IRC 951B Foreign-Controlled U.S. Shareholder (FCUS) and FCFC: OBBBA Practitioner Guide

The One Big Beautiful Budget Act (OBBBA), signed into law on July 4, 2025, made two paired changes to the controlled foreign corporation (CFC) framework. First, it restored IRC 958(b)(4), the provision that blocks downward attribution of stock ownership from foreign persons through U.S. entities, effective for tax years of foreign corporations beginning after December 31, 2025. Second, it simultaneously enacted a new provision, IRC 951B, that creates a distinct set of inclusion rules for U.S. persons controlled by foreign interests. These U.S. persons are defined as Foreign-Controlled U.S. Shareholders, or FCUSes. The foreign corporations they are treated as owning through the FCUS mechanism are Foreign-Controlled Foreign Corporations, or FCFCs.

Understanding these rules requires tracing a story that begins with the 2017 Tax Cuts and Jobs Act (TCJA) repeal of Sec. 958(b)(4), continues through the unintended CFC designations that repeal produced for thousands of U.S. subsidiaries of foreign multinationals, and ends with the OBBBA's carefully calibrated but not yet fully implemented correction. This guide is written for CPAs, tax attorneys, and in-house international tax counsel advising U.S. entities with foreign parent or foreign sister relationships. It assumes a working knowledge of Subpart F mechanics, the CFC definition, and basic stock attribution rules. All statutory citations must be verified against current IRS.gov resources before reliance in any specific client matter. This guide is for informational purposes only and does not constitute legal or tax advice.

Section 1: Why IRC 958(b)(4) Mattered

The Pre-TCJA Attribution Framework

The CFC regime under Subpart F (IRC 951-965) requires a foreign corporation to be "controlled" by U.S. shareholders before its undistributed income can be taxed currently in U.S. hands. Control, for Subpart F purposes, means that U.S. shareholders own more than 50 percent of the total combined voting power or total value of the corporation's stock, as determined under the stock ownership rules in IRC 958.

IRC 958 provides two ownership-measurement mechanisms. Section 958(a) is direct and indirect actual ownership: a U.S. person owns stock directly or through a chain of ownership in which each intermediate entity is itself owned by a U.S. person. Section 958(b) is constructive ownership, which applies the attribution rules of IRC 318(a) to the extent provided in Sec. 958(b) itself.

Before 2018, IRC 958(b)(4) contained a crucial limitation. It provided that Sec. 318(a)(3)(A), (B), and (C) (the so-called "downward attribution" rules, which attribute stock held by a partner, beneficiary, or shareholder downward to a partnership, estate, trust, or corporation) were NOT to be applied so as to consider a U.S. person as owning stock owned by a person who is not a U.S. person. In plain English: if a foreign parent owned both a U.S. subsidiary and a foreign sibling corporation, you could not use downward attribution to treat the U.S. subsidiary as a constructive owner of the foreign sibling's stock merely because the foreign parent was a common owner.

This limitation was not a loophole. It reflected a deliberate policy judgment that U.S. subsidiaries of foreign multinationals should not be treated as Subpart F shareholders of foreign sister corporations simply by reason of their common foreign parent. The practical effect was that brother-sister structures, where a single foreign parent owns both a U.S. subsidiary (U.S. Sub) and one or more foreign subsidiaries (Foreign Subs), did not cause the Foreign Subs to become CFCs on account of U.S. Sub's constructive ownership of them.

The TCJA 2017 Repeal of Sec. 958(b)(4)

The Tax Cuts and Jobs Act of 2017 (P.L. 115-97) repealed IRC 958(b)(4), effective for the last tax year of a foreign corporation beginning before January 1, 2018. The stated purpose was to prevent certain avoidance structures where U.S. persons used foreign entities to circumvent the Subpart F rules. The practical effect, however, was far broader than anyone anticipated.

Once Sec. 958(b)(4) was removed, downward attribution from a foreign parent through its U.S. subsidiary to a foreign sister corporation became permissible. In the simple brother-sister structure described above, U.S. Sub was now deemed to constructively own the stock of Foreign Sub held by Foreign Parent. If that constructive ownership crossed the more-than-50-percent threshold, Foreign Sub became a CFC, with U.S. Sub treated as a U.S. shareholder under Sec. 951(b).

This result was structurally unintended for many taxpayers. U.S. Sub had no actual economic interest in Foreign Sub. It was not managing Foreign Sub's business, receiving dividends from it, or making operational decisions for it. Yet under the post-TCJA attribution rules, U.S. Sub was a deemed U.S. shareholder of a deemed CFC, with all the accompanying Subpart F filing obligations and potential income inclusion consequences.

Practical Impact: Category 5 Filers and Subpart F Burdens

The immediate compliance consequence for affected U.S. subsidiaries was Form 5471 reporting. A U.S. person who is a Category 5 filer (a U.S. shareholder of a CFC) must file Form 5471 annually and include with it Schedules I, J, P, Q, R, and others depending on the CFC's activities. For a U.S. subsidiary that had no pre-TCJA relationship with its foreign sister corporation for Subpart F purposes, this was entirely new administrative burden.

