Pi (Rust): High-performance AI coding agent CLI written in Rust

Pi (Rust), a high-performance AI coding agent CLI written in Rust, has been released as a port of the original Pi Agent. It offers instant startup, stable streaming, and a smaller memory footprint compared to Node.js or Python-based tools, with security features like capability-gated hostcalls and two-stage extension enforcement. The tool is designed for large-session, multi-agent, and extension-heavy workloads.

pi agent rust - High-performance AI coding agent CLI written in Rust Why Should You Care? why-should-you-care • TL;DR tldr-piopenclaw-users • Methodology benchmark-methodology-and-claim-integrity • Quick Start quick-start • Features features • Installation installation • Commands commands • Configuration configuration Install latest release curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/install.sh?$ date +%s " | bash You want an AI coding assistant in your terminal, but existing tools are: Slow to start : Node.js/Python runtimes add 500ms+ before you can type Memory hungry : Electron apps or heavy runtimes eat gigabytes Unreliable : Streaming breaks, sessions corrupt, tools fail silently Hard to extend : Closed ecosystems or complex plugin systems pi agent rust is a from-scratch Rust port of Pi Agent https://github.com/badlogic/pi by Mario Zechner https://github.com/badlogic made with his blessing . Single binary, instant startup, stable streaming, and 8 built-in tools. Rather than a direct line-by-line translation, this port builds on two purpose-built Rust libraries: : A structured concurrency async runtime with built-in HTTP, TLS, and SQLite asupersync https://github.com/Dicklesworthstone/asupersync : A Rust port of rich rust https://github.com/Dicklesworthstone/rich rust Rich https://github.com/Textualize/rich by Will McGugan https://github.com/willmcgugan , providing beautiful terminal output with markup syntax Start a session pi "Help me refactor this function to use async/await" Continue a previous session pi --continue Single-shot mode no session pi -p "What does this error mean?" < error.log If you already use Pi Agent, especially through OpenClaw, this project keeps the core workflow while upgrading the engine under the hood: Substantially faster in realistic end-to-end flows not synthetic microbenchmarks Dramatically smaller memory footprint in long-running sessions Materially stronger security model for extension/tool execution, including command-level blocking of dangerous extension shell patterns Security is a first-class design goal here, not a bolt-on: - Capability-gated hostcalls tool / exec / http / session / ui / events - Two-stage extension exec enforcement: capability gate first, then command mediation that blocks critical shell classes by default for example recursive delete, disk/device writes, reverse shell and can tighten to block high-tier classes in strict/safe policy - Policy + runtime risk + quota enforcement on the execution path - Per-extension trust lifecycle pending - acknowledged - trusted - killed with kill-switch audit logs and explicit operator provenance - Hostcall-lane emergency controls that can force compatibility-lane execution globally or for one extension when fast-lane behavior needs immediate containment - Structured concurrency via asupersync for more predictable cancellation/lifecycle behavior - Auditable runtime signals/ledgers and redacted security alerts for extension behavior The Rust port is designed around large-session, multi-agent, and extension-heavy workloads. Release-facing performance numbers are published only when the checked-in evidence artifacts are current, have matching run provenance, and report no CI no-data or data-contract failures. Historical benchmark snapshots are retained in planning/evidence artifacts, but they are not treated as current README claims until the performance evidence gate is regenerated cleanly. Extension runtime guarantees are also concrete: | Extension assurance signal | Why you should care | |---|---| Two-stage exec guard exec capability policy + command-level mediation + DCG/heredoc AST signals | Dangerous shell intent is caught before spawn, including destructive payloads hidden in multiline wrappers | Trust lifecycle + kill switch pending/acknowledged/trusted/killed | You can quarantine an extension instantly, log who pulled the switch and why, and require explicit re-acknowledgement before restoring access | Hostcall lane kill-switch controls forced compat global kill switch , forced compat extension kill switch | Fast-path regressions can be contained immediately by forcing compatibility-lane execution without disabling the extension system | | Deterministic hostcall reactor mesh shard affinity, bounded SPSC lanes, backpressure telemetry, optional NUMA slab tracking | Runtime behavior stays predictable under contention; queue pressure and routing decisions are observable instead of opaque | | Startup prewarm + warm isolate reuse for JS runtimes | Runtime creation overlaps startup and warm reuse keeps repeated extension runs low-latency without a Node/Bun process model | Tamper-evident runtime risk ledger verify / replay / calibrate | Security decisions are hash-linked and can be replayed or threshold-tuned from real runtime traces | Bottom line: Pi's architecture targets lower latency, lower memory use, and stronger extension runtime safety under real workload pressure; current numeric claims must come from fresh, provenance-matched evidence artifacts. Data source: docs/planning/BENCHMARK COMPARISON BETWEEN RUST VERSION AND ORIGINAL GPT.md latest secure-path + full orchestrator checkpoints, 2026-04-23 . All numeric performance claims in this README include inline citations with format: from artifact-path , run correlation-id Example: from artifact-path , run correlation-id CI checks both file freshness and artifact content so stale, no-data, or correlation-mismatched evidence cannot back user-facing performance claims. The README evidence checker reports line-numbered proof obligations for cited claims and extracts claim-gated performance phrases for reviewer audit. Explicit historical snapshot citations are mapped separately and do not satisfy current release-facing claims. In this README, we means the project owner and collaborating coding agents. The speed gains come from runtime design, not one trick. | Technique | What we do | Runtime effect | |---|---|---| | Cold-start minimization | Single static binary, no Node/Bun runtime bootstrap, no JIT warmup, startup prewarm for extension runtime paths | Faster time-to-first-interaction | | Less copying on hot paths | Arc / Cow message flow, zero-copy hostcall/tool payload handling, reduced clone-heavy provider/session paths | Lower CPU and allocation pressure | | Deterministic dispatch core | Typed hostcall opcodes, fast-lane/compat-lane routing, bounded shard queues with reactor-mesh telemetry | Better tail latency under concurrent extension load | | Efficient long-session storage | SQLite session index + v2 sidecar segmented log + offset index with O index+tail reopen path | Fast resume on large histories | | Streaming parser tuned for real networks | SSE parser tracks scanned bytes, handles UTF-8 tails, normalizes chunk boundaries, interns event-type strings | Lower streaming overhead and fewer parser stalls | | Safe fast-path controls | Shadow dual execution sampling, automatic backoff on divergence/overhead, compatibility-lane kill switches for containment | Keeps optimizations fast without silent behavior drift | | CI-level performance governance | Scenario matrices, strict artifact contracts, fail-closed perf gates | Regressions are caught before release | If you want the full implementation inventory, see Performance Engineering performance-engineering . The benchmark evidence policy is designed to keep results realistic, reproducible, and hard to game. What we measured: Matched-state workloads : resume a large session and append the same 10 messages. Realistic E2E workloads : resume + append + extension activity + slash-style state changes + forks + exports + compactions. Scale levels : from 100k up to 5M token-class session states. Startup/readiness : command-level readiness --help , --version separately from long-session workflows. How we kept comparisons fair: Two scopes in the benchmark report:- apples-to-apples pi agent rust vs legacy coding-agent - apples-to-oranges legacy stack components included where legacy behavior is outsourced - apples-to-apples Release-mode binaries and repeated runs per matrix cell. No paid-provider noise in core latency/footprint tables provider-call costs are excluded from these core comparisons . How we kept claims honest: Security controls stayed on during secure-path measurements no policy/risk/quota bypasses for speed claims . Raw artifacts are preserved JSON/trace/time outputs and called out in the benchmark report. Blockers are explicitly disclosed : when direct legacy reruns were blocked by missing workspace deps, we state that and compare against prior validated legacy artifacts instead of pretending reruns succeeded. Interpretation notes are explicit : the report distinguishes baseline sections vs fresh reruns so readers can see exactly which values came from which run set. Reproducibility over marketing : methodology, caveats, and known limits are included alongside wins. If you want full details, see: docs/planning/BENCHMARK COMPARISON BETWEEN RUST VERSION AND ORIGINAL GPT.md methodology + results + caveats + raw artifact paths | Feature | Pi Rust | Typical TS/Python CLI | |---|---|---| Startup | <100ms | 500ms-2s | Binary size | ~21.1 MiB default release | 100MB+ with runtime | Memory idle | <50MB | 200MB+ | Streaming | Native SSE parser | Library-dependent | Tool execution | Process tree management | Basic subprocess | Sessions | JSONL with branching | Varies | Unsafe code | Forbidden | N/A | 1 Start an