5Codex offers the ability to increase the speed of the model for increased5Codex offers the ability to increase the speed of the model for increased

6credit consumption.6credit consumption.

7 7 

8Fast mode is currently supported on GPT-5.4. When enabled, speed is increased8Fast mode increases supported model speed by 1.5x and consumes credits at a

9by 1.5x and credits are consumed at a 2x rate.9higher rate than Standard mode. It currently supports GPT-5.5 and GPT-5.4,

10consuming credits at 2.5x the Standard rate for GPT-5.5 and 2x the Standard

11rate for GPT-5.4.

10 12 

11Use `/fast on`, `/fast off`, or `/fast status` in the CLI to change or inspect13Use `/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 is14the current setting. You can also persist the default with `service_tier = "fast"` plus `[features].fast_mode = true` in `config.toml`. Fast mode is

20 22 

21## Codex-Spark23## Codex-Spark

22 24 

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,25GPT-5.3-Codex-Spark is a separate fast, less-capable Codex model optimized for

24Codex-Spark is its own model choice and has its own usage limits.26near-instant, real-time coding iteration. Unlike fast mode, which speeds up a

27supported model at a higher credit rate, Codex-Spark is its own model choice

28and has its own usage limits.

25 29 

26During research preview Codex-Spark is only available for ChatGPT Pro subscribers.30During research preview Codex-Spark is only available for ChatGPT Pro subscribers.

27 31