Codex Fast mode: how much faster it burns your usage

Fast mode trades allowance for speed. OpenAI's own numbers, and what they mean for a 5-hour window.

Data verified 2026-10-13 from official pricing pages.

OpenAI's published multipliers

Mode	Included plan limits	Purchased credits / Enterprise pay-as-you-go
Standard	1x	1x
Fast	2.5x	2x
Ultrafast (GPT-6 Astra, GPT-6.1 Sol; Pro $500 and eligible Enterprise/Edu)	8x	6x

Fast mode speeds up supported models, including GPT-6.1 Sol, GPT-6 Astra, GPT-6 Sol and GPT-6 Luna, where available. For GPT-5.6 the speed increase is 1.5x.
Toggle it with /fast in the CLI. It's available in the ChatGPT desktop app, Codex CLI and IDE extension when signed in with ChatGPT.
With an API key, ChatGPT credit multipliers don't apply; Codex uses API token pricing.
OpenAI notes workspace admins can set whether Fast Mode is on by default, and that it is enabled by default.

What 2.5x means for your allowance

Our arithmetic, assuming usage scales linearly: OpenAI's Plus estimate of 15-160 local GPT-6.1 Sol messages per 5 hours would shrink to roughly 6-64 messages in Fast mode (15÷2.5 and 160÷2.5). That's an illustration, not an OpenAI figure.

Tip: keep Fast off for long, unattended or batch work, and turn it on only when you're waiting on the result. If you're near a limit, OpenAI suggests switching to a lower-cost model. See Codex pricing and how to stop hitting usage limits.

Sources

OpenAI: Speed (Fast and Ultrafast modes) (checked Oct 16, 2026)
OpenAI Help Center: ChatGPT Rate Card (checked Oct 16, 2026)
OpenAI Help Center: Using Codex with your ChatGPT plan (checked Oct 16, 2026)

FAQ

How much faster does Fast mode use my Codex limit?

OpenAI says Fast mode uses included subscription limits at 2.5x the Standard rate. Purchased credits and Enterprise pay-as-you-go usage are billed at 2x.

What about Ultrafast?

Ultrafast (GPT-6 Astra and GPT-6.1 Sol) uses included limits at 8x and credits at 6x. It's available on Pro $500 and eligible Enterprise and Edu plans, not other self-serve plans.

Does Fast mode apply when I use an API key?

No. With an API key, Codex uses API token pricing and ChatGPT credit multipliers don't apply.