In 2026, developers choosing between terminal AI coding agents will weigh Atlas, a terminal-native TUI agent, against Greptile, a pull request reviewer that uniquely executes code in a sandbox. Atlas offers a free core and local Ollama embeddings for privacy, while Greptile provides execution evidence and a memory system, though it logged 11 false positives in one 50-PR benchmark.
Change Review and Safety: Approval Workflows and Execution Evidence
For developers in 2026, ensuring safe code changes is paramount, and Greptile's TREX system uniquely runs code in a sandbox, attaching execution evidence to pull requests, which its evaluations credit with roughly 20% more bugs caught. Atlas, by contrast, prioritizes explicit developer control, drafting a plan in a read-only plan agent and asking for approval before switching to a build agent.
Atlas provides a robust safety mechanism by drafting a plan in a read-only plan agent and asking for developer approval before it switches to a build agent. It computes a unified diff for every file edit and surfaces it for approval before writing, ensuring transparency and control. Atlas also snapshots file changes as git patches so edits can be diffed and rolled back, and reads git branches, status, and diffs, with the ability to stage and create commits on your behalf. Greptile, on the other hand, integrates into the pull request workflow, using its TREX system to execute the code under review in a sandbox. This execution evidence is attached to the pull request, and Greptile's evaluations credit TREX with roughly 20% more bugs caught. However, TREX inherits execution flakiness, meaning unstable environments and flaky tests can create their own class of false positives.
Code Execution and Verification: Sandbox Runs vs. Permission-Gated Tools
Greptile distinguishes itself by executing code under review in a sandbox via its TREX system, a feature credited with catching approximately 20% more bugs, though it can suffer from execution flakiness. Atlas, on the other hand, focuses on permission-gated tool calls, where every tool call is checked against allow, ask, and deny rules before it runs, providing a different layer of control.
Greptile's core verification strength lies in its TREX system, which runs the code under review in a sandbox environment. This unique capability allows Greptile to attach execution evidence directly to pull requests, a method that its evaluations suggest leads to roughly 20% more bugs being caught. However, the effectiveness of TREX can be hampered by execution flakiness, where unstable environments or unreliable tests can generate false positives. Atlas approaches code verification through permission-gated tool calls. Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, giving developers granular control over what actions the agent can take. Atlas also connects to Model Context Protocol servers and exposes their tools to the agent, and is extensible through plugins that contribute tools and hook into agent lifecycle events.
Accuracy and False Positives: Benchmarks and Developer Control
In third-party head-to-head benchmarks, Greptile recorded the highest absolute false-positive count, with one 50-PR benchmark logging 11 false positives compared to 2 for CodeRabbit, indicating a potential challenge for developers. Atlas addresses accuracy through its explicit approval workflow, computing a unified diff for every file edit and surfacing it for approval before writing, giving developers direct control over changes.
Greptile's approach, while innovative with its TREX system, has shown a higher incidence of false positives. A specific 50-PR benchmark recorded 11 false positives for Greptile, significantly more than the 2 logged for CodeRabbit in the same test. This can be partly attributed to TREX's inherited execution flakiness, where unstable environments or flaky tests can lead to incorrect bug detections. Atlas mitigates false positives by integrating the developer into a continuous approval loop. It drafts a plan, asks for approval, and then computes a unified diff for every file edit, which is surfaced for approval before any changes are written. This human-in-the-loop design ensures that only intended and verified changes are applied. Atlas also searches code with hybrid semantic and keyword retrieval fused by reciprocal rank fusion, and indexes code by AST declarations using tree-sitter, not blind line windows, contributing to its understanding of the codebase.
Pricing Models and Open Source Accessibility
Greptile offers a Starter free tier for 1 developer with 50 credits per month, and provides 50% off for pre-Series A startups, making it accessible for certain projects. Atlas, conversely, operates on a free core model, requiring users to bring their own model keys, which allows for flexibility in model choice and cost management.
Greptile provides a tiered pricing structure designed to accommodate various user needs. Its Starter plan is free for 1 developer and includes 50 credits per month. For larger teams, the Pro plan costs $30 per seat per month, with Enterprise pricing available as a custom solution. Overage credits are priced at $1 per review, and TREX runs consume 3 credits each. Greptile also supports the open-source community by being free for MIT and Apache non-commercial open source projects, and offers a 50% discount for pre-Series A startups. Atlas, in contrast, ships as a single self-contained binary with a free core. Its model is 'bring your own model keys,' meaning users are responsible for their own API costs with AI providers. This approach offers developers maximum flexibility in choosing their preferred models and managing their AI expenditure directly, without being tied to a specific credit system or subscription for core functionality.
Code Indexing and Data Privacy: Local Embeddings vs. Codebase Graph
Atlas offers a strong privacy stance by building its code index with local Ollama embeddings, ensuring code remains off third-party servers, a significant advantage for sensitive projects. Greptile, while building a graph of the whole codebase for its review process, does not specify local embedding options, which might be a consideration for teams with strict data residency requirements in 2026.
