Side-by-side API comparison
| Feature | OpenAI | Claude |
|---|---|---|
| Top Model | GPT-4o | Claude Opus 4 |
| Fast Model | GPT-4o-mini | Claude Haiku 3.5 |
| Context Window | 128K tokens | 200K tokens Best |
| Vision | ✅ Yes | ✅ Yes |
| Function Calling | ✅ Native | ✅ Tool Use |
| JSON Mode | ✅ Native | Via prompting |
| Streaming | ✅ Yes | ✅ Yes |
| Embeddings | ✅ Yes | ❌ No (use Voyage) |
Basic API call in Python
from openai import OpenAI
client = OpenAI()
response = client.chat.completions.create(
model="gpt-4o",
messages=[
{"role": "user",
"content": "Hello!"}
]
)
print(response.choices[0].message.content)
import anthropic
client = anthropic.Anthropic()
message = client.messages.create(
model="claude-sonnet-4-20250514",
max_tokens=1024,
messages=[
{"role": "user",
"content": "Hello!"}
]
)
print(message.content[0].text)
200K context vs 128K. Claude handles entire codebases and long documents better.
Claude is generally better at following detailed, multi-step instructions precisely.
Both have excellent vision capabilities. GPT-4o slightly faster.
OpenAI has more third-party integrations, plugins, and tooling.
Native JSON mode is more reliable than prompting for JSON.
Both excellent. Claude slightly better at explaining, GPT-4 at quick fixes.
Constitutional AI provides more consistent safety behavior.
GPT-4o-mini is typically faster than Haiku for simple tasks.
| Aspect | OpenAI | Claude |
|---|---|---|
| Response Access | .choices[0].message.content |
.content[0].text |
| Max Tokens | Optional (has default) | Required parameter |
| System Prompt | In messages array | Separate parameter |
| Auth Header | Authorization: Bearer |
x-api-key |
| Version Header | Not required | anthropic-version |