What Pi is
Pi is an upstream agent harness project. HarnessRouter describes it as an extensible agent harness that can be driven as one of its backends. This page is about the verified relationship between UHP, HarnessRouter and Pi; it does not speak for the Pi project's own roadmap or protocol choices.
What HarnessRouter added
HarnessRouter Community Edition tagged v0.7.0 on 20 August 2026 and added Pi as a backend. The tag's conformance commit reports a Full-class UHP run with 52/52 checks executed through the new Pi backend path, with task checks run on gpt-5.4-mini via TokenRouter.
Conformance evidence through Pi
The v0.7.0 evidence is a published Full-class 52/52 UHP conformance report executed through the Pi harness path. It demonstrates that HarnessRouter's Pi integration satisfies the same Full-class behavioral expectations as its earlier backends. It does not, by itself, expand the UHP conformance suite beyond 52 checks.
The MCP adapter is part of the HarnessRouter path
In HarnessRouter's Pi integration, an MCP adapter is installed alongside Pi. That adapter belongs to the HarnessRouter integration, not to the upstream Pi project. Do not describe this as native MCP support by Pi unless the Pi project states so in its own primary source.
What is not proven
Why the distinction matters
A reference implementation can adapt an existing harness without that harness vendor changing its own API. Native adoption would be a stronger ecosystem signal: it would mean a vendor, tool or independent runtime exposes or consumes UHP directly, reducing dependence on one adapter implementation.
Related pages
Read HarnessRouter Community Edition, conformance, the adoption tracker, the ecosystem map, and the other harness pages: Codex, Claude Code, Hermes, and DeepSeek Harness.