interactive session pi 2 Ask a codebase question pi "Summarize the architecture in src/" 3 Attach a file inline pi @src/main.rs "Explain startup flow" 4 Run single-shot mode for scripting pi -p "List likely regression risks for this diff" 5 Continue your last project session pi --continue 6 Inspect available models/providers pi --list-models pi --list-providers asupersync https://github.com/Dicklesworthstone/asupersync is a structured concurrency async runtime designed for applications that need predictable resource cleanup. Key features used by pi agent rust: Capability-based context : Async functions receive an explicit context that controls what they can do HTTP, filesystem, time . This makes testing deterministic. Cx HTTP client with TLS : Built-in HTTP API with rustls, avoiding OpenSSL dependency hell Structured cancellation : When a parent task cancels, all child tasks cancel cleanly. No orphaned futures. pi agent rust runs on asupersync end-to-end today runtime + HTTP/TLS + cancellation . Provider streaming uses a minimal HTTP client src/http/client.rs feeding a custom SSE parser src/sse.rs . rich rust https://github.com/Dicklesworthstone/rich rust is a Rust port of Will McGugan's Rich https://github.com/Textualize/rich Python library. It provides: Markup syntax : bold red error / renders as bold red text Tables : ASCII/Unicode table rendering with alignment and borders Panels : Boxed content with titles Progress bars : Animated progress indicators Markdown : Terminal-rendered markdown with syntax highlighting Themes : Consistent color schemes across components The terminal UI uses rich rust for all output formatting, providing the same visual quality as Rich-based Python tools. Install latest release binary curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/install.sh?$ date +%s " | bash If you already have the original TypeScript pi installed, the installer asks whether to make Rust Pi canonical as pi and automatically create legacy-pi for the old command. export ANTHROPIC API KEY="sk-ant-..." Interactive mode pi With an initial message pi "Explain this codebase structure" Read files as context pi @src/main.rs "What does this do?" Real-time token streaming with extended thinking support: pi "Write a quicksort implementation" Watch the response appear token-by-token, with thinking blocks shown inline. | Tool | Description | Example | |---|---|---| read | Read file contents, supports images | Read src/main.rs | write | Create or overwrite files | Write a new config file | edit | Surgical string replacement | Fix the typo on line 42 | hashline edit | Precise edits using LINE HASH tags | Apply edits to specific lines using hashline anchors | bash | Execute shell commands with timeout | Run the test suite | grep | Search file contents with context | Find all TODO comments | find | Discover files by pattern | Find all .rs files | ls | List directory contents | What's in src/? | All tools include: - Automatic truncation for large outputs 2000 lines / 1MB - Detailed metadata in responses - Process tree cleanup for bash no orphaned processes Sessions persist as JSONL files with full conversation history: Continue most recent session pi --continue Open specific session pi --session ~/.pi/agent/sessions/--home-user-project--/2024-01-15T10-30-00.jsonl Ephemeral no persistence pi --no-session Sessions support: - Tree structure for conversation branching - Model/thinking level change tracking - Automatic compaction for long conversations Enable deep reasoning for complex problems: pi --thinking high "Design a distributed rate limiter" Thinking levels: off , minimal , low , medium , high , xhigh Skills : Drop SKILL.md under ~/.pi/agent/skills/ or .pi/skills/ and invoke with /skill:name . Prompt templates : Markdown files under ~/.pi/agent/prompts/ or .pi/prompts/ ; invoke via /<template args . Packages : Share bundles with pi install npm:@org/pi-packages skills, prompts, themes, extensions . Pi provides context-aware autocomplete in the interactive editor: : Type @ file references @ followed by a path fragment to attach file contents. The completion engine indexes project files respecting .gitignore via the ignore crate's WalkBuilder , capping at 5,000 entries.: Built-in commands / slash commands /help , /model , /tree , /clear , /compact , /exit and user-defined prompt templates and skills all appear as completions. Fuzzy scoring : Prefix matches rank above substring matches. Results are sorted by match quality, then by kind commands templates skills files paths . Background refresh : A background thread re-indexes the project file tree every 30 seconds, so completions stay current without blocking the input loop. Pi runs in three modes, each suited to different workflows: | Mode | Invocation | Use Case | |---|---|---| Interactive | pi default | Full TUI with streaming, tools, session branching, autocomplete | Print | pi -p "..." | Single response to stdout, no TUI, scriptable | RPC | pi --mode rpc | Headless JSON protocol over stdin/stdout for IDE integrations | Interactive mode provides the full experience: a multi-line text editor with history, scrollable conversation viewport, model selector Ctrl+L , scoped model cycling Ctrl+P / Ctrl+Shift+P , session branch navigator /tree , and real-time token/cost tracking. Print mode sends one message, streams the response to stdout, and exits. Useful for shell scripts and one-off queries. RPC mode exposes a line-delimited JSON protocol for programmatic control. Clients send commands prompt , steer , follow-up , abort , get-state , compact and receive streaming events. This is how IDE extensions and custom frontends integrate with Pi. See RPC Protocol rpc-protocol for the wire format. Pi supports two extension runtime families with capability-gated host connectors: - JS/TS entrypoints run without Node or Bun in an embedded QuickJS runtime. - .native.json descriptors run in the native-rust descriptor runtime. - Extension entrypoints are auto-detected: .js/.ts/.mjs/.cjs/.tsx/.mts/.cts run directly in embedded QuickJS no descriptor conversion . .native.json loads the native-rust descriptor runtime.- One session currently uses one runtime family at a time JS/TS or native descriptor . - Sub-100ms cold load P95 , sub-1ms warm load P99 - Node API shims for fs , path , os , crypto , child process , url , and more - Capability-based security: extensions call explicit connectors tool/exec/http/session/ui with audit logging - Command-level exec mediation: dangerous shell signatures are classified and blocked before spawn, with redacted denial alerts and mediation ledger entries - Trust-state lifecycle and kill-switch controls with audited state transitions pending / acknowledged / trusted / killed - Hostcall reactor mesh with deterministic shard routing, bounded queue backpressure, and optional NUMA-aware telemetry - Runtime prewarm path with warm isolate reuse so extension startup cost is mostly paid before the first prompt /model or Ctrl+L opens a selector focused on models that are ready to run with current credentials. Ctrl+P and Ctrl+Shift+P cycle through the scoped model set without opening the overlay.- Provider IDs and aliases are matched case-insensitively in model selection and /login . - Models that do not require configured credentials can run keyless. Extensions can register tools, slash commands, event hooks, flags, providers, and shortcuts. See EXTENSIONS.md /Dicklesworthstone/pi agent rust/blob/main/docs/planning/EXTENSIONS.md for the full architecture and docs/extension-catalog.json /Dicklesworthstone/pi agent rust/blob/main/docs/extension-catalog.json for the 223-entry catalog with per-extension conformance status and perf budgets. This project validates extension compatibility with a three-track pipeline: Vendored corpus 224 : deterministic conformance, compatibility matrix, and scenario suites. Unvendored corpus 777 : source acquisition and onboarding prioritization. Release-binary live-provider E2E : real target/release/pi execution against a non-mocked provider/model path. - Catch runtime/API regressions in QuickJS host shims and capability policy. - Catch dangerous extension shell call patterns with real command mediation on the release binary path. - Verify extension behavior against real provider responses, not just fixture/mocked flows. - Keep extension support measurable instead of anecdotal. - Produce a prioritized queue for onboarding unvendored candidates into vendored conformance. - Fetch unvendored source corpus - Binary: ext unvendored fetch run - Typical command: cargo run --example ext unvendored fetch run -- run-all --workers 8 --no-probe - Purpose: - Clones GitHub repos and unpacks npm tarballs into .tmp-codex-unvendored-cache/ - Produces machine-readable acquisition status for all unvendored candidates - Clones GitHub repos and unpacks npm tarballs into - Artifacts: tests/ext conformance/reports/pipeline/unvendored fetch probe report.json tests/ext conformance/reports/pipeline/unvendored fetch probe events.jsonl - Binary: - Run end-to-end validation orchestration - Binary: ext full validation - Typical command: cargo run --example ext full validation -- - Stages in order : refresh onboarding queue runs ext onboarding queue conformance shard 0..N runs ext conformance generated sharded matrix conformance failure dossiers provider compat matrix scenario conformance suite auto repair full corpus differential suite optional, enabled via --run-diff ; npm diff via --run-npm-diff - Artifacts: tests/ext conformance/reports/pipeline/full validation report.json tests/ext conformance/reports/pipeline/full validation report.md - Plus stage-specific reports under tests/ext conformance/reports/ - Binary: - Run dev-firstset live-provider gate must pass before release build - Binary: ext release binary e2e - Typical command: cargo build --bin pi --bin ext release binary e2e PI HTTP REQUEST TIMEOUT SECS=0 target/debug/ext release binary e2e --pi-bin target/debug/pi --provider ollama --model qwen2.5:0.5b --jobs 10 --timeout-secs 600 --max-cases 20 --extension-policy balanced --out-json tests/ext conformance/reports/release binary e2e/ollama firstset dev 20260219 jobs10 timeout600.json --out-md tests/ext conformance/reports/release binary e2e/ollama firstset dev 20260219 jobs10 timeout600.md - Purpose: - Proves the current codepath works end-to-end on a representative first-set before paying release-build cost. - Serves as the promotion gate to full release-binary validation. - Gate: - Require pass=20 / total=20 with fail=0 . - Require - Artifacts: tests/ext conformance/reports/release binary e2e/ollama firstset dev 20260219 jobs10 timeout600.json tests/ext conformance/reports/release binary e2e/ollama firstset dev 20260219 jobs10 timeout600.md - Binary: - Run full release-binary live-provider E2E after step 3 passes - Binary: ext release binary e2e - Typical command: cargo build --release --bin pi --bin ext release binary e2e PI HTTP REQUEST TIMEOUT SECS=0 target/release/ext release binary e2e --pi-bin target/release/pi --provider ollama --model qwen2.5:0.5b --jobs 10 --timeout-secs 600 --extension-policy balanced --out-json tests/ext conformance/reports/release binary e2e/ollama full release 20260219 jobs10 timeout600.json --out-md tests/ext conformance/reports/release binary e2e/ollama full release 20260219 jobs10 timeout600.md - Purpose: - Executes target/release/pi directly for each selected extension case. - Uses a live provider/model path default ollama + qwen2.5:0.5b to exercise non-mocked end-to-end behavior. - Emits per-case stdout/stderr captures plus summary artifacts pi.ext.release binary e2e.v1 . - Executes - Artifacts: tests/ext conformance/reports/release binary e2e/ollama full release 20260219 jobs10 timeout600.json tests/ext conformance/reports/release binary e2e/ollama full release 20260219 jobs10 timeout600.md tests/ext conformance/reports/release binary e2e/cases/ - Binary: - Aggregate and triage full validation report.json combines:- Stage-level pass/fail stageSummary , stageResults - Corpus counts corpus - Vendored conformance totals conformance - Provider matrix totals providerCompat - Scenario totals scenario - Review queue + verdict classification reviewQueue , verdictCounts - Stage-level pass/fail - Important interpretation rule: not tested unvendored indicates unvendored candidates not yet in vendored conformance; this is inventory status, not a vendored regression. These runs compile many crates and can be disk-heavy. Point Cargo artifacts and temp files to a large volume: export CARGO TARGET DIR="/data/tmp/pi agent rust cargo/${USER:-agent}/target" export TMPDIR="/data/tmp/pi agent rust cargo/${USER:-agent}/tmp" mkdir -p "$CARGO TARGET DIR" "$TMPDIR" Then run: cargo run --example ext unvendored fetch run -- run-all --workers 8 --no-probe cargo run --example ext full validation -- From: - tests/ext conformance/reports/gate/must pass gate verdict.json generated 2026-05-15T17:03:02.000Z , run local-20260515T170218075Z - tests/ext conformance/reports/health delta/health delta report.json generated 2026-05-13T03:37:59.568Z - tests/ext conformance/reports/journeys/journey report.json generated 2026-05-13T02:59:58.302Z - tests/evidence bundle/index.json generated 2026-05-12T19:26:21.441Z , run local-20260512T192621Z - tests/full suite gate/certification verdict.json generated 2026-05-14T19:59:37.227Z - docs/evidence/dropin-certification-verdict.json generated 2026-05-18T19:37:26Z - Strict drop-in status: 22/22 certification gates PASS, 16/16 blocking gates PASS - CERTIFIED from docs/evidence/dropin-certification-verdict.json; strict replacement wording remains governed by docs/contracts/dropin-certification-contract.json and this verdict artifact - Unified evidence bundle: 29/29 sections present, 0 missing, 0 invalid from tests/evidence bundle/index.json - Extension must-pass gate: 123/123 must-pass extensions passed; informational stretch set 100/101 passed with one non-blocking stretch failure from tests/ext conformance/reports/gate/must pass gate verdict.json - Extension health delta: 223/223 tested extensions passed 100.0% , 0 regressions, 13 fixes vs the 2026-02-07 baseline, with 1 intentionally excluded test fixture disclosed in the report from tests/ext conformance/reports/health delta/health delta report.json - Health-delta full-manifest non-pass extensions: 0 ; base fixtures is a test-only negative fixture excluded from release-facing pass-rate claims with disposition recorded in docs/evidence/extension-health-delta-failure-disposition.json . - Extension journey coverage: 123/123 journey scenarios passed 100.0% ; command, event-subscriber, multi-capability, passive, and tool-provider categories are green from tests/ext conformance/reports/journeys/journey report.json - Stress triage: 1,500 events, 0 errors, p99 latency 396us , RSS growth 0.0% from tests/perf/reports/stress triage.json, run bd-2zcs5.71-darkgoose-20260510T0058Z Latest release curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/install.sh?$ date +%s " | bash Non-interactive + auto PATH update curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/install.sh?$ date +%s " | bash -s -- --yes --easy-mode Pin a release tag curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/install.sh?$ date +%s " | bash -s -- --version v0.1.0 Install from explicit artifact URL + checksum URL curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/install.sh?$ date +%s " | \ bash -s -- \ --artifact-url "https://github.com/Dicklesworthstone/pi agent rust/releases/download/v0.1.0/pi-linux-amd64.tar.xz" \ --checksum-url "https://github.com/Dicklesworthstone/pi agent rust/releases/download/v0.1.0/SHA256SUMS" Skip completion setup CI/non-interactive minimal install curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/install.sh?$ date +%s " | \ bash -s -- --yes --no-completions The installer is idempotent and supports a migration path from TypeScript Pi: - Detect existing TS pi command - Prompt to install Rust Pi as canonical pi - Preserve old CLI behind legacy-pi - Record state for clean uninstall/restore Notable installer flags: --offline TARBALL : enforce offline mode; optional local artifact path .tar.gz , .tar.xz , .zip , or raw binary --artifact-url : force a specific release artifact URL --checksum / --checksum-url : override checksum source for explicit artifacts --sigstore-bundle-url : override Sigstore bundle URL used by cosign verify-blob --completions auto|off|bash|zsh|fish : force shell completion install target off is equivalent to --no-completions --no-completions : disable completion installation --no-agent-skills : skip automatic installation of the pi-agent-rust skill into ~/.claude/skills/ and ~/.codex/skills/ --no-verify : skip checksum + signature verification testing only --artifact-url without --version uses a synthetic tag for release mode only; if artifact download fails, install exits instead of attempting source fallback- Installer honors HTTPS PROXY / HTTP PROXY for all network fetches By default, the installer also installs a pi-agent-rust skill for both Claude Code and Codex CLI: - Claude Code: ~/.claude/skills/pi-agent-rust/SKILL.md - Codex CLI: ~/.codex/skills/pi-agent-rust/SKILL.md or $CODEX HOME/skills/pi-agent-rust/SKILL.md if CODEX HOME is set - During upgrades, installer-managed legacy pre-tool entries from older versions are removed automatically idempotent, path-scoped, and non-destructive when prior installer state is present. Installer regression harness options + checksum + signature + completions : bash tests/installer regression.sh For migration adoption, packaging and invocation compatibility follows this contract: - This section covers packaging/invocation behavior only; functional parity and certification status are tracked in docs/contracts/dropin-certification-contract.json . - Canonical executable name is pi across release assets and installer-managed installs. - Installer-managed installs also create an rpi compatibility launcher when no conflicting rpi command already exists on your PATH. - Existing TypeScript pi installs can be migrated in place; the prior command is preserved as legacy-pi . - If you keep TypeScript pi as canonical --keep-existing-pi , Rust Pi is installed as pi-rust . - On Apple Silicon, the installer prefers the native arm64 artifact even when launched from a Rosetta-translated shell. - Version-pinned installs are supported via install.sh --version vX.Y.Z for deterministic rollouts. - Every GitHub release ships platform binaries plus SHA256SUMS for integrity validation. Representative smoke checks: Canonical command should exist and execute command -v pi pi --version pi --help /dev/null If a TS migration was performed, legacy command remains available command -v legacy-pi && legacy-pi --version Requires Rust nightly 2024 edition features : Install Rust nightly rustup install nightly rustup default nightly Clone and build git clone https://github.com/Dicklesworthstone/pi agent rust.git cd pi agent rust cargo build --release Binary is at target/release/pi ./target/release/pi --version To install system-wide --locked ensures reproducible dependency resolution cargo install --path . --locked Pi has minimal runtime dependencies: fd : Required for the find tool install via apt install fd-find or brew install fd rg : Required for the grep tool install via apt install ripgrep or brew install ripgrep curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/pi agent rust/main/uninstall.sh" | bash By default, uninstall removes installer-managed Rust binaries/aliases and skill directories, then restores a migrated TypeScript pi if one was preserved. pi OPTIONS MESSAGE ... Examples pi Start interactive session pi "Hello" Start with message pi @file.rs "Explain this" Include file as context pi -p "Quick question" Print mode no session Interactive file references: - Type @relative/path in the