator

Price calculator

Input tokens

/ req.

Output tokens

/ req.

Requests

Total

US$0.72

72 credits

Per request

US$0.0072 · 0.72 credits

Each request is rounded up to 0.01 credits.

API

Call GPT-4.1 with your Railwail API key. Use this model ID in the request:

gpt-4-1API documentation Get an API key

curl https://railwail.com/api/v1/chat/completions \
  -H "Authorization: Bearer $RAILWAIL_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-4-1",
    "messages": [
      {
        "role": "user",
        "content": "Explain what a vector database is in two sentences."
      }
    ],
    "max_tokens": 1024
  }'

import os
from openai import OpenAI

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

completion = client.chat.completions.create(
    model="gpt-4-1",
    messages=[
        {
            "role": "user",
            "content": "Explain what a vector database is in two sentences.",
        },
    ],
    max_tokens=1024,
)

print(completion.choices[0].message.content)

import OpenAI from "openai";

const client = new OpenAI({
  apiKey: process.env.RAILWAIL_API_KEY,
  baseURL: "https://railwail.com/api/v1",
});

const completion = await client.chat.completions.create({
  model: "gpt-4-1",
  messages: [
    {
      role: "user",
      content: "Explain what a vector database is in two sentences."
    }
  ],
  max_tokens: 1024
});

console.log(completion.choices[0].message.content);

// npm install railwail
import railwail from "railwail";

const rw = railwail(process.env.RAILWAIL_API_KEY);

const res = await rw.chat("gpt-4-1", [
  { role: "user", content: "Explain what a vector database is in two sentences." },
], { max_tokens: 1024 });

console.log(res.choices[0].message.content);

Set your key as RAILWAIL_API_KEYCreate API key

Specifications

Model ID: gpt-4-1
Developer: OpenAI
Category: Text & chat
Input: Text
Output: Text
Context window: 1,000,000 tokens
Max. output: 32,768 tokens
Billing: By usage (tokens or GPU time)
Model size: Undisclosed (estimated multi-hundred billion parameters dense)
License: Proprietary commercial license via OpenAI API and Azure OpenAI Service. Not available through the ChatGPT consumer product.
Catalog entry updated: September 23, 2026

Example prompts

Examples from the Railwail catalog. They were not generated live on this page.

System Design
Design a URL shortener service. What are the key components and how would you handle 10 million requests per day?
Show example answer
A URL shortener at 10M req/day needs: 1) An API layer behind a load balancer to accept long URLs and return short codes. 2) A base62 encoding scheme (a-z, A-Z, 0-9) generating 6-character codes, yielding 56 billion unique URLs. 3) A distributed key-value store like Redis for fast lookups with a persistent database (PostgreSQL) as the source of truth. 4) A caching layer (CDN + Redis) since reads vastly outnumber writes. 5) Rate limiting per IP/API key to prevent abuse. At ~115 req/sec average, a few application servers with horizontal scaling can handle the load comfortably.
Instruction Following
Write exactly 3 sentences about black holes. Each sentence must contain exactly 10 words. Do not use the word 'space'.
Show example answer
Black holes form when massive stars collapse under their gravity. Light cannot escape the intense gravitational pull they create. Scientists study these mysterious objects using powerful telescopes and math.

Use cases

What it is used for

Autonomous coding agents
IDE copilots and pair programmers
Long-document and codebase analysis
Customer support over 1M token transcripts
Enterprise RAG and chat assistants
Tool-using agents in production

Related guides

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Frequently asked questions

What is GPT-4.1?

GPT-4.1 is a model by OpenAI in the Text & chat category. On Railwail you can call it with an API key through the Railwail API.

How much does GPT-4.1 cost on Railwail?

On Railwail, GPT-4.1 costs US$2.40 per 1M input tokens and US$9.60 per 1M output tokens. You are charged for what each request actually uses. Usage is paid from prepaid credits; 1 credit equals US$0.01.

What is the context window of GPT-4.1?

The context window of GPT-4.1 holds 1,000,000 tokens. One response can be up to 32,768 tokens long.

How fast is GPT-4.1?

There are not enough measured runs of GPT-4.1 on Railwail yet to state a run time. It depends on the input, the settings and the load at the provider.

Is GPT-4.1 better than Claude Fable 5.1?

That depends on the task. GPT-4.1 (OpenAI) and Claude Fable 5.1 (Anthropic) are both models in the Text & chat category. The comparison page shows their prices and specifications side by side.

Compare GPT-4.1 and Claude Fable 5.1

How do I use GPT-4.1 through the API?

Create a Railwail API key and send your request with the model ID gpt-4-1. Code examples for curl, Python and JavaScript are in the API section of this page.

Comparable models

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Claude Fable 5.1Anthropic
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US$12.00/1M in
400 % more expensive per unit
Compare GPT-4.1 vs. Claude Fable 5.1
Claude Opus 4.8Anthropic
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US$6.00/1M in
150 % more expensive per unit
Compare GPT-4.1 vs. Claude Opus 4.8
Claude Opus 5.5Anthropic
Anthropic's current Opus model for long-running agentic coding and knowledge work. 1M-token context window, up to 128K output tokens, adaptive thinking that is always on.
US$4.80/1M in
100 % more expensive per unit
Compare GPT-4.1 vs. Claude Opus 5.5

Use GPT-4.1 via the API

One API key for every model on Railwail. Usage is charged from prepaid credits, 1 credit = US$0.01.

Get API key Browse all models