Pi Agent

SDK

Source: https://pi.dev/docs/latest/sdk

Reviewed against Pi 0.99.2 and the package versions listed in ../SKILL.md on 2026-09-30.

The SDK ships in the main package:

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

Use it to embed Pi, build custom UIs, automate workflows, spawn sub-agents, test behavior, or customize tools/resources in process.

Quick Start

import { createAgentSession, ModelRuntime, SessionManager } from "@earendil-works/pi-coding-agent";

const modelRuntime = await ModelRuntime.create();
const { session } = await createAgentSession({
  sessionManager: SessionManager.inMemory(),
  modelRuntime,
});

session.subscribe((event) => {
  if (event.type === "message_update" && event.assistantMessageEvent.type === "text_delta") {
    process.stdout.write(event.assistantMessageEvent.delta);
  }
});

try {
  await session.prompt("What files are in the current directory?");
} finally {
  await session.extensionRunner.emit({ type: "session_shutdown", reason: "quit" });
  session.dispose();
}

createAgentSession() returns { session, extensionsResult, modelFallbackMessage? } and uses DefaultResourceLoader when no resourceLoader is passed.

AgentSession

Methods: prompt(text, options?), steer(text), followUp(text), subscribe(listener) (returns unsubscribe), setModel, setThinkingLevel, cycleModel, cycleThinkingLevel, navigateTree(targetId, { summarize, customInstructions, replaceInstructions, label }), compact(customInstructions?), abortCompaction(), abort(), dispose().

State: sessionFile, sessionId, agent, model, thinkingLevel, messages, isStreaming.

session.agent.state exposes messages, model, thinkingLevel, systemPrompt, tools, streamingMessage, errorMessage; SessionManager is authoritative for finalized context: assigning agent.state.messages does not replace persisted history. Restore external history with SessionManager.inMemory(cwd, options, entries) before creating the session. Use session.waitForIdle() to wait for the full session run.

Session replacement (new/resume/fork/clone/import) lives on AgentSessionRuntime, not AgentSession.

Runtime API

const createRuntime: CreateAgentSessionRuntimeFactory = async ({ cwd, sessionManager, sessionStartEvent }) => {
  const services = await createAgentSessionServices({ cwd });
  return {
    ...(await createAgentSessionFromServices({ services, sessionManager, sessionStartEvent })),
    services,
    diagnostics: services.diagnostics,
  };
};

const runtime = await createAgentSessionRuntime(createRuntime, {
  cwd: process.cwd(),
  agentDir: getAgentDir(),
  sessionManager: SessionManager.create(process.cwd()),
});

await runtime.dispose() emits extension shutdown and releases the active session. AgentSessionRuntime owns newSession(), switchSession(path), fork(entryId), clone via fork(entryId, { position: "at" }), and importFromJsonl(). runtime.session changes after each, so re-subscribe to events and call runtime.session.bindExtensions(...) again if you manage extensions manually. Creation returns runtime.diagnostics; failures throw.

Prompting and Queueing

interface PromptOptions {
  expandPromptTemplates?: boolean;
  images?: ImageContent[];
  streamingBehavior?: "steer" | "followUp";
  source?: InputSource;
  preflightResult?: (disposition: "started" | "queued" | "handled") => void;
}

preflightResult is an internal RPC hook called only after acceptance with a disposition string. It is not called when preflight rejects; it no longer receives a boolean. Failures after acceptance surface through events and messages. prompt() resolves only after the full accepted run finishes, including retries.

Extension commands execute immediately even during streaming. File-based prompt templates expand before sending or queueing. Calling prompt() while streaming without streamingBehavior throws — use session.steer() (delivered after the current assistant turn's tool calls) or session.followUp() (after all work finishes). Both pass through extension input handlers, expand templates, reject extension commands, and return "queued" or "handled".