Beyond filing, the substantive income consequences were potentially significant. If the newly designated CFC (the foreign sister) had Subpart F income, the deemed U.S. shareholder (U.S. Sub) was required to include its pro rata share in gross income under Sec. 951(a). Many foreign sister corporations of U.S. subsidiaries of foreign multinationals had substantial foreign base company sales income, foreign base company services income, or passive income that was now suddenly Subpart F income in U.S. Sub's hands.

Rev. Proc. 2019-40: Transitional Safe Harbors

Recognizing the scope of the unintended consequences, the IRS issued Rev. Proc. 2019-40, which provided safe harbors for certain U.S. shareholders who became U.S. shareholders of previously non-CFC foreign corporations solely as a result of the TCJA repeal of Sec. 958(b)(4). Rev. Proc. 2019-40 addressed, among other things, the application of the Sec. 951(a)(2)(B) limitation on inclusions for shareholders who hold stock through the relevant chain of ownership, and provided simplified methods for computing pro rata shares for certain affected taxpayers.

Rev. Proc. 2019-40 applies to the TCJA-era years (2018 through 2025) and remains the controlling transitional guidance for those years. Practitioners advising clients on their 2018-2025 filing positions under the post-TCJA downward attribution rules should consult Rev. Proc. 2019-40 directly. This guide does not provide transitional advice for those prior years beyond this general reference.

Section 2: OBBBA Restoration of IRC 958(b)(4)

The OBBBA Amendment: What Changed

The One Big Beautiful Budget Act (OBBBA), enacted July 4, 2025, restored IRC 958(b)(4). Specifically, the OBBBA re-enacted the rule that Sec. 318(a)(3)(A), (B), and (C) (the downward attribution rules) are not applied so as to consider a U.S. person as owning stock owned by a person who is not a U.S. person, for purposes of the CFC-related determinations under Sec. 958. The restoration was prospective only: it applies to tax years of foreign corporations beginning after December 31, 2025.

This means that for tax years of foreign corporations beginning in 2026 and later, the TCJA-era downward attribution no longer applies for standard CFC status determinations. A U.S. subsidiary of a foreign parent is no longer treated as constructively owning the foreign parent's stake in a foreign sister corporation for purposes of determining whether that sister is a CFC. The brother-sister structures that became unintended CFCs under the TCJA will, for the most part, exit CFC status beginning with 2026 foreign corporation tax years.

Which Structures Exit CFC Status

The most directly affected structures are those in which:

• A foreign parent (Foreign Parent) owns both a U.S. corporation (U.S. Sub) and one or more foreign corporations (Foreign Sub);
• Foreign Sub had CFC status solely because U.S. Sub was attributed Foreign Parent's ownership in Foreign Sub through the TCJA's downward attribution rules; and
• No actual U.S. person independently owns more than 50 percent of Foreign Sub's stock on a combined vote-or-value basis.

For these structures, the restoration of Sec. 958(b)(4) removes the downward attribution, U.S. Sub no longer holds constructive ownership of Foreign Sub's stock, Foreign Sub is no longer controlled by U.S. shareholders, and Foreign Sub exits CFC status for the first tax year of the foreign corporation beginning after December 31, 2025.

Structures where U.S. persons hold actual (Sec. 958(a)) ownership, or where there are additional attribution chains beyond the brother-sister pattern, require case-by-case analysis. The restoration of Sec. 958(b)(4) does not affect upward attribution (stock owned by a subsidiary attributed to its parent) or sideways attribution outside the scope of Sec. 318(a)(3). All conclusions about CFC exit must be verified under the current statutory text.

The FCUS Carve-Out: Sec. 958(b)(4) Remains Inapplicable for FCUS Determinations

Here is where the OBBBA's structural design becomes critical. Although the OBBBA restored Sec. 958(b)(4) for standard CFC purposes, it simultaneously enacted IRC 951B, which explicitly provides that Sec. 958(b) is applied WITHOUT regard to paragraph (4) when determining FCUS status and FCFC status. In other words, for the FCUS/FCFC framework, downward attribution is kept alive by statutory design.

The policy logic is apparent: Congress intended to relieve the unintended CFC designation burden for ordinary U.S. subsidiaries of foreign multinationals (by restoring Sec. 958(b)(4)) while simultaneously creating a targeted inclusion regime for those U.S. subsidiaries that are themselves controlled by foreign interests at the greater-than-50-percent threshold (through the FCUS framework). The two provisions work in tandem to calibrate the U.S. tax reach over the earnings of foreign subsidiaries of foreign-controlled U.S. companies.

