SoL-Pi

// Overview

SoL-Pi is a standalone extension for the Pi coding agent that packages four reusable efficiency mechanisms. It does not replace the agent or change which model drives it — Pi still controls the main model through its own configuration. What SoL-Pi changes is how many tokens and how many model turns the agent spends getting to the same result on long-horizon coding tasks.

The four mechanisms are Action Fusion, which merges a file edit and the command that immediately follows it into a single tool call rather than paying for a round trip; ObservationPack, which archives large tool outputs locally and leaves only a handle and a short excerpt in context, recalling exact pages when they are actually needed; an Evidence-Preserving Reducer, which lets cheaper agents read diagnostic logs and summarise them, with every quoted line checked against the archived record before a more expensive agent sees it; and Online Context Compact, which treats a completed subtask as a candidate compaction point instead of compacting only when the window runs out.

The mechanisms were selected rather than designed. NVlabs ran an auto-research loop that fanned 152 proposals across independent lineages, each generating trajectory rollouts, analysing them with map-reduce, implementing a candidate, passing a separate reviewer, and finally facing a fully isolated held-out set that no agent inside the loop could see. Four proposals survived. On the 51-task EdgeBench evaluation the resulting harness retains roughly 94% of Pi's average score on both model backends tested while using 45-49% fewer tokens, at about one third less API cost than Pi and 50-54% less than the native Codex and Claude Code harnesses. SoL-Pi is released under the MIT License.

// What it does

• Action Fusion merges an edit and its follow-up command into one tool call, removing a model round trip
• ObservationPack archives large tool outputs on disk, keeping a handle and excerpt in context
• Evidence-Preserving Reducer delegates log reading to cheaper agents, verifying every quoted line against the archive
• Online Context Compact uses completed subtasks as compaction points rather than compacting late
• Each mechanism is independently switchable through a sol-pi.json config file
• Project-level (.pi/sol-pi.json) or user-level (~/.pi/agent/sol-pi.json) configuration

// Getting started

SoL-Pi installs into an existing Pi install through Pi's own extension command. It needs Node.js 22.19 or newer and pins to pi-coding-agent 0.85.1.

npm install --global @earendil-works/pi-coding-agent@0.85.1

pi install git:github.com/NVlabs/SoL-Pi

pi install git:github.com/NVlabs/SoL-Pi --local --approve

{
  "version": 1,
  "actionFusion": true,
  "observationPack": true,
  "evidencePreservingReducer": false,
  "onlineContextCompact": false,
  "cacheWriteReadRatio": 12.5
}

Commands and code are distilled from the project's own documentation — always check the official repo for the latest.

// When to use it

• Cut the token bill of a Pi coding agent that runs continuously on long-horizon tasks
• Keep large test output and build logs out of the context window without losing the ability to re-read them
• Delegate log triage to a cheaper model while keeping quoted evidence verifiable
• Study which harness-level changes actually generalise, using the held-out methodology in the paper

// How SoL-Pi compares

SoL-Pi alongside other open-source coding-agent harnesses & runtimes tools AI/TLDR tracks, ranked by GitHub stars.