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Head to head · Agent harnesses · October 2026 research run

Letta vs T3 Code

Letta scores 59.7 (C) on agent readiness against T3 Code's 51.9 (D), and leads in 5 of 7 scored categories. Both do agent harnesses.

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LettaLetta · Agent harness C59.7/100#684 of 1486 T3 CodeT3 Tools Inc. · Agent harness D51.9/100#1002 of 1486

Which one, for what

Letta C

Best for Long-lived coding agents and assistants that keep memory and identity across sessions and machines.

Ahead on

  • Reliability, 58 against 43
  • Schema & documentation, 70 against 55
  • Agent ergonomics, 67 against 60
  • Maintenance & community, 85 against 75

Also in its favour

  • Runs on your own machine

Watch for

The default permission mode is unrestricted, the renamed bypassPermissions, so tool calls aren't confirmed unless the user picks another mode

T3 Code D

Best for Developers who want one app, including on their phone, to drive several coding agents they already pay for.

Also in its favour

  • No key needed to call it

Watch for

Usage data on by default, with hashed OpenAI and Claude account identifiers, and relay traces to Axiom

Why the edge

Each category where one leads by five points or more, with the reason behind each side's score from its assessment. The numbers are in the table below; this is what they stand for.

Reliability Letta +15

Letta 58

Local-software lines, read for the harness. @letta-ai/letta-code on npm with Node.js 22.19 or newer, and PyPI wheels for glibc Linux, macOS 14 and Windows x64 with Python 3.9 or newer stated (20). ci.yml, nightly update smoke tests and Telegram live smoke tests exist, but GitHub's API answered with a rate limit, so run results were unread (15 of 25, unchecked). 332 open issues and pull requests, mostly pull requests; recent bug reports such as recall reading the wrong conversation have no reply yet (15 of 25). 398 tags at 0.34.x with release notes on GitHub, no changelog file, and breaking removals such as AgentFile announced in the README (8 of 15). Pre-1.0 (0). Total 58.

T3 Code 43

Local software. An install script and desktop and mobile apps from the vendor (20). ci.yml and windows-tests.yml run on the repository; pass state not read (15). GitHub issues and pull requests weren't read (GitHub's pages refuse these sessions), so that line is scored absent (0). Stable tags v0.1.5 to v0.1.7 with many nightlies, no changelog file (8). Version 0.1.7 (0). 20 + 15 + 0 + 8 + 0 = 43.

Schema & documentation Letta +15

Letta 70

Harness reading. docs.letta.com serves llms.txt and a Markdown version of every page, with an applies_to block saying which backend and interface each page covers (10). TypeScript types for the Agent SDK and a documented App Server WebSocket protocol, but no JSON Schema or OpenAPI for the harness (15 of 25). Pages say when to use local or cloud backends, subagents and channels (14 of 20). Permission modes and options are typed in the SDK (12 of 15). Example applications and a remote client reference (11 of 15). Releases most days but no changelog file (8 of 15). Total 70.

T3 Code 55

Harness reading. User docs in the repository (managed policy, handoffs, providers, telemetry), AGENTS.md for contributors, a server other clients connect to (55).

Maintenance & community Letta +10

Letta 85

v0.34.42 on 6 November 2026 (30). Dozens of releases in 90 days (20). Pull requests are merged daily; recent issues from users have few replies (15 of 25). npm and PyPI packages and the Agent SDK track the releases (12 of 15). Lock files, CI and nightly smoke tests (8 of 10). Total 85.

T3 Code 75

Commits and nightly tags on 6 November 2026 (30). More than three releases in 90 days (20). GitHub issues and pull requests weren't read (GitHub's pages refuse these sessions), so that line is scored absent (0). Current official apps and install script (15). CI on push (10). 30 + 20 + 0 + 15 + 10 = 75.

Agent ergonomics Letta +7

Letta 67

Harness reading. Toolsets switch with /model, skills load per agent, and subagents run in the background (18 of 25). Context is managed through memory blocks, reflection and dreaming (12 of 20). letta -p --output-format json for scripted runs and an App Server for programmatic control (12 of 20). Conversations resume by agent and conversation id, and memory is git-tracked so changes can be reverted (15 of 20). Runs with no account on the local backend, with one SDK language, TypeScript (10 of 15). Total 67.

T3 Code 60

Harness reading. Remote control from phone or browser, portable handoffs between providers and managed policies for teams (60).

Score by category

CategoryWeight this runLettaT3 CodeEdge
Reliability16%205843Letta +15
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.27055Letta +15
Agent ergonomics13%16.26760Letta +7
Security & auth14%17.53535even
Payments & pricing10%12.56060even
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88575Letta +10
Transparency & trust7%8.85551Letta +4
Negative events≤1500
TotalC 59.7/100D 51.9/100

Facts side by side

FactLettaT3 Code
KindAgent harnessAgent harness
VendorLettaT3 Tools Inc.
Hosted endpointno (local only)no (local only)
Transportsstdio
AuthOAuth or keyNone
PricingFreemiumFree
x402nono
LicenceApache-2.0MIT
Read-only variant documentednono
llms.txtyesno
Last release2026-11-062026-11-06
Terms last updatedno date givenno document linked
Privacy policy last updatedno date givenno document linked
Customer content may train modelsnot found in the textnot read yet
Terms restrict automated accessnot found in the textnot read yet
Terms restrict benchmarkingnot found in the textnot read yet
Terms or service can change without noticenot found in the textnot read yet
Arbitration or class-action waiveryesnot read yet
Popularity3.8k stars, 86k npm/wk, 2.2k PyPI/wknone

Verdicts

Letta

Letta's open-source harness gives agents git-tracked memory blocks, skills, subagents and headless JSON runs, with a $0 plan and public per-agent API prices. It starts in the unrestricted permission mode, defaults to Letta Cloud, sends usage telemetry unless LETTA_CODE_TELEM=0 is set, and the V1 API server the comparisons describe is retired.

T3 Code

A fast-moving open-source way to run and steer several coding agents from desktop, browser or phone, using the subscriptions you already have. It's pre-1.0, and it sends usage data by default, including hashed identifiers for your OpenAI and Claude accounts, with the opt-out documented outside the README.

Before you call either

Letta

  1. Start headless runs with an explicit permission mode such as standard or strict; the default auto-approves tools
  2. Pass --backend local for work that must stay on the machine, since Letta Cloud is the default
  3. Set LETTA_CODE_TELEM=0 in unattended runs if usage events must not be sent
  4. Use letta -p --output-format json for scripted runs and parse the JSON, not the terminal output
  5. Don't plan on the retired V1 REST server or .af AgentFile import; both are gone

T3 Code

  1. Set T3CODE_TELEMETRY_ENABLED=false before starting the server if you don't want usage events sent
  2. Install and log in to at least one provider CLI first, such as codex login or claude auth login
  3. Use a managed policy to fix settings across a team

Questions

Which is better for AI agents, Letta or T3 Code?

Letta scores 59.7 (C) on agent readiness against T3 Code's 51.9 (D), and leads in 5 of 7 scored categories.

Are Letta and T3 Code open source?

Yes. Letta is open source (Apache-2.0). T3 Code is open source (MIT).

Other comparisons with Letta or T3 Code

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