Speed

Work mode and Codex share usage. Work mode usage inside ChatGPT uses the same pricing, credits, and usage limits as Codex. See Codex pricing for details.

Fast mode

Codex offers the ability to increase the speed of the model for increased credit consumption.

Fast mode increases supported model speed by 1.5x and consumes credits at a higher rate than Standard mode. It currently supports GPT-5.6, GPT-5.5, and GPT-5.4. GPT-5.6 and GPT-5.5 consume credits at 2.5x the Standard rate; GPT-5.4 consumes credits at 2x the Standard rate.

Use /fast on, /fast off, or /fast status in the CLI to change or inspect the current setting. You can also persist the default with service_tier = "fast" plus [features].fast_mode = true in config.toml. Fast mode is available in the ChatGPT desktop app, Codex CLI, and IDE extension when you sign in with ChatGPT. Fast mode is a ChatGPT credit feature. With an API key, Codex uses API token pricing instead, and ChatGPT credit multipliers don't apply. API Priority processing has its own billing rate; for GPT-5.6, it costs 2x the Standard API token rate.

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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 a supported model 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.