editor to attach a file’s contents autocomplete inserts the @ form . | Option | Description | |---|---| -c, --continue | Continue most recent session | -r, --resume | Open session picker UI | --session <PATH | Open specific session file | --session-dir <DIR | Override session storage directory for this run | | --session-durability strict | balanced | --no-session | Don't persist conversation | -p, --print | Single response, no interaction | | --mode text | json | --provider <NAME | Force provider for this run aliases supported | --model <MODEL | Model to use auto-select fallback: anthropic/claude-sonnet-4-6 , then anthropic/claude-opus-4-7 , then openai/gpt-5.1-codex | --thinking <LEVEL | Thinking level: off/minimal/low/medium/high/xhigh | --tools <TOOLS | Comma-separated tool list | --api-key <KEY | API key or use provider-specific env vars such as ANTHROPIC API KEY , OPENAI API KEY , etc. | | --extension-policy safe | balanced | | --repair-policy off | suggest | --list-models PATTERN | List available models optional fuzzy filter | --list-providers | List canonical provider IDs, aliases, and auth env keys | --export <PATH | Export session file to HTML | Additional high-leverage flags: --no-migrations to skip startup migration checks --explain-extension-policy to print effective capability decisions and exit --explain-repair-policy to print effective repair-policy resolution and exit Package management pi install <source -l|--local Install a package source and add to settings pi remove <source -l|--local Remove a package source from settings pi update source Update all or one non-pinned packages pi list List user + project packages from settings Configuration pi config Show settings paths + precedence More utility subcommands: Extension catalog index + discovery pi update-index pi search "git" pi info pi-search-agent Environment and extension diagnostics pi doctor pi doctor --only sessions --format json pi doctor --only swarm --format json pi doctor ./path/to/extension --policy safe --fix Read-only swarm progress SLO evaluation from normalized evidence pi swarm-progress --input progress-slo-input.json --format json pi swarm-progress --input progress-slo-input.json --since HEAD~1 --out-json progress-slo.json Session storage migration JSONL - v2 sidecar store pi migrate ~/.pi/agent/sessions --dry-run pi migrate ~/.pi/agent/sessions update-index refreshes extension index metadata used by search and info . search and info let you discover and inspect extension metadata without leaving the CLI. doctor checks config, directories, auth, shell setup, sessions, swarm coordination readiness, and extension compatibility. pi doctor --only swarm --format json also reports cgroup CPU quota, cpuset size, NUMA topology, cgroup memory limits, target/tmp headroom, and recommended concurrency budgets before large multi-agent runs. swarm-progress evaluates a normalized progress SLO snapshot and emits advisory JSON/text only; it does not mutate Beads, git, Agent Mail, RCH, validation broker slots, runpacks, or source files. Operator workflow, privacy boundaries, degraded Agent Mail/RCH interpretation, stale-Beads handling, and no-open-work convergence guidance lives in docs/swarm-operations-runbook.md progress-slo-operator-workflow /Dicklesworthstone/pi agent rust/blob/main/docs/swarm-operations-runbook.md progress-slo-operator-workflow . migrate validates or creates the v2 session sidecar format for faster resume on larger histories. Pi reads configuration from ~/.pi/agent/settings.json : { "default provider": "anthropic", "default model": "claude-opus-4-5", "default thinking level": "medium", "compaction": { "enabled": true, "reserve tokens": 8192, "keep recent tokens": 20000 }, "retry": { "enabled": true, "max retries": 3, "base delay ms": 1000, "max delay ms": 30000 }, "images": { "auto resize": true, "block images": false }, "terminal": { "show images": true, "clear on shrink": false }, "shell path": "/bin/bash", "shell command prefix": "set -e" } Settings are resolved in priority order first match wins : CLI flags --model , --thinking , --provider , etc. Environment variables ANTHROPIC API KEY , PI CONFIG PATH , etc. Project settings .pi/settings.json in the working directory Global settings ~/.pi/agent/settings.json Built-in defaults This means a CLI flag always overrides a settings.json value, and a project-level setting overrides the global one. Skills, prompt templates, themes, and extensions follow the same resolution order: - CLI-specified paths --skill , --prompt-template , --theme , -e - Project directory .pi/skills/ , .pi/prompts/ , .pi/themes/ , .pi/extensions/ - Global directory ~/.pi/agent/skills/ , ~/.pi/agent/prompts/ , etc. - Installed packages ~/.pi/agent/packages/ When multiple resources share the same name, the first occurrence wins. Collisions are logged as diagnostics. Prompt template expansion supports positional arguments: $1 , $2 , $@ all args , and slice syntax ${@:start} , ${@:start:length} . For example, a template invoked as /review src/main.rs --strict receives src/main.rs as $1 and --strict as $2 . | Variable | Description | |---|---| ANTHROPIC API KEY | Anthropic API key | OPENAI API KEY | OpenAI API key | GOOGLE API KEY | Google Gemini API key | AZURE OPENAI API KEY | Azure OpenAI API key | COHERE API KEY | Cohere API key | GROQ API KEY | Groq API key OpenAI-compatible | DEEPINFRA API KEY | DeepInfra API key OpenAI-compatible | CEREBRAS API KEY | Cerebras API key OpenAI-compatible | OPENROUTER API KEY | OpenRouter API key OpenAI-compatible | MISTRAL API KEY | Mistral API key OpenAI-compatible | MOONSHOT API KEY | Moonshot/Kimi API key OpenAI-compatible | DASHSCOPE API KEY | DashScope/Qwen API key OpenAI-compatible | DEEPSEEK API KEY | DeepSeek API key OpenAI-compatible | FIREWORKS API KEY | Fireworks API key OpenAI-compatible | TOGETHER API KEY | Together API key OpenAI-compatible | PERPLEXITY API KEY | Perplexity API key OpenAI-compatible | XAI API KEY | xAI API key OpenAI-compatible | PI CONFIG PATH | Custom config file path | PI CODING AGENT DIR | Override the global config directory | PI PACKAGE DIR | Override the packages directory | PI SESSIONS DIR | Custom sessions directory | ┌─────────────────────────────────────────────────────────────────┐ │ CLI clap │ │ • Argument parsing • @file expansion • Subcommands │ └─────────────────────────────────┬───────────────────────────────┘ │ ┌─────────────────────────────────▼───────────────────────────────┐ │ Agent Loop │ │ • Message history • Tool iteration • Event callbacks │ └────────┬──────────────────────┬──────────────────────┬──────────┘ │ │ │ ┌────────▼────────┐ ┌─────────▼──────────┐ ┌───────▼──────────┐ │ Provider Layer │ │ Tool Registry │ │ Extension Mgr │ │ • Anthropic │ │ • read • bash │ │ • QuickJS JS/TS │ │ • OpenAI Chat/ │ │ • write • grep │ │ • Native descriptor│ │ Responses │ │ • edit • find │ │ runtime │ │ • Gemini/Cohere │ │ • ls │ │ • Capability policy│ │ • Azure/Bedrock │ │ • ext-registered │ │ • Node shims │ │ • Vertex/Copilot│ │ │ │ • Event hooks │ │ • GitLab/Ext │ │ │ │ • Runtime risk ctl │ └────────┬────────┘ └─────────┬──────────┘ └───────┬──────────┘ │ │ │ ┌────────▼─────────────────────▼──────────────────────▼──────────┐ │ Session Persistence │ │ • JSONL format v3 • Tree structure • Session index/cache │ │ • Per-project dirs • Default-enabled SQLite backend support │ └─────────────────────────────────────────────────────────────────┘ Provider-count rule: Pi has 10 native provider implementation modules, counted as the Rust files under src/providers/ excluding mod.rs . Those modules are anthropic , openai , openai responses , gemini , cohere , azure , bedrock , vertex , copilot , and gitlab . User-visible provider IDs, aliases, OpenAI-compatible presets, and extension-provided streamSimple providers are counted separately because several native modules expose multiple routes. No unsafe code : forbid unsafe code enforced project-wide Streaming-first : Custom SSE parser, no blocking on responses Process tree management : sysinfo crate ensures no orphaned processes Structured errors : thiserror with specific error types per component Size-budgeted release profile : LTO + strip + opt-level = "z" for budget-compliant shipping artifacts This Rust port preserves Pi's user experience, but intentionally changes the runtime substrate. The original TypeScript Pi pi-mono , packages/coding-agent is built on Node.js + package-level abstractions. pi agent rust moves those same behaviors onto asupersync primitives so lifecycle guarantees are explicit in the runtime model. | Concern | TypeScript Pi pi-mono baseline | pi agent rust + asupersync | |---|---|---| Runtime model | Node event loop + Promise/AbortSignal conventions | RuntimeBuilder + explicit reactor and runtime handle | Async ownership | Task lifetimes coordinated by framework/library code | Structured task ownership and explicit cross-thread channels TUI/RPC bridging | Cancellation semantics | Primarily API- and tool-layer conventions | Runtime-aware cancellation checks + bounded timeout handling in tools | I/O capability shape | Ambient Node APIs + extension layer policies | Capability-scoped context AgentCx over asupersync::Cx and explicit hostcall policy | HTTP streaming | Provider/client dependent | Purpose-built asupersync HTTP/TLS client feeding custom SSE parser | Deterministic test hooks | Conventional async test setup | asupersync test/runtime hooks used widely in unit/integration tests | Why this is useful in practice: More predictable failure behavior during aborts/timeouts because cancellation is checked in explicit loop boundaries and tool runners. Cleaner resource lifetimes because the runtime, timers, and I/O paths all share one concurrency substrate. Less hidden coupling because the main invariants live in Rust types/algorithms rather than spread across framework conventions. These are the concrete invariants we rely on in this implementation: - Turn-scoped agent lifecycle - The main loop emits AgentStart , TurnStart , TurnEnd , and AgentEnd in a stable order. - Tool recursion is bounded by max tool iterations default 50 to avoid unbounded self-tool loops. - Benefit: stable event ordering for TUI/RPC consumers and predictable termination behavior. - The main loop emits - Abort and timeout behavior is explicit - Agent abort checks happen at turn boundaries and around tool execution. bash timeout follows a clear escalation path: terminate process tree, grace period, then hard kill.