To determine the extent to which VINCI should utilize hybrid bonds relative to S&P Global Ratings' cap, we must analyze the company's current capital structure, the cost of capital environment, and the strategic benefits of hybrid instruments under the specified rating agency constraints.

**1. Analysis of Capital Structure and Rating Constraints**
S&P Global Ratings typically allows up to 15% equity credit for hybrid debt instruments within the "Total Adjusted Capital" (Debt + Equity). This means that for every €100 of hybrid bonds issued, only €15 counts as equity and €85 counts as debt for leverage ratio calculations.
*   **Current Leverage:** VINCI is a large infrastructure concession and construction group. These businesses are capital intensive but generate stable cash flows.
*   **Equity Base:** Total Equity (2023-01-01) is €29,409 million.
*   **Debt Base:** Total Liabilities are significantly higher, but we look at interest-bearing debt. Noncurrent bonds + Other borrowings + Current borrowings + Lease liabilities approximate the financial debt.
    *   Noncurrent Bonds: €20,425m
    *   Other Noncurrent Borrowings: €3,205m
    *   Short-term Borrowings: €6,368m
    *   Lease Liabilities (Current + Noncurrent): ~€2,100m
    *   Total Financial Debt ≈ €32,100m.
*   **Adjusted Capital:** Debt (€32.1bn) + Equity (€29.4bn) ≈ €61.5bn.
*   **Hybrid Capacity:** 15% of €61.5bn is approximately €9.2bn. VINCI currently has no significant hybrid bonds listed in the explicit breakdown (though "Other Noncurrent Liabilities" or specific bond tranches might contain them, the prompt implies a decision on *utilization*). If they have not issued hybrids, they have significant headroom.

**2. Market Environment and Cost of Capital**
*   **Interest Rates:** The swap curves for 2022 show a dramatic increase in rates compared to 2020-2021 (e.g., 10Y swap average went from -0.143% in 2020 to 1.927% in 2022). This increases the cost of senior debt.
*   **Credit Spreads:** The iBoxx EUR Non-Financial IG spread increased from 1.298% in 2021 to 2.295% in 2022.
*   **Hybrid Coupon:** Hybrid bonds carry a higher coupon than senior debt due to subordination and deferral risks. However, in a rising rate environment, the tax shield of debt remains valuable. More importantly, hybrids are treated as equity for leverage ratios.

**3. Strategic Rationale for Hybrids**
*   **Leverage Management:** VINCI operates in sectors (concessions) where maintaining an investment-grade rating is crucial for low-cost financing. Hybrids allow the company to raise capital that strengthens the balance sheet (via the 15% equity credit) without diluting existing shareholders (unlike issuing new shares).
*   **Rating Agency View:** S&P's 15% cap is a standard benchmark for strong investment-grade issuers. Utilizing hybrids up to this cap is a common strategy for companies like VINCI to optimize their Weighted Average Cost of Capital (WACC) while keeping reported leverage ratios within target bands for their desired credit rating (typically A-range for VINCI).
*   **Extent of Utilization:**
    *   **0%:** Too conservative. Ignores the benefit of equity credit for leverage optimization.
    *   **25%, 50%, 75%:** These percentages refer to the *extent relative to the cap*. If the cap is 15% of capital, utilizing 100% of the cap means issuing hybrids equal to 15% of adjusted capital.
    *   **100%:** This implies issuing hybrids up to the maximum limit allowed by S&P (15% of adjusted capital). For a company with VINCI's stable cash flows, large asset base, and need to fund growth (CAPEX of ~€2.6bn + acquisitions) while maintaining financial flexibility, maximizing the equity credit within the agency's guidelines is the optimal financial strategy. It provides the maximum leverage relief per euro of debt issued. Given VINCI's strong market position and the desire to maintain robust credit metrics amidst rising rates, filling the available hybrid "bucket" is standard best practice for such issuers.

Therefore, the company should utilize hybrid bonds to the fullest extent permitted by the rating agency's equity credit cap to optimize its capital structure.

<answer>100%</answer>