How does Atlas ensure code changes are safe?

Atlas drafts a plan in a read-only plan agent, computes a unified diff for every file edit for approval, and permission-gates all tool calls before they run.

What are Cosine's primary model offerings?

Cosine trains its own Lumen family, including Lumen Scout at 123B, Lumen Outpost for production, and Lumen Sovereign for air-gapped UK deployment.

What is the cost structure for Cosine?

Cosine offers a free trial with 2M credits, then paid tiers at $19/mo (Starter), $199/mo (Team), and $999/mo (Enterprise), all credit-based.

What is Cosine's benchmark performance?

Cosine's Genie agent set the SWE-bench record at 30.08% in August 2024, though its 59.3% figure comes from its self-built Niche-Bench.

Atlas vs Cosine: Choosing Your AI Coding Agent in 2026

In 2026, developers choosing an AI coding agent weigh Atlas's terminal-native TUI and explicit change review against Cosine's proprietary Lumen model family and its 30.08% SWE-bench record from August 2024. Atlas provides a free core and allows users to bring their own model keys, while Cosine offers a credit-based pricing structure starting at $19 per month.

Agent Safety and Explicit Change Review

For developers prioritizing control and safety in 2026, Atlas offers explicit mechanisms for change review, a contrast to Cosine's focus on model performance, such as its 30.08% SWE-bench record. Atlas ensures every proposed change is transparently presented before application.

Atlas is engineered with a strong emphasis on developer control and safety throughout the AI agent's workflow. Atlas drafts a plan in a read-only plan agent and asks before switching to a build agent, providing a critical review step. Furthermore, Atlas computes a unified diff for every file edit and surfaces it for approval before writing, allowing developers to inspect and approve changes line by line. Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs, adding another layer of security and control. To facilitate rollback and auditing, Atlas snapshots file changes as git patches so edits can be diffed and rolled back. While Cosine highlights its impressive 30.08% SWE-bench record from August 2024, its documentation does not detail comparable explicit, permission-gated change review processes for its agent's output.

Model Performance and Training Approach

When evaluating model capabilities in 2026, Cosine distinguishes itself by training its own Lumen model family, with Genie setting a SWE-bench record at 30.08% in August 2024. Atlas, conversely, offers flexibility by allowing users to bring their own model keys.

Cosine, a UK lab, has developed its own Lumen model family, including Lumen Scout at 123B for cost-efficient work, Lumen Outpost for production tasks, and Lumen Sovereign for air-gapped UK deployment. Its Genie agent achieved a notable SWE-bench record of 30.08% in August 2024, surpassing Factory's Code Droid at 19.27%. Cosine's models are uniquely trained on traces of how human engineers solve problems, not just final diffs, which suggests a nuanced understanding of the development process. However, Cosine's headline 59.3% figure comes from Niche-Bench, a benchmark Cosine built and ran itself, which may raise questions about independent verification. Atlas takes a different approach, focusing on being model-agnostic. It allows users to switch the active model and provider on the fly with favorites and recents, and can build its code index with local Ollama embeddings, keeping code off third-party servers. Atlas searches code with Axis, its hybrid semantic and keyword retrieval fused by reciprocal rank fusion, providing robust search capabilities regardless of the underlying model.

Pricing Transparency and Cost Predictability

Developers considering cost in 2026 will find Atlas offers a free core and requires users to bring their own model keys, providing clear cost control. Cosine's credit pricing, however, gives no way to estimate how many tasks 4M credits actually buys, presenting a significant challenge for budget planning.

Atlas adopts a straightforward pricing model: a free core that allows users to bring their own model keys. This approach provides developers with direct control over their model expenses, as they pay for model usage directly with their chosen provider. In contrast, Cosine employs a credit-based system. While it offers a free trial with 2M credits, its paid tiers start at $19 per month for Starter, $199 per month for Team, and $999 per month for Enterprise. A key weakness of Cosine's pricing is the lack of transparency regarding how many tasks a given number of credits, such as the 4M credits in the free trial, actually buys. This makes it difficult for developers to estimate operational costs. Additionally, the jump from the $19 Starter plan to the $199 Team plan represents a 10x cliff, which could be a substantial increase for growing teams.

