fast

A pi extension that provides one /fast toggle for supported OpenAI Codex and Anthropic Claude models. It selects the provider-specific Fast-mode request shape from the currently selected model.

For eligible OpenAI Codex models it injects:

{
  "service_tier": "priority"
}

For eligible Anthropic Claude models it injects:

{
  "speed": "fast"
}

It also adds the required Anthropic beta header value:

anthropic-beta: fast-mode-2026-02-01

Eligibility

OpenAI Fast mode requires all of the following:

• Provider openai-codex.
• API openai-codex-responses.
• Model gpt-5.5, gpt-5.6-sol, gpt-5.6-terra, or gpt-5.6-luna.
• ChatGPT OAuth/subscription auth, not API-key auth.
• No existing service_tier field in the request payload.

Anthropic Fast mode requires all of the following:

• Provider anthropic.
• API anthropic-messages.
• Model claude-opus-4-8 or claude-opus-5.
• No existing speed field in the request payload.

Anthropic Fast mode supports both API-key and Claude Code OAuth access when the account has access to the research preview.

Commands

/fast

Run /fast to toggle Fast mode for the current session/runtime. The enabled state follows model changes: switching between eligible OpenAI and Anthropic models automatically changes the request format without resetting the toggle. The footer shows fast only while the selected model is eligible and Fast mode is enabled.

The extension defaults to off so installing the full collection does not accidentally spend Fast-mode credits.

Config

Optional global config:

~/<pi-config-dir>/agent/extensions/fast.json

Optional project config:

<project>/<pi-config-dir>/fast.json

Here <pi-config-dir> is Pi's runtime config directory name (CONFIG_DIR_NAME; .pi by default). Project config overrides global config after Pi reports that the project is trusted.

{
  "enabled": false,
  "showStatus": true
}

• enabled: default Fast-mode state when there is no session override.
• showStatus: show a compact fast status when Fast mode is active for the selected model.

The unified extension intentionally does not read openai-fast.json or claude-fast.json; those files belong to the provider-specific standalone packages and may contain conflicting defaults.

Install

Standalone npm package

pi install npm:@diegopetrucci/pi-fast

Collection package

pi install npm:@diegopetrucci/pi-extensions

GitHub package

pi install git:github.com/diegopetrucci/pi-extensions

Then reload pi:

/reload

Legacy provider-specific packages

The collection package loads this unified extension instead of openai-fast and claude-fast. Both provider-specific packages remain available as standalone alternatives. Do not load them together with this extension: independent Fast-mode state and duplicate /fast registrations can produce conflicting behavior.

Notes

• Anthropic Fast mode has separate rate limits, costs more than standard speed, and does not share prompt-cache prefixes with standard-speed requests.
• OpenAI Fast mode intentionally does not affect API-key models.
• Existing speed and service_tier fields are never overwritten.
• Cost accounting still depends on the provider reporting the effective tier in its streamed response.