Pi Coding Agent

Operator Read

Pi is a deliberately minimal terminal coding harness maintained by Earendil Works (formerly Mario Zechner / badlogic). What's notable is what it refuses to ship: subagents, plan mode, approval popups, MCP, built-in governance. The core stays small; the platform grows via extensions. The provider list is deliberately volatile -- treat it as "what Pi tests against today," not a forever-API. The canonical repo is now earendil-works/pi.

Where Pi Is Useful

Use Pi when your own wrapper owns the product surface. TypeBox 1.x validation makes custom tools and SDK integrations portable to eval-restricted runtimes such as Cloudflare Workers -- the previous validator couldn't run there. Custom tools can declare terminate: true to end the agent turn on a final tool call and skip the automatic follow-up LLM request -- useful for tools with predictable terminal behavior. If you embed Pi inside your own UI or CI runner, capture stream transport as part of the run contract: stream configuration (SimpleStreamOptions, Transport) is exposed through the harness, but Pi will not record governance receipts for you.

For leaner embeds, register only the providers you ship: the selective provider base entry points (@earendil-works/pi-ai/base, @earendil-works/pi-agent-core/base) let a bundled application register providers explicitly and exclude unused provider transports, shrinking bundle size and removing dead network code paths -- a real win for Cloudflare-Workers-style runtimes.

Tune provider behavior in Pi when local inference or provider SDK behavior is part of the run contract; do not treat defaults as production policy. Timeout and retry controls (retry.provider.timeoutMs, retry.provider.maxRetries, retry.provider.maxRetryDelayMs) are available in /settings. Provider-side prompt caching is tracked accurately where supported: Mistral sessions now use session-affinity prompt caching with cached-token cost accounting, continuing Pi's billing-accuracy cadence.

Findings: 2026-06-23-pi-selective-provider-base-entrypoints, 2026-06-23-pi-mistral-prompt-caching.

What Pi Refuses To Own

Pi's governance posture is explicit refusal: no approval dialogs, no plan mode, no permission popups, no MCP in the default surface. The refusal is the design statement: those concerns belong to the operator or a layer above the harness. No governance additions shipped in this window; the posture is stable. The plan-mode references that surfaced this window are to an extension example, not a core feature -- consistent with Pi's delegation posture.

Findings: 2026-06-23-pi-extension-compaction-event-context.

Harness Receipts To Capture

Pi exposes the right inputs for an operator-owned governance layer to record: session identity through $PI_SESSION_DIR, provider retry/timeout metadata, provider selection, transport type, and extension TypeBox schema version. Pi exposes them cleanly and leaves their recording to the operator.

This window strengthens that thesis at the context-shaping layer: extension compaction events now carry reason and willRetry, so session_before_compact and session_compact can distinguish a manual /compact from threshold auto-compaction from an overflow retry -- compaction is now self-describing and inspectable from the extension surface. An operator-owned governance layer gets a clean hook to record why context was reshaped. Compaction is itself a context-shaping event worth a receipt, and Pi now hands you the inputs to write one.

Findings: 2026-06-23-pi-extension-compaction-event-context.

Maintenance And Hardening

Routine but real CVE-class maintenance landed this window: vulnerable runtime dependencies were updated (including undici and the packaged protobufjs transitive dependency), and deep session branches no longer take quadratic time to build context or branch paths -- the session path construction was linearized (on a 600k-entry pathological session, ~20.3s with Array.unshift() dropped to ~35ms with push() plus reverse()), a low-positive hardening against a pathological-input slowdown. Operators pinning Pi should move past v0.79.8 for the dependency fixes and past v0.79.9 for the session-tree fix.

Findings: 2026-06-23-pi-vulnerable-dependency-update.

Migration Watch

Pin and audit Pi installs during the Earendil Works migration: the npm package is moving from @mariozechner/pi-coding-agent to @earendil-works/pi-coding-agent and the repo from badlogic/pi-mono to earendil-works/pi-mono (now earendil-works/pi). The pi update --self command handles global installs; CI references and infrastructure pins need manual updates. Note a behavior change worth carrying into pinning guidance: bare pi update now updates only Pi -- use pi update --all to bump packages too -- and update installs the exact checked version with no unversioned reinstall fallback.

Posture basis: 2026-05-06-pi-thin-harness-provider-churn, 2026-05-07-pi-thin-harness-churn, 2026-05-12-pi-earendil-migration-and-harness-sdk, 2026-06-23-pi-extension-compaction-event-context, 2026-06-23-pi-selective-provider-base-entrypoints.

Open Questions

• Does the leaner standalone SDK arrive as a fully separate distributable, or stay as composable entry points within the CLI packages? Partially answered (2026-06-23): the /base entry points (@earendil-works/pi-ai/base, @earendil-works/pi-agent-core/base) are a concrete step toward leaner, explicitly-composed SDK consumption -- but they still live inside the same packages rather than a standalone leaner SDK. Watch whether Earendil splits these into a distinct distributable.
• Does the Earendil Works transition include any governance, pricing, cloud, or enterprise changes that would affect Pi's current "no governance in core" posture? Still no (verified 2026-06-23): no plan mode, approval surface, or MCP in core shipped this window; the project-trust system is static and the only /trust touchpoints were documentation/label fixes.
• The $PI_SESSION_DIR env var is exposed to tools and extensions. Is it also exposed to the system prompt or context files, making it available for self-referential session logs?

What To Watch Next

• Source contract update: earendil-works/pi is now confirmed canonical; ensure sources/pi-coding-agent.yml points to the new URL.
• Earendil Works organizational posture: cloud offering, enterprise tier, or governance additions that would change Pi's minimalism claim.
• Whether the /base selective-provider entry points evolve into a fully separate, leaner SDK distributable from the CLI.
• Any plan mode or approval surface addition, which would signal a departure from Pi's core design stance.