@pathcourse/langchain

LangChain.js integration for PathCourse Health. Autonomous agent inference with USDC billing on Base L2 — no accounts, no credit cards, no KYC.

Install

npm install @pathcourse/langchain

Quick Start

import { ChatPathCourse } from "@pathcourse/langchain";
import { ChatPromptTemplate } from "@langchain/core/prompts";

const llm = new ChatPathCourse({ model: "pch-fast" });   // set PCH_API_KEY env var

const prompt = ChatPromptTemplate.fromTemplate("Explain {topic} in one paragraph.");
const chain = prompt.pipe(llm);
const result = await chain.invoke({ topic: "autonomous agent billing" });
console.log(result.content);

Drop-in replacement for ChatOpenAI

// Before
import { ChatOpenAI } from "@langchain/openai";
const llm = new ChatOpenAI({ model: "gpt-4o-mini" });

// After
import { ChatPathCourse } from "@pathcourse/langchain";
const llm = new ChatPathCourse({ model: "pch-fast" });

Every LangChain chain, agent, tool, and memory module keeps working unchanged.

Embeddings

import { PathCourseEmbeddings } from "@pathcourse/langchain";
import { MemoryVectorStore } from "langchain/vectorstores/memory";

const embeddings = new PathCourseEmbeddings();
const store = await MemoryVectorStore.fromTexts(
  ["hello world", "goodbye world"],
  [{}, {}],
  embeddings,
);
const results = await store.similaritySearch("greeting");

Models

| Model | Rate | Min tier | Notes | |---|---|---|---| | pch-fast | $0.44 / M tokens | uncertified | Fast reasoning, classification, routing | | pch-coder | $3.50 / M tokens | uncertified | Code generation, debugging | | pch-embed | $0.015 / M tokens | uncertified | Text embeddings for semantic search / RAG | | pch-translate | $0.08 / M chars | uncertified | Multilingual translation | | pch-pro | $1.96 / M tokens | bronze | Deep reasoning, multi-step planning | | pch-audio | $1.85 / M chars | bronze | Text-to-speech, standard quality | | pch-documents | $0.26 in / $1.48 out per M tokens | bronze | Document parsing / OCR | | pch-transcribe | $0.0008 / minute | bronze | Speech-to-text | | pch-extract | $0.012 / M tokens | bronze | Structured data extraction | | pch-rerank | $0.025 / M tokens | bronze | Reranking for RAG pipelines | | pch-image | $0.028 / image | silver | Text-to-image | | pch-audio-premium | $37.00 / M chars | silver | Text-to-speech, premium quality | | pch-talk | $0.001 / minute | silver | Voice conversation | | claude-haiku | Common rate | silver | Anthropic Claude Haiku | | claude-sonnet | Common rate | gold | Anthropic Claude Sonnet |

The full list above shows what's reachable through the gateway. ChatPathCourse and PathCourseEmbeddings only operate on chat-completion and embedding shapes — for image, audio, transcription, etc., use the PCH JS SDK directly.

Choosing a chat model:

• Fast response, simple task → pch-fast
• Complex reasoning, multi-step → pch-pro
• Writing or reviewing code → pch-coder
• Long context or premium reasoning → claude-sonnet (Gold tier)

Authentication

Set PCH_API_KEY in your environment, or pass pchApiKey to the constructor.

export PCH_API_KEY=pch_prod_b_...

Developer access — $5 USDC. Send $5+ USDC on Base (chain ID 8453) to the PCH treasury wallet, then call claimKey({ txHash, wallet }) to retrieve your key. No accounts, no credit card, no KYC. $5 buys thousands of pch-fast calls — enough to verify any integration. Top up to $25 lifetime and your account auto-upgrades to Uncertified with pch-coder access. Treasury address: see payment.treasury_wallet in /.well-known/agent.json.

Links

• Platform: pathcoursehealth.com
• npm SDK: npmjs.com/package/@pathcourse/sdk
• Python SDK: pypi.org/project/pathcourse-sdk
• Integration examples: github.com/pathcourse-health/pch-integration-examples

License

MIT