pi-codex-fast

This pi extension adds Fast and Ultrafast service tiers to supported OpenAI requests.

Usage

Inside pi:

• /codex-fast toggles Fast mode.
• /codex-ultrafast toggles Ultrafast mode.

From CLI:

• pi --fast
• pi --ultrafast

You cannot enable both modes at the same time.

Persistence

The extension reads the mode from these pi settings files:

• global: $PI_CODING_AGENT_DIR/settings.json (or ~/.pi/agent/settings.json)
• project override: <cwd>/.pi/settings.json

Use the key pi-codex-fast.mode. The allowed values are off, fast, and ultrafast. The extension also accepts the old enabled key.

Writes go to the global settings file.

Behavior

Fast mode sets service_tier: "priority" for these models:

• openai-codex/gpt-5.4
• openai-codex/gpt-5.5
• openai-codex/gpt-5.6-sol
• openai-codex/gpt-5.6-terra
• openai-codex/gpt-5.6-luna
• openai-codex/gpt-6-astra
• openai-codex/gpt-6-sol
• openai-codex/gpt-6-luna
• openai-codex/gpt-6.1-sol

Ultrafast mode sets service_tier: "ultrafast" for these models:

• openai/gpt-5.6-sol
• openai/gpt-6-astra
• openai-codex/gpt-6-astra

Before you use Ultrafast mode, check the Codex access requirements or the API access requirements.

The extension does not change other requests.

Example benchmark

A local live benchmark is available in this repository under evals/. Three paired trials per model produced:

| Model | TTFB speedup | Turn speedup | Wall speedup | | --- | ---: | ---: | ---: | | gpt-5.6-sol | 1.52x | 1.58x | 1.57x | | gpt-5.6-terra | 1.05x | 1.34x | 1.33x | | gpt-5.6-luna | 1.30x | 2.31x | 2.25x | | gpt-6-astra | 2.24x | 2.59x | 2.55x | | gpt-6-sol | 1.25x | 1.07x | 1.06x | | gpt-6-luna | 1.02x | 2.02x | 1.98x | | gpt-6.1-sol | 2.74x | 1.92x | 1.89x |