GPT-5.1 Codex is a version of GPT-5.1 optimized for agentic coding inside the Codex environment, with regular underlying model refreshes. It supports a 400,000-token input context with 128,000 output tokens, accepts text and image inputs, and exposes reasoning tokens, streaming, function calling, and structured outputs. Available exclusively through the Responses API.
Chat Completions API
/api/v1/chat/completions
OpenAI-compatible endpoint with a messages array. Standard interface for chat-based interactions.
Responses API
/api/v1/responses
Native OpenAI Responses format with a simplified input parameter for single-turn requests.
These providers haven't been health-probed for this model yet. The router still routes around upstreams that fail live requests — uptime fills in once probe history accrues.
curl https://anyrouter.dev/api/v1/chat/completions \
-H "Authorization: Bearer $ANYROUTER_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"model": "openai/gpt-5.1-codex",
"messages": [
{"role": "user", "content": "Say hi in 3 words."}
]
}'ANYROUTER_API_KEY — Dashboard → Keys{
"model": "openai/gpt-5.1-codex",
"messages": [
{
"role": "user",
"content": "Say hi in 3 words."
}
]
}Change sort, ZDR, effort, or pin a provider to add routing params.