Pi Agent

Custom Providers

Source: https://pi.dev/docs/latest/custom-provider

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

Extensions register providers with pi.registerProvider() for proxies, private deployments, OAuth/SSO, and non-standard streaming APIs. Two forms exist: a complete pi-ai Provider (preferred when you need custom authentication, filtering, refresh, or streaming) and the legacy provider-config object. models.json overrides compose above registered native providers.

Complete Provider Form

import { createProvider } from "@earendil-works/pi-ai";
import * as openaiCompletionsApi from "@earendil-works/pi-ai/api/openai-completions";
import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";

export default function (pi: ExtensionAPI) {
  pi.registerProvider(createProvider({
    id: "native-local",
    name: "Native Local",
    baseUrl: "http://localhost:8080/v1",
    auth: {
      apiKey: {
        name: "Local server API key",
        async login(interaction) {
          return { type: "api_key", key: await interaction.prompt({ type: "secret", message: "API key" }) };
        },
        async resolve({ credential }) {
          return credential?.key ? { auth: { apiKey: credential.key }, source: "stored API key" } : undefined;
        },
      },
    },
    models: [],
    api: openaiCompletionsApi,
  }));
}

The object form accepts a complete Provider, including native auth, getModels, refreshModels, filterModels, stream, and streamSimple.

Legacy Config Form

// Override baseUrl and/or headers only — existing models are preserved
pi.registerProvider("anthropic", { baseUrl: "https://proxy.example.com" });
pi.registerProvider("openai", { headers: { "X-Custom-Header": "value" } });

// New provider with models — replaces all existing models for that provider
pi.registerProvider("my-provider", {
  name: "My Provider",
  baseUrl: "https://api.example.com",
  apiKey: "$MY_API_KEY",
  api: "openai-completions",
  models: [{
    id: "my-model",
    name: "My Model",
    reasoning: false,
    input: ["text", "image"],
    cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
    contextWindow: 128000,
    maxTokens: 4096,
  }],
});

Use an async extension factory for dynamic model discovery so models are registered before startup finishes and are visible to pi --list-models. Dynamic providers can also implement refreshModels(context). Complete Providers return nothing and call context.publish({ update }) to install provider-owned state exposed by getModels(). Legacy config callbacks return model definitions. Use the generation-checked publish persistence contract, never the removed context.store pattern; pass context.signal to I/O.

pi.unregisterProvider(name) removes that provider's dynamic models, API key fallback, OAuth registration, and custom stream handlers, restoring overridden built-in behavior. Calls made after the initial load phase take effect immediately — no /reload.

API Types

anthropic-messages, openai-completions, openai-responses, azure-openai-responses, openai-codex-responses, mistral-conversations, google-generative-ai, google-vertex, bedrock-converse-stream.

Most OpenAI-compatible providers work with openai-completions; use model-level thinkingLevelMap for thinking levels and compat for quirks (full flag list in references/models.md). xhigh and max are opt-in and require non-null map entries. Mistral moved from openai-completions to mistral-conversations (native Mistral Chat Completions streaming) — use the latter for native Mistral models.

Auth Header and Secrets

authHeader: true adds Authorization: Bearer <apiKey>; the key is resolved per request and an explicit request Authorization header wins. apiKey and custom header values use the same syntax as models.json: leading !command executes for the whole value, $ENV/${ENV} interpolate, $$ and $! escape literals.

OAuth

oauth: {
  name: "Corporate AI (SSO)",
  async login(callbacks: OAuthLoginCallbacks): Promise<OAuthCredentials>,
  async refreshToken(credentials: OAuthCredentials, signal: AbortSignal): Promise<OAuthCredentials>,
  getApiKey(credentials: OAuthCredentials): string,
}

OAuthLoginCallbacks: onAuth({ url }) (open in browser), onDeviceCode({ userCode, verificationUri, intervalSeconds?, expiresInSeconds? }), onProgress?(message), onPrompt({ message }): Promise<string>, onSelect({ message, options: { id, label }[] }): Promise<string | undefined>.

