Speed
Fast mode
Codex offers the ability to increase the speed of the model for increased credit consumption.
Fast mode is currently supported on GPT-5.4. When enabled, speed is increased by 1.5x and credits are consumed at a 2x rate.
Enable it by typing /fast. It is available in Codex IDE Extensions, Codex
CLI, and the Codex app.
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Codex-Spark
GPT-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, Codex-Spark is its own model choice and has its own usage limits.
During research preview Codex-Spark is only available for ChatGPT Pro subscribers.