GPT 5.1 Codex Max: Release Facts and Evaluation Steps
OpenAI released gpt-5.1-codex-max on December 4, 2025. This article details the official changelog facts, input modalities, and a practical evaluation…
Official Announcement Details
The original announcement date recorded in the source data is December 4, 2025. This historical date distinguishes the event from the current publication date of this article. On that day, OpenAI released the model identified as gpt-5.1-codex-max to the v1/responses API endpoint. The official changelog entry categorizes this event as a feature release within the GPT family.
- Event Date: December 4, 2025
- Model Identifier: gpt-5.1-codex-max
- API Endpoint: v1/responses
- Provider: OpenAI
Documented Specifications and Limits
The source explicitly states that GPT-5.1-Codex is optimized for long-horizon, agentic coding tasks. OpenAI characterizes it as their most intelligent coding model. Regarding technical specifications, the model accepts both text and image inputs. However, the output modality is restricted to text only. The source does not provide information on context window size or maximum output tokens. Additionally, open weights are not confirmed for this release. This status records that open weights are unavailable; it does not establish whether local installation is possible or impossible, nor does it define any specific hosting arrangement or deployment architecture.
- Input Modalities: Text, Image
- Output Modality: Text
- Optimization Target: Long-horizon, agentic coding tasks
- Open Weights: Not confirmed
Practical Evaluation Procedure
Engineers can evaluate the model by designing a controlled testing environment using the v1/responses API. First, select a representative set of complex coding tasks that require multi-step reasoning or agent-like behavior. Second, measure the model's output accuracy and consistency against these specific tasks. Third, compare these results against baseline models if available in your existing test suite. Finally, validate whether the model handles image inputs effectively when visual context is required for code generation. This process allows developers to determine if the model meets specific project requirements based on observed performance rather than unverified claims about speed or cost efficiency.
Primary sources
Frequently asked questions
What input types does GPT 5.1 Codex Max support?
According to the source facts, the model supports text and image inputs. It generates text-only outputs.
Is the model available for local installation?
The source indicates that open weights are not confirmed. Therefore, there is no verified information establishing that local installation is possible or impossible based solely on this release note.