Harness vs Letta

Harness 40

No payment protocol (0). Read with the self-hosted rule. The software is free and the optional hardware prices are public, per the 17 October check, not re-read on 4 November, since Autonomous's terms forbid access to its sites by automated means, including scripts or web crawlers, and its hosts are paused pending the founder (20). Free with no card (20). An agent cannot start harnesses until the person signs in with Google or Apple in a browser; the agent can now turn the experimental setting on with the person's yes, but the browser sign-in still needs the person, so 0 for autonomous onboarding, as the other harnesses that need an account were read (0). 0 + 20 + 20 + 0 = 40.

Letta 60

No x402, MPP or L402 (0 of 40). Per-unit API prices are public, $0.10 per active agent a month and $0.00015 a second of tool execution, plus plan prices (20). A $0 plan with bring-your-own keys; no card is mentioned (20). The CLI runs locally without signing in (20). Total 60.

Harness 54

Harness reading of the framework checklist, as for the other harnesses. 30 for what leaves the machine by default, 20 for approvals and sandboxing, 15 for prompt-injection posture, 15 for audit and 20 for the security programme. Product usage counts are on by default, disclosed with an opt-out in the repository's measurement document (updated 31 October) and without prompts, code or files. Remote traffic is end-to-end encrypted and relays carry ciphertext. Local use needs no account. The daemon updates itself from a checksummed manifest without asking (18). Agents may start harnesses only with the account's Agents can start other agents setting on, with four live harnesses at most and closes limited to their own. Since v0.4.69_cli (26 October 2026) an agent can turn that setting, and the other agent settings, on itself with harness settings <name> on --person-said-yes or the harness_settings tool, after asking the person; the source says the yes is the agent's word and is logged with the agent's name. The tool carries no safe hint, and the command is not in Harness's allow rules, so the engine's own permission prompt still applies. Against that, installing Harness adds its other commands to Claude Code's and Codex's allow rules, Codex runs them outside its sandbox, there is no sandbox of its own, and the device page listed spoken tasks as auto-allowed on 17 October. 13 on 17 October, when an agent could not turn the setting on, so 10 now. The instructions tell an agent never to answer a harness's question or permission prompt. Harness output is another agent's text, and no further guidance on it was found (9). Every harness shows in the person's app with who started it, the device key log keeps an add and remove history, and an agent's settings change is named in the daemon's log. No per-call audit log found (9). SECURITY.md with an email and a three-working-day acknowledgement, and a documented trust model. No security.txt (17 October check), bug bounty or certification found. OSV lists no advisory for @autonomous-ai/harness-mcp (8). 18 + 10 + 9 + 9 + 8 = 54.

Letta 35

Harness reading of the framework checklist, as for the other harnesses. 30 for what leaves the machine by default, 20 for approvals and sandboxing, 15 for injection posture, 15 for audit and 20 for the security programme. Letta Cloud is the default backend, so agent state and conversations go to Letta's servers, and telemetry is on by default (10 of 30). The default permission mode is unrestricted; standard, acceptEdits and strict are opt-in, and cloud sandboxes exist for remote work (4 of 20). No prompt-injection guidance found for fetched pages or channel messages (5 of 15). Conversation search and git history of memory give an operator a record of what the agent saw and changed (10 of 15). SECURITY.md routes reports to support@letta.com and scopes out the retired server; no security.txt, bounty or certification found (6 of 20). Total 35.