- Benefit: fewer "hung" sessions and reduced orphan-process risk during aggressive tool use. - Session writes are crash-resilient - JSONL saves write to a temp file and persist atomically. - Session indexing uses SQLite WAL + lock file coordination for concurrent instances. - Benefit: better durability and resume reliability under multi-process usage. - Compaction is threshold-driven and boundary-aware - Trigger: estimated context tokens exceed context window - reserve tokens . - Cut-point logic prefers user-turn boundaries and preserves recent context budget. - Benefit: compaction recovers context without collapsing near-term task continuity. - Trigger: estimated context tokens exceed - Capability policy is fail-closed and precedence-defined - Resolution order: per-extension deny - global deny - per-extension allow - default caps - mode fallback. - Benefit: policy outcomes are explainable, deterministic, and auditable. - Streaming parser tolerates real network chunking - SSE parser handles CR/LF variants, multi-line data: fields, partial UTF-8 tails, and end-of-stream flush. - Benefit: incremental rendering remains robust across providers and network fragmentation. - SSE parser handles CR/LF variants, multi-line The following asupersync principles are reflected directly in pi agent rust architecture: Single async substrate : runtime, timers, fs, and HTTP/TLS all run on one coherent foundation. Explicit context threading : AgentCx wraps asupersync::Cx at subsystem boundaries agent/tools/session/rpc . Bounded operations over best-effort cleanup : timeout paths and compaction thresholds are parameterized and enforceable. Determinism hooks for tests : timer-driver aware sleeps and asupersync test helpers reduce nondeterministic flakiness. Compared to the original TypeScript implementation, this shifts more correctness responsibility into the runtime and core algorithms themselves, instead of relying primarily on ecosystem conventions. This is a second comparison pass focused on high-impact architectural deltas and rationale. | Area | Original pi-mono packages/coding-agent | pi agent rust | Why this divergence exists | |---|---|---|---| Distribution model | npm package npm install -g @mariozechner/pi-coding-agent | Single Rust binary pi | Remove Node runtime dependency and improve startup/deployment portability | Execution surfaces | Interactive + print + JSON mode + RPC + SDK | Interactive + print + JSON mode + RPC + Rust SDK | Rust SDK provides idiomatic companion API for embedding Pi programmatically documented in docs/sdk.md | Default built-in tool posture | Defaults to read/write/edit/bash others available | Eight built-ins treated as first-class read/write/edit/bash/grep/find/ls/hashline edit | Keep common code-navigation, shell, and hashline-anchored edit workflows available without extra configuration | Extension trust model | Extension/package model documented as full system access | Embedded runtime with capability-gated hostcalls and policy profiles | Reduce ambient authority and make extension behavior auditable/deny-by-default | Session architecture emphasis | JSONL tree session model and branch navigation | JSONL v3 tree + explicit session index SQLite sidecar + default-enabled SQLite session backend support | Faster resume/lookups at scale and safer multi-instance coordination | Streaming transport stack | Node runtime networking stack | Purpose-built HTTP/TLS client + custom SSE parser on asupersync | Tighter control over chunking, parsing, and failure handling in long streams | Cancellation/timeout mechanics | Platform/event-loop cancellation conventions | Explicit abort signaling, bounded tool iterations, process-tree termination | Minimize hangs/orphans and make stop behavior deterministic under load | Runtime context model | Framework-level conventions and extension APIs | Explicit AgentCx / asupersync::Cx capability-scoped context threading | Make effect boundaries and testability first-class architectural constraints | Practical consequence of these deltas: - Extension/package workflows are compatible across both implementations. - The goal is functional equivalence to pi-mono with Rust-idiomatic patterns and performance improvements. - The Rust SDK provides a companion API that delivers equivalent capabilities without requiring TypeScript-specific adaptation patterns. docs/parity-certification.json tracks functional parity progress and certification status. This section compares concrete implementation mechanics for equivalent high-level behavior. | Algorithm | pi-mono baseline mechanism | Rust implementation mechanism | Why the Rust variant exists | |---|---|---|---| Session context rebuild after compaction | buildSessionContext emits compaction summary, then messages from firstKeptEntryId pre-compaction path , then post-compaction entries | to messages for current path uses the same ordering and adds a fallback if first kept entry id is missing | Avoid silent context loss when compaction anchors are orphaned/corrupted | JSONL persistence | Incremental append appendFileSync plus full rewrite writeFileSync for migrations/rewrites | Save via temp file + atomic persist/replace | Keep on-disk session state crash-resilient during save operations | Session discovery/resume | Directory/file scan and mtime sorting of JSONL files | SQLite session index sidecar + WAL + lock file + staleness-triggered full reindex | Bound resume lookup cost and coordinate concurrent processes | Compaction token accounting | Uses assistant usage totalTokens else input+output+cacheRead+cacheWrite plus heuristic trailing estimates | Uses assistant usage total tokens else input+output plus heuristic trailing estimates; fixed image token estimate | Keep accounting stable across providers with uneven cache-token reporting while staying conservative | Cut-point + split-turn handling | Valid cut points exclude tool results; split turns are summarized as history + turn-prefix context | Same cut-point class and split-turn strategy, implemented in Rust entry/message model | Preserve tool-call/result adjacency and turn coherence under budget pressure | Bash timeout/process cleanup | Timeout/abort kills process tree killProcessTree and returns tail-truncated output | Timeout escalation TERM then grace then KILL + process-tree walk + shell exit trap + tail truncation | Enforce bounded cleanup and reduce descendant-process leaks from background jobs | Streaming event decoding | Transport semantics are exposed sse / websocket / auto ; parser details are runtime-internal | Explicit SSE parser with BOM stripping, CR/LF normalization, UTF-8 tail buffering, and flush-on-end | Make byte-to-event behavior deterministic and provider-SDK-independent | The sections above compare mechanics. This section calls out concrete features present in this Rust port that are not part of the pi-mono baseline implementation model. | Rust-port feature | Why it is useful/compelling | |---|---| pi doctor diagnostics command text / json / markdown , --only , --fix , swarm preflight, extension compatibility checks | Gives actionable environment + compatibility diagnostics, supports CI gating non-zero on failures , can auto-fix safe issues like missing dirs/permissions, and reports read-only multi-agent readiness before swarm work | Capability-gated extension policy profiles safe / balanced / permissive with per-extension overrides | Lets operators run shared extensions with explicit capability boundaries instead of ambient full-system access | Secret-aware extension env filtering pi.env blocklist for keys/tokens/secrets | Reduces accidental credential exposure from extension code paths | Per-extension trust lifecycle + kill-switch audit trail pending / acknowledged / trusted / killed , kill switch , lift kill switch | Supports immediate containment, explicit operator provenance, and controlled re-entry after review | Hostcall compatibility-lane emergency controls global/per-extension forced-compat switches + reason codes | Gives operators a deterministic rollback path for fast-lane incidents without losing extension availability | Runtime risk controller for extension hostcalls configurable, fail-closed by default | Adds another enforcement layer beyond static policy for suspicious runtime behavior in extension call flows | Argument-aware runtime risk scoring for shell paths dcg rule hit , dcg heredoc hit , heredoc AST inspection across Bash/Python/JS/TS/Ruby | Detects destructive intent hidden in multiline scripts and wrapper commands before hostcall execution | Tamper-evident runtime risk ledger tooling ext runtime risk ledger verify | replay | Unified incident evidence bundle export risk ledger, security alerts, hostcall telemetry, exec mediation, secret-broker events | Incident response can triage from one structured artifact set instead of stitching ad-hoc logs | Deterministic hostcall reactor mesh with optional NUMA slab pool shard affinity, global-order drain, bounded SPSC lanes, telemetry | Keeps extension dispatch predictable under load and surfaces queue/backpressure behavior for tuning | Warm isolate pool + startup prewarm handoff | Moves JS runtime preparation off the first interactive turn and reuses warmed state safely between runs | Extension preflight static analysis imports/forbidden-pattern scan with policy-aware hints | Catches risky extension patterns before runtime execution | Node/Bun-compatible extension runtime without Node/Bun dependency embedded QuickJS + shims | Runs legacy extension workflows in a single native binary deployment model | Extension compatibility scanner + conformance harness | Makes extension support measurable and auditable instead of anecdotal | SQLite session index sidecar WAL + lock + stale reindex path | Gives fast session resume/list operations at scale without scanning every JSONL file on each query | Session Store V2 rollback and migration ledger segmented log + checkpoints + rollback events | Long-session recovery can unwind to a known checkpoint with explicit migration/rollback provenance | Default-enabled SQLite session storage support sqlite-sessions feature | Supports deployments that want database-backed session persistence in addition to JSONL; disable with --no-default-features when building a minimal binary | Crash-resilient session save path temp file + atomic persist | Improves session-file durability during writes and reduces partial-write failure modes | Unified hostcall dispatcher with typed taxonomy mapping timeout / denied / io / invalid request / internal | Produces consistent extension/runtime error semantics and easier client handling | Fail-closed evidence-lineage gates run id / correlation id + cross-artifact lineage checks | Rejects stale or cherry-picked conformance/perf artifacts at release-gate time | Structured auth diagnostics with stable machine codes | Improves troubleshooting and operational visibility without leaking sensitive credential material | Pi deliberately uses advanced math where it improves runtime behavior or benchmark confidence. The goal is not “fancy formulas in docs”; it is safer policy decisions, faster recovery from workload shifts, and more trustworthy performance attribution. In the extension dispatcher, Pi combines CUSUM and Bayesian online change-point detection to detect load-regime changes early for example when hostcall traffic suddenly spikes or stalls . Intuition: CUSUM catches persistent drift; BOCPD catches sudden regime changes without brittle fixed thresholds. Pi tracks nonconformity scores absolute residuals from the running mean and treats out-of-interval events as anomalies. Intuition: thresholds adapt from recent behavior instead of hard-coding one static latency cutoff. Pi’s safety envelope includes a PAC-Bayes-kl bound over extension outcomes, and can veto aggressive optimization when the bound is too high. Intuition: this gives an explicit uncertainty-aware ceiling on true error risk before allowing more aggressive runtime behavior. Before approving policy moves, Pi evaluates candidate behavior from trace data: Intuition: Pi fails closed if sample support is weak, uncertainty is high, or estimated regret is above threshold. The VOI planner prioritizes probes that provide the most expected learning under a strict overhead budget. Intuition: run only the experiments that are likely to change decisions; skip stale or low-value probes. For phase-1 matrix benchmarking, Pi computes stage attribution weighted by realistic workload size session messages and reports confidence intervals. \frac{\sum i w i,m {i,s}}{\sum i w i,t i}\cdot 100, \quad w i=\text{session messages} i $$ Intuition: prioritize what dominates real end-to-end latency, not just isolated microbench hotspots. Pi also includes an online tuner path for batch/time-slice controls with explicit rollback behavior: \mathrm{clip} \left \tau t - \eta\nabla {\tau}\mathcal{L} t,;\tau {\min},\tau {\max}\right $$ Intuition: the system adapts continuously, but if instantaneous loss exceeds a rollback threshold it immediately returns to a safer profile. | Technique | Where in Pi | Why it helps | |---|---|---| | CUSUM + BOCPD | Extension dispatcher regime detector | Detects traffic regime shifts early and robustly | | Conformal intervals | Safety envelope | Adaptive anomaly gating without static magic numbers | | PAC-Bayes bound | Safety envelope veto path | Fails closed when uncertainty/risk is too high | | IPS/WIS/DR + ESS | Off-policy evaluator | Approves policy changes only with adequate support | | VOI planning | Experiment scheduler | Uses overhead budget on highest-value probes | | Weighted attribution + CI | Phase-1 perf matrix reports | Ranks optimization work by realistic user impact | | OCO + regret rollback | Runtime controller | Adapts under load while bounding unsafe drift | The SSE Server-Sent Events parser is a custom implementation that handles Anthropic's streaming response format. Unlike library-based approaches, the parser operates as a state machine that processes bytes incrementally: Bytes → Line Accumulator → Event Parser → Typed StreamEvent Key characteristics: | Property | Implementation | |---|---| Buffering | Zero-copy where possible; lines accumulated only when incomplete | Event types | 12 distinct variants: MessageStart, ContentBlockStart, ContentBlockDelta, ContentBlockStop, MessageDelta, MessageStop, Ping, Error, and thinking-specific events | Error recovery | Malformed events logged but don't crash the stream | Memory | Fixed-size rolling buffer prevents unbounded growth | The parser handles edge cases like: - Multi-line data: fields concatenated with newlines - Events split across TCP packet boundaries - The event: field appearing before or after data: - CRLF and LF line endings interchangeably Large outputs from tools file reads, command output, grep results must be truncated to avoid exhausting the LLM's context window. The truncation algorithm preserves usefulness while staying within limits: ┌─────────────────────────────────────────┐ │ Original Content │ │ potentially huge │ └─────────────────────────────────────────┘ │ ▼ ┌─────────────────────────────────────────┐ │ HEAD: First N/2 lines │ │ ───────────────────────── │ │ ... X lines truncated ... │ │ ───────────────────────── │ │ TAIL: Last N/2 lines │ └─────────────────────────────────────────┘ Constants: | Limit | Value | Rationale | |---|---|---| MAX LINES | 2000 | Balances context usage vs. completeness | MAX BYTES | 1MB | Prevents binary file accidents | GREP MAX LINE LENGTH | 500 chars | Truncates minified code | The algorithm: - Splits content into lines - If line count exceeds MAX LINES , takes first 1000 and last 1000 - Inserts a marker showing how many lines were omitted - If byte count still exceeds MAX BYTES , applies byte-level truncation - Returns metadata indicating truncation occurred, enabling the LLM to request specific ranges The bash tool must handle runaway processes, infinite loops, and fork bombs without leaving orphans. The implementation uses the sysinfo crate to walk the process tree: // Pseudocode for process cleanup fn kill process tree root pid: Pid { let system = System::new ; let children = find all descendants root pid, &system ; // Kill children first deepest first , then parent for child in children.iter .rev { kill child, SIGKILL ; } kill root pid, SIGKILL ; } Timeout behavior: - Command starts with configurable timeout default 120s - Output streams to a rolling buffer in real-time - On timeout: SIGTERM sent, 5s grace period, then SIGKILL - Process tree walked and all descendants killed - Exit code set to indicate timeout vs. normal termination To avoid orphaned background jobs e.g. cmd & , the bash script installs an EXIT trap that waits for any remaining child processes and then exits with the original command's status. This prevents the common failure mode where killing a shell leaves its children running. Sessions use a tree structure rather than a flat list, enabling conversation branching useful when exploring different approaches : ┌─────────┐ │ Message │ root │ 1 │ └────┬────┘ │ ┌────▼────┐ │ Message │ │ 2 │ └────┬────┘ │ ┌──────────┼──────────┐ │ │ ┌────▼────┐ ┌────▼────┐ │ Message │ │ Message │ branch │ 3 │ │ 3b │ └────┬────┘ └────┬────┘ │ │ ┌────▼────┐ ┌────▼────┐ │ Message │ │ Message │ │ 4 │ │ 4b │ └─────────┘ └─────────┘ JSONL format v3 : Each line is a self-contained JSON object with a type discriminator: {"type":"session","version":3,"cwd":"/project","created":"2024-01-15T10:30:00Z"} {"type":"message","id":"a1b2c3d4","parent":"root","role":"user","content": ... } {"type":"message","id":"e5f6g7h8","parent":"a1b2c3d4","role":"assistant","content": ... } {"type":"model change","id":"i9j0k1l2","parent":"e5f6g7h8","model":"claude-sonnet-4-20250514"} The parent field creates the tree. Replaying a session walks the tree from root to the current leaf. Branching creates a new message with a different parent than the previous continuation. The Provider trait abstracts over different LLM backends: php async trait pub trait Provider: Send + Sync { fn name &self - &str; fn models &self - & Model ; async fn stream &self, context: &Context, options: &StreamOptions, - Result<impl Stream<Item = Result<StreamEvent ; } Context structure: pub struct Context { pub system: Option<String , // System prompt pub messages: Vec<Message , // Conversation history pub tools: Vec<ToolDef , // Available tools with JSON schemas } StreamOptions: pub struct StreamOptions { pub model: String, pub max tokens: u32, pub temperature: Option<f32 , pub thinking: Option<ThinkingConfig , // Extended thinking settings pub stop sequences: Vec<String , } This design allows adding new providers OpenAI, Gemini without modifying the agent loop. Each provider translates the common types to its wire format and emits a unified StreamEvent stream. Long conversations eventually exceed the model's context window. Pi's compaction algorithm reclaims space by summarizing older messages while preserving recent context. The algorithm runs automatically after each agent turn when estimated token usage exceeds context window - reserve tokens : ┌──────────────────────────────────────────────────────────────┐ │ Full Conversation │ │ msg1 → msg2 → msg3 → ... → msgN-5 → msgN-4 → ... → msgN │ │ ├──── older messages ─────┤ ├─── recent messages ──────────┤ │ │ │ │ Step 1: Find cut point at a valid turn boundary │ │ Step 2: LLM summarizes msgs 1..N-5 into compact paragraph │ │ Step 3: Store Compaction entry in session JSONL │ │ Step 4: Next agent call uses summary + msgs N-4..N │ └──────────────────────────────────────────────────────────────┘ Token estimation uses a conservative chars ÷ 4 heuristic for text and a flat 1,200 tokens per image. When an assistant message includes a usage field from the API, that measured value takes precedence over the heuristic. Cut point selection prefers boundaries between complete user-assistant turns. If the budget forces a mid-turn cut, the algorithm includes prefix messages from the split turn so the model retains context about what was being discussed at the boundary. File operation tracking extracts read , write , and edit tool calls from the messages being summarized. The compaction prompt includes these paths so the summary preserves awareness of which files were examined or modified: <read-files src/main.rs src/config.rs </read-files <modified-files src/auth.rs </modified-files Configurable parameters: | Parameter | Default | Purpose | |---|---|---| reserve tokens | 8% of context window | Safety margin for response generation | keep recent tokens | 10% of context window | Minimum recent context preserved | Compaction can also be triggered manually with /compact in interactive mode or the compact RPC command. Pi routes model requests through a provider factory that resolves the correct backend implementation from a provider, model, api tuple. Resolution flow: User specifies --provider openai --model gpt-4o │ ▼ ┌──────────────────────────┐ │ Provider Metadata Table │ Maps "openai" → canonical ID, │ │ determines API type Completions │ │ vs Responses vs custom └────────────┬──────────────┘ │ ┌────────────▼──────────────┐ │ URL Normalization │ Appends /chat/completions, │ │ /responses, or /chat depending │ │ on detected API type └────────────┬──────────────┘ │ ┌────────────▼──────────────┐ │ Compat Config │ Applies per-model overrides: │ │ system role name, max tokens │ │ field name, feature flags └────────────┬──────────────┘ │ ┌────────────▼──────────────┐ │ Provider Instance │ Anthropic | OpenAI | Gemini │ │ Cohere | Azure | Bedrock | ... └───────────────────────────┘ models.json overrides : Users can define custom providers in ~/.pi/agent/models.json or .pi/models.json . Each entry specifies a model ID, base URL, API type, and optional compat flags, letting you route to self-hosted models, proxies, or providers that Pi does not natively support. Compat config handles the differences between OpenAI-compatible APIs: | Override | Example | Purpose | |---|---|---| system role name | "developer" | o1 models use "developer" instead of "system" | max tokens field | "max completion tokens" | Some models require a different field name | supports tools | false | Suppress tool definitions for models that reject them | supports streaming | false | Fall back to non-streaming for incompatible endpoints | custom headers | {"X-Custom": "val"} | Per-provider header injection | Fuzzy matching : When a provider name doesn't match any known provider, Pi computes edit distance against all registered names and suggests the closest match in the error message. Extensions run in an embedded QuickJS runtime rquickjs crate and communicate with Pi through a structured hostcall protocol. This is the mechanism that lets JavaScript code invoke Pi's built-in tools, make HTTP requests, and interact with the session, all without direct OS access. Execution model: ┌─────────────────── QuickJS VM ───────────────────┐ │ │ │ extension.js calls: │ │ pi.tool "read", {path: "src/main.rs"} │ │ │ │ │ ▼ │ │ enqueue HostcallRequest { │ │ call id: "hc-0042", │ │ kind: Tool { name: "read" }, │ │ payload: { path: "src/main.rs" }, │ │ } │ │ │ │ │ ▼ │ │ return Promise resolve/reject stored in map │ │ │ └────────────────────────┬──────────────────────────┘ │ drain hostcall requests │ ▼ ┌─────────────── ExtensionDispatcher ──────────────┐ │ │ │ 1. Check capability policy: │ │ read tool → requires "read" capability │ │ → Policy says: Allow / Deny / Prompt │ │ │ │ 2. If allowed → dispatch to ToolRegistry │ │ → Execute read tool │ │ → Get ToolOutput │ │ │ │ 3. complete hostcall "hc-0042", Ok result │ │ → Resolves the Promise in QuickJS │ │ │ │ 4. runtime.tick │ │ → Drains Promise .then chains │ │ → Extension JS continues execution │ │ │ └───────────────────────────────────────────────────┘ Capability mapping : Each hostcall kind maps to a required capability: | Hostcall | Required Capability | Dangerous? | |---|---|---| pi.tool "read", ... | read | No | pi.tool "write", ... | write | No | pi.tool "bash", ... | exec | Yes | pi.http request | http | No | pi.exec cmd, args | exec | Yes | pi.env key | env | Yes | pi.session op, ... | session | No | pi.ui op, ... | ui | No | pi.log entry | log | No always allowed | Deduplication : Each hostcall's parameters are canonicalized object keys sorted, structure normalized and SHA-256 hashed. Identical requests within a short window can be deduplicated to avoid redundant tool executions. Fast lane vs compatibility lane : Pi has two execution lanes for hostcalls: Fast lane is used when the call shape matches known safe patterns for example common tool and session operations . This avoids extra allocation and parsing work. Compatibility lane is the fallback for uncommon or partially-specified calls.- Both lanes still enforce the same capability policy and permission checks. - Operators can force compatibility-lane routing globally or per extension as an emergency control path. For observability, each call is tagged with a stable lane key for example tool|tool.read|filesystem or tool|fallback|filesystem so latency and failure trends can be grouped consistently. Built-in consistency guard shadow dual execution : Pi can sample a small subset of read-only hostcalls, execute them through both lanes, and compare canonical output fingerprints. If divergence crosses a configured budget, Pi automatically backs off the fast lane for a period. This gives performance wins without silently changing behavior. Adaptive dispatch mode under load : Pi can switch between: sequential fast path for simpler/low-contention workloads interleaved batching when contention and queue pressure rise Mode changes are gated by sample coverage and risk checks, so Pi does not switch based on thin or cherry-picked evidence. Runtime telemetry for debugging and tuning : Pi records structured hostcall telemetry pi.ext.hostcall telemetry.v1 with lane choice, fallback reason, dispatch latency share, marshalling path, and optimization hit/miss fields. This is used by perf reports and reliability diagnostics. Auto-repair pipeline : When an extension fails to load or produces runtime errors, Pi's repair system can automatically fix common issues: | Repair Mode | Behavior | |---|---| Off | No repairs | Suggest | Log suggestions, don't apply | AutoSafe default | Apply provably safe fixes missing file paths, asset references | AutoStrict | Apply aggressive heuristic fixes pattern-based transforms | Compatibility scanner : Before loading, Pi statically analyzes extension source code for imports, require calls, and forbidden patterns eval , Function , process.binding , dlopen . The scan produces a capability evidence ledger that informs policy decisions. Environment variable filtering : Extensions calling pi.env hit a blocklist that denies access to API keys, credentials, tokens, and private keys. The filter blocks exact matches ANTHROPIC API KEY , AWS SECRET ACCESS KEY , suffix patterns API KEY , SECRET , TOKEN , and prefix patterns AWS SECRET , AWS SESSION . Only PI variables are unconditionally allowed. Trust lifecycle and kill switch : Extension trust state is tracked explicitly pending , acknowledged , trusted , killed . A kill switch demotes an extension to killed , quarantines it in the runtime risk controller, emits a critical alert, and writes an audit record. Lifting the switch requires an explicit operator action and moves the extension back to acknowledged . The extension runtime includes a few small decision engines so behavior stays stable as workload patterns change: Value-of-information planner VOI : Ranks candidate probes by "expected learning per millisecond" and picks the best set under a strict overhead budget. Stale or low-value candidates are skipped with explicit reasons. Shard load controller : Adjusts routing weights, batch budgets, and backoff/help factors based on queue pressure, latency, and starvation risk. Damping and oscillation guards prevent overreaction. Policy safety evaluator : Replays historical samples with multiple estimators and only approves a policy when sample support is strong, uncertainty is low, and predicted regret stays within limit. These pieces are intentionally conservative: if confidence is weak, Pi holds steady instead of making an aggressive switch. The interactive mode uses the Elm Architecture Model-Update-View via the charmed rust library family, which is a Rust port of Go's Bubble Tea https://github.com/charmbracelet/bubbletea framework. Component stack: ┌────────────────────────────────────────────────────┐ │ Terminal crossterm │ │ Raw mode │ Alt screen │ Keyboard/Mouse events │ └──────────────────────┬─────────────────────────────┘ │ ┌──────────────────────▼─────────────────────────────┐ │ bubbletea Program Loop │ │ Init → Update Msg → View → render cycle │ └──────────────────────┬─────────────────────────────┘ │ ┌──────────────────────▼─────────────────────────────┐ │ PiApp Model │ │ │ │ ┌─────────────┐ ┌──────────────┐ ┌─────────────┐ │ │ │ TextArea │ │ Viewport │ │ Spinner │ │ │ │ editor │ │ convo │ │ status │ │ │ └─────────────┘ └──────────────┘ └─────────────┘ │ │ │ │ ┌─────────────────────────────────────────────┐ │ │ │ Overlay Stack │ │ │ │ Model Selector │ Session Picker │ /tree │ │ │ │ Settings UI │ Theme