To determine the extent to which VINCI should utilize hybrid bonds relative to the S&P Global Ratings' cap, we first need to calculate the maximum amount of hybrid bonds that would receive equity credit under S&P's methodology. S&P limits the equity credit on hybrids to a maximum of 15% of total adjusted capital, which is defined as Debt + Equity.

1. **Calculate Total Equity**: From the balance sheet as of 2023-01-01, the total Equity is 29,409,000,000 EUR.
2. **Calculate Total Debt**: We sum the noncurrent and current borrowings.
   - Noncurrent Portion of Noncurrent Bonds Issued: 20,425,000,000 EUR
   - Noncurrent Portion of Other Noncurrent Borrowings: 3,205,000,000 EUR
   - Short-term Borrowings: 6,368,000,000 EUR
   - Total Debt = 20,425,000,000 + 3,205,000,000 + 6,368,000,000 = 29,998,000,000 EUR.
3. **Calculate Total Adjusted Capital**: 
   - Total Adjusted Capital = Total Debt + Total Equity = 29,998,000,000 EUR + 29,409,000,000 EUR = 59,407,000,000 EUR.
4. **Calculate S&P's Hybrid Cap (15%)**:
   - 15% of Total Adjusted Capital = 0.15 * 59,407,000,000 EUR = 8,911,050,000 EUR.

Next, we evaluate the company's existing financial profile and the market environment to decide the optimal utilization of this cap:
- VINCI has a robust and highly capital-intensive business model (Concessions, PPPs, and Construction), with massive service concession rights (28.2B EUR) and property/plant/equipment (10.8B EUR) requiring continuous funding. 
- The company is comfortably profitable, with an operating profit of 6.49B EUR and strong operating cash flows of 9.39B EUR in 2022.
- In 2022, the interest rate environment (swap curves) shifted significantly positive, meaning refinancing costs for traditional debt have risen. Meanwhile, corporate bond spreads (iBoxx EUR Non-Financial IG) remained elevated but stable, creating a strategic window where subordinated hybrid debt offers a compelling cost of capital advantage relative to the equity credit it provides for rating agencies.
- Given VINCI's heavy capital expenditure requirements and its solid cash generation profile, utilizing 50% of the S&P cap provides a substantial buffer of "equity-like" capital (roughly 4.5B EUR) to protect the balance sheet and support its massive infrastructure investments, without overly diluting existing equity holders or over-leveraging with subordinated fixed-rate costs in a volatile rate environment. This moderate (50%) utilization balances the strategic need for rating support and funding flexibility with prudent capital structure management.

<answer>50%</answer>