Events

message_update (with assistantMessageEvent deltas such as text_delta, thinking_delta), tool_execution_start / _update / _end, message_start / message_end, agent_start / agent_end / agent_settled, entry_appended, session_info_changed, thinking_level_changed, turn_start / turn_end, queue_update, compaction_start / compaction_end, auto_retry_start / auto_retry_end, summarization_retry_scheduled / summarization_retry_attempt_start / summarization_retry_finished.

Models and Auth

ModelRuntime replaces the older AuthStorage + ModelRegistry pair (a synchronous ModelRegistry facade remains exported for extension compatibility).

const modelRuntime = await ModelRuntime.create({ authPath, modelsPath, credentials });
modelRuntime.getModel(provider, id);        // built-ins + models.json, no auth check
await modelRuntime.getAvailable();          // only models with valid auth
await modelRuntime.checkAuth(providerId);
modelRuntime.getProviders();                // provider.auth methods and status
await modelRuntime.setRuntimeApiKey(provider, key); // not persisted

Credential priority: runtime overrides → auth.json → configured models.json API key → provider environment/ambient auth (native provider extensions can define their own resolution). getModel(provider, id) from @earendil-works/pi-ai/compat looks up built-ins only. Inject any pi-ai CredentialStore (for example InMemoryCredentialStore) via credentials.

Catalog Refresh and Deadlines

create() restores cached catalogs but does not refresh them from pi.dev by default. Opt in with ModelRuntime.create({ allowModelNetwork: true, modelRefreshTimeoutMs: 15_000 }). Remote catalogs persist to ~/.pi/agent/models-store.json (override with modelsStorePath, or inject modelsStore); refreshes are throttled to once per provider every four hours unless forced, and PI_OFFLINE disables model network access entirely.

Public model/auth operations and ModelRuntime.create({ signal }) accept optional abort signals and are unbounded when omitted — SDK applications own deadline policy:

const result = await modelRuntime.refresh({ providers: ["anthropic"], signal: AbortSignal.timeout(15_000) });
if (result.aborted) console.warn("Catalog refresh timed out; using cached models");
for (const [providerId, error] of result.errors) console.warn(providerId, error);

Force an immediate refresh with await modelRuntime.refresh({ allowNetwork: true, force: true, signal }). Each refresh() starts a new provider generation, so it does not queue behind a stalled refresh and stale generations cannot publish afterward. A failed or timed-out refresh never undoes a successful credential operation.

login(), logout(), setRuntimeApiKey(), and removeRuntimeApiKey() are async and resolve once the affected provider's cached/built-in catalog, composition, and availability snapshot are locally consistent; they do not wait for remote freshness. If credentials committed but local synchronization failed, they reject with the exported CredentialSynchronizationError — inspect providerId, operation, credential, and cause rather than blindly retrying the credential mutation.

To match CLI parsing, use resolveCliModel({ cliModel, modelRuntime }) (uses all registered models so --api-key first-run flows resolve before stored auth exists) and resolveModelScopeWithDiagnostics(patterns, modelRuntime) (matches --models/enabledModels semantics and returns warnings instead of printing).

Session options also accept model, thinkingLevel (off…max), and scopedModels: [{ model, thinkingLevel }] for Ctrl+P cycling. With no model: restore from session, then settings default, then first available.

Tools

Built-ins: read, bash, powershell (native Windows), edit, write, grep, find, ls. Defaults: read, bash, edit, write. tools allowlists, excludeTools disables specific names after the allowlist, noTools: "all" disables everything, noTools: "builtin" keeps extension/custom tools. The edit tool returns details.diff for the TUI and details.patch as a standard unified patch for SDK consumers.

Define custom tools with defineTool() and pass them as customTools; include their names in tools if you use an allowlist. Tool factories are exported too: createCodingTools, createReadOnlyTools, createReadTool, createBashTool, createPowerShellTool, createEditTool, createWriteTool, createGrepTool, createFindTool, createLsTool.

Passing a custom cwd makes createAgentSession() build the selected built-in tools for that directory.