For developers concerned with data privacy and residency in 2026, Atlas provides a compelling option by allowing its code index to be built with local Ollama embeddings. This capability ensures that sensitive code never leaves local machines or third-party servers, offering enhanced security and compliance. Atlas indexes code by AST declarations using tree-sitter, providing a precise and structured understanding of the codebase. Greptile, on the other hand, builds a comprehensive 'graph of the whole codebase' to facilitate its review process. While this approach is central to its functionality, the context does not specify options for local embedding generation or explicit data residency controls, which could be a factor for organizations with stringent privacy policies. Atlas's ability to keep code off third-party servers by default for indexing purposes presents a clear differentiator in this regard.
Workflow and User Experience: Terminal-Native TUI vs. PR Reviewer
Atlas provides a terminal-native TUI that runs directly in your shell, offering a deeply integrated developer experience with a TUI theme system and many presets. Greptile, on the other hand, functions primarily as a reviewer that attaches evidence to pull requests, integrating into existing code review workflows rather than providing a direct terminal agent experience for developers in 2026.
Atlas is designed as a terminal-native TUI, providing a direct experience directly within the developer's shell. It ships with a TUI theme system, including a charcoal-and-blue default theme and many presets, allowing for personalization. This deep integration means Atlas can read git branches, status, and diffs, and can stage and create commits on your behalf, making it a comprehensive terminal-based coding agent. Atlas also lets you switch the active model and provider on the fly with favorites and recents, and fans out work to subagents that can run in the foreground or in parallel background sessions. Greptile operates as a pull request reviewer, integrating into existing code review platforms. Its primary function is to analyze code, execute it in a sandbox via TREX, and attach execution evidence to pull requests. Greptile also features a memory system that learns from the team's comments, replies, and reactions, suppressing suggestion classes that are consistently ignored, thereby adapting to team preferences over time. This positions Greptile as an enhancement to the PR review process, distinct from Atlas's direct terminal interaction model.
How to choose
Choose SeaShell if
- You prioritize a terminal-native TUI experience that runs directly in your shell.
- You require explicit approval for every code change, with unified diffs before writing.
- You need to keep code off third-party servers by building your code index with local Ollama embeddings.
- You prefer a free core model where you bring your own model keys for flexibility.
- You value permission-gated tool calls against allow, ask, and deny rules.
- You need an agent that can read git branches, status, and diffs, and stage and create commits.
Choose the alternative if
- You need a pull request reviewer that executes code in a sandbox via TREX, crediting it with roughly 20% more bugs caught.
- Your team benefits from a memory system that learns from comments and reactions to suppress ignored suggestions.
- You are an MIT or Apache non-commercial open source project, eligible for free usage, or a pre-Series A startup with 50% off.
- You are comfortable with a higher absolute false-positive count, as logged in one 50-PR benchmark (11 false positives).
- You operate within a workflow where 50 credits per seat per month is sufficient, or you are prepared for overage costs at $1 per review and 3 credits per TREX run.
Frequently asked questions
- What is Atlas's approach to code changes?
- Atlas drafts a plan in a read-only plan agent, asks for approval, then switches to a build agent, computing a unified diff for every file edit and surfacing it for approval before writing.
- How does Greptile verify code?
- Greptile uniquely executes code under review in a sandbox through its TREX system, attaching execution evidence to the pull request, which its evaluations credit with roughly 20% more bugs caught.
- Does Atlas support local code indexing?
- Yes, Atlas can build its code index with local Ollama embeddings, keeping code off third-party servers, and indexes code by AST declarations using tree-sitter.
- What are Greptile's pricing options for open source?
- Greptile is free for MIT and Apache non-commercial open source projects, and offers 50% off for pre-Series A startups, with a Starter free tier for 1 developer with 50 credits per month.
- What is a known weakness of Greptile?
- Greptile has the highest absolute false-positive count in third-party head-to-heads; one 50-PR benchmark logged 11 false positives against 2 for CodeRabbit, partly due to TREX execution flakiness.
- Can Atlas integrate with existing models?
- Atlas allows users to bring their own model keys and lets them switch the active model and provider on the fly with favorites and recents, and connects to Model Context Protocol servers.
- How does Greptile learn from team feedback?
- Greptile features a memory system that learns from the team's comments, replies, and reactions, and suppresses suggestion classes that are consistently ignored.
- What kind of user interface does Atlas provide?
- Atlas provides a terminal-native TUI that runs in your shell, rendered with a TUI theme system including a charcoal-and-blue default theme and many presets.
Try SeaShell in your terminal
The terminal-native AI coding agent. Free core, single binary.
Install SeaShellSources
- Greptile official site (greptile.com)
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