LangChain vs LlamaIndex vs Semantic Kernel 2026

Three frameworks dominated the AI agent conversation heading into 2026: LangChain, LlamaIndex, and Microsoft’s Semantic Kernel. But the landscape has shifted dramatically since we last compared them. LangChain is maturing into an agent platform with v1.x, LlamaIndex is doubling down on data infrastructure, and Semantic Kernel has been folded into Microsoft Agent Framework 1.0 GA — a consolidation that changes everything for .NET shops.

We’ve built production systems across all three at Turion. Here’s what’s real in 2026.

The Short Answer

• LangChain — Best for teams building complex multi-agent workflows, especially those already using LangGraph and LangSmith. The ecosystem is unmatched.
• LlamaIndex — Best for heavy data ingestion, RAG, and document-heavy agents. Its parsing and retrieval primitives are still best-in-class.
• Semantic Kernel → Microsoft Agent Framework 1.0 — Best for .NET-first enterprises embedded in the Azure ecosystem. Semantic Kernel as a standalone concern is effectively deprecated; the future is the unified Microsoft.Agents.AI SDK.

If you’re starting a greenfield project and your stack is Python-first: LangChain or LlamaIndex, depending on whether your bottleneck is orchestration complexity or data pipeline quality. If you’re a .NET shop: you’re all-in on Microsoft Agent Framework now.

LangChain in 2026: The Agent Platform

LangChain has consolidated from a “chain” library into a full agent development platform spanning Python and JavaScript, with tight coupling to LangSmith for evaluation and tracing.

What’s New (April 2026)

• v1.3.x series with content-block-centric streaming v2, enabling structured output over streaming responses — a real improvement for agents that need to stream partial tool calls before committing. (Source)
• LangSmith self-hosted — you can now run LangSmith’s evaluation and tracing platform on your own infrastructure. This matters for regulated industries that can’t send traces to a SaaS. (Source)
• 30+ evaluator templates in LangSmith covering safety, response quality, and hallucination detection. (Source)
• MCP support — LangChain agents can consume Model Context Protocol servers natively.
• Upcoming “Interrupt” conference — LangChain’s own developer event, signaling the company’s move toward a full platform play, not just an open-source library.

Architecture

LangChain’s current structure is organized as:

Package	Role
langchain-core	Base abstractions (models, prompts, tools, messages)
langchain	Higher-level chains, agents, utilities
langgraph	Graph-based state machine orchestration for agents
langsmith	Observability, evaluation, prompt management
langchain-community	400+ third-party integrations

The critical insight: LangGraph is now the recommended way to build agents, not the legacy AgentExecutor. LangGraph gives you explicit state graphs with human-in-the-loop support, checkpointing, and conditional edges. We’ve written about this extensively.

from langgraph.graph import StateGraph, START, END
from typing import TypedDict, Annotated
import operator

class AgentState(TypedDict):
    messages: Annotated[list, operator.add]
    current_step: str

def research_node(state: AgentState) -> AgentState:
    # Your agent logic here
    return {"current_step": "research_complete"}

graph = StateGraph(AgentState)
graph.add_node("research", research_node)
graph.add_edge(START, "research")
graph.add_edge("research", END)

app = graph.compile()
result = app.invoke({"messages": [], "current_step": "init"})

Pros

• Largest ecosystem: 400+ integrations, massive community, most Stack Overflow answers
• LangGraph gives you explicit control flow — no black-box agent loops
• LangSmith provides production-grade evals, tracing, and prompt versioning
• Python and JavaScript parity
• MCP-native — can consume any MCP server

Cons

• Still complex: the surface area is enormous, and picking the right abstraction layer takes experience
• Breaking changes between 0.x and 1.x required significant migrations
• Package bloat: langchain-community pulls in hundreds of dependencies you may never use
• Learning curve is steep for teams new to agent patterns

LlamaIndex in 2026: The Data Pipeline

LlamaIndex’s strategy is clear: own the data layer. While LangChain expands into orchestration and evaluation, LlamaIndex is investing heavily in document parsing, indexing structures, and retrieval optimization.

What’s New

• LiteParse — a new open-source document parsing tool from the LlamaIndex team, designed for high-fidelity extraction from PDFs, presentations, and scanned documents. (Source)
• Enhanced visual understanding — improved multimodal parsing that handles charts, tables, and diagrams in documents.
• Workflow engine improvements — the Workflow abstraction enables more complex multi-step data pipelines with event-driven execution.
• Changelog active through April 2026 — consistent release cadence with core package bumps across all sub-packages. (Source)

Architecture

LlamaIndex is organized around the data lifecycle:

Component	Role
llama-index-core	Base abstractions (documents, indices, query engines)
llama-parse / LiteParse	Document ingestion and parsing
llama-index-indices	Index structures (vector, tree, keyword, summary)
llama-index-retrievers	Retrieval strategies (hybrid, recursive, auto-merging)
llama-index-agent	Agent abstractions built on top of the data layer
LlamaIndex Cloud	Managed RAG pipelines and observability

from llama_index.core import SimpleDirectoryReader, VectorStoreIndex
from llama_index.llms.openai import OpenAI
from llama_index.core.retrievers import AutoMergingRetriever
from llama_index.core.node_parser import HierarchicalNodeParser

# Parse documents with advanced node splitting
node_parser = HierarchicalNodeParser.from_defaults(
    chunk_sizes=[2048, 512, 128]
)
documents = SimpleDirectoryReader("./data").load_data()
nodes = node_parser.get_nodes_from_documents(documents)

# Build multi-level index
index = VectorStoreIndex(nodes)

# Auto-merging retriever: retrieves small chunks
# but returns parent context for better LLM grounding
retriever = AutoMergingRetriever(
    index.as_retriever(),
    storage_context=index.storage_context,
)