Section 3: IRC 951B Statutory Mechanics

The Core Substitution Rule

IRC 951B operates primarily through substitution. The statute directs that, for purposes of applying the provisions of Subpart F (Secs. 951 through 965, except as provided), "FCUS" is substituted for "U.S. shareholder," and "FCFC" is substituted for "CFC" or "controlled foreign corporation." This substitution approach means that the existing Subpart F machinery, including income definition, pro rata share computation, and the mechanics of various income categories, applies to FCUSes and FCFCs without the need for entirely new computational rules. Practitioners who already know how to compute Subpart F inclusions for standard U.S. shareholders of CFCs are working with familiar mechanics, applied to a new class of obligors.

The statute specifies the provisions excluded from this substitution. Sec. 951A (the NCTI/GILTI provision) and Sec. 951(b) (the standard U.S. shareholder definition) are addressed separately. The exclusion of Sec. 951(b) from the substitution is logical: Sec. 951(b) defines what a U.S. shareholder is, and that definition is not being changed; what changes is the definition of FCUS, which is provided directly in IRC 951B itself.

Subpart F Income Inclusion: IRC 951B(a)(1)

Under IRC 951B(a)(1), an FCUS must include in gross income its pro rata share of the FCFC's Subpart F income for any tax year. The inclusion follows Sec. 951(a)(2), which provides the pro rata share computation. An FCUS's pro rata share of Subpart F income is generally the portion of the FCFC's Subpart F income attributable to the stock actually held by the FCUS on the last day of the FCFC's tax year on which the FCFC is an FCFC, taking into account the FCFC's earnings and profits.

The categories of Subpart F income that apply to FCFCs follow the standard Subpart F categories: foreign personal holding company income (Sec. 954(c)), foreign base company sales income (Sec. 954(d)), foreign base company services income (Sec. 954(e)), and the other categories enumerated in Sec. 952. These are all computed using the FCFC's relevant facts (income, expenses, earnings and profits) in the same manner as they are computed for CFCs. The FCUS reports the inclusion on its U.S. return in the same manner as a U.S. shareholder of a CFC would report a Sec. 951(a)(1) inclusion.

Net Controlled Taxable Income (NCTI): IRC 951B(a)(2)

IRC 951B(a)(2) extends the NCTI rules (the OBBBA's replacement for GILTI, effective for tax years beginning after December 31, 2025) to FCUSes and FCFCs. Under this provision, an FCUS is treated as a U.S. shareholder and the FCFC is treated as a CFC for purposes of Sec. 951A. The OBBBA's changes to the NCTI regime, including modifications to the deduction available under Sec. 250 and to the deemed-paid foreign tax credit rate, apply to the FCUS's NCTI inclusion from FCFCs.

Section 956 U.S. Property Investments: IRC 951B(a)(3)

IRC 951B also requires FCUSes to include Sec. 956 amounts from FCFCs. Sec. 956 provides that a U.S. shareholder of a CFC must include in income the lesser of the CFC's average aggregate amount invested in U.S. property or the CFC's earnings and profits (subject to applicable adjustments). Under IRC 951B, FCUSes are subject to the same inclusion as if the FCFC were a CFC. This means that if an FCFC makes loans to its FCUS or to related U.S. persons, or holds U.S. property (within the meaning of Sec. 956(c)) in excess of the applicable thresholds, the FCUS must include the Sec. 956 amount in its gross income.

Note that whether the 2019 proposed regulations under Sec. 956 (which provided a dividend-received-deduction analog for domestic corporations) extend to FCUSes is not addressed in any current guidance as of mid-2026. Practitioners should treat the Sec. 956 extension to FCUSes as a live inclusion risk until IRS guidance clarifies any exceptions.

Treasury Regulatory Authority: IRC 951B(d)

IRC 951B(d) grants the Treasury Secretary broad regulatory authority to carry out the purposes of Sec. 951B. This authority expressly includes the power to issue regulations addressing the interaction between the FCUS/FCFC rules and the PFIC rules under Secs. 1291 through 1298, among other matters. The grant of authority under Sec. 951B(d) is an important signal that Congress recognized the need for regulatory clarification in several areas, including PFIC overlap, and that the current statutory text alone does not fully resolve those interactions. Treasury has issued proposed regulations under this authority (IR-2026-03), but those proposed regulations are not final.

Section 4: Who Is an FCUS?

The FCUS Definition: Two Required Elements

An FCUS is a U.S. person who satisfies both of the following conditions simultaneously:

1. Threshold element: The U.S. person would qualify as a U.S. shareholder of the foreign corporation under Sec. 951(b) if Sec. 951(b) substituted "more than 50 percent" for "10 percent or more" wherever "10 percent or more" appears. In other words, the person must own (directly, indirectly, or constructively) more than 50 percent of the total combined voting power or total value of all classes of the foreign corporation's stock.
2. Attribution element: The ownership determination in element (1) must be made by applying Sec. 958(b) without regard to paragraph (4). This means downward attribution from foreign persons through U.S. entities is active for FCUS purposes, even though Sec. 958(b)(4) has been restored for standard CFC determinations.

