Choosing a Model for Claude for Excel | How to Use Sonnet and Opus

What Is Claude for Excel — The AI Assistant Living in Your Spreadsheet Sidebar

What You Can Do with the Sidebar

Claude for Excel is an add-in that sits as a sidebar on the right side of Microsoft Excel, understands the open workbook, and responds conversationally. Ask it a question about your spreadsheet and it answers while showing which cells it referenced — handling everything from formula creation and editing to building new models. The big win is replacing the manual work of hand-writing functions with natural-language instructions.

The key point is that Claude transparently tracks and explains what it changed to the user. In spreadsheets, one cell change can cascade through many others, so AI edits can easily become a black box. Claude for Excel shows the changes and their rationale, making it practical for finance professionals who need to verify results (Anthropic official announcement).

From the October 2025 Announcement to General Availability

Claude for Excel emerged as part of the "Claude for Financial Services" enhancements Anthropic announced on October 27, 2025. At launch it was positioned as a beta feature for Max, Enterprise, and Team plans, but after subsequent updates it is now generally available (GA) for all paid Claude plans across Excel, PowerPoint, and Word (Claude for Excel official page). The rapid move from beta to GA reflects strong demand from heavy spreadsheet users in finance and accounting.

The Models Behind Claude for Excel — How Sonnet and Opus Split the Work

The Foundation: Sonnet 4.5, Which Topped Financial Tasks

The model underpinning Claude for Excel is Claude Sonnet 4.5, which Anthropic put front and center in its financial services announcement. Sonnet 4.5 achieved 55.3% accuracy on Vals AI's Finance Agent benchmark — a measure of how accurately AI models handle multi-step financial tasks — setting a state-of-the-art mark at the time (Anthropic official announcement). Vals AI is an independent third-party benchmark provider that evaluates AI models on real-world task execution, and Finance Agent specifically measures how far a model can complete multi-step financial work. The fact that the benchmark creator and evaluator are separate is what gives the 55.3% figure its credibility. Spreadsheets are a domain of chained numerical calculations and conditional logic, so benchmark strength translates directly into real-world reliability.

Speed with Sonnet, Depth with Opus — Which Should You Choose?

The practical guideline for Claude for Excel is deciding whether you need processing speed or reasoning depth. The Sonnet tier responds quickly and suits everyday tasks like lightweight aggregation, formula generation, and single-sheet formatting. For serious financial modeling that requires reconciling assumptions across multiple tabs, or scenario analysis with complex dependencies, switching to the higher-capability Opus tier tends to deliver more consistent accuracy. Third-party practical guides also recommend the upper-tier model for complex models and multi-tab analysis (DataCamp tutorial).

Note that "Sonnet tier" and "Opus tier" in this article do not refer to fixed version numbers — the system automatically applies the latest generation of the Sonnet or Opus family available in your Claude plan. Anthropic does not officially disclose the specific model version tied to Claude for Excel, so this article avoids asserting specific version numbers and proceeds on the assumption that the latest generation is assigned based on your plan (the available generation varies by plan).

Practical Decision Criteria for Model Selection

When you are unsure which model to use, work through these questions in order:

1. First look at the depth of recalculation needed. Aggregation or formatting within a single sheet can be handled quickly by the Sonnet tier.
2. Then check for cross-tab dependencies. If you need to reconcile assumptions across multiple tabs, switch to the Opus tier.
3. Finally consider verification cost. For financial models where errors directly affect downstream decisions, prioritize accuracy with the upper-tier model even if it is slower.

The models available to you depend on your Claude plan. See the Claude pricing comparison article for plan-by-plan differences. Since Anthropic continuously updates model generations, it is also worth noting that both Sonnet and Opus keep improving in accuracy with each new generation.

Cell-Level Citations — The Core Feature of Claude for Excel

Cell-Level Quotes Show Exactly "What It Looked At"

The biggest differentiator of Claude for Excel is that it attaches cell-level citations to its answers. Ask "What's the basis for this sales forecast?" and Claude answers while showing the cell addresses it referenced. Because you can immediately trace back to the source data without blindly trusting the AI's output, it is easy to adopt even in workflows that involve audits or manager reviews.

Detecting and Repairing Formula Errors

Formula errors like #REF!, #VALUE!, and #DIV/0! are frequent headaches in real spreadsheet work. Claude for Excel detects these errors, identifies the broken references or type mismatches causing them, and presents a fix. This shortens the root-cause investigation that used to mean chasing cells one by one.

Cross-Tab Workbook Analysis

Real financial models often split inputs, assumptions, calculations, and outputs across multiple tabs. Claude for Excel seamlessly traverses workbooks spanning multiple tabs, performing consistency checks and summaries across them (Claude Help Center). This is also the domain where the Opus tier's reasoning power pays off — large-scale models that a single prompt cannot fully handle benefit from deeper inference.

