本文宣布了 OpenAI 的 `gpt-5-codex` 模型的完整 API 发布，该模型之前仅限于 CLI 工具。文章详细说明了其定价与 `gpt-5` 相同，并强调了缓存输入 token 的 90% 显著折扣，这对 Agentic 工作流程的成本控制至关重要。该模型可通过 Responses API 访问，需要 `llm-openai-plugin` 进行 LLM 集成，新增的工具支持大部分由 GPT-5 Codex 自动生成。文章重点介绍了该模型在 Agentic 和交互式编码方面的专业性质，提倡“少即是多”的提示原则，因为它内置了编码最佳实践。实际演示包括 pelican 基准测试和成功的多模态图像描述，展示了其多功能能力。
GPT-5-Codex. OpenAI half-relased this model earlier this month, adding it to their Codex CLI tool but not their API.
Today they've fixed that - the new model can now be accessed as gpt-5-codex. It's priced the same as regular GPT-5: $1.25/million input tokens, $10/million output tokens, and the same hefty 90% discount for previously cached input tokens, especially important for agentic tool-using workflows which quickly produce a lengthy conversation.
It's only available via their Responses API, which means you currently need to install the llm-openai-plugin to use it with LLM:
llm install -U llm-openai-plugin
llm -m openai/gpt-5-codex -T llm_version 'What is the LLM version?'
Outputs:
The installed LLM version is 0.27.1.
I added tool support to that plugin today, mostly authored by GPT-5 Codex itself using OpenAI's Codex CLI.
The new prompting guide for GPT-5-Codex is worth a read.
GPT-5-Codex is purpose-built for Codex CLI, the Codex IDE extension, the Codex cloud environment, and working in GitHub, and also supports versatile tool use. We recommend using GPT-5-Codex only for agentic and interactive coding use cases.
Because the model is trained specifically for coding, many best practices you once had to prompt into general purpose models are built in, and over prompting can reduce quality.
The core prompting principle for GPT-5-Codex is “less is more.”
I tried my pelican benchmark at a cost of 2.156 cents.
llm -m openai/gpt-5-codex "Generate an SVG of a pelican riding a bicycle"
I asked Codex to describe this image and it correctly identified it as a pelican!
llm -m openai/gpt-5-codex -a https://static.simonwillison.net/static/2025/gpt-5-codex-api-pelican.png \
-s 'Write very detailed alt text'
Cartoon illustration of a cream-colored pelican with a large orange beak and tiny black eye riding a minimalist dark-blue bicycle. The bird’s wings are tucked in, its legs resemble orange stick limbs pushing the pedals, and its tail feathers trail behind with light blue motion streaks to suggest speed. A small coral-red tongue sticks out of the pelican’s beak. The bicycle has thin light gray spokes, and the background is a simple pale blue gradient with faint curved lines hinting at ground and sky.