Both elements must be satisfied at once. A U.S. person who owns more than 50 percent of a foreign corporation on an actual Sec. 958(a) basis, without any need for downward attribution, is a standard U.S. shareholder of a potential CFC under the normal rules and does not require the FCUS framework. The FCUS framework is specifically targeted at U.S. persons who reach the more-than-50-percent threshold only because downward attribution is applied without the paragraph (4) block.

The 50-Percent Threshold in Detail

The substitution of "more than 50 percent" for "10 percent or more" is a dramatic threshold change from the standard Subpart F U.S. shareholder definition. Under Sec. 951(b), a U.S. shareholder is any U.S. person who owns 10 percent or more of the total combined voting power (or, under the TCJA, total value) of a foreign corporation. The FCUS definition requires more than 50 percent, not merely 10 percent or more.

This means a U.S. person who, through the combined operation of actual ownership and downward attribution without paragraph (4), holds exactly 50 percent of the vote or value of a foreign corporation is NOT an FCUS. The statute uses "more than" 50 percent, not "50 percent or more." This boundary matters in structures with exactly 50/50 U.S./foreign splits and must be carefully analyzed at the time of the ownership determination.

Vote Versus Value: Both Tests

The FCUS determination, like the standard Sec. 951(b) determination, applies both a vote test and a value test. A U.S. person is an FCUS if it meets the more-than-50-percent threshold with respect to total combined voting power OR total value. Meeting either test is sufficient. Structures that use multiple share classes with disproportionate vote-to-value ratios must be analyzed under both metrics independently.

Actual Sec. 958(a) Ownership Required for Income Inclusion

A critical distinction in the FCUS framework is the separation between the ownership test for FCUS status and the ownership requirement for income inclusion. FCUS status is determined using constructive ownership (Sec. 958(b) without paragraph (4)) in addition to actual ownership (Sec. 958(a)). But income inclusion under IRC 951B(a) requires that the FCUS hold actual Sec. 958(a) ownership of stock in the FCFC.

This means a U.S. person can be classified as an FCUS for status purposes through downward attribution, but if that same U.S. person holds only constructive and no actual ownership of FCFC stock, no income inclusion is triggered. The income inclusion attaches only to the portion of FCFC stock that the FCUS holds under Sec. 958(a). Practitioners must carefully distinguish the status test from the inclusion trigger and not assume that merely meeting FCUS status automatically generates an income inclusion.

Section 5: What Is an FCFC?

The FCFC Definition

A Foreign-Controlled Foreign Corporation (FCFC) is a foreign corporation (not otherwise a CFC under Secs. 951(b) and 957) that would be a CFC if FCUSes were substituted for U.S. shareholders in the CFC definition, applying Sec. 958(b) without paragraph (4). The definition has three key structural elements.

First, the entity must be a foreign corporation. Domestic corporations and other entity types are excluded.

Second, the entity must NOT already be a CFC under the standard rules. The FCFC designation is a residual category: it captures foreign corporations that sit outside the CFC definition (because, with Sec. 958(b)(4) restored, they are no longer deemed controlled by standard U.S. shareholders) but that would be deemed controlled if the FCUS framework applies. This exclusion of actual CFCs from FCFC status prevents double-counting: a foreign corporation cannot simultaneously be a CFC generating Sec. 951(a) inclusions for its U.S. shareholders and an FCFC generating IRC 951B(a) inclusions for its FCUSes.

Third, the control test applies Sec. 958(b) without paragraph (4). This is the same no-paragraph-(4) rule that applies to FCUS status determinations. The FCFC is therefore identified using downward attribution, just as the FCUS is identified using downward attribution.

No Minimum Per-Person Foreign Ownership Threshold

The FCFC definition does not require any individual FCUS to hold a minimum percentage of the foreign corporation's stock. The standard CFC definition requires that the foreign corporation be controlled by U.S. shareholders who each own 10 percent or more and who collectively own more than 50 percent. Under the FCFC definition, the controlling group is FCUSes (each holding more than 50 percent through Sec. 958(b) without paragraph (4)), and the control threshold for the foreign corporation to be an FCFC is that FCUSes together would cause CFC treatment under the substituted framework.

This is an area where IR-2026-03 (proposed, not final) addresses aggregation rules. Practitioners should monitor IRS.gov for finalization of those rules before committing to positions about how multiple FCUSes' ownership stakes are aggregated for FCFC-status purposes.

Section 6: Computing the FCUS Inclusion

Subpart F Pro Rata Share Computation

An FCUS's pro rata share of an FCFC's Subpart F income follows the Sec. 951(a)(2) mechanics. In general, the FCUS's pro rata share is the amount that would be distributed to the FCUS with respect to its Sec. 958(a) actual ownership if the FCFC distributed an amount equal to its Subpart F income for the year. The computation takes into account the FCFC's earnings and profits, the FCUS's percentage of actual ownership, and the period during the tax year on which the FCFC is an FCFC.

Note that the pro rata share is computed on the basis of the Sec. 958(a) actual ownership, not the constructive ownership used to establish FCUS and FCFC status. An FCUS that holds 15 percent of the FCFC's stock on a Sec. 958(a) actual basis but is attributed 80 percent constructively (by reason of the no-paragraph-(4) rule) computes its inclusion on the 15 percent actual ownership, not the 80 percent constructive ownership.

