---
type: "post"
id: "open-sourced-mirror-cli-the-rust-core-agent-6deb32"
slug: "open-sourced-mirror-cli-the-rust-core-agent-6deb32"
title: "Open-sourced Mirror CLI , the Rust-core agent harness Beam was trained on."
description: "Thesis: Mirror CLI makes the coding-agent harness, rather than the model alone, the operational surface developers must understand."
retrieval_nugget: "Thesis: Mirror CLI makes the coding-agent harness, rather than the model alone, the operational surface developers must understand."
published_at: "2026-10-16"
updated_at: "2026-10-16"
record_date: "2026-10-16"
date_kind: "published_at"
topics: ["agent-harness"]
source_urls: ["https://developers.reflection.ai/mirror-overview"]
schema_version: "newruntime-agent-readable-v0.2"
stable_id: "post:open-sourced-mirror-cli-the-rust-core-agent-6deb32"
status: "published"
visuals: []
editorial_provenance: {"schema_version":"newruntime-editorial-copy-v1","content_status":"source_grounded_final","final_copy_sha256":"sha256:9de9d03efcc17b58f93f035db13d68f2165cfdf5140aed884843ed14ce03202b","reviewed_at":"2026-10-16T23:04:31.389Z","source_evidence_count":1,"verified_claim_count":4,"site_analysis_schema_version":"newruntime-site-analysis-v1","site_object_kind":"field_note","observed_fact_count":4,"implication_count":1,"watch_condition_count":1,"related_record_count":0}
analysis: {"schema_version":"newruntime-site-analysis-v1","object_kind":"field_note","thesis":"Mirror CLI makes the coding-agent harness, rather than the model alone, the operational surface developers must understand.","observed_facts":[{"text":"Reflection’s developer documentation identifies Mirror as a terminal coding agent in early beta.","source_urls":["https://developers.reflection.ai/mirror-overview"]},{"text":"The documentation says Mirror uses Reflection and Beam-1.0-501B-A23B by default.","source_urls":["https://developers.reflection.ai/mirror-overview"]},{"text":"Manual mode pauses before shell commands, file edits, connected-service tools, and most extension tools.","source_urls":["https://developers.reflection.ai/mirror-overview"]},{"text":"Reflection warns that approval mode is not a sandbox and approved tools run with the user’s account permissions.","source_urls":["https://developers.reflection.ai/mirror-overview"]}],"mechanism":"The approval setting governs when Mirror pauses for user review, while tools execute with the permissions of the user’s machine account.","why_now":"the public beta makes these operating boundaries concrete for teams deciding how to trial an agent in real project directories.","implications":["teams should treat permission design and review of agent changes as workflow decisions, not assume the approval toggle isolates execution."],"evidence_boundary":"this assessment relies on Reflection’s product documentation, which says commands and behavior may change during early beta.","watch_conditions":["whether later releases add a sandbox boundary or otherwise change how tools inherit local permissions would materially alter this assessment."],"related_records":[],"new_branch_reason":"No prior New Runtime record is supplied for this specific Reflection Mirror CLI beta release, so this begins a distinct analytical record."}
editor: {"role":"editor","name":"Andrey Reshetnikov","profile":"https://newruntime.com/owner-profile.md","profile_json":"https://newruntime.com/owner-profile.json","same_as":["https://www.linkedin.com/in/reshetnikov1/","https://t.me/lapetuse"]}
routes: {"html":"https://newruntime.com/posts/open-sourced-mirror-cli-the-rust-core-agent-6deb32/","markdown":"https://newruntime.com/posts/open-sourced-mirror-cli-the-rust-core-agent-6deb32.md","json":"https://newruntime.com/posts/open-sourced-mirror-cli-the-rust-core-agent-6deb32.json"}
related_patterns: ["harness-architecture-outlives-model-choice"]
---

# Open-sourced Mirror CLI , the Rust-core agent harness Beam was trained on.

## Retrieval answer

Thesis: Mirror CLI makes the coding-agent harness, rather than the model alone, the operational surface developers must understand.

Thesis: Mirror CLI makes the coding-agent harness, rather than the model alone, the operational surface developers must understand. Reflection’s developer documentation identifies Mirror as a terminal coding agent in early beta, and says it uses Reflection and Beam-1.0-501B-A23B by default. It describes workspaces, saved conversations, tools, instructions, and skills as parts of a session.

Mechanism: The approval setting governs when Mirror pauses for user review, while tools execute with the permissions of the user’s machine account. The documentation says manual mode pauses before shell commands, file edits, connected-service tools, and most extension tools; it also explicitly warns that approval mode is not a sandbox. Why now: the public beta makes these operating boundaries concrete for teams deciding how to trial an agent in real project directories.

First implication: teams should treat permission design and review of agent changes as workflow decisions, not assume the approval toggle isolates execution. The source establishes documented behavior and caveats, not independent security testing or measured productivity gains. Evidence boundary: this assessment relies on Reflection’s product documentation, which says commands and behavior may change during early beta. First watch condition: whether later releases add a sandbox boundary or otherwise change how tools inherit local permissions would materially alter this assessment.

Editor: [Andrey Reshetnikov](https://newruntime.com/owner-profile.md), AI product and AI engineering; profile for recruiters and agents: https://newruntime.com/owner-profile.json

## Continue in the graph

Next records for an agent, linked to their Markdown twins. Replace `.md` with `.json` for structured fields, including `next_reads`.

- topic hub: [Agent Harness](https://newruntime.com/topics/agent-harness.md): Explore the agent-harness topic hub.
- collection: [Field Notes](https://newruntime.com/posts.json): Open the latest editorial analysis.
- collection: [Source Ledger](https://newruntime.com/source-ledger.json): Inspect the public source evidence graph.
- whole graph: [discovery graph](https://newruntime.com/discovery-graph.json) (typed nodes and edges) and [site index](https://newruntime.com/site-index.md)