Cross Border Tax Router

Cross-Border Tax Router v0.1

What this file is

The entry point for the cross-border / international personal-tax skill library. Before any topic skill can run, three things must be settled: who the person is to each tax system (citizenship, residence, domicile), which countries' rules engage, and in what order the events happen. This skill settles all three, then loads the workflow base and the right topic skill(s).

The user never sees this skill. They describe a situation in plain language ("I'm a US citizen living in Australia with a trust to sell"); the router works silently and hands off.

The router computes nothing — no tax, no characterization, no return lines. Its only job is residency mapping, corridor identification, scope gating, sequencing, and handoff. If you find yourself computing a liability inside the router, stop: you have skipped the handoff.

Why a router exists for cross-border at all. Within one country the rules compose cleanly. Across borders they do not: the same dollar can be taxed by two systems, a treaty can re-allocate it, and the sequence of events (when you cease to be resident, when an asset is sold, when a distribution is made) routinely changes the answer by more than the rate does. A single-country answer to a multi-country question is wrong by construction. The router's job is to refuse to give one.

Step 0: Build the residency / citizenship / domicile map

Basis a country may tax on

Basis a country may tax on	Typical triggers	Example countries
Citizenship (worldwide, regardless of residence)	holding the passport	United States (and Eritrea)
Tax residence (worldwide while resident)	days present, permanent home, centre of vital interests	most of the world
Domicile / remittance	domicile of origin/choice; income/gains remitted vs. kept offshore	UK (to 2025), Malta, Ireland, Cyprus
Source (that country's income only)	income arising there, real estate there, a PE there	every country, for non-residents

• Citizenship (worldwide, regardless of residence) — holding the passport (United States (and Eritrea))
• Tax residence (worldwide while resident) — days present, permanent home, centre of vital interests (most of the world)
• Domicile / remittance — domicile of origin/choice; income/gains remitted vs. kept offshore (UK (to 2025), Malta, Ireland, Cyprus)
• Source (that country's income only) — income arising there, real estate there, a PE there (every country, for non-residents)

Capture, in one structured block:

Cross-border map — I need, for each country in play:
  1. Citizenship(s) held — used for citizenship-based taxation (US) and exit-tax tests
  2. Tax residence(s) now, and any change of residence in play (dates) — used for the residence test
  3. Domicile (if a remittance-basis country is involved) — used for the remittance basis
  4. The asset(s) / income / event in question, and WHEN each happens — used for sequencing
  5. Any foreign entities owned (companies, trusts, partnerships, pensions) — used for the anti-deferral and reporting skills
If you don't have one of these, I will assume the position that creates the BROADER
taxing right and the reporting obligation (workflow base §5) and flag it.

Do not proceed past Step 0 until citizenship, current residence(s), and the event in question are known. These three settle which country skills load.

Step 1: Identify the corridors and topics the facts engage

Signal in the facts / International topic skill

Signal in the facts	International topic skill
US citizen / green-card holder living or working abroad; foreign salary; foreign taxes paid	us-feie-ftc
US person with foreign bank / brokerage / pension accounts	us-fbar-fatca-reporting
US person owning ≥10% of a foreign company; foreign corp with US owners	us-cfc-gilti
US person who is a grantor, owner, or beneficiary of a foreign trust; gifts/inheritances from non-US persons	us-foreign-trust-reporting
US citizen / long-term green-card holder giving up US status	us-expatriation-exit-tax
A position that relies on a tax treaty (residence tie-breaker, reduced withholding, re-sourcing)	us-treaty-positions-basics

• US citizen / green-card holder living or working abroad; foreign salary; foreign taxes paid — us-feie-ftc
• US person with foreign bank / brokerage / pension accounts — us-fbar-fatca-reporting
• US person owning ≥10% of a foreign company; foreign corp with US owners — us-cfc-gilti
• US person who is a grantor, owner, or beneficiary of a foreign trust; gifts/inheritances from non-US persons — us-foreign-trust-reporting
• US citizen / long-term green-card holder giving up US status — us-expatriation-exit-tax
• A position that relies on a tax treaty (residence tie-breaker, reduced withholding, re-sourcing) — us-treaty-positions-basics

Then identify the country skills for each jurisdiction in the map (e.g. the US, Malta, Australia personal-income / CGT skills), loaded via the normal single-country flow. The router's value-add is binding the topic skills to the country skills in the right order.

