OpenAI: GPT-5.1-Codex-Max
openai/gpt-5.1-codex-max · OpenAINot yet established- Declared family
- GPT
- Evidence confidence
- Unknown
- Declared tokenizer tag
- GPT
- Entered catalogue
- 4 December 2025
- Last tested
- Not yet measured
- Measurement
- Awaiting measurement
Evidence stack
Signals of different kinds, weighed together| Signal | Result | Reference |
|---|---|---|
| Tokenizer signature | Not measured | – |
| API surface | No other entry shares this exact contract | api_b9598bff |
| Context and output | 400,000 context · 128,000 max output | declared |
| Reasoning contract | Mandatory · efforts xhigh, high, medium, low · default medium | declared |
| Serving providers observed | None recorded yet | – |
Declared record
What the catalogue claims about this modelGPT-5.1-Codex-Max is OpenAI’s latest agentic coding model, designed for long-running, high-context software development tasks. It is based on an updated version of the 5.1 reasoning stack and trained on agentic...
- Modalities
- text+image->text
- Declared tokenizer
- GPT
- Prompt price
- $1.25 / M tokens
- Completion price
- $10.0 / M tokens
Supported parameters
include_reasoningmax_completion_tokensreasoningreasoning_effortresponse_formatseedstructured_outputstool_choicetools
defaults: {"temperature":null,"top_p":null,"top_k":null,"frequency_penalty":null,"presence_penalty":null,"repetition_penalty":null}
History
Every observation, kept as taken- 4 December 2025Enters the OpenRouter catalogue declared as GPT.
Cite this page as the evidence record for OpenAI: GPT-5.1-Codex-Max: the URL is stable, measurements are dated, and revisions append to the history above. Method: tokenizer fingerprinting, v1, 50 strings. The raw data behind every figure is on the data page.
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