Step‑by‑Step Guide: Integrate the New DeepSeek‑V4‑Flash into Codex (ChatGPT) with Real‑World Tests

DeepSeek announced the official release of DeepSeek‑V4‑Flash API, which natively supports the Responses API format and is pre‑adapted for Codex, allowing Codex users to switch the underlying model without format conversion.

Official benchmarks show DeepSeek‑V4‑Flash surpasses the April‑released DeepSeek‑V4‑Pro‑Preview on several code‑agent and automation tasks: Terminal Bench 2.1 score 82.7 vs 72.1, and improvements on NL2Repo, Cybergym, DeepSWE, Toolathlon‑Verified. In the Frontend Code Arena it ranks 7th with 1,586 points, behind Claude Opus 5 Max (1,704), Kimi K3 Max (1,675) and Claude Opus 5 High (1,664). Its AI Analysis Index (AII) score is 50, comparable to Gemini 3.6 Flash and only about one point lower than GPT‑5.6 Luna and GLM‑5.2.

The model’s token price is $0.14 per million tokens (≈ $0.28 per million), making it the most cost‑effective option among peers.

1. Prerequisites

Install the ChatGPT desktop client and run it once to create the ~/.codex directory.

Obtain an API key from the DeepSeek Open Platform ( https://platform.deepseek.com/api_keys).

2. Configure DeepSeek as the model provider

DeepSeek supplies a one‑click installation script. Execute the appropriate command for your OS:

bash <(curl -fsSL https://cdn.deepseek.com/api-docs/codex-deepseek-setup.sh)

For Windows PowerShell:

irm https://cdn.deepseek.com/api-docs/codex-deepseek-setup-en.ps1 | iex

The script presents a menu; select “1” to modify the Codex configuration and choose deepseek‑v4‑flash as the model. If an API key is not set in the environment, the script will prompt for it; otherwise it reads DEEPSEEK_API_KEY from the environment.

To revert to the default configuration, run the script again and choose option “3”.

3. Example tests

After configuration, the new model appears in the ChatGPT UI. The article demonstrates two prompts:

Data‑visualization dashboard : a request to generate a single‑page HTML dashboard with ECharts, including a line chart, bar chart, pie chart, and gauge, responsive layout, theme switch, and animation.

3‑D interactive solar‑system scene : a request to generate a single‑page HTML file using Three.js, featuring a sun, at least five planets with distinct sizes, colors, orbital speeds, mouse‑drag rotation, zoom, click‑to‑focus with info card, pause/resume button, starfield background, and loading indicator.

Both prompts are followed by the generated HTML code wrapped in

<pre><code>…</code></pre> blocks, and the resulting screenshots are shown.

Reference links for DeepSeek‑V4‑Flash updates, Codex configuration documentation, and the official API are provided at the end of the article.