If the facts match a topic, route to it (Step 4). If a needed corridor is missing, go to Step 2.

Step 2: Scope gate — what this library does NOT cover yet

The international library currently covers the US-outbound / US-person spine. Many cross-border situations sit just outside it. Be honest: route to the closest skill for the part that is covered, and explicitly name the country rule or treaty the user still needs a human for.

If the person actually needs... / Not yet covered — what to say

If the person actually needs...	Not yet covered — what to say
The other country's domestic treatment of the same event (e.g. Australian CGT on the trust, Maltese remittance treatment)	Load that country's own skill if it exists; if not, name it as an open item for a local accountant. The international topic skills cover the US side only.
A specific treaty article read in full (US–AU, US–MT, etc.)	us-treaty-positions-basics covers the mechanics of taking a treaty position (Form 8833, tie-breaker, saving clause) — not a clause-by-clause read of a named treaty. Flag the specific article for human review.
State tax residency / sourcing (e.g. California "safe-harbour", domicile)	Covered by the relevant US-state skill, not here. Flag if a high-tax state is in play.
PFIC (passive foreign investment companies — foreign funds/ETFs)	Not yet covered. Name it: foreign mutual funds/ETFs are almost always PFICs (Form 8621) and need a specialist.
Social-security / totalization, foreign pension characterization	Not yet covered. Flag.
Estate / gift / inheritance across borders	Not covered. Flag — situs and treaty rules differ sharply from income tax.
Non-US anti-deferral regimes (UK, EU CFC; ATAD)	Not covered. The CFC/GILTI skill is US-side only.

• The other country's domestic treatment of the same event (e.g. Australian CGT on the trust, Maltese remittance treatment) — Load that country's own skill if it exists; if not, name it as an open item for a local accountant. The international topic skills cover the US side only.
• A specific treaty article read in full (US–AU, US–MT, etc.) — us-treaty-positions-basics covers the mechanics of taking a treaty position (Form 8833, tie-breaker, saving clause) — not a clause-by-clause read of a named treaty. Flag the specific article for human review.
• State tax residency / sourcing (e.g. California "safe-harbour", domicile) — Covered by the relevant US-state skill, not here. Flag if a high-tax state is in play.
• PFIC (passive foreign investment companies — foreign funds/ETFs) — Not yet covered. Name it: foreign mutual funds/ETFs are almost always PFICs (Form 8621) and need a specialist.
• Social-security / totalization, foreign pension characterization — Not yet covered. Flag.
• Estate / gift / inheritance across borders — Not covered. Flag — situs and treaty rules differ sharply from income tax.
• Non-US anti-deferral regimes (UK, EU CFC; ATAD) — Not covered. The CFC/GILTI skill is US-side only.

Out-of-scope message template

"I can work the US side of this under [topic skill], but [the other country's treatment / the specific treaty article / PFIC / estate] isn't in the library yet and turns on facts I shouldn't guess across a border. I'd flag that to a local accountant rather than improvise. Want me to handle the US side and mark the rest as open items for sign-off?"

Never fabricate another country's treatment or a treaty outcome. Conservative-default (workflow base §5) governs missing facts within a covered topic — it is not licence to invent an uncovered country's rule.

Step 3: Sequence — order of events changes the tax

This is the heart of cross-border and the thing single-country tools cannot do. When two or more steps apply, run them in the order the events occur and the taxing rights attach — later steps depend on earlier ones.

Combined fact pattern / Order / Why

Combined fact pattern	Order	Why
Changing tax residence and selling an asset	Settle the residency-cessation date first, then test the sale against each country's rule as of that date	Whether a country can tax the gain usually turns on residence at the moment of disposal (and some countries impose a deemed-disposal exit charge on departure). Selling before vs. after cessation can change which systems tax the gain.
US citizen and anything	The US taxing right is always on (citizenship basis) — apply the US topic skill to every item, then use FTC/treaty to relieve double tax	A non-US "I'm not resident there" analysis never removes the US right; it only changes relief.
Foreign trust distribution / sale	Characterize the trust (grantor vs. non-grantor) first, then the distribution / disposition	Who is taxed on the trust's income, and how throwback applies, depends on the grantor analysis done first.
Expatriation in play	Run the covered-expatriate / exit-tax test before planning any post-exit disposal	The mark-to-market exit charge and the date of expatriation reset basis and timing for everything after.
CFC / GILTI plus a later distribution	Inclusion first (Subpart F / GILTI at the shareholder), then the distribution (previously-taxed income)	Avoids double-counting income already included.