Resource Loading

DefaultResourceLoader discovers extensions, skills, prompts, themes, and context files. Options: cwd, agentDir, additionalExtensionPaths, extensionFactories (bare functions or InlineExtension { name, factory } so the startup list shows <inline:my-provider> instead of <inline:1>), settingsManager, systemPromptOverride, skillsOverride, promptsOverride, agentsFilesOverride, eventBus (from createEventBus()). Call await loader.reload(), then read getExtensions(), getSkills(), getPrompts(), getThemes(), getAgentsFiles().agentsFiles.

cwd drives project discovery (.pi/extensions, .pi/skills, .agents/skills up to the git root, .pi/prompts, AGENTS.md walk-up, session naming); agentDir drives global resources (extensions/, skills/, ~/.agents/skills/, prompts/, AGENTS.md, settings.json, models.json, auth.json, sessions/). With a custom ResourceLoader, cwd/agentDir still influence session naming and tool path resolution but no longer control discovery.

Sessions and Settings

SessionManager.inMemory(cwd?), create(cwd), continueRecent(cwd), open(path), list(cwd), listAll(onProgress?). Tree API: getEntries, getTree, getBranch, getLeafEntry, getEntry, getChildren, getLabel, appendLabelChange, branch, branchWithSummary, createBranchedSession. Full API in references/session-format.md.

SettingsManager.create(cwd?, agentDir?) merges global plus project settings; SettingsManager.inMemory(settings?) avoids file I/O for tests. applyOverrides({ compaction, retry, ... }) layers overrides. Getters/setters are synchronous for in-memory state and enqueue writes asynchronously — call await flush() for a durability boundary and drainErrors() to report write errors yourself (the manager never prints them).

Run Modes

InteractiveMode (full TUI), runPrintMode(runtime, { mode: "text", initialMessage, initialImages, messages }), runRpcMode(runtime). All take an AgentSessionRuntime. InteractiveMode options include migratedProviders, modelFallbackMessage, initialMessage, initialImages, initialMessages.

SDK vs RPC

Prefer the SDK for type safety, same-process integration, direct state access, or programmatic tools/extensions. Prefer RPC for other languages, process isolation, or language-agnostic clients.

Important Exports

createAgentSession, createAgentSessionRuntime, AgentSessionRuntime, createAgentSessionServices, createAgentSessionFromServices, ModelRuntime, ModelRegistry, CredentialSynchronizationError, resolveCliModel, resolveModelScopeWithDiagnostics, DefaultResourceLoader, ResourceLoader type, createEventBus, CONFIG_DIR_NAME, defineTool, getAgentDir, getPackageDir, getReadmePath, getDocsPath, getExamplesPath, SessionManager, SettingsManager, the tool factories above, InteractiveMode, runPrintMode, runRpcMode, and types for options, results, extensions (ExtensionAPI, ExtensionFactory, InlineExtension), tools, skills, and prompt templates.

Native MCP and codemode in SDK hosts

SDK sessions do not load the CLI's built-in extensions automatically. Add createCodemodeExtension(), createToolSearchExtension(), and createMcpExtension() to a DefaultResourceLoader through extensionFactories, enable the tools through defaultTools or MCP exposure, then call await session.bindExtensions({}) so session_start connects MCP servers. For a bare AgentSession, close extension-owned subprocesses before disposing: await session.extensionRunner.emit({ type: "session_shutdown", reason: "quit" }); session.dispose();. session.dispose() alone only disconnects session resources and did not close the MCP fixture in the local check. A host using AgentSessionRuntime should instead await runtime.dispose(). Follow the upstream SDK example.

ModelRuntime now also exposes getModelsOfType, getModelOfType, getAvailableOfType, getAllModels, getAllAvailable, generateImages, and classify. Chat and image entries may share an upstream ID; select by operation type. These operations resolve credentials through the runtime. They may incur provider charges and were not called against live providers in this review.