LangChain vs LlamaIndex for AI Agents: Which to Choose

If you’re building an AI agent in 2026, you’ll likely evaluate both LangChain and LlamaIndex before committing to one. They’re the two most widely adopted open-source frameworks for LLM-powered applications – but they were built for different problems, and that distinction matters more when you’re deploying agents than when you’re running a prototype.

The short version: LangChain is a general-purpose agent orchestration framework. LlamaIndex is a data framework that has grown into agent territory. The right choice depends on whether your agent’s core challenge is workflow orchestration or knowledge retrieval.

TL;DR – Framework Selection at a Glance

Official Docs and References

• LangChain Documentation
• LangGraph Documentation
• LlamaIndex Documentation
• OpenInference / Arize Phoenix

What Each Framework Was Built to Solve

LangChain: Orchestration First

LangChain launched in late 2022 as a framework for chaining LLM calls together – connecting prompts, memory, tools, and APIs into coherent workflows. Its core abstraction is the chain: a sequence of steps that can include LLM inference, tool use, conditional branching, and memory reads.

Over time, LangChain added:

• LangGraph – a graph-based orchestration layer for stateful, multi-step agents
• LangSmith – observability and tracing for production deployments
• LangServe – deployment and serving infrastructure

LangChain’s strength is breadth. It integrates with 700+ tools, APIs, and data sources. If your agent needs to call an external API, write to a database, trigger a webhook, or hand off to another agent, LangChain has a built-in integration or a pattern for it.

LlamaIndex: Retrieval First

LlamaIndex (originally GPT Index) was built to solve a specific problem: how do you connect an LLM to your own data? Its core abstractions are nodes, indexes, and query engines – the building blocks for ingesting, structuring, and retrieving information at query time.

LlamaIndex has since added agent capabilities through:

• AgentRunner – a stateful agent runtime that supports tool use and multi-step reasoning
• Workflows – an event-driven framework for building complex agent pipelines
• LlamaHub – a registry of data loaders, tools, and integrations focused on retrieval

LlamaIndex’s strength is depth of retrieval. If your agent’s performance depends on how accurately it finds and synthesizes information from a knowledge base, LlamaIndex gives you more control over chunking strategies, embedding models, reranking, and query transformations.

Core Architecture Differences

When LangChain Is the Right Choice

Your agent orchestrates tools more than it retrieves documents. If the agent’s primary job is to call APIs, trigger actions, write to databases, or coordinate between multiple services – LangChain’s tool ecosystem and LangGraph’s stateful orchestration are hard to beat.

You need complex multi-step workflows with branching logic. LangGraph’s graph model lets you define explicit state machines with conditional edges, interrupts, and human-in-the-loop checkpoints. This is better suited for production agentic workflows where you need predictable control flow. See our guide to AI agent architecture patterns for a breakdown of where LangGraph fits relative to other orchestration approaches.

You’re building on a team that values ecosystem breadth. LangChain has more tutorials, community answers, third-party integrations, and production case studies. If your team is newer to agent development, the ecosystem advantage reduces friction.

Examples:

• Customer support agent that routes tickets, looks up account data, and triggers CRM updates
• Automated report generation pipeline that pulls from 5 data sources and formats output
• AI assistant that calls internal APIs and writes results to Notion or Slack

When LlamaIndex Is the Right Choice

Your agent’s value is answering questions from a large, structured knowledge base. If retrieval accuracy is the core product – legal document Q&A, technical documentation search, financial report analysis – LlamaIndex gives you more fine-grained control over how documents are chunked, indexed, retrieved, and reranked.

You need advanced RAG patterns. LlamaIndex supports hybrid search (vector + keyword), query routing across multiple indexes, sentence-window retrieval, recursive retrieval, and HyDE (hypothetical document embeddings). These techniques materially improve answer quality for complex knowledge retrieval. In our experience and across client evaluations, the gap between naive vector search and well-configured hybrid retrieval with reranking is large enough to be the deciding factor in whether an agent is production-viable – not a marginal quality improvement.

Your documents are highly structured or heterogeneous. LlamaIndex has purpose-built loaders for PDFs, spreadsheets, SQL databases, Notion, Confluence, Slack, and more – with metadata extraction and filtering built in.

Examples:

• Internal knowledge base agent that searches across SharePoint, Notion, and Confluence simultaneously
• Contract analysis agent that retrieves specific clauses and synthesizes across 50-page documents
• Financial analyst agent that answers questions from 10-K filings and earnings transcripts

The Hybrid Approach

In practice, many production systems combine both frameworks. LangChain handles orchestration, routing, and tool use. LlamaIndex manages the retrieval layer. The two integrate cleanly – you can use a LlamaIndex query engine as a LangChain tool, or expose LlamaIndex Workflows as steps within a LangGraph agent.

This isn’t an either/or decision at the architectural level. It becomes an either/or decision when you’re choosing where to invest your team’s expertise and which framework’s abstractions to standardize on.

This hybrid pattern is particularly common in multi-agent systems where one agent handles retrieval (LlamaIndex) and another handles action execution (LangGraph).

Real-World Example: Legal Tech SaaS, Contract Review Agent

A 95-person legal tech company needed to automate first-pass contract review – flagging non-standard clauses, summarizing key terms, and surfacing risk items across NDAs, MSAs, and SOWs.

The challenge: Contracts varied in structure and length (8–120 pages). The agent needed to retrieve specific clause types across heterogeneous documents, then reason about risk level and generate structured summaries for attorneys.

Framework decision: LlamaIndex for the retrieval and indexing layer (recursive document parsing, metadata-tagged clause extraction, hybrid keyword + semantic search), LangGraph for the review workflow (intake → classify → retrieve → reason → summarize → flag → output).

Build: 9 weeks with a 3-person team. Total cost: $68K.