OAuthCredentials is { refresh, access, expires } (expiry in ms), persisted in ~/.pi/agent/auth.json. Users authenticate with /login <provider-name>. refreshToken receives an AbortSignal — pass it to blocking I/O and call signal.throwIfAborted() early.

Custom Streaming

Implement streamSimple(model, context, options?) with a normalized TranscriptContext: read prompt/tools with getCurrentSystemPrompt(context.messages) and getCurrentTools(context.messages), or use collapseSystemMessages(context) for transports that cannot represent mid-conversation updates. Do not read removed context.systemPrompt/context.tools. Return an AssistantMessageEventStream from createAssistantMessageEventStream(). Initialize an AssistantMessage (role, content: [], api, provider, model, zeroed usage, stopReason: "pending", timestamp), then:

1. stream.push({ type: "start", partial: output })

2. Content events, tracking contentIndex per block: text_start, text_delta, text_end, thinking_start, thinking_delta, thinking_end, toolcall_start, toolcall_delta, toolcall_end

3. stream.push({ type: "done", reason, message }) or { type: "error", reason, error }, then stream.end()

stopReason: "pending" marks the partial message; set a terminal reason before pushing done (throw for "error"/"aborted"). Content/start events carry partial with the current AssistantMessage state; terminal events instead carry message or error — mutate output.content as data arrives and pass output. Tool calls accumulate JSON deltas, parse into { id, name, arguments }, and finish with toolcall_end carrying the full toolCall. Update usage from the API response and call calculateCost(model, output.usage). Register with streamSimple on the provider config.

Reference implementations live in packages/ai/src/api/, including anthropic-messages.ts, mistral-conversations.ts, openai-completions.ts, openai-responses.ts, google-generative-ai.ts, and bedrock-converse-stream.ts. Honor options.onPayload, options.onResponse, and awaited options.onProviderStreamEvent plus cancellation and provider-scoped environment.

Context Overflow Errors

Pi auto-recovers from context overflow by compacting and retrying once, but only when it recognizes the failure: stopReason === "error" and errorMessage matching a known pattern (see packages/ai/src/utils/overflow.ts). If your provider's message is unrecognized, normalize it from the same extension with a message_end handler so errorMessage starts with a recognized phrase — context_length_exceeded is the safest:

pi.on("message_end", (event, ctx) => {
  const message = event.message;
  if (message.role !== "assistant" || message.stopReason !== "error") return;
  if (message.provider !== "my-provider" && ctx.model?.provider !== "my-provider") return;
  const errorMessage = message.errorMessage ?? "";
  if (errorMessage.includes("context_length_exceeded")) return;
  if (!MY_PROVIDER_OVERFLOW_PATTERN.test(errorMessage)) return;
  return { message: { ...message, errorMessage: `context_length_exceeded: ${errorMessage}` } };
});

message_end runs before Pi tracks the message for auto-compaction, so the rewrite is what Pi checks. Scope it to your provider, match a provider-specific pattern (never Pi's generic ones — rewriting rate-limit errors would trigger compaction instead of retry-with-backoff), and skip when the phrase is already present so the handler is idempotent.

Testing

Adapt the suites in packages/ai/test/ for your provider/model pairs: stream.test.ts, tokens.test.ts, abort.test.ts, empty.test.ts, context-overflow.test.ts, image-limits.test.ts, unicode-surrogate.test.ts, tool-call-without-result.test.ts, image-tool-result.test.ts, total-tokens.test.ts, cross-provider-handoff.test.ts. Verify registration with pi --list-models, then exercise auth, tools, thinking levels, image input, cache behavior, retries, and context overflow.

Config Reference

ProviderConfig: name?, baseUrl?, apiKey?, api?, streamSimple?, headers?, authHeader?, models?, refreshModels?, oauth?.

ProviderModelConfig: id, name, api?, baseUrl? (per-model endpoint override), reasoning, thinkingLevelMap?, input, cost (input, output, cacheRead, cacheWrite per million tokens), contextWindow, maxTokens, headers?, compat?.

Example extensions: examples/extensions/custom-provider-anthropic/ and examples/extensions/custom-provider-gitlab-duo/.