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o3
openaiopenai/o3
API guide
Chat completion
Standard OpenAI-compatible chat. o3 is available via /v1/chat/completions on TheRouter β same endpoint, same SDK as gpt-4o or gpt-5.
cURL
curl https://api.therouter.ai/v1/chat/completions \
-H "Authorization: Bearer $THEROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "openai/o3",
"messages": [
{"role": "user", "content": "Prove that the sum of two odd numbers is even."}
]
}'Reasoning effort control
o3 supports reasoning_effort = low | medium | high. Higher effort = deeper chains and more reasoning tokens (which you are billed for as output). Default is medium.
cURL
curl https://api.therouter.ai/v1/chat/completions \
-H "Authorization: Bearer $THEROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "openai/o3",
"reasoning_effort": "high",
"messages": [
{"role": "user", "content": "Walk through the failure modes of a 2-of-3 Raft cluster losing a leader."}
]
}'Vision input
o3 accepts text + image inputs. Pass image_url parts in the user message β same shape as gpt-4o multimodal calls. Output is text only.
cURL
curl https://api.therouter.ai/v1/chat/completions \
-H "Authorization: Bearer $THEROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "openai/o3",
"messages": [
{"role": "user", "content": [
{"type": "text", "text": "What is wrong with this architecture diagram?"},
{"type": "image_url", "image_url": {"url": "https://therouter.ai/assets/vision-sample.png"}}
]}
]
}'Function calling / tools
o3 supports OpenAI-style function calling and structured outputs. Per OpenAI's reasoning best-practices, prefer fewer, well-described tools over long flat tool lists.
cURL
curl https://api.therouter.ai/v1/chat/completions \
-H "Authorization: Bearer $THEROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "openai/o3",
"messages": [{"role": "user", "content": "What is the weather in Tokyo right now?"}],
"tools": [
{
"type": "function",
"function": {
"name": "get_weather",
"description": "Get the current weather for a city.",
"parameters": {
"type": "object",
"properties": {"city": {"type": "string"}},
"required": ["city"]
}
}
}
]
}'Fact ledger β every claim on this page traces here
| source | URL | retrieved | |
|---|---|---|---|
| Release date | openai.com β | 2026-05-31 | verified |
| Snapshot | developers.openai.com β | 2026-05-31 | verified |
| Knowledge cutoff | developers.openai.com β | 2026-05-31 | verified |
| Context window | developers.openai.com β | 2026-05-31 | verified |
| Max output tokens | developers.openai.com β | 2026-05-31 | verified |
| Reasoning tokens | developers.openai.com β | 2026-05-31 | verified |
| Status | developers.openai.com/deprecations β | 2026-05-31 | verified |
| Codeforces | openai.com β | 2026-05-31 | verified |
| SWE-bench Verified | openai.com β | 2026-05-31 | verified |
| AIME 2024 | openai.com β | 2026-05-31 | verified |
| AIME 2025 | openai.com β | 2026-05-31 | verified |
| GPQA Diamond | datacamp.com β | 2026-05-31 | to verify |
| MMMU | openai.com β | 2026-05-31 | to verify |
| o3-pro available to API and ChatGPT Pro | OpenAI Help Center β | 2026-05-31 | verified |
| OpenAI o3 and o4-mini launch | openai.com β | 2026-05-31 | verified |
| Is o3 deprecated yet? | developers.openai.com β | 2026-05-31 | to verify |
| What is o3's context window and max output? | developers.openai.com β | 2026-05-31 | to verify |
| Does o3 accept image input? | developers.openai.com β | 2026-05-31 | to verify |
| How does o3 compare to GPT-5 on price? | developers.openai.com β | 2026-05-31 | to verify |