Summary of Arthur Proposal Project William August 28, 2020

2 Summary of Arthur Proposal Parties to Proposal Arch Capital Group, Ltd.Kelso & CompanyWarburg Pincus LLCCollectively, the “Consortium” Purchase Price $25.00 per Share, or 0.65x P/TBV at 6/30/2020 Assumes no dividends paid from 06/30/2020 to close, and that debt and preferred stay in place Consideration 100% cash Acquiror Newly formed Bermuda vehicle capitalized by Consortium Strategy Stabilize William’s ratings profile, eliminating risk of potential downgradeEliminate exposure to current investment portfolio’s volatilityPrivate ownership more suited for underwriting strategy Conditions Approval of Arthur board of directors and investment committees of Kelso and Warburg PincusSatisfactory completion of due diligenceExecution of definitive documentation Financing 100% equity financedClosing would not be contingent on financing Timing Believe they can complete due diligence and finalize definitive agreement within 3 weeks

3 William Stock Price Analysis Since William Listing Source: Capital IQ, SNL Financial (08/21/2020) 10/29/2019: All-Time High of $28.90 5/14/2020: All-Time Low of $10.86 $16.40 2/19/2020 (Pre-COVID S&P500 High): $24.42 Stock Price ($) Volume (Shares, MM) $25.76Pre-COVID Listing-to-Date VWAP $25.00Arthur Proposal

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