Harness 40

Read as local software, since the agents run on the owner's machines. A one-line installer from Autonomous's CDN, DMG and AppImage builds, and App Store and Google Play apps, with macOS and Linux stated as supported and Node managed by the installer, per the 17 October check, not re-read on 4 November, since Autonomous's terms forbid access to its sites by automated means, including scripts or web crawlers, and its hosts are paused pending the founder. Not on a package registry we could read (20). A public CI workflow plans a run per changed component, with Linux unit tests, the desktop suite in four shards, repository tooling tests, typechecks and a bundle test, and a separate CLI end-to-end workflow. We could not read run results, so 15, the value this run gives public CI that runs the tests with an unreadable result (10 on 17 October, corrected). Open issues could not be read, because github.com answers our proxy with 403. Unchecked, so scored absent (0). Tags follow semver per component, but there is no changelog for the app or CLI and breaking changes are not marked in the repository (5). The CLI went from 0.4.x to 0.5.x on 29 October (v0.5.1_cli); a 0.x minor is exempt from the breaking-change term under this run's provisional reading. The CLI agents call is 0.5.33 (3 November 2026), the npm MCP package is 0.2.0, and Agents can start other agents is still an experiment, so the agent surface is pre-1.0 (0). 20 + 15 + 0 + 5 + 0 = 40. Accounts and the relay are hosted by Autonomous with no status page found on 17 October.

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.

Harness 85

Read as an MCP server and CLI. Eleven tools in source at v0.5.33, each with a typed JSON Schema input built by one helper, required fields marked, plus --json on every command. No OpenAPI, which a stdio server does not need (23). llms.txt and a Markdown-like agents page written for agents, per the 17 October check, not re-read on 4 November, since Autonomous's terms forbid access to its sites by automated means, including scripts or web crawlers, and its hosts are paused pending the founder (10). The tool descriptions and server instructions say when to call whoami first, to prefer a new project over an existing folder, to read before telling a harness more, and that turning a setting on is the person's yes to give (20). An enum on agent and on the setting name, minItems on wait names, minimum and maximum on timeout_seconds, a minimum on chars and limit. machine, folder, project and model are free strings (12). Worked examples, the exit code table and the Next: line per the 17 October reading of the agents page and llms.txt, with exit codes still in the source (13). Per-component semver tags, but the only CHANGELOG.md covers the provider protocol (0.3.0, 6 August 2026), and GitHub's release pages could not be read (7). 23 + 10 + 20 + 12 + 13 + 7 = 85.

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.

Harness 77

Eleven tools at v0.5.33 (seven on 17 October). Added since then are harness_search, harness_machines, harness_tell and harness_settings; harness_send and harness_tell are listed only inside a harness, so an agent outside one sees nine. Descriptions total about 4,000 characters. Judgement call. By the total, 11 tools fall in the 11 to 30 band (15), with 5 back for listing two tools only inside a harness (20). Counting only the nine an outside agent sees gives 25. We took the stricter reading, as the 17 October check counted the total (20). chars sizes a read (4,000 characters by default), limit sizes a search (10 by default), all widens the list, and any returns on the first finished harness. No pagination (14). Exit codes, refusals returned as answers rather than errors so a model does not retry them, and a timed-out wait reported as still working, in the source (19). readOnlyHint on whoami, list, search, machines, wait and read, destructiveHint false on start, tell and send, idempotentHint on close, and no hint on settings so an engine that asks before an unmarked tool asks the person (16). Two required fields on start, defaults of Claude Code and a 45-second wait. No SDK, but a CLI, an MCP server and a plugin with a skill (8). 20 + 14 + 19 + 16 + 8 = 77.

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.

Harness 75

v0.5.33_cli and v1.3.56_desktop on 3 November 2026 (30). 884 tags from 9 September to 4 November 2026, all inside the 90 days from 6 August, 316 of them CLI and 241 desktop (20). Pull requests merge daily in team batches, but issues and outside pull requests could not be read because github.com answers our proxy with 403 (5). In the official MCP registry since 19 October 2026 as ai.autonomous.harness/harness, a reverse-domain namespace for harness.autonomous.ai, with npm package @autonomous-ai/harness-mcp 0.2.0 and a checksummed MCPB file. The registry's latest entry is 0.4.20 while the CLI is 0.5.33 (15; 0 on 17 October, when there was no entry). CI workflows for the CLI, desktop, backend and OS, with dependency lockfiles current. Run results unread (5). 30 + 20 + 5 + 15 + 5 = 75.

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.