Letta vs Prime Agent

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.

Prime Agent 45

Harness reading of the framework line. --mode json emits a session event stream and rpc and acp modes exist, but we found no published schema or reference for them outside the source (10). docs.primeintellect.ai serves an llms.txt that still had no Prime Agent page on 3 November 2026 (0). The README states what the agent does, how it differs and that it is not a sandbox, and the bundled skills say when to use each function (10). CLI values are validated with messages that list the valid choices, and MCP tool schemas are read live from the server (7). The README gives the install line and the main commands, the repository's docs folder adds Slack and Google Workspace MCP connector guides, and the MCP skill documents its error types, but there is no headless or configuration guide (5). Versioned stable releases and, since 0.10.1 on 21 October 2026, a dated CHANGELOG.md in the repository. 0.10.0 has no entry and the nightly betas have none of substance (13). 10 + 0 + 10 + 7 + 5 + 13 = 45.

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.

Prime Agent 50

Harness reading of the framework checklist, as used 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. Usage telemetry is on by default. It is pseudonymous, limited to primitive values with no prompts, tool content or file paths per the source, disclosed on first run and mirrored to a local telemetry.jsonl (18). No approval prompts were found and there is no sandbox, which the README states. MCP tools can be limited with enabledTools and disabledTools, and the agent is told to recommend a connection, not make one (4). The README tells users to work only with trusted repositories, instructions and skills. No detection or mitigation found (5). Append-only JSONL session files, a prime-agent incident timeline command and the local telemetry mirror (12). The vendor's security policy has a reporting address, safe harbour, response times and discretionary rewards, scoped to its website and API. The repository has no SECURITY.md and no published advisories, CONTRIBUTING.md says to report privately without naming an address, and security.txt returned 404. security.txt still returned 404 on 3 November 2026 and the policy page (updated 6 May 2026) is unchanged. Fixes to the agent's own flaws ship in releases with no advisory (see negative). cargo-deny runs in CI (11). 18 + 4 + 5 + 12 + 11 = 50.

Letta 55

Apache-2.0 (30). The privacy policy has no date, no legal entity and no retention periods, and says hosted message data may train future models (8 of 30). The README and docs mark AgentFile, the Electron app and the V1 server as deprecated or retired, without dated notice periods (12 of 20). Telemetry is described in the privacy policy only as basic and opt-out when supported; the LETTA_CODE_TELEM=0 switch appears only in the source (5 of 20). Total 55.

Prime Agent 67

MIT in the LICENSE file and Cargo.toml, with a notice that the code is a port of a TypeScript product originally copyright Mario Zechner (30). The first-run notice and the telemetry crate README say what is sent and what is excluded, and name the endpoint and PostHog, but the vendor privacy policy, re-read on 3 November 2026, is still dated 23 February 2024, does not describe agent telemetry and gives no retention period for it (12). No deprecation policy found. Removed flags are recorded in change fragments and, since 0.10.1, in CHANGELOG.md (5). Telemetry is disclosed with a setting, a command and two environment variables to turn it off (20). 30 + 12 + 5 + 20 = 67.

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.

Prime Agent 73

Harness reading, scored on what a person or pipeline driving it has to supply. The model sees three tools (bash, edit, ipython), and MCP tools are searched, described and called from Python instead of being loaded into the prompt (23). Autonomous mode has limits for turns, tokens, time and continuations, a goal token budget and automatic compaction (17). A JSON event stream and exit codes for headless runs, described in the crate README and source only (10). Sessions resume, the daemon restarts workers and restores from JSONL files, refinements can be rolled back and quality gates retry (15). One command starts it and no SDK was found. A provider must be chosen through an interactive /login or supplied as a key first (8).

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.

Prime Agent 79

Stable v0.10.2 on 28 October 2026, six days before this check (30). 20 stable tags from v0.6.1 (5 August) to v0.10.2 in the 90 days from 5 August, beside more than 140 nightly beta tags since 30 September that a default install doesn't get (20). About 800 commits on main since 5 August. Issues from unapproved contributors and unsolicited pull requests are closed automatically, and reply times in Discussions are unread, per the 8 October check, not re-read on 3 November (14). Binaries for five targets from one release workflow and Homebrew definitions in the repository. No SDK and no registry package found (8). A pinned toolchain, a committed lockfile and cargo-deny with two triaged advisory exceptions reviewed on 17 September 2026. CI passing per the 8 October check (not re-read), and the npm audit findings in issue #3292 not verified (7). 30 + 20 + 14 + 8 + 7 = 79.