Open source frameworks - verified October 18, 2026

Letta (formerly MemGPT)

Letta is listed under open source frameworks. The letta-ai/letta README says the current source code lives in letta-ai/letta-code. No date given. The same README says the archive branch contains the retired Letta V1 API server. No date given. Letta Code's README says AgentFile (.af) export and import are deprecated and have been removed from Letta Code. No date given. Its first listed price, in its own words: $0/month (Free plan). Stated on its pages: automatic extraction and self-hosting. Read from the product's own pages on October 18, 2026.

Read from 4 official sites. Docs - Pricing - License - Compare every memory product

What changed

Source moved to letta-codeLetta (formerly MemGPT)
The letta-ai/letta README says the current source code lives in letta-ai/letta-code. No date given.
“The current source code lives in letta-ai/letta-code, which includes the agent harness, interactive terminal UI, App Server, channels, and the runtime used by the desktop and web apps.”
github.com
V1 API server retiredLetta (formerly MemGPT)
The same README says the archive branch contains the retired Letta V1 API server. No date given.
“The archive branch contains the retired Letta V1 API server.”
github.com
AgentFile removedLetta (formerly MemGPT)
Letta Code's README says AgentFile (.af) export and import are deprecated and have been removed from Letta Code. No date given.
“AgentFile (.af) export and import are deprecated and have been removed from Letta Code.”
github.com

Launch stage, as stated: Actively developed
“Letta (f.k.a. MemGPT) is actively developed.”
github.com

How Letta charges

Every price line Letta states, in its own words and units, with the quote. Nothing is converted.

6 price lines for Letta (formerly MemGPT), in the product's own words and units
Price, in the product's words	Unit	Quote and source
$0/monthinferredInferred: Plan name from the column or card the price sits in on the pricing page; the quoted text does not name the plan. Limited to 3 stateful agents	Free plan	“$0 /month” docs.letta.com “Free plans are limited to 3 stateful agents.” Limit - docs.letta.com
$20/monthinferredInferred: Plan name from the column or card the price sits in on the pricing page; the quoted text does not name the plan. Up to 20 stateful agents	per month (Pro, personal)	“$20 /month” docs.letta.com “Up to 20 stateful agents” Limit - docs.letta.com
$0.10 per active agent per monthinferredInferred: Plan name from the column or card the price sits in on the pricing page; the quoted text does not name the plan.	per active agent per month (listed under the API Plan)	“$0.10 / active agent / mo” docs.letta.com
$0.00015 per second of tool executioninferredInferred: Plan name from the column or card the price sits in on the pricing page; the quoted text does not name the plan.	per second (listed under the API Plan)	“$0.00015 / sec tool execution” docs.letta.com
$20 per seat per monthinferredInferred: Plan name from the column or card the price sits in on the pricing page; the quoted text does not name the plan.	per seat per month (Teams Pro)	“$20 /seat/month” docs.letta.com
LLM usage at underlying model token cost	tokens	“LLM usage is charged based on the underlying token costs of the model used.” docs.letta.com

Memory model

Memory types and scopes: Memory blocks (system prompt learning) and skill learning
“Agents programmatically rewrite their context to improve and adapt over time, including system prompt learning (through memory blocks) and skill learning.”
github.com
Storage backend: MemFS: git-backed memory filesystem
“Letta agents use MemFS, a git-backed memory filesystem that they can inspect and edit.”
docs.letta.com
Knowledge graph: Not stated
Not stated on the memory or README pages reviewed.
Retrieval: Message search across agents and conversations
“Search across all messages and agents with /search.”
github.com
Automatic extraction: Background 'dreaming' subagents consolidate lessons and update memory
“Dreaming uses background subagents to review recent conversations, consolidate useful lessons, and update memory without interrupting your active work.”
docs.letta.com

MCP, SDKs and integrations

Official MCP server: Not stated
No official Letta MCP server is described on the pages reviewed (the pricing page only covers calling remote MCP tools).
SDKs: Python (letta-client)
“The official Python library for the letta API”
pypi.org
TypeScript (@letta-ai/letta-client)
“The official TypeScript library for the Letta API”
registry.npmjs.org
Framework integrations: Not stated
The README lists messaging channels (Slack, Telegram, Discord), not agent-framework integrations.

Self-hosting, license, retention and compliance

Self-hosting: Yes, App Server for local or self-hosted agents
“Run the App Server for local or self-hosted agents:”
github.com
License: Apache License 2.0 (letta-code)
“Apache License Version 2.0, January 2004”
github.com
Retention and deletion: Not stated
Not stated on the pricing, memory or README pages reviewed.
Compliance: Not stated
Not stated on the pricing page.

Vendor-stated claims

Benchmark and latency figures as Letta states them about itself. Vendor-stated, not measured.

Vendor-stated: Not stated
No benchmark claims on the pages relied on.

Dataset note

Letta's product is now centred on Letta Code (stateful agent harness) plus Letta Cloud; memory is a built-in agent capability rather than a standalone memory API.

FAQ

How much does Letta cost?

In Letta's own terms: $0/month (Free plan); $20/month (per month (Pro, personal)); $0.10 per active agent per month (per active agent per month (listed under the API Plan)); $0.00015 per second of tool execution (per second (listed under the API Plan)); $20 per seat per month (per seat per month (Teams Pro)); LLM usage at underlying model token cost (tokens). As of October 18, 2026; prices are not converted.

Does Letta build a knowledge graph?

Not stated. Not stated on the memory or README pages reviewed.

Can I self-host Letta?

Per the vendor: "Run the App Server for local or self-hosted agents:" License: Apache License 2.0 (letta-code).

What changed at Letta (Source moved to letta-code)?

The letta-ai/letta README says the current source code lives in letta-ai/letta-code. No date given.

What changed at Letta (V1 API server retired)?

The same README says the archive branch contains the retired Letta V1 API server. No date given.

What changed at Letta (AgentFile removed)?

Letta Code's README says AgentFile (.af) export and import are deprecated and have been removed from Letta Code. No date given.

Sources

Source: docs.letta.com
Source: docs.letta.com/pricing
Source: github.com/letta-ai/letta/blob/main/README.md
Source: github.com/letta-ai/letta-code/blob/main/LICENSE
Source: github.com/letta-ai/letta-code/blob/main/README.md
Source: docs.letta.com/configuration/memory
Source: pypi.org/pypi/letta-client/json
Source: registry.npmjs.org/@letta-ai/letta-client/latest
Source: github.com/letta-ai/letta-code

Last verified 2026-10-18 from each product's own docs, pricing pages, READMEs and license files; every quote was string-matched against the page that day. This is not a benchmark. Prices are shown in the product's own unit and change without notice, so check the linked source before you commit.

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