NCTI Inclusion: Application to FCUSes

The OBBBA replaced GILTI (global intangible low-taxed income) with NCTI (Net Controlled Taxable Income) effective for tax years beginning after December 31, 2025. The OBBBA's NCTI framework eliminated the Qualified Business Asset Investment (QBAI) return deduction that had been part of the GILTI computation, changed the Sec. 250 deduction to 40 percent (from 50 percent under prior law), and set the deemed-paid foreign tax credit rate at 90 percent for standard U.S. shareholders of CFCs.

IRC 951B(a)(2) directs that FCUSes be treated as U.S. shareholders and FCFCs be treated as CFCs for purposes of Sec. 951A. On its face, this suggests that the same NCTI computation, including the elimination of QBAI, the 40 percent Sec. 250 deduction, and the 90 percent FTC rate, applies to FCUSes computing NCTI inclusions from FCFCs. However, as noted in the amber alert at the top of this guide, neither the 40 percent deduction rate nor the 90 percent FTC rate for FCUS-specific NCTI has been explicitly confirmed in binding guidance as of mid-2026.

Section 956 Inclusion Mechanics

Sec. 956 was most significant for domestic corporations before the TCJA. After the TCJA, the 2019 proposed regulations (REG-114540-18) addressed whether a deemed-paid dividend under Sec. 956 for domestic corporate shareholders would be reduced to the extent a Sec. 245A dividends-received deduction would be available. For FCUSes, none of the 2019 guidance or the current Sec. 956 proposed regulations were drafted with the FCUS framework in mind. Whether an FCUS can avail itself of any analog to the Sec. 245A DRD for Sec. 956 inclusions from FCFCs is an open question not addressed in any current guidance.

Practitioners should note that Sec. 956 inclusions from FCFCs can arise from relatively common intercompany arrangements, including loans from the FCFC to the FCUS or to U.S. affiliates of the FCUS, pledges of FCFC stock to secure U.S. debt, and certain intercompany guarantees. Review existing intercompany financial arrangements to assess potential Sec. 956 risk under the FCUS framework before the first FCFC tax year begins.

Section 7: Transition Issues

Applicable Transition Notices

The IRS has issued several notices addressing transition mechanics around the Subpart F and NCTI changes enacted by the OBBBA. Three notices have direct relevance for practitioners managing FCUS issues:

• Notice 2025-75: Addresses the Sec. 951(a)(2)(B) dividend exclusion for pre-2026 periods. This notice is relevant to the TCJA-era transition, including the treatment of dividends paid from CFCs during the period when Sec. 958(b)(4) was repealed. Practitioners should review Notice 2025-75 to confirm whether any positions taken by affected U.S. subsidiaries on pre-2026 Subpart F inclusions are consistent with the notice's guidance.
• Notice 2025-77: Addresses previously taxed earnings and profits (PTEP) reclassification for Sec. 951A amounts. As entities exit CFC status and potentially enter FCFC status, the characterization of their PTEP accounts may shift. Notice 2025-77 provides guidance on how PTEP built up under the GILTI regime is reclassified under the NCTI regime and how it interacts with OBBBA effective-date transitions. This is directly relevant to entities transitioning from CFC to FCFC status (or to neither status) in 2026.
• Notice 2025-72: Requested comments on foreign tax allocation rules in connection with the OBBBA's changes. While not a rule-making notice in itself, it signals areas where Treasury anticipates future guidance. Practitioners with clients whose FCFC structures involve significant foreign tax credits or complex foreign tax allocation questions should monitor the response to Notice 2025-72.

TCJA-Era Years Still Under Old Law

The single most important transition point for practitioners is that the OBBBA changes are prospective only. There is no relief from, and no retroactive application of, the FCUS/FCFC framework to tax years of foreign corporations beginning before January 1, 2026. U.S. subsidiaries of foreign multinationals that were treated as U.S. shareholders of newly designated CFCs during 2018-2025 were subject to all the compliance obligations and income inclusions that flowed from that designation. Those obligations are not retroactively eliminated by the OBBBA or by IRC 951B.

Rev. Proc. 2019-40 remains the applicable guidance for safe harbors related to the TCJA-era downward attribution consequences. Clients with open examination years in 2018-2025 that involve the TCJA repeal of Sec. 958(b)(4) should continue to rely on Rev. Proc. 2019-40 and the TCJA statutory text for those years. The OBBBA provisions do not affect the legal analysis for those prior periods.

