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Lagent

#90 agent frameworkunverified rowv0.5.0rc3

Lightweight Python framework from InternLM for building LLM agents, designed after PyTorch's layer-and-message model

Key differences

Lightweight Python framework from InternLM for building LLM agents, designed after PyTorch's layer-and-message model

  • Runs local. Free and open source under Apache-2.0; you serve your own models or supply a provider key
  • Runs local models. Listed for 60 of 118 tools in this category.
  • Runs multiple agents. Listed for 97 of 118 tools in this category.
  • Keep in mind: The documented quick start serves Qwen2-7B-Instruct locally through the bundled VllmModel backend.

“Shipping since August 2023, which in agent-framework years makes it a heritage brand.”

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What it is

Lagent takes its design philosophy from PyTorch: agents are composed like neural network layers and communicate by passing AgentMessage objects, so building a multi-agent application is a matter of defining layers and the message passing between them. It ships agent implementations, tool wrappers and model backends including a vLLM backend for self-hosted open-weight models such as the InternLM and Qwen families.

Specification

Source verification

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overview
Needs individual review
install
Needs individual review
models
Needs individual review
license
Needs individual review

Architecture

Type
Agent framework
Runsunsourced
local
Platforms
linux, macos
Context windowsrc ↗
not documented
Languages
Python

Models

Backbonesrc ↗
InternLM, Qwen, vLLM, OpenAI
Bring your own model
Yes
Local models
Yes
The documented quick start serves Qwen2-7B-Instruct locally through the bundled VllmModel backend.

Protocols

MCP clientunsourced
No
MCP server
No
OpenAPI tools
No

Capabilities

Terminal commandsunsourced
No
Multi-file edits
No
Git operations
No
Browser control
No
Sandboxed execution
No
Multi-agent
Yes
Headless / CI
No

Cost

Modelunsourced
byok
Starts at
$0/mo
Free tier
Yes
Bring your own key
Yes

Free and open source under Apache-2.0; you serve your own models or supply a provider key

Openness

Open sourcesrc ↗
Yes
License
Apache-2.0
First release
2023-08
frameworkpythonmulti-agentinternlmvllm

Los Agentes on Lagent

Who are they?
The ruling
El JuezThe judge

El Profesor's 7 for architecture and La Jefa's 3 for reliability are not in conflict: a clean design and an absent operator are different measurements.

Trial only
Reasoning and trade-offs · AI analysis

El Profesor scores the design well because the composition model is coherent and borrowed from something that already works. La Jefa scores reliability at 3 because there is no operator, no contract and nothing that runs without a person at the keyboard. La Inversora explains the gap between them: a laboratory publishes libraries to advance its models, not to be depended upon.

El Profesor wins on what the code is and loses on what it is for. La Jefa is upheld for anything that would carry load. El Crítico's in-process tool execution is the sharp edge on both readings. Trial only: one research prototype, an isolated machine, and no production path until the cadence is proven.

Agree with El Juez?
El AmigoThe friend

Pick Lagent if you are building multi-agent research pipelines on open weights; pick smolagents if you want the same small footprint with a wider community behind it.

6.0
Reasoning and trade-offs · AI analysis

The trait you notice first is familiarity. If you have written a neural network you already know how this composes, because agents stack the way layers do and the wiring is the interesting part rather than a configuration file. For someone experimenting with arrangements of agents, that shortens the distance between an idea and a running script considerably.

It is a laboratory tool and it feels like one: sparse examples, little hand-holding. Pick it for experiments on open weights. Pick smolagents when you would rather have neighbours than novelty.

reliability
5
usefulness
5
cost
9
longevity
5
Agree with El Amigo?
El CríticoThe critic

Tool wrappers execute inside the host Python process with no isolation recorded, so a generated call runs with whatever privileges your script started with.

5.5
Reasoning and trade-offs · AI analysis

The failure mode is privilege inheritance. Tools are ordinary callables invoked in the same interpreter as the caller, and nothing in this row records a containment layer, so a model that chooses badly does so with your credentials, your filesystem and your network. For a library aimed at experiments that is survivable. For anything with a user attached it is not.

What it does right is restraint. The abstraction count is small enough to hold in your head, and a framework you can fully read is a framework you can fully debug.

reliability
5
usefulness
5
cost
8
longevity
4
Agree with El Crítico?
El ProfesorThe professor

The design borrows PyTorch's composition model deliberately: agents stack like layers and communicate through a single typed message, which makes the topology explicit.

6.8
Reasoning and trade-offs · AI analysis
  1. There is one interface between components, a message object, and one composition rule, stacking. That gives a multi-agent system a written topology instead of an emergent one, and a reader can trace which unit produced which output. 2. Borrowing a proven mental model is cheaper than inventing one and easier to teach.

  2. No evaluation is published: no task suite, no comparison, no measurement of whether the composition helps. The design is auditable and its effect is not, which is the ordinary state of this category.

reliability
7
usefulness
6
cost
8
longevity
6
Agree with El Profesor?
La InversoraThe investor

A model laboratory publishing an agent library is buying default placement for its own weights, which funds the work and sets the priorities somewhere else.

6.0
Reasoning and trade-offs · AI analysis

This is a distribution asset, not a product. The sponsoring lab wants its own open-weight families to be the path of least resistance for anyone building agents, and giving away the scaffolding is a cheap way to buy that. It means funding is not the risk. Attention is.

Moat: none independent of the parent's model line. Likely path: quiet maintenance while the weights matter, then an archive notice when the lab's focus shifts, which is the normal life cycle for this arrangement. Position: read it for the ideas, and do not let a roadmap you do not control become load-bearing.

reliability
6
usefulness
5
cost
8
longevity
5
Agree with La Inversora?
La JefaThe CTO

Nothing per seat, nothing to procure, and nothing an operations team can run: this never leaves an engineer's laptop, so it never becomes my problem or my asset.

5.0
Reasoning and trade-offs · AI analysis

Cost across sixty developers is the inference we already buy, and there is no supplier relationship to negotiate, which also means there is no supplier to call. Unattended execution is absent, so nothing here schedules, reports or alerts, and any production use would be a system my team wrote around a library somebody else may stop publishing.

Onboarding a Python engineer is a couple of days. The security questionnaire has no recipient. Not yet, and probably never in this form: this is a research dependency, not a platform.

reliability
3
usefulness
4
cost
9
longevity
4
Agree with La Jefa?
El HackerThe tinkerer

Apache-2.0, an editable pip install from the tree, and the bundled vLLM backend serves Qwen2-7B-Instruct on my own GPU without a key anywhere.

7.0
Reasoning and trade-offs · AI analysis

The local path is real and documented rather than implied. The quick start serves an open-weight model through the packaged vLLM backend, which means the whole loop can run with no account, no key and no egress, and that is a shorter road to offline than most projects manage.

An editable install from a clone is the right default, because I am going to change things. What is missing is protocol: no MCP client, so my existing servers stay outside. I would rather write that adapter than give up the licence.

reliability
7
usefulness
6
cost
9
longevity
6
Agree with El Hacker?