Model capability probe

OpenAI: GPT-5 Codex | JSON mode

Whether OpenAI: GPT-5 Codex supports JSON mode cannot be decided from the name alone. Check model ID openai/gpt-5-codex, provider OpenAI, catalog params, modality, a lightweight runtime probe, and the error body together.

Model

openai/gpt-5-codex

OpenAI: GPT-5 Codex

Provider

OpenAI

62 models in catalog

Capability

JSON mode

json-mode

Catalog signal

catalog shows support

Context: 400,000

Capability probe summary

Model

openai/gpt-5-codex

Capability

json-mode

Catalog signal

catalog shows support

Read-only check. Detection data burns after 5 minutes.

How to judge this capability

Whether OpenAI: GPT-5 Codex supports JSON mode cannot be decided from the name alone. Check model ID openai/gpt-5-codex, provider OpenAI, catalog params, modality, a lightweight runtime probe, and the error body together.

Model: openai/gpt-5-codex
Provider: OpenAI
Capability: JSON mode

How to prove it during checking

Read-only check. Detection data burns after 5 minutes.

Start with the catalog signal: catalog shows support, then verify with a real key in read-only mode.
The capability probe must bind model ID openai/gpt-5-codex; do not test another model from the same provider.
JSON mode · supports include_reasoning · supports max_tokens · supports reasoning · supports response_format

Next action

OpenAI: GPT-5 Codex JSON mode should turn into an operator action: confirm sale tags, fill the capability matrix, change route, suggest a fallback model, or mark unsupported for now.

Read-only check. Detection data burns after 5 minutes.
Catalog signal: catalog shows support
Context: 400,000

Open key checker

Read-only check. Detection data burns after 5 minutes.