Supported Plans and Versions — Know Exactly What Environment You Need

Before setting up, confirm that your Excel environment and Claude plan are compatible. The main compatibility details are as follows (Claude Help Center):

Note that perpetual-license versions Excel 2016 and 2019 are not supported — a Microsoft 365 subscription is required. The Android version of Excel is also currently out of scope.

Setup Instructions — Installation Differs for Individual Users and Admins

Step 1: Individual Users Enable the Add-in

To try it on your own, enable it with these steps:

1. Open "Claude by Anthropic for Excel" in the Microsoft Marketplace and install it with "Get it now."
2. Launch Excel and enable Claude from the ribbon or the add-in list.
3. Sign in to your Claude account in the sidebar that appears.
4. Open your target workbook, type an instruction in the sidebar, and you are ready to go.

Step 2: Admins Deploy to the Entire Organization

To distribute it across an organization, an IT admin deploys it in bulk from the admin center:

1. Sign in to the Microsoft 365 admin center and go to Settings > Integrated apps.
2. Upload the Claude for Excel manifest XML.
3. Specify the target users or groups and deploy.
4. Guide users to sign in to their Claude accounts and confirm access permissions.

For delegated access concepts and general Microsoft 365 integration settings, the Claude Cowork Guide will help you get up to speed quickly.

Putting the Model to Work — Practical Examples in Financial Modeling

Sample Instructions to Type in the Sidebar

"Give instructions through conversation" is easy to say but hard to know where to start, so here are example prompts to actually type in the sidebar, organized by model tier. Swap in your own workbook's cell addresses and tab names and you can reproduce these almost as-is.

For the Sonnet tier (speed-focused, everyday single-sheet tasks)

Calculate the year-over-year growth rate from monthly sales in B2:B13 and put the results in column D.

Based on the sales table, summarize regional totals and percentage shares in the empty columns to the right.

For the Opus tier (cross-tab, full-scale modeling that preserves dependencies)

Change the discount rate in the Assumptions tab from 8% to 10% and recalculate how the enterprise value in the DCF tab changes while keeping all dependencies intact.

Update the median EV/EBITDA multiple in the Comparable Companies tab, reflect it in the Valuation tab assumptions, and explain how the target share price changes along with the source cells.

In all cases, Claude responds by showing the cells it changed and the rationale behind them. Rather than taking the output at face value, verify the cited source cells as you go — that is the safe approach.

Updating Assumptions Safely

In financial modeling, you often explore multiple scenarios by changing assumption values like growth rates or discount rates. Claude for Excel can update assumptions while preserving formula dependencies, reducing the risk that changing one assumption breaks the entire model. The more complex the dependency structure, the more the Opus tier's reasoning helps prevent incorrect updates.

Building Models from Templates

Beyond building models from scratch, Claude for Excel is also designed for building new models on top of existing templates. Standard financial models like comparable company analysis and DCF (Discounted Cash Flow) come together faster when combined with Anthropic's reference implementations for financial use cases. The Claude finance agent templates article covers template-based approaches in detail.

Things to Watch Out For — Accuracy, Verification Workflows, and Data Scope

As convenient as it is, using AI output directly for decision-making is not advisable. Even though Claude for Excel shows cell-level citations, your workflow should assume that humans verify the final numbers. Especially in fields like finance and accounting where errors translate directly into losses, it is essential to build a human final-review step into any important calculation.

Also, Claude can only access the workbook the user has open — it does not read internal data without limits. When handling confidential data, clarifying the scope of use in line with your organization's data governance policy will make it easier to get sign-off from your information security team. Just like model selection, balancing "speed" and "caution" based on the importance of the task is the key to making Claude for Excel work for you long-term.

Summary — Automate Your Spreadsheets by Choosing the Right Model

Claude for Excel, built on Sonnet 4.5 and purpose-built for spreadsheets, is already in general availability across all paid plans. Keep the rule simple: Sonnet tier for everyday speed, Opus tier for the depth needed in complex financial modeling — and you will avoid waste on both accuracy and cost. By leveraging the transparency of cell-level citations and pairing it with a human verification workflow, you have the most reliable path to trustworthy automation. If you want to deepen your understanding of Claude's model lineup overall, check out the Claude Opus article as well.

References — Official Anthropic Materials and External Resources Cited in This Article

• Anthropic: Advancing Claude for Financial Services (2025-10-27)
• Claude for Excel official page
• Claude Help Center: Use Claude for Excel
• DataCamp: Claude in Excel Tutorial