The Company's reserves for losses and loss expenses are comprised of case reserves and incurred but not reported liabilities ("IBNR"). When a claim is reported, a case reserve is established for the estimated ultimate payment based upon known information about the claim. As more information about the claim becomes available over time, case reserves are adjusted up or down as appropriate. Reserves are also established on an aggregate basis to provide for IBNR liabilities and expected loss reserve development on reported claims.

Loss reserves included in the Company’s financial statements represent management’s best estimates based upon an actuarially derived point estimate and other considerations. The Company uses a variety of actuarial techniques and methods to derive an actuarial point estimate for each operating unit. These methods include paid loss development, incurred loss development, paid and incurred Bornhuetter-Ferguson methods and frequency and severity methods. In circumstances where one actuarial method is considered more credible than the others, that method is used to set the point estimate. The actuarial point estimate may also be based on a judgmental weighting of estimates produced from each of the methods considered. Industry loss experience is used to supplement the Company’s own data in selecting “tail factors” in areas where the Company’s own data is limited. The actuarial data is analyzed by line of business, coverage and accident or policy year, as appropriate, for each operating unit.

The establishment of the actuarially derived loss reserve point estimate also includes consideration of qualitative factors that may affect the ultimate losses. These qualitative considerations include, among others, the impact of re-underwriting initiatives, changes in the mix of business, changes in distribution sources and changes in policy terms and conditions.

The key assumptions used to arrive at the best estimate of loss reserves are the expected loss ratios, rate of loss cost inflation, and reported and paid loss emergence patterns. Expected loss ratios represent management’s expectation of losses at the time the business is priced and written, before any actual claims experience has emerged. This expectation is a significant determinant of the estimate of loss reserves for recently written business where there is little paid or incurred loss data to consider. Expected loss ratios are generally derived from historical loss ratios adjusted for the impact of rate changes, loss cost trends and known changes in the type of risks underwritten. Expected loss ratios are estimated for each key line of business within each operating unit. Expected loss cost inflation is particularly important for the long-tail lines, such as excess casualty, and claims with a high medical component, such as workers’ compensation. Reported and paid loss emergence patterns are used to project current reported or paid loss amounts to their ultimate settlement value. Loss development factors are based on the historical emergence patterns of paid and incurred losses, and are derived from the Company’s own experience and industry data. The paid loss emergence pattern is also significant to excess and assumed workers’ compensation reserves because those reserves are discounted to their estimated present value based upon such estimated payout patterns.

Loss frequency and severity are measures of loss activity that are considered in determining the key assumptions described in our discussion of loss and loss expense reserves, including expected loss ratios, rate of loss cost inflation and reported and paid loss emergence patterns. Loss frequency is a measure of the number of claims per unit of insured exposure, and loss severity is a measure of the average size of claims. Factors affecting loss frequency include the effectiveness of loss controls and safety programs and changes in economic activity or weather patterns. Factors affecting loss severity include changes in policy limits, retentions, rate of inflation and judicial interpretations.

Another factor affecting estimates of loss frequency and severity is the loss reporting lag, which is the period of time between the occurrence of a loss and the date the loss is reported to the Company. The length of the loss reporting lag affects our ability to accurately predict loss frequency (loss frequencies are more predictable for lines with short reporting lags) as well as the amount of reserves needed for incurred but not reported losses (less IBNR is required for lines with short reporting lags). As a result, loss reserves for lines with short reporting lags are likely to have less variation from initial loss estimates. For lines with short reporting lags, which include commercial automobile, primary workers’ compensation, other liability (claims-made) and property business, the key assumption is the loss emergence pattern used to project ultimate loss estimates from known losses paid or reported to date. For lines of business with long reporting lags, which include other liability (occurrence), products liability, excess workers’ compensation and liability reinsurance, the key assumption is the expected loss ratio since there is often little paid or incurred loss data to consider. Historically, the Company has experienced less variation from its initial loss estimates for lines of business with short reporting lags than for lines of business with long reporting lags.