Practical Steps for Entities Exiting CFC Status in 2026

For entities that will exit CFC status in 2026 by reason of the Sec. 958(b)(4) restoration, practitioners should work through the following practical steps before the first affected tax year begins:

1. Determine the final year as a CFC: For calendar-year foreign corporations, the last CFC tax year is the year ending December 31, 2025. Confirm the transition date for fiscal-year foreign corporations based on when their tax year begins.
2. Close out PTEP accounts: Review Notice 2025-77 for guidance on reclassifying Sec. 951A (GILTI) PTEP. Determine the earnings and profits pools as of the last day of the final CFC year.
3. Assess FCFC status: Apply the FCUS definition (Sec. 958(b) without paragraph (4), more than 50 percent) to determine whether the entity that exits CFC status becomes an FCFC. If the former CFC becomes an FCFC, FCUS inclusion obligations begin for the first FCFC year.
4. Assess PFIC risk: Apply the PFIC passive-income test and the asset test to former CFCs. For any holder who was relying on the CFC/PFIC overlap exception under Sec. 1297(e), evaluate whether that exception continues to apply after CFC status terminates. See Section 9 for the open question on PFIC/FCFC overlap.
5. Intercompany arrangements: Review intercompany loans, guarantees, and property arrangements for potential Sec. 956 exposure under the FCUS framework if the entity becomes an FCFC.

Section 8: Form 5471 Implications

Who Exits Category 5 Filer Status

A Category 5 filer under Form 5471 is a U.S. shareholder of a CFC on the last day of the CFC's tax year during which the foreign corporation was a CFC. When a foreign corporation exits CFC status after the Sec. 958(b)(4) restoration, its former U.S. shareholders who held that status solely by reason of TCJA downward attribution will no longer have a Form 5471 filing obligation as Category 5 filers for the foreign corporation's tax years beginning after December 31, 2025 (assuming the foreign corporation is also not otherwise a CFC through actual ownership).

Practitioners should confirm the category determination for each Form 5471 filing that is affected. Category 5 filers generally include both Category 5a (U.S. shareholders of section 951 inclusions), Category 5b (persons who are shareholders by reason of attribution), and Category 5c (persons in certain specified situations). Each sub-category has specific rules and the transition may affect different sub-categories differently.

FCUS Filer Category: Form 5471 Update Pending

The IRS has not yet updated Form 5471 or its instructions to add a reporting category for FCUSes. Under the current (pre-update) Form 5471 instructions, there is no dedicated filer category for an FCUS holding an interest in an FCFC. Practitioners may need to use existing categories (including Category 5, if it is the closest analog) or attach supplemental disclosures to the return for 2026 filings until the IRS issues the updated form and instructions.

Schedules and Supporting Information

Under current Form 5471 requirements, a Category 5 filer must generally attach: Schedule I (summary of shareholder's income from the CFC), Schedule J (accumulated earnings and profits), Schedule P (previously taxed earnings and profits by shareholder), Schedule Q (CFC income by country), Schedule R (distributions from the CFC), and Schedule E (taxes paid or accrued by the CFC). For FCUSes filing under an analog category until the updated form is available, the same categories of information will be relevant, and practitioners should capture them from the FCFC's books and records.

Foreign corporations that become FCFCs may not have historically maintained the records needed to complete all required Form 5471 schedules, because they were not CFCs before 2026. Practitioners should work with clients to establish record-keeping systems for FCFCs during 2026, before the first required Form 5471 is due.

Section 9: Interactions with Other Code Provisions

NCTI and the 951B Framework

As discussed in Section 6, IRC 951B(a)(2) extends the NCTI framework to FCUSes and FCFCs by treating them as U.S. shareholders and CFCs respectively for purposes of Sec. 951A. The interaction between the NCTI modifications enacted by the OBBBA (elimination of QBAI, 40 percent Sec. 250 deduction, 90 percent FTC) and the FCUS framework requires careful verification of each rate and deduction before computing any FCUS NCTI inclusion. Neither the Sec. 250 deduction rate nor the FTC rate is confirmed in final guidance specifically for FCUS purposes.

PFIC and FCFC Overlap

IRC 267A and FCFCs

IRC 59A BEAT and FCFCs

IRC 163(j) Business Interest Limitation and FCUSes

Portfolio Interest Exemption and FCFCs

Transfer Pricing: IRC 482 Still Applies

Unlike the unresolved interactions described above, the application of IRC 482 and the arm's-length standard to transactions between FCUSes and FCFCs is settled in one important respect: nothing in IRC 951B or the OBBBA limits the IRS's authority to reallocate income between related parties under Sec. 482. FCUSes and FCFCs in brother-sister structures controlled by common foreign parents are related parties for IRC 482 purposes, and intercompany pricing for controlled transactions between them must comply with the arm's-length standard under Treas. Reg. 1.482-1 through 1.482-9. The existence of the FCUS/FCFC income inclusion rules does not substitute for, or excuse compliance with, Sec. 482.

Section 10: Outstanding Guidance and Open Questions

IR-2026-03: Proposed Regulations (Not Final)

IR-2026-03 is the IRS announcement of proposed regulations under IRC 951B. The proposed regulations are reported to address, among other matters: FCFC definitions and the control threshold; aggregation of FCUS ownership for FCFC-status purposes; NCTI allocation among FCUSes with FCFC interests; and transition relief for certain structures affected by the shift from CFC to FCFC status.

