fast

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

For eligible direct OpenAI API-key models it injects:

{
  "service_tier": "fast"
}

For eligible direct OpenAI ChatGPT OAuth models it injects:

{
  "service_tier": "priority"
}

For eligible OpenAI Codex OAuth 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

Direct OpenAI API Fast mode requires all of the following:

• Provider openai.
• API openai-responses or openai-completions.
• Model gpt-6.1-sol, gpt-6-astra, gpt-6-sol, or gpt-6-luna.
• API-key auth sets service_tier: "fast"; Pi's openai ChatGPT OAuth sets priority.
• No existing service_tier field in the request payload.

The direct OpenAI route stays on OpenAI's direct API contract but selects the tier by auth type. OAuth uses priority because its endpoint rejected fast; acceptance or application of priority on Pi's OAuth endpoint has not been live-verified. This direct route is never forwarded to legacy openai-codex or its subscription-usage endpoint. The request shape is support evidence, not certification; tests use mocked eligibility and payloads only, with no live or paid provider calls.

Ultrafast support (initial, fail-closed)

Ultrafast is intentionally narrower than ordinary Fast mode. It requires all of the following on every activation and provider request:

• Provider openai.
• API openai-responses.
• Model gpt-6-astra.
• Direct API-key auth, not Codex OAuth or direct OpenAI OAuth.
• Base URL exactly https://api.openai.com/v1 (a single trailing slash is also accepted).

It does not support Chat Completions, preview models, regional or proxy endpoints, or Anthropic Ultrafast. Eligible payloads receive the requested service_tier: "ultrafast" only when they do not already contain a service_tier field. Existing values and mismatched/malformed payloads are left untouched. The extension reports a requested tier; it does not claim that OpenAI accepted or applied it, and it never silently falls back to ordinary Fast.

OpenAI documents this request shape in the Ultrafast API guide and lists the account/model pricing in its API pricing. Actual Ultrafast API pricing is 6x Standard, while Pi's current cost display omits that premium. Treat the activation warning as a deliberate paid-usage warning.

OpenAI Codex 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, gpt-5.6-luna, gpt-6-astra, gpt-6.1-sol, gpt-6-sol, or gpt-6-luna.
• ChatGPT OAuth/subscription auth, not API-key auth.
• No existing service_tier field in the request payload.

Codex evidence, 2026-10-03: the maintainer's PR #103 review reports that the Codex model list advertises Fast as priority for gpt-6-astra, gpt-6.1-sol, gpt-6-sol, and gpt-6-luna. The official Codex CLI sends Fast as priority. The maintainer's live check through Pi 1.0.0 on that date returned HTTP 200 and completed normally for gpt-6-astra and gpt-6.1-sol; gpt-6-sol and gpt-6-luna are enabled based on the model list only. In that check, response.completed always reported service_tier: "default", with or without priority, so the response cannot confirm Fast was applied.

Pi trusts the requested tier and applies a 2× multiplier to its displayed cost estimate for priority; this does not measure included subscription allowance consumption or confirm Fast was applied. OpenAI's Codex speed documentation, checked on 2026-10-03, lists gpt-6-sol and gpt-6-luna among supported Fast models where available. It specifies 2.5× the Standard rate for included subscription limits and 2× for purchased credits and Enterprise pay-as-you-go billing. Treating Pi's 2× estimate as a subscription-limit multiplier would understate the documented allowance consumption.

Anthropic Fast mode requires all of the following:

• Provider anthropic.
• API anthropic-messages.
• Model claude-opus-4-8, claude-opus-5, or claude-opus-5-5.
• 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
/ultrafast
/fast ultrafast

Run /fast to toggle ordinary 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.

/ultrafast and /fast ultrafast are equivalent toggles for the session-only Ultrafast override. Ultrafast defaults off, is never enabled by global or project configuration, and can be undone with either command. Running ordinary /fast while Ultrafast is selected turns Ultrafast off rather than silently switching to another paid tier. Switching to an unsupported model or endpoint disables Ultrafast and does not re-enable it when gpt-6-astra is selected again. The footer uses ultrafast while an eligible request is selected; status text says that the tier is requested, not remotely applied.

The extension defaults to off so installing the full collection does not accidentally spend Fast-mode credits. Ultrafast verification is mocked-only: tests use local eligibility checks, fake payloads, and a fake fetch through Pi's openai-responses streamSimple; they make no live or paid provider requests.

Config

Optional global config:

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

Optional project config, from the nearest ancestor of the working directory (the working directory itself counts):

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

Here <pi-config-dir> is Pi's runtime config directory name (CONFIG_DIR_NAME; .pi by default). The loader uses that nearest ancestor fast.json, which 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 reads only fast.json. It does not read openai-fast.json or claude-fast.json.

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 only (extensions/fast/index.ts). openai-fast and claude-fast remain published as deprecated standalone leftovers. On session start they warn, clear their leftover footer status, and remove fast-mode-2026-02-01 from the current model header. They do not read config, register commands, or inject Fast fields into requests.

Notes

• Anthropic Fast mode has separate rate limits, costs more than standard speed, and does not share prompt-cache prefixes with standard-speed requests.
• Direct OpenAI Fast mode is limited to the confirmed GPT-6 API models above; Fast pricing, availability, and rate limits remain provider- and account-dependent.
• Authoritative support evidence: OpenAI Fast mode explicitly uses gpt-6.1-sol with service_tier: "fast" and documents priority as an equivalent alias for supported API models; the GPT-6.1 Sol model page documents the model itself.
• Codex Fast availability depends on plan, client, workspace settings, and rollout. Local eligibility is not live-provider certification.
• Pi's provider catalog remains the source of reported model pricing, including any tiered pricing; this extension does not apply guessed discounts or rewrite cost metadata.
• OpenAI Codex Fast mode intentionally does not affect API-key models.
• Deprecated openai-fast and claude-fast packages no longer implement Fast mode. New provider/auth behavior belongs only to this unified extension.
• Existing speed and service_tier fields are never overwritten.
• Pi's model catalog may not include a Fast-mode premium. Cost accounting depends on the provider reporting the effective tier in its streamed response, and this extension does not patch usage totals.