The Tool Desk
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How to choose a Copilot Cowork model
- Start with Auto for everyday work. Microsoft recommends Auto for most tasks. It chooses from the models enabled by your organization. See Microsoft’s Copilot Cowork model guide.
- Override only for a concrete reason. Use Microsoft’s task descriptions as a starting point: Claude Sonnet 5 is positioned for everyday tasks and fast responses; Opus 5 for complex, high-stakes work; GPT 6 Astra for tough problems; GPT 5.6 Terra for common tasks; and GPT 5.6 Sol for hard work. These are Microsoft’s descriptions, not independent head-to-head test results.
- Choose reasoning effort separately. Medium is the default. Light suits lighter tasks; High or Extra High is intended for deeper analysis or more complex reasoning; Max is available for the hardest work. Higher effort can produce more thorough responses, but it takes longer and uses more credits.
- Check the selection when the task changes. The effort setting persists for later tasks until you change it. Look at the conversation’s model badge to confirm which model is selected.
- Check your organization’s rules. The picker shows what your organization makes available. Administrators can disable the Anthropic model family tenant-wide, in which case Auto selects from the other enabled models.
- Read model-specific notices before using an option. Microsoft says some models, including Claude Fable 5 (Preview), require data retention and display a notice in the picker and a banner while selected. Fable 5 Preview is off by default and requires administrator enablement. Follow the notice and your organization’s policy.
What the available model descriptions mean
Microsoft’s model guide, updated September 14, 2026, describes these options. The list visible in your Cowork picker may differ because availability depends on organization settings. Model names and availability can change, so check the live picker.
| Picker option | Microsoft’s stated positioning | Provider or hosting detail |
|---|---|---|
| Auto | Default for most day-to-day work; Cowork selects based on models enabled by the organization. | Not applicable; selection is automatic. |
| GPT 5.5 (Frontier) | Capable model for medium-effort work. | Hosted in Azure AI Foundry. |
| GPT 5.6 Sol | Intelligent and efficient for hard work. | Provided by OpenAI as a subprocessor. |
| GPT 5.6 Terra | Balanced effort for common tasks. | Provided by OpenAI as a subprocessor. |
| GPT 6 Astra | Latest model for tough problems. | Not stated in Microsoft’s model guide. |
| Opus 5 | For complex, high-stakes work. | Not stated in Microsoft’s model guide. |
| Claude Sonnet 5 | For everyday tasks and fast responses, including drafting, quick lookups, and day-to-day work. | Not stated in Microsoft’s model guide. |
| Claude Fable 5.1 | Most advanced model for ambitious work. | Not stated in Microsoft’s model guide. |
The model guide does not establish that one option is objectively best across tasks. Use the descriptions to narrow a choice, then judge whether the result suits the work. Microsoft’s Copilot Cowork release notes, updated September 25, 2026, record the September additions of Fable 5.1 and GPT 6 Astra.
How to decide whether a manual model choice is worthwhile
- Routine, low-stakes work: Keep Auto. If you specifically want a quick draft or lookup, Sonnet 5 is Microsoft’s clearest stated fit for fast, everyday responses.
- Harder analysis: Consider Sol for hard work or Astra for tough problems, based on Microsoft’s descriptions. Raise reasoning effort if you need deeper or more thorough analysis and can accept the time and credit trade-off.
- High-stakes work: Opus 5 is described for complex, high-stakes tasks. Treat that as guidance for choosing a starting point, not a guarantee of correctness; check its output against source material before acting.
- Common work where you want a balanced approach: Terra is positioned for common tasks. Auto remains appropriate if you have no specific reason to select it.
Compare options by task difficulty and stakes, desired response speed and depth, effort-related time and credit use, and whether the model is permitted under your organization’s settings. Microsoft says model choice can affect response depth and style. Its official guidance is product positioning, not independent performance benchmarking.
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Review the answer before relying on it
Check important Cowork output against the documents or other source material it used, and review consequential work before taking action. Microsoft’s Responsible AI FAQ for Cowork provides additional context on Auto, safety policies, and data access. A model selection does not remove the need to verify important results.
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