These proposed regulations are NOT final. They are not binding on taxpayers and do not have the force of law. The notice-and-comment period under the Administrative Procedure Act must be completed, Treasury must consider the comments received, and a final Treasury Decision must be published before the regulations carry binding legal force. Practitioners may wish to consult the proposed regulations for guidance on how Treasury is thinking about these questions, but no client position should be taken that depends solely on proposed regulations without acknowledging their non-binding status and the risk that they will be modified in finalization.

Complete List of Open Questions as of Mid-2026

The following questions remain unresolved in final guidance as of the date of this guide. Each one requires monitoring and may require conservative modeling until resolved:

1. IR-2026-03 finalization: The proposed regulations address definitional and computational mechanics but are not yet final. The finalized regulations may differ from the proposed version in ways that materially affect FCUS and FCFC status determinations.
2. Form 5471 FCUS filer category: No updated Form 5471 or instructions have been issued. An FCUS filer category is anticipated in late 2026 or early 2027 but has not yet been released. Until then, practitioners must make good-faith disclosure using the current form.
3. PFIC/FCFC overlap: Whether the CFC/PFIC overlap exception under Sec. 1297(e) extends to FCFCs is an unresolved open question. Treasury has authority to issue regulations under Sec. 951B(d) but has not done so in final form. No assumption of exception availability is warranted.
4. IRC 267A and FCFCs: Whether payments to or from FCFCs are hybrid or specified payments within the meaning of IRC 267A and its regulations is open. No guidance has addressed this interaction.
5. IRC 59A BEAT and FCFCs: Whether deductible payments to FCFCs constitute base erosion payments is an open question. No guidance has addressed the BEAT/FCFC interaction.
6. IRC 163(j) and FCUSes: How the business interest limitation applies to FCUSes, and whether any look-through or allocation rules differ from the CFC context, is not addressed in any current guidance.
7. Portfolio interest exemption for FCFCs: The application of the IRC 881(c)(3)(C) 10-percent shareholder exclusion in the FCFC context is open and unaddressed.
8. Deemed-paid FTC confirmation for FCUS NCTI: The 90 percent deemed-paid FTC rate applicable to standard U.S. shareholder NCTI inclusions has not been explicitly confirmed for FCUS inclusions from FCFCs. The statutory structure suggests parallel treatment but confirmation in binding guidance is absent.
9. Grandfathering and partial-year computation: No grandfathering rules exist for entities exiting CFC status in 2026, and no guidance addresses partial-year computation for entities moving between CFC, FCFC, and neither status. IR-2026-03 may address transition mechanics, but the proposed regulations are not final.

Anticipated Guidance Timeline

The IRS has not published a formal priority guidance plan item for IRC 951B as of mid-2026 that would establish a committed timeline. Based on the scope of the open questions and the complexity of the proposed regulations already issued, practitioners should anticipate a finalization cycle of 12 to 24 months from the close of the comment period on IR-2026-03, assuming a normal administrative process. Form 5471 updates may arrive sooner (late 2026 or early 2027 based on IRS statements), given the compliance urgency of the 2026 filing season. All timeline statements in this guide are estimates only. Monitor IRS.gov for official announcements.

Section 11: Practitioner Checklist

The following checklist summarizes the key steps for practitioners advising clients who may be affected by IRC 951B and the FCUS/FCFC framework. Each step should be completed for any client with a non-U.S. parent or significant foreign related-party relationships before filing returns for tax years beginning after December 31, 2025.

