GPT-5.4 / GPT-5.5 API Guide 2026

GPT-5.4 and GPT-5.5 are OpenAI's frontier models with strong reasoning, coding, and multimodal capabilities. GPT-5.4 is our top recommendation: at $2.50/M input tokens it's lower than Claude Sonnet 4.6 ($3.00/M) and half the cost of Claude Opus 4.8 ($5.00/M)—making it one of the best value frontier models available. This guide covers how to access both APIs and use them via APIMaster.ai.

What Are GPT-5.4 and GPT-5.5?

Both models are part of OpenAI's GPT-5 family released in 2025–2026:

• GPT-5.4: balanced performance and cost — $2.50/M input, $15/M output
• GPT-5.5: OpenAI's most capable model — $5.00/M input, $30/M output
• Advanced reasoning: significantly better than GPT-4o on complex multi-step tasks
• Coding: state-of-the-art on HumanEval and SWE-bench
• Vision: accepts image inputs, describes and reasons about visual content

GPT-5 API Access

Direct from OpenAI:

• Requires OpenAI API account with billing
• Pay-as-you-go or subscription

Via APIMaster.ai:

• Multiple payment methods (epay, PayPal, credit card, USDT)
• Discounted rates
• Fingerprint-verified authentic models

GPT-5 API Quickstart

from openai import OpenAI

client = OpenAI(
    api_key="YOUR_APIMASTER_KEY",
    base_url="https://apimaster.ai/v1",
)

response = client.chat.completions.create(
    model="gpt-5.4",  # or gpt-5.5
    messages=[
        {"role": "system", "content": "You are a senior software architect."},
        {"role": "user", "content": "Design a scalable microservices architecture for an e-commerce platform."},
    ],
    max_tokens=2048,
)

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

GPT-5.4 vs GPT-5.5 Pricing

Model	Input (per 1M)	Output (per 1M)	Cached Input
GPT-5.4 ⭐ Recommended	$2.50	$15.00	$0.25
GPT-5.5	$5.00	$30.00	$0.50
Claude Sonnet 4.6	$3.00	$15.00	—
Claude Opus 4.8	$5.00	$25.00	—

Start with GPT-5.4: input price is 17% lower than Claude Sonnet and 50% lower than Claude Opus, with comparable or stronger output quality. GPT-5.5 is for scenarios where maximum quality justifies the higher cost.

See APIMaster marketplace for discounted rates.

GPT-5.4 / 5.5 vs Other Models

Model	Reasoning	Coding	Vision	Cost
GPT-5.5	★★★★★	★★★★★	★★★★	★
GPT-5.4	★★★★★	★★★★★	★★★★	★★★
Claude Opus 4.8	★★★★★	★★★★	★★★★	★
GPT-4o	★★★★	★★★★	★★★★★	★★★
Claude Sonnet 4.6	★★★★	★★★★★	★★★	★★★★
DeepSeek V4 Flash/Pro	★★★★	★★★★★	❌	★★★★★
o3	★★★★★	★★★★	❌	★★

Code Examples

Complex Code Analysis

with open("codebase.py") as f:
    code = f.read()

response = client.chat.completions.create(
    model="gpt-5.4",
    messages=[
        {
            "role": "user",
            "content": f"Review this code for security vulnerabilities, performance issues, and anti-patterns:\n\n```python\n{code}\n```",
        }
    ],
    max_tokens=3000,
)
print(response.choices[0].message.content)

Image Analysis

response = client.chat.completions.create(
    model="gpt-5.4",
    messages=[
        {
            "role": "user",
            "content": [
                {
                    "type": "image_url",
                    "image_url": {"url": "https://example.com/architecture-diagram.png"},
                },
                {"type": "text", "text": "Identify potential bottlenecks in this system architecture."},
            ],
        }
    ],
)

Streaming

with client.chat.completions.stream(
    model="gpt-5.4",
    messages=[{"role": "user", "content": "Write a complete REST API in FastAPI with auth, tests, and docs."}],
    max_tokens=4096,
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

Model Selection Guide

Start with GPT-5.4 (most use cases):

• Complex reasoning, coding, structured output
• Multimodal tasks combining text and vision
• Frontier model quality at lower cost than Claude Sonnet or Opus

Upgrade to GPT-5.5 (maximum quality):

• Production-critical tasks demanding the best possible output
• When GPT-5.4 is not sufficient

Step down to cheaper models (budget-sensitive):

• Simple chat or summarization: GPT-4o mini is sufficient
• Pure coding on a tight budget: DeepSeek V4 Flash/Pro

Frequently Asked Questions

What's the difference between GPT-5.4 and GPT-5.5? GPT-5.5 is OpenAI's most capable model, priced at $5/$30 per 1M tokens vs GPT-5.4's $2.50/$15. For most tasks GPT-5.4 is sufficient; use GPT-5.5 when maximum output quality is required.

How much does GPT-5 API cost? GPT-5.4: $2.50/M input, $15/M output. GPT-5.5: $5.00/M input, $30/M output. APIMaster offers competitive discounts — see live pricing.

Can I use GPT-5.4 / 5.5 through APIMaster? Yes. Use model ID gpt-5.4 or gpt-5.5 with base_url="https://apimaster.ai/v1" in any OpenAI-compatible SDK.

Are the GPT-5 models on APIMaster authentic? Yes — fingerprint-verified. Check https://apimaster.ai/ai-api-model-tester for the latest results.

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