Pros

• Best-in-class document ingestion: LiteParse + visual understanding gives the highest-fidelity extraction
• Auto-merging retriever and hierarchical indexing are unique strengths for long-document RAG
• Clear separation of concerns: data pipeline → index → query → agent
• LlamaIndex Cloud offers managed RAG for teams that don’t want to build infrastructure
• Strong Python focus with no JavaScript split to manage

Cons

• Agent orchestration is less mature than LangGraph — you’ll still need LangGraph or a custom state machine for complex multi-agent flows
• Smaller community than LangChain — fewer third-party integrations, fewer Stack Overflow answers
• The API surface changes frequently — expect to pin versions tightly
• JavaScript/TypeScript support is behind Python

Semantic Kernel → Microsoft Agent Framework 1.0

Here’s the biggest shift: Semantic Kernel as a standalone framework is effectively over. On April 3, 2026, Microsoft shipped Agent Framework 1.0 GA, which unifies Semantic Kernel and AutoGen into a single SDK (Microsoft.Agents.AI) supporting both .NET and Python. (Source)

What This Means

• Semantic Kernel’s plugin model, kernel abstractions, and planner patterns form the foundation layer of Agent Framework
• AutoGen’s multi-agent orchestration patterns run as graph workflows on top of that foundation
• The new framework ships native MCP and A2A (Agent-to-Agent) protocol support — not bolted on, but first-class at 1.0
• Long-term support commitment from Microsoft, with a stable API surface and documented upgrade path
• Six LLM providers out of the box: Azure OpenAI, OpenAI, Anthropic Claude, Amazon Bedrock, Google Gemini, and Ollama. Swapping providers is a one-line change.

// Microsoft Agent Framework 1.0 — .NET
using Microsoft.Agents.AI;
using Microsoft.Agents.AI.Models;

var kernel = new AgentKernelBuilder()
    .AddAzureOpenAIChatService(
        deploymentName: "gpt-4o",
        endpoint: new Uri("https://your-resource.openai.azure.com/"),
        credential: new AzureKeyCredential("your-key"))
    .Build();

// Plugins are Semantic Kernel's core concept — preserved in Agent Framework
kernel.ImportPluginFromFunctions("WeatherPlugin",
[
    KernelFunctionFactory.CreateFromMethod(
        (string location) => $"Weather in {location}: 72°F, Sunny",
        "GetWeather",
        "Get the current weather for a location"),
]);

var agent = new ChatCompletionAgent(kernel)
{
    Instructions = "You are a travel assistant.",
};

Pros

• Enterprise-grade: LTS commitment, type-safe .NET API, native Azure integration
• Two languages, one API: C# and Python share the same conceptual model
• MCP + A2A at 1.0 — no retrofits, no waiting for community plugins
• DevUI — a local debugger for agents with trace inspection and step-through
• Azure App Service deployment is a first-class experience

Cons

• Tied to the Microsoft ecosystem — if your infrastructure isn’t Azure-centric, the value proposition shrinks
• Younger ecosystem — 75K+ stars merged from SK and AutoGen, but the unified framework is brand new; expect rough edges and migration questions
• Community is smaller — no LangChain-scale third-party integration library
• AutoGen’s conversational multi-agent model may not suit all teams — the orchestration style favors message-passing between agents over explicit state graphs

Head-to-Head: Decision Matrix

Criteria	LangChain	LlamaIndex	Microsoft Agent Framework
Primary strength	Agent orchestration (LangGraph)	Data ingestion & retrieval	Enterprise .NET integration
Languages	Python, JavaScript	Python (primary), JS (lagging)	.NET, Python
LLM support	Any (400+ integrations)	Any (broad but smaller set)	6 built-in, extensible
Evaluation	LangSmith (30+ templates, self-hostable)	LlamaIndex Cloud	DevUI debugger (local)
MCP support	✅ Native	⚠️ Via community	✅ Native at 1.0
Multi-agent	LangGraph (explicit state graphs)	Custom workflows	AutoGen-style graph workflows
Enterprise readiness	High (with LangSmith)	Medium (community-driven)	High (Microsoft LTS)
Best for	Python teams building complex agents	Data-heavy RAG pipelines	.NET / Azure enterprises

Our Recommendation

The choice depends on your starting constraints, not on some abstract “best framework” ranking:

Choose LangChain if: Your team is Python-first and you’re building agents with non-trivial control flow — conditional routing, human-in-the-loop, parallel tool execution. LangGraph is the most mature explicit-state agent orchestration library available, and LangSmith’s evaluation suite gives you production confidence. The ecosystem size means when you hit a problem, someone has already solved it. We use LangChain + LangGraph for building production AI agents across most of our Python deployments.

Choose LlamaIndex if: Your agent’s bottleneck is data quality, not orchestration complexity. If you’re parsing PDFs, extracting tables from presentations, building RAG over legal documents or technical manuals, LlamaIndex’s ingestion pipeline — LiteParse plus hierarchical indexing plus auto-merging retrieval — is the strongest stack we’ve used. Pair it with LangGraph for orchestration; they complement each other well.

Choose Microsoft Agent Framework if: You’re a .NET shop, your infrastructure is Azure-centric, and you need a vendor-backed SDK with LTS guarantees. The convergence of Semantic Kernel and AutoGen into one framework with native MCP and A2A is genuinely compelling — but only if you’re already operating in the Microsoft ecosystem. If you’re Python-first and cloud-agnostic, the vendor lock-in risk outweighs the convenience.

The frameworks aren’t converging into a single winner. They’re specializing: LangChain owns orchestration, LlamaIndex owns data, and Microsoft Agent Framework owns the enterprise .NET stack. Pick the one that matches your bottleneck, and don’t try to force a square peg.