• Identify potentially affected clients: Any U.S. entity with a foreign parent, foreign grandparent, or other non-U.S. controlling person that also owns foreign subsidiaries may be affected. The brother-sister structure (Foreign Parent owns U.S. Sub and Foreign Sub) is the archetype, but any structure involving downward attribution from a foreign person should be reviewed.
• Map the ownership structure: Prepare a full entity chart showing all U.S. and non-U.S. entities, ownership percentages (actual and constructive), and the vote/value attributes of each ownership stake. Identify all Sec. 958(a) actual ownership chains and all constructive ownership paths that would be active under Sec. 958(b) without paragraph (4).
• Determine CFC vs. FCFC vs. neither status for each foreign entity: For each foreign corporation in the structure, apply the standard CFC test first (Sec. 958 with paragraph (4) restored). If not a CFC, apply the FCFC test (Sec. 958(b) without paragraph (4), substituting FCUSes for U.S. shareholders). Confirm that actual CFCs are excluded from FCFC status.
• Identify all FCUSes: For each foreign corporation that is an FCFC, determine which U.S. persons qualify as FCUSes (more than 50 percent threshold, Sec. 958(b) without paragraph (4)). Separate the FCUS status determination from the income inclusion requirement: identify which FCUSes also hold Sec. 958(a) actual ownership in the FCFC.
• Model the Subpart F and NCTI inclusions: For each FCUS with actual Sec. 958(a) ownership in an FCFC, compute the estimated Subpart F and NCTI inclusions for the FCFC's first tax year beginning after December 31, 2025. Note that NCTI rates (Sec. 250 deduction and FTC) require verification in binding guidance before finalizing computations.
• Review intercompany arrangements for Sec. 956 risk: Identify any loans, guarantees, or pledges between FCFCs and the FCUS or its U.S. affiliates. Assess whether these arrangements could generate Sec. 956 inclusions for the FCUS and consider restructuring if the exposure is material.
• Assess PFIC risk for entities exiting CFC status: For each entity exiting CFC status in 2026, apply the PFIC passive-income and asset tests independently. Do not assume the CFC/PFIC overlap exception under Sec. 1297(e) applies to FCFCs or to any holder whose CFC status terminates. See the PFIC warning in Section 9.
• Track Form 5471 filing obligations: Determine which entities will no longer require Form 5471 filings (exit of CFC status), which entities require new FCUS-category filings (FCFC status beginning 2026), and what current form instructions apply in the absence of updated FCUS-category instructions. Monitor IRS.gov for updated Form 5471 before filing 2026 returns.
• Review IRC 267A, BEAT, and 163(j) for FCFC-related transactions: Flag all intercompany transactions with FCFCs for review under IRC 267A (hybrid payments), IRC 59A BEAT (base erosion payments), and IRC 163(j) (interest expense). Each of these is an open question; flag them for qualified counsel and do not assume a default position.
• Establish FCFC record-keeping systems: Ensure each entity classified as an FCFC establishes earnings and profits tracking, Subpart F income category analysis, and NCTI computation records as of the first day of its first FCFC tax year. Retroactive reconstruction is difficult and may not be possible for foreign corporations without existing U.S. GAAP or tax-basis accounting records.
• Monitor IRS.gov for guidance: Set a monitoring schedule for IRS.gov, the Federal Register, and the priority guidance plan to track finalization of IR-2026-03, issuance of updated Form 5471, and resolution of the nine open questions identified in Section 10.

Frequently Asked Questions

What is a Foreign-Controlled U.S. Shareholder (FCUS) under IRC 951B?

An FCUS is a U.S. person who would be a U.S. shareholder of a foreign corporation under Sec. 951(b) if the ownership threshold were substituted from "10 percent or more" to "more than 50 percent," and if Sec. 958(b) were applied without regard to paragraph (4). The without-paragraph-(4) requirement means downward attribution from non-U.S. persons through U.S. entities to foreign corporations remains active for FCUS analysis, even though OBBBA generally restored Sec. 958(b)(4) for standard CFC determinations. Verify the exact statutory definition in the text of IRC 951B and at IRS.gov before applying it to specific client facts.

When do the IRC 951B FCUS rules first apply?

IRC 951B and the companion restoration of Sec. 958(b)(4) are both effective for tax years of foreign corporations beginning after December 31, 2025. For calendar-year foreign corporations, the first affected year is 2026. The TCJA-era rules, including the repeal of Sec. 958(b)(4) and its consequences for brother-sister structures, continue to govern all tax years of foreign corporations beginning before January 1, 2026. There is no retroactive application of the FCUS framework to prior years.

Does an FCUS have to include income from an FCFC if the FCUS holds only constructive ownership?

No. IRC 951B(a) requires that an FCUS hold actual Sec. 958(a) ownership in an FCFC to be subject to the pro rata income inclusion. Constructive ownership under Sec. 958(b) (applied without paragraph (4)) is used to determine whether an entity qualifies as an FCUS and whether the foreign corporation is an FCFC. But constructive ownership alone does not generate an income inclusion under IRC 951B(a). An FCUS that holds only constructive and no actual Sec. 958(a) ownership in an FCFC is not required to include FCFC Subpart F income, NCTI, or Sec. 956 amounts. Verify this distinction in the current statutory text and any applicable final regulations before advising clients.

Are the proposed Treasury regulations in IR-2026-03 binding law?

No. IR-2026-03 contains only proposed regulations. Proposed regulations are not final law and are not binding on taxpayers until finalized through the notice-and-comment process under the Administrative Procedure Act and published as a Treasury Decision with an effective date. Practitioners may consult the proposed regulations for insight into Treasury's intended approach, but no formal client position should rest on proposed regulations alone, particularly for positions on tax returns. Monitor IRS.gov for the final regulations.

Do entities that exit CFC status automatically avoid the PFIC rules after the 958(b)(4) restoration?

This is an open and unresolved question. The CFC/PFIC overlap exception under IRC 1297(e) may protect U.S. shareholders of CFCs from PFIC treatment in certain circumstances, but it is unclear whether that exception extends to FCFCs or to former CFCs whose CFC status terminates after the restoration of Sec. 958(b)(4). IRC 951B(d) grants Treasury the authority to issue regulations on this interaction, but no final regulations addressing it have been issued as of mid-2026. Practitioners should not assume the exception applies to FCFCs without binding guidance. Assess the PFIC passive-income and asset tests for each entity exiting CFC status and flag the PFIC risk for affected holders before the first FCFC year begins.