	June 30,
(In thousands)	2026		2025
Net reserves at beginning of period	$	18,953,674	$	17,166,641


Net provision for losses and loss expenses:
Claims occurring during the current year (1)	3,866,535		3,822,512
Increase in estimates for claims occurring in prior years (2) (3)	13,624		17,823
Loss reserve discount accretion	16,397		15,881
Total	3,896,556		3,856,216
Net payments for claims:
Current year	427,861		431,981
Prior years	2,666,383		2,537,599
Total	3,094,244		2,969,580
Foreign currency translation	(10,153)		164,747
Net reserves at end of period	19,745,833		18,218,024
Ceded reserves at end of period	3,436,407		3,278,099
Gross reserves at end of period	$	23,182,240	$	21,496,123

During the six months ended June 30, 2026, favorable prior year development (net of additional and return premiums) of $3 million included $10 million of favorable prior year development for the Reinsurance & Monoline Excess segment partially offset by $7 million of adverse prior year development for the Insurance segment.

For the Insurance segment, the development during the six months of 2026 resulted primarily from favorable development for short tail-lines of business which was offset by adverse development for other liability and auto liability. The favorable development for short-tail lines of business during the six months of 2026 related to the 2025 accident year, and resulted from favorable settlements of both catastrophe and non-catastrophe property claims below our expectations.

The adverse other liability development was driven mainly by umbrella and excess liability claims, and to a lesser extent from the Company’s primary surplus lines casualty business. The other liability development was concentrated in accident years 2019 through 2023. The umbrella and excess liability development included a significant component stemming from underlying auto exposures. The Company believes that auto-related claims are being particularly impacted by social inflation, which is contributing to an increase in the frequency of large losses beyond expectations. An increase in the frequency of litigated claims is also driving up both indemnity and loss adjustment expense costs in these lines of business beyond expectations.

For the Reinsurance & Monoline Excess segment, the favorable development during the six months of 2026 was driven mainly by favorable development in non-proportional reinsurance assumed property, partially offset by adverse development in the non-proportional reinsurance assumed liability line of business. Similarly to the Insurance segment, the favorable property reinsurance development was driven by favorable claim settlements, below our expectations, related to the 2025 accident year. The unfavorable development for non-proportional reinsurance assumed liability was associated primarily with our U.S. assumed reinsurance businesses, and was concentrated mainly in accident years 2020 through 2023.

During the six months ended June 30, 2025, favorable prior year development (net of additional and return premiums) of $1 million included $20 million of favorable prior year development for the Reinsurance & Monoline Excess segment largely offset by $19 million of adverse prior year development for the Insurance segment.

For the Insurance segment, the adverse development during the first half of 2025 was driven by other liability and commercial auto liability and was partially offset by favorable development for short tail lines of business, including commercial property and commercial auto physical damage. The adverse other liability development was driven primarily by

umbrella and other claims attaching excess of primary policy limits and included a significant component stemming from underlying auto exposures. A secondary driver of the other liability development related to the Company’s excess and surplus lines casualty business. The other liability development was concentrated in accident years 2017 through 2022. The adverse commercial auto liability development was concentrated in accident years 2021 and 2022. The Company believes that auto-related claims are being particularly impacted by social inflation, which is contributing to an increase in the frequency of large losses beyond expectations. Social inflation can include higher settlement demands from plaintiffs, use of tactics such as litigation funding by the plaintiffs’ bar, negative public sentiment towards large businesses and corporations, and erosion of tort reforms, among others.

For the Reinsurance & Monoline Excess segment, the favorable development during the first half of 2025 was driven mainly by favorable development in non-proportional reinsurance for assumed property. Similar to the Insurance segment, the favorable property reinsurance development was driven by favorable claim settlements, below our expectations, related mainly to the 2024 accident year.