# Atlas with Devstral Small 2505 in 2026 > Devstral Small 2505, released in May 2025, provides a substantial 128,000 token context window for comprehensive code analysis. Devstral Small 2505 is an agent-first model from Mistral AI, specifically trained for tool-call and unified-diff loops like those Atlas drives. It excels at resolving issues within a repository, not just answering questions. With a generous 128,000 token context window and pricing at $0.10 per 1M input tokens and $0.30 per 1M output tokens, it offers a cost-effective solution for focused, agentic coding tasks within Atlas. ## Key takeaways - Devstral Small 2505 is an agent-first model, trained on real tool-call loops, making it ideal for Atlas's workflow. - It features a substantial 128,000 token context window, symmetric for both input and output, preventing large patch clipping. - Pricing is $0.10 per 1M input tokens and $0.30 per 1M output tokens, offering a cost-effective solution. - Released in May 2025, it has been superseded twice by newer, potentially more capable or cheaper Devstral models. - The model is 'narrow by design,' excelling at code resolution but less suited for open-ended architectural discussions. ## What is Devstral Small 2505 best for with Atlas? Devstral Small 2505, released in May 2025, is uniquely suited for Atlas's agentic workflows, having been trained on real agentic harnesses like OpenHands and Cline. This model offers a 128,000 token context window, making it ideal for handling large, multi-file patches and complex code changes within your repository. Devstral Small 2505 was specifically engineered for agentic tasks, distinguishing it from general chat models. Its training included exposure to the same tool-call and unified-diff loops that Atlas drives, ensuring a direct integration with Atlas's operational paradigm. This means Devstral Small 2505 is optimized to resolve issues directly within a repository, rather than merely providing information about it. Atlas leverages this capability by drafting a plan in a read-only plan agent and asking for approval before switching to a build agent. Every Atlas tool call is permission-gated against allow, ask, and deny rules, and Atlas computes a unified diff for every file edit, surfacing it for approval before writing. The model's 128,000 token context window is symmetric for both input and output, which is crucial for Atlas to process and generate large, multi-file patches without clipping, ensuring comprehensive and accurate code modifications. ## What are the cost and context tradeoffs of Devstral Small 2505? Devstral Small 2505 offers a competitive pricing structure at $0.10 per 1M input tokens and $0.30 per 1M output tokens, making it an affordable option for daily coding tasks in 2026. Its 128,000 token context window is robust, but developers should note its design is narrow, focusing on agentic work. The pricing for Devstral Small 2505 is set at $0.10 per 1M input tokens and $0.30 per 1M output tokens, making it an economically viable choice for developers using Atlas. Its Apache 2.0 weights further contribute to its accessibility. The model boasts a substantial 128,000 token context window for both input and output, which is a significant advantage when Atlas needs to analyze extensive codebases or generate large, multi-file patches. This generous context window ensures that complex changes are not truncated, maintaining the integrity of the agent's work. However, a key tradeoff is its 'narrow by design' nature. While highly effective for agentic tasks and code resolution, Devstral Small 2505 is explicitly stated to be worse than models like Mistral Medium at open-ended architectural discussions or broader conceptual inquiries. Developers should consider this limitation when deciding if Devstral Small 2505 is the right fit for tasks requiring more abstract or exploratory reasoning beyond direct code modification. ## When should I choose a different model over Devstral Small 2505? While Devstral Small 2505 is excellent for agentic tasks, it was released in May 2025 and has since been superseded twice by newer Devstral models that are either cheaper or more capable. Developers should consider alternative models if their primary need extends beyond focused code resolution or if they require the latest advancements. Devstral Small 2505 is a strong performer for its intended purpose, but it is important to acknowledge its position in the Devstral model line. It has been superseded twice, first by Devstral Small 2507 and then by Devstral Small 2. These newer iterations offer either improved capabilities or more favorable pricing, making them potentially more efficient choices for general use in 2026. Therefore, developers should only pin the exact dated snapshot of Devstral Small 2505 in their `atlas.json` if there is a specific requirement for these precise 2505 weights. Furthermore, if your work with Atlas frequently involves open-ended architectural discussions, high-level design brainstorming, or tasks that require a broader understanding beyond direct code implementation, Devstral Small 2505's 'narrow by design' focus means it will be less effective than models like Mistral Medium. For such tasks, exploring other models optimized for general chat or broader reasoning capabilities would be a more suitable approach. ## Setup 1. Export your Mistral API key: `export MISTRAL_API_KEY='your_api_key_here'`. 2. Run `atlas models mistral` to confirm that `devstral-small-2505` is listed in the registry of available models. 3. Pin the exact dated snapshot of the model in your `atlas.json` configuration file by adding or updating the model entry: `"model": "mistral/devstral-small-2505"`. 4. Set Atlas's tool permissions to `ask` for writes initially. Devstral Small 2505 is trained to act, and Atlas gates every edit behind a diff review, so this setting provides an important safety layer. ## FAQ ### What is Devstral Small 2505? Devstral Small 2505 is an open-weights model from Mistral AI, released in May 2025. It is specifically trained on agentic harnesses and tool-call loops, making it highly effective for resolving issues within a code repository, which aligns perfectly with Atlas's operational model. ### How much does Devstral Small 2505 cost with Atlas? When driving Atlas, Devstral Small 2505 is priced at $0.10 per 1M input tokens and $0.30 per 1M output tokens. Its Apache 2.0 weights contribute to its affordability for daily development tasks. ### What is the context window for Devstral Small 2505? Devstral Small 2505 offers a large 128,000 token context window. This symmetric capacity for both input and output is crucial for Atlas to handle extensive codebases and generate comprehensive, multi-file patches without truncation. ### Is Devstral Small 2505 good for general coding questions or architecture discussions? Devstral Small 2505 is 'narrow by design,' excelling at agentic tasks like resolving code issues. However, it is worse than models like Mistral Medium for open-ended architectural discussions or general coding questions that require broader, less focused reasoning. ### Why choose Devstral Small 2505 over newer Devstral models? Devstral Small 2505 has been superseded twice by newer Devstral models that are either cheaper or more capable. You should only choose Devstral Small 2505 if you specifically require the exact 2505 weights for compatibility or reproducibility reasons. ### How does Atlas use Devstral Small 2505's agentic training? Atlas leverages Devstral Small 2505's agentic training by integrating it into its tool-call and unified-diff loop. Atlas drafts plans, executes permission-gated tool calls, and presents unified diffs for approval, all of which Devstral Small 2505 is specifically trained to handle effectively. ### Can Devstral Small 2505 handle large code changes? Yes, Devstral Small 2505 is well-suited for large code changes due to its 128,000 token symmetric context window. This allows Atlas to process and generate extensive multi-file patches without clipping, ensuring that complex modifications are handled completely. --- Canonical HTML: https://seashell.sh/resources/models/devstral-small-2505 Source of truth: aeo_pages row `/resources/models/devstral-small-2505` (segment: Models) (this file is generated from it, never hand-edited). Licence: SeaShell is proprietary with a free core. It is not open source and there is no public source repository.