Picker │ Branches │ │ │ │ Capability Prompt extension UI │ │ │ └─────────────────────────────────────────────┘ │ └──────────────────────┬─────────────────────────────┘ │ async channels mpsc │ ┌──────────────────────▼─────────────────────────────┐ │ Agent Async Task │ │ Runs on asupersync runtime │ │ Streams provider responses │ │ Executes tools │ │ Sends PiMsg events back to TUI thread │ └────────────────────────────────────────────────────┘ The async/sync bridge : The agent runs on the asupersync async runtime in a separate thread. It communicates with the bubbletea UI thread through mpsc channels. Each streaming event text delta, tool start, tool update, agent done becomes a PiMsg variant delivered to PiApp::update , keeping the UI responsive during API streaming and tool execution. Viewport scrolling : The conversation viewport tracks whether the user is at the bottom. When new content arrives and the user hasn't scrolled up, the viewport auto-follows the stream tail. Scrolling up disables auto-follow; pressing End or typing a new message re-enables it. Overlay system : Modal UIs model selector, session picker, branch navigator, extension capability prompts stack on top of the main conversation view. Each overlay captures keyboard input until dismissed. Only the topmost active overlay receives events. Slash commands available in the interactive editor: | Command | Action | |---|---| /help | Show available commands and keybindings | /model or Ctrl+L | Open model selector with fuzzy search | Ctrl+P / Ctrl+Shift+P | Cycle scoped models forward/backward | /tree | Browse and fork the conversation tree | /clear | Clear conversation and start fresh | /compact | Trigger manual compaction | /thinking <level | Change thinking level mid-conversation | /share | Export session to GitHub Gist | /exit or Ctrl+C | Exit Pi | The RPC mode pi --mode rpc exposes a line-delimited JSON protocol over stdin/stdout for programmatic integration. Each line is a self-contained JSON object. Client → Pi stdin : {"type": "prompt", "message": "Explain this function", "id": "req-001"} {"type": "steer", "message": "Focus on error handling"} {"type": "follow up", "message": "Now add tests"} {"type": "abort"} {"type": "get state"} {"type": "compact", "reserveTokens": 8192, "keepRecentTokens": 20000} Pi → Client stdout : {"type": "agent start", "sessionId": "..."} {"type": "message update", "message": {...}, "assistantMessageEvent": {"type": "text delta", "delta": "The function", "contentIndex": 0}} {"type": "tool execution start", "toolCallId": "...", "toolName": "read", "args": {}} {"type": "tool execution end", "toolCallId": "...", "toolName": "read", "result": {}, "isError": false} {"type": "agent end", "sessionId": "...", "messages": ... } {"type": "response", "id": "req-001", "command": "prompt", "success": true, "data": {"status": "ok"}} I/O architecture : Two dedicated threads handle stdin reading and stdout writing, bridged to the async agent runtime via channels. The stdin thread retries on transient errors to prevent dropped input. The stdout thread flushes after every line to prevent buffering delays. Message queuing : While the agent is streaming a response, incoming messages are routed to one of two queues: | Queue | Behavior | Use Case | |---|---|---| Steering | Interrupts current response; processed on next turn | Course corrections | Follow-up | Queued until current response completes | Sequential instructions | Queue modes All or OneAtATime control whether multiple queued messages are batched into a single turn or processed individually. Extension UI over RPC : When an extension requests user input capability prompt, selection dialog , Pi emits an extension ui request event. The client renders the prompt in its own UI and responds with an extension ui response message. IDE extensions can then present native UI for capability decisions instead of falling back to terminal prompts. Session resume pi -c or pi -r needs to find the most recent session for the current project without scanning every JSONL file on disk. Pi maintains a SQLite index session-index.sqlite that provides constant-time lookups. Schema: CREATE TABLE sessions path TEXT PRIMARY KEY, id TEXT NOT NULL, cwd TEXT NOT NULL, timestamp TEXT NOT NULL, message count INTEGER NOT NULL, last modified INTEGER NOT NULL, size bytes INTEGER NOT NULL, name TEXT ; Update lifecycle: - After saving a session JSONL file, Pi upserts its metadata into the index pi -c queries WHERE cwd = ? ORDER BY last modified DESC LIMIT 1 pi -r queries the same table and presents a picker sorted by recency Concurrency : A file-based lock session-index.lock serializes writes from concurrent Pi instances. Reads use WAL mode for non-blocking access. Staleness-based reindexing : If the index is older than a configurable threshold, Pi runs a full re-scan of the sessions directory to catch files created by other instances or manual edits. The re-scan keeps the index accurate without a centralized daemon. Pi also supports a v2 sidecar store next to JSONL sessions for faster resume and stronger corruption checks on long histories. What it adds: - Segmented append log files instead of one ever-growing JSONL file - Offset index rows for direct seeks and fast tail reads - Periodic checkpoints and a manifest snapshot - Migration ledger entries for auditability - Checkpoint-based rollback path with explicit rollback event logging How resume works: - If a v2 sidecar exists and is fresh, Pi opens from the sidecar index + segments. - If sidecar data is stale relative to the source JSONL, Pi falls back to JSONL parsing. - If index data is missing/corrupt but segments are valid, Pi rebuilds the index. Integrity strategy: - Segment frames carry payload and chain hashes. - Index rows store byte offsets plus CRC32C checksums. - Validation checks offset bounds, checksum matches, and frame/index alignment before trusting the sidecar. - Truncated trailing frames are recoverable during rebuild; non-EOF frame corruption fails closed instead of silently dropping data. CLI support: pi migrate <path --dry-run validates migration without writing. pi migrate <path performs JSONL-to-v2 migration and verifies parity. Beyond simple API keys, Pi supports OAuth, AWS credential chains, service key exchange, and bearer-token auth. Credentials are stored in ~/.pi/agent/auth.json with file-locked access to prevent corruption from concurrent instances. Stored API keys can be literal strings, $ENV:VAR NAME references, or $CMD:shell command / $COMMAND:shell command sources that resolve trimmed stdout at request time. | Mechanism | Providers | Details | |---|---|---| API Key | Anthropic, OpenAI, Gemini, Cohere, and many OpenAI-compatible providers | Static key via env var or settings | OAuth | Anthropic, OpenAI Codex, Google Gemini CLI, Google Antigravity, Kimi for Coding, GitHub Copilot, GitLab, and extension-defined OAuth providers | PKCE/state-validated flow with automatic refresh; Kimi uses device flow | AWS Credentials | Bedrock | Access key + secret + optional session token; region-aware | Service Key | SAP AI Core | Client ID/secret exchange for bearer token | Bearer Token | Custom providers | Static token in auth storage | OAuth token lifecycle: - User runs pi with an OAuth-configured provider - Pi checks auth.json for an existing token - If missing: opens browser to authorization URL, user authenticates, Pi receives authorization code, exchanges it for access + refresh tokens, stores both with expiry timestamp - If expired but refresh token valid: exchanges refresh token for new access token, updates auth.json - Bearer token attached to API requests Google CLI-style OAuth providers carry project metadata with the token payload. Pi preserves and refreshes that payload and can resolve project IDs from GOOGLE CLOUD PROJECT or local gcloud config when needed. Credential status reporting : pi config shows the status of each configured provider's credentials: Missing , ApiKey , OAuthValid with time until expiry , OAuthExpired with time since expiry , AwsCredentials , or BearerToken . Diagnostic codes : Auth failures produce specific diagnostic codes MissingApiKey , InvalidApiKey , QuotaExceeded , OAuthTokenRefreshFailed , MissingAzureDeployment , MissingRegion , etc. with context-specific error hints rather than generic messages. Read file contents optionally images : Input: { "path": "src/main.rs", "offset": 10, "limit": 50 } - Supports images jpg, png, gif, webp with optional auto-resize - Streams file bytes in chunks with hard size limits to reduce peak memory usage - Applies defensive image decode limits to block decompression-bomb/OOM inputs - Truncates at 2000 lines or 1MB - Returns continuation hint if truncated Execute shell commands with timeout and output capture: Input: { "command": "cargo test", "timeout": 120 } - Default 120s timeout, configurable per-call - Set timeout: 0 to disable the default timeout - Process tree cleanup on timeout kills children - Rolling buffer for real-time output - Full output saved to temp file if truncated Surgical string replacement: Input: { "path": "src/lib.rs", "old": "fn foo ", "new": "fn bar " } - Exact string matching no regex - Fails if old string not found or ambiguous - Returns diff preview Search file contents: Input: { "pattern": "TODO", "path": "src/", "context": 2, "limit": 100 } - Regex patterns supported - Context lines before/after matches - Respects .gitignore Discover files by pattern: Input: { "pattern": " .rs", "path": "src/", "limit": 1000 } - Glob patterns via fd - Sorted by modification time - Respects .gitignore List directory contents: Input: { "path": "src/", "limit": 500 } - Alphabetically sorted - Directories marked with trailing / - Truncates at limit CLI tools have different performance requirements than servers or GUI applications. The critical metric is time-to-first-interaction : how quickly can the user start typing after invoking the command?