The "Oligarch Act of 2025" proposes to amend the Internal Revenue Code of 1986 by establishing a new federal wealth tax on the net value of taxable assets held by certain individuals and trusts. This tax would be levied annually on the last day of the calendar year, applying to individuals and most trusts, with married individuals treated as a single taxpayer. The bill sets a significant threshold amount for taxation, defined as 1,000 times the greater of $50,000 or the annually determined median household wealth. For individuals, the tax features a progressive rate structure, starting at 2% for assets exceeding the threshold and increasing to 8% for the highest wealth brackets. Trusts, however, would face a flat 8% tax on assets above the threshold. The legislation defines "net value of all taxable assets" as the total value of all property, real or personal, tangible or intangible, wherever situated, minus any debts, with specific exclusions for certain low-value tangible personal property. To ensure compliance, the bill mandates that the Secretary of the Treasury establish comprehensive rules for asset valuation within 12 months, including methods for non-publicly traded assets and the use of formulaic approaches. It also requires the Secretary to implement information reporting regulations and to annually audit at least 30% of taxpayers subject to the wealth tax. Furthermore, the bill introduces new accuracy-related penalties for substantial wealth tax valuation understatements and allows for extensions of payment for taxpayers facing severe liquidity constraints or undue hardship.