LangChain 1.0 for JavaScript: the legacy modules moved to @langchain/classic

LangChain 1.0 cut langchain down to the agent building blocks and published the rest as @langchain/classic. Imports of chains, legacy agents, retrievers, memory, document loaders, output parsers or stores from a langchain/... subpath stop resolving on upgrade. The code behind them did not change; the package name in front of the subpath did.

What changed

• 85 subpaths moved to @langchain/classic, same names. langchain/agents, langchain/chains, langchain/retrievers/*, langchain/memory, langchain/document_loaders/*, langchain/output_parsers, langchain/text_splitter, langchain/tools/*, langchain/stores/*, langchain/vectorstores/memory, langchain/evaluation, langchain/smith, the experimental tree and the util helpers. The map was derived by comparing the exports of langchain 0.3.36 with 1.0.1 and keeping every subpath @langchain/classic 1.0.0 publishes.
• Ten subpaths stayed. langchain, langchain/hub and langchain/chat_models/universal are unaffected.
• One subpath was removed. langchain/runnables/remote and its RemoteRunnable have no replacement in the v1 packages.

Before and after

A v0 program built from parts that moved:

import { createRetrievalChain } from 'langchain/chains/retrieval';
import { EnsembleRetriever } from 'langchain/retrievers/ensemble';
import { RecursiveCharacterTextSplitter } from 'langchain/text_splitter';
import { StructuredOutputParser } from 'langchain/output_parsers';

After npx emendant fix, only the package in front of each subpath changes:

import { createRetrievalChain } from '@langchain/classic/chains/retrieval';
import { EnsembleRetriever } from '@langchain/classic/retrievers/ensemble';
import { RecursiveCharacterTextSplitter } from '@langchain/classic/text_splitter';
import { StructuredOutputParser } from '@langchain/classic/output_parsers';

There is no after for RemoteRunnable.

Migration guidance and its limits

Apply the patch, then install @langchain/classic. The patch rewrites specifiers and does not touch your manifest, so until the package is installed the verification run reports it as failing. Add the dependency and run the fix again.

A langchain/... subpath the map does not name went somewhere other than @langchain/classic, or was never public, and Emendant reports nothing for it rather than guessing. langchain/runnables/remote is report only. The new agent API in langchain 1.0 is outside this page: a clean scan says your imports still resolve, not that your agents behave as before.

A major upgrade moves @langchain/core to 1.0 as well. Read @langchain/core 1.0.0: predict and predictMessages removed with this page. A repository still on 0.2 has the 0.3 move of 39 entrypoints to @langchain/community to make first. The LangChain.js migration guide lists the later 1.x release pages.

What Emendant detects, fixes and verifies

2 changes in langchain 1.0.1. 1 automatic fixes, 0 fixes requiring a model provider you choose, 1 report only. Each patch states which checks passed. Understand patch evidence.

emendant explain <change-id> prints any row's entry, guidance and sources at the terminal.

Coverage

Requires emendant@0.1.0 or later. Run emendant feed update to get the latest coverage.

Primary sources

• Langchain v1langchain-ai/docs at commit bff16d7f
• @langchain/classic@1.0.0npm, the published package

Scan your repository

Find affected code without editing your files.

npx emendant scan

Then npx emendant fix writes the patches the table says exist. The getting started guide covers the flags and the patch grades.

Related release pages

• Earlier langchain release: LangChain 0.3 for JavaScript: 39 entrypoints move to @langchain/community, six are gone
• Later langchain release: langchain 1.0.3 for JavaScript: getContextVariable and setContextVariable removed
• Upgrade together with: @langchain/core 1.0.0: predict and predictMessages removed, and what else went

The LangChain.js migration guide lists every release page and says which to read for your upgrade.