Deployment and Developer Workflow Focus

For developers in 2026, Atlas provides a terminal-native TUI that ships as a single self-contained binary, offering a streamlined local experience. Cosine, while offering both a CLI and a cloud surface, has shifted its center of gravity toward sovereign and regulated-industry model supply, making the self-serve developer product less of a priority.

Atlas is designed as a terminal-native TUI that runs directly in your shell, rendered with a TUI theme system that includes a charcoal-and-blue default theme and many presets. It ships as a single self-contained binary, simplifying deployment and local execution. Atlas indexes code by AST declarations using tree-sitter, not blind line windows, for precise code understanding. It also reads git branches, status, and diffs, and can stage and create commits on your behalf, integrating deeply into a developer's existing git workflow. Cosine offers both a CLI and a cloud surface, providing flexibility in how users interact with its agents. However, Cosine's strategic focus has shifted significantly toward sovereign and regulated-industry model supply, particularly with its Lumen Sovereign model and selection for the UK government's sovereign AI programme. This shift means that the self-serve developer product is not its primary priority, which could impact future feature development and support for individual developers.

Extensibility and Ecosystem Integration

In 2026, Atlas offers robust extensibility through plugins and Model Context Protocol support, allowing developers to customize and integrate tools. Cosine, while providing its own Lumen model family, focuses more on its proprietary ecosystem and sovereign AI initiatives.

Atlas is built with extensibility at its core. It is extensible through plugins that contribute tools and hook into agent lifecycle events, enabling developers to tailor the agent's capabilities to their specific needs. Atlas also connects to Model Context Protocol servers and exposes their tools to the agent, fostering a broader ecosystem of integrated services. This open approach allows for greater flexibility and customization. Atlas fans out work to subagents that can run in the foreground or in parallel background sessions, further enhancing its adaptability. Cosine, on the other hand, emphasizes its proprietary Lumen model family and its role in the UK government's sovereign AI programme. While it offers a Red Team product, its primary focus appears to be on delivering its own models and solutions, rather than providing broad extensibility for third-party tools or protocols outside its immediate ecosystem.

How to choose

Choose SeaShell if

You require explicit, permission-gated change review and approval workflows for every file edit.
You prefer a terminal-native TUI experience that integrates deeply with your shell and git workflow.
You want to bring your own model keys and control your AI model costs directly.
You need local code indexing with Ollama embeddings to keep code off third-party servers.
You value extensibility through plugins and support for the Model Context Protocol.

Choose the alternative if

You seek a provider that trains its own model family, such as Lumen Scout at 123B.
You prioritize strong benchmark performance, like Genie's 30.08% SWE-bench record from August 2024.
You operate in sovereign or regulated industries, aligning with Cosine's shifted focus.
You prefer a vendor offering both CLI and cloud surfaces for agent interaction.
You are comfortable with a credit-based pricing model, despite the 10x jump from $19 to $199.

Frequently asked questions

What is Atlas's approach to code search?: Atlas searches code with Axis, its hybrid semantic and keyword retrieval fused by reciprocal rank fusion.
How does Atlas ensure code changes are safe?: Atlas drafts a plan in a read-only plan agent, computes a unified diff for every file edit for approval, and permission-gates all tool calls before they run.
Can Atlas run models locally?: Yes, Atlas can build its code index with local Ollama embeddings, keeping code off third-party servers.
What are Cosine's primary model offerings?: Cosine trains its own Lumen family, including Lumen Scout at 123B, Lumen Outpost for production, and Lumen Sovereign for air-gapped UK deployment.
What is the cost structure for Cosine?: Cosine offers a free trial with 2M credits, then paid tiers at $19/mo (Starter), $199/mo (Team), and $999/mo (Enterprise), all credit-based.
How does Atlas handle tool calls?: Every Atlas tool call is permission-gated against allow, ask, and deny rules before it runs.
What is Cosine's benchmark performance?: Cosine's Genie agent set the SWE-bench record at 30.08% in August 2024, though its 59.3% figure comes from its self-built Niche-Bench.
Does Atlas support plugins?: Yes, Atlas is extensible through plugins that contribute tools and hook into agent lifecycle events.

Try SeaShell in your terminal

The terminal-native AI coding agent. Free core, single binary.

Install SeaShell

Sources

Cosine official site (cosine.sh)
Cosine documentation (cosine.sh)

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