Results after 6 months in production:

• First-pass review time reduced from 3.2 hours per contract to 22 minutes (86% reduction)
• Attorney capacity freed: ~14 hours per week per attorney (4-attorney team)
• Annualized labor savings: approximately $290K
• Payback period: under 4 months

The hybrid architecture added 2–3 weeks of integration work compared to a single-framework build, but retrieval accuracy – measured by clause identification precision – was 23 percentage points higher than an equivalent LangChain-only implementation tested during the evaluation phase.

Framework Maturity and Ecosystem Size

Both frameworks have matured significantly since their 2022–2023 launches, but they’re at different stages of production adoption.

LangChain crossed 90,000 GitHub stars and is used by organizations including Elastic, Rakuten, and Klarna for production workloads. LangSmith, its observability platform, has become a de facto standard for teams that need tracing and evaluation integrated with their framework.

LlamaIndex has built a more specialized but highly engaged community around enterprise knowledge retrieval. Its LlamaParse document parsing service – purpose-built for accurate PDF and table extraction – addresses one of the most common failure modes in RAG systems: poor document ingestion that degrades retrieval before a single query is run.

A practical note on cost: teams using LlamaIndex’s advanced retrieval features (reranking, query transformations) often report 20–35% lower token costs in production compared to naive retrieval, because the retrieval layer surfaces more relevant context with fewer tokens passed to the LLM. For high-volume agents, this adds up quickly. See our analysis in cost of building an AI agent for how retrieval architecture affects total operating cost.

Decision Framework

Start with this question: Is the hard part of your agent connecting to systems, or finding the right information?

• If the hard part is connecting to systems → start with LangChain / LangGraph
• If the hard part is retrieving accurate information → start with LlamaIndex
• If both are hard → start with whichever matches your team’s existing Python skills, then integrate the other at the retrieval or tool layer

Secondary criteria:

• Need production observability out of the box? LangSmith (LangChain) is more mature.
• Building for a highly specialized knowledge corpus? LlamaIndex’s retrieval depth is worth the learning curve.
• Prototyping quickly with a small team? LangChain’s tutorial ecosystem accelerates early stages.

For a broader view of where LangChain and LlamaIndex fit relative to other tooling, see our AI agent frameworks comparison.

What Doesn’t Differentiate Them

Both frameworks:

• Support the major LLM providers (OpenAI, Anthropic, Google, Cohere, local models)
• Support vector store integrations (Pinecone, Weaviate, Chroma, pgvector, etc.)
• Are Python-first with TypeScript/JavaScript versions available
• Have active open-source communities and regular releases
• Support streaming responses
• Can be deployed on any cloud provider

The debate between LangChain and LlamaIndex is narrower than the marketing suggests. Most teams that have been in production for 6+ months end up using components from both.

arsum’s Approach

We’re framework-agnostic and make the choice based on the specific agent architecture. For retrieval-heavy agents – document Q&A, knowledge bases, contract analysis – we default to LlamaIndex’s retrieval layer with LlamaParse for document ingestion. For orchestration-heavy agents – multi-step workflows, API integrations, CRM automation – we use LangGraph.

Most client systems end up using both frameworks in combination. The integration work is well-understood and the combined architecture reliably outperforms either framework alone for complex agents.

If you’re evaluating these frameworks for a production agent, the most useful exercise isn’t comparing documentation – it’s prototyping the retrieval or orchestration layer that represents your agent’s hardest problem and measuring accuracy or latency before committing to a full build. See our agentic AI workflow automation guide for how to structure that evaluation process.

FAQ

Q: Can I switch frameworks later if I pick the wrong one? Yes, but it’s expensive. The core abstractions – chains vs. indexes, LangGraph state vs. LlamaIndex Workflows – don’t map cleanly to each other. Plan to refactor significant portions of your agent logic if you switch after building substantial features. The switching cost is roughly 40–60% of the original build effort, based on what we see in remediation projects.

Q: Which framework is faster to prototype with? LangChain’s tutorial ecosystem and community examples are larger, which tends to mean faster initial prototyping. LlamaIndex can be faster if your use case is clearly retrieval-focused, since you won’t need to build retrieval primitives from scratch. For a greenfield project, expect 2–4 weeks to a working prototype with either framework.

Q: Is one framework more production-ready than the other? Both run in production at scale. LangChain’s LangSmith observability tooling is a meaningful advantage for teams that need tracing, debugging, and evaluation tooling integrated with their framework. LlamaIndex’s production story has improved significantly with the addition of Workflows and better async support.

Q: What about AutoGen or CrewAI? AutoGen (Microsoft) and CrewAI focus on multi-agent collaboration patterns – multiple agents working together on a task. They address a different layer than LangChain or LlamaIndex. Many teams use AutoGen or CrewAI for the agent collaboration layer with LangChain or LlamaIndex handling the underlying retrieval and tool execution. See our multi-agent systems guide for how these layers interact.

Q: How do I evaluate retrieval quality before committing to a framework? Build a small evaluation set: 20–30 representative queries with expected answers drawn from your actual documents. Run both frameworks against this set using default retrieval configurations. Measure hit rate (did the correct document chunk appear in the top 3 results?) and answer quality (did the LLM produce the correct answer?). LlamaIndex typically scores higher on this benchmark for knowledge-intensive agents; LangChain is competitive for agents with shallow retrieval needs.

Q: Does framework choice affect inference cost? Yes, indirectly. More accurate retrieval (LlamaIndex’s strength) means fewer tokens passed to the LLM per query – the retrieval layer surfaces higher-signal context. Teams running high-volume retrieval agents often find that LlamaIndex’s retrieval depth reduces LLM inference costs by 20–35% compared to simpler retrieval implementations, enough to offset any additional retrieval infrastructure cost.