speed.md Codex Docs, 2026-03-03 18:20 UTC → 2026-03-23 18:22 UTC

1# Speed

2 

3## Fast mode

4 

5Codex offers the ability to increase the speed of the model for increased

6credit consumption.

7 

8Fast mode is currently supported on GPT-5.4. When enabled, speed is increased

9by 1.5x and credits are consumed at a 2x rate.

10 

11Use `/fast on`, `/fast off`, or `/fast status` in the CLI to change or inspect

12the current setting. You can also persist the default with `service_tier = "fast"` plus `[features].fast_mode = true` in `config.toml`. Fast mode is

13available in the Codex IDE extension, Codex CLI, and the Codex app when you

14sign in with ChatGPT. With an API key, Codex uses standard API pricing instead

15and you can't use Fast mode credits.

16 

17[

18Your browser does not support the video tag.

19](/videos/codex/fast-mode-demo.mp4)

20 

21## Codex-Spark

22 

23GPT-5.3-Codex-Spark is a separate fast, less-capable Codex model optimized for near-instant, real-time coding iteration. Unlike fast mode, which speeds up GPT-5.4 at a higher credit rate,

24Codex-Spark is its own model choice and has its own usage limits.

25 

26During research preview Codex-Spark is only available for ChatGPT Pro subscribers.