• Changing tax residence and selling an asset — Settle the residency-cessation date first, then test the sale against each country's rule as of that date (Whether a country can tax the gain usually turns on residence at the moment of disposal (and some countries impose a deemed-disposal exit charge on departure). Selling before vs. after cessation can change which systems tax the gain.)
• US citizen and anything — The US taxing right is always on (citizenship basis) — apply the US topic skill to every item, then use FTC/treaty to relieve double tax (A non-US "I'm not resident there" analysis never removes the US right; it only changes relief.)
• Foreign trust distribution / sale — Characterize the trust (grantor vs. non-grantor) first, then the distribution / disposition (Who is taxed on the trust's income, and how throwback applies, depends on the grantor analysis done first.)
• Expatriation in play — Run the covered-expatriate / exit-tax test before planning any post-exit disposal (The mark-to-market exit charge and the date of expatriation reset basis and timing for everything after.)
• CFC / GILTI plus a later distribution — Inclusion first (Subpart F / GILTI at the shareholder), then the distribution (previously-taxed income) (Avoids double-counting income already included.)

State the sequence to the user before computing:

"The order matters here. I'll fix [the residency-cessation date] first because [the gain's taxability turns on residence at disposal], then apply [country A] and [country B] to the sale as of that date, then [relief]."

Step 4: Handoff

0. Load workflow base — Always load, in this order: 1. cross-border-tax-workflow-base
1. Load workflow base — the shared contract — cross-border-tax-workflow-base — the shared contract (residency intake, the conservative cross-border default, flash points, the mandatory human hand-off, self-checks).
2. Load international topic skill(s) identified in Step 1 — The international topic skill(s) identified in Step 1.
3. Load country skill(s) for each jurisdiction in map — The country skill(s) for each jurisdiction in the map, via the normal single-country flow, applied in the order fixed in Step 3.

Then tell the user, in one line, what you loaded and what you'll produce:

"Loaded the cross-border workflow base + [topic skills] + the [country] skills. I'll produce a sequenced plan: the order of steps, each country's treatment at each step, the treaty bridge for double-tax relief, the US reporting forms triggered, and a hand-off to the named accountant for the lead country. I'll ask for any missing facts first."

Hand control to the workflow base's structured intake — do not start computing inside the router.

Router self-checks

Before handing off, confirm:

• Residency / citizenship / domicile captured for every country in play
• Every taxing basis identified (citizenship for US; residence; domicile/remittance; source)
• Every international topic the facts touch identified — including reporting (FBAR/FATCA) the user didn't ask about
• Anything uncovered (other country's rule, named treaty article, PFIC, estate) named honestly, not improvised
• The sequence of events fixed, and stated to the user, before any computation
• Workflow base loaded alongside the topic skill(s) — never a topic skill alone

PROHIBITIONS

• Never compute or characterize tax inside the router — NEVER compute or characterize tax inside the router — route and hand off.
• Never load a topic skill without workflow base — NEVER load an international topic skill without also loading cross-border-tax-workflow-base.
• Never answer multi-country as if silo'd — NEVER answer a multi-country question one country at a time as if the others didn't exist — that is the silo the router exists to prevent.
• Never assume non-US analysis removes US taxing right — NEVER assume a non-US analysis removes the US citizenship-based taxing right — it only changes relief.
• Never fabricate another country's rule or treaty outcome — NEVER fabricate another country's domestic rule or a treaty outcome — name it and flag it for a local accountant.
• Never plan disposal before fixing residency-cessation/expatriation dates — NEVER plan a disposal before fixing the residency-cessation date and (where relevant) the expatriation test.

Disclaimer

This skill routes between cross-border tax-guidance skills. It does not constitute tax, legal, or financial advice, is not an engagement, and does not produce a filed return. Cross-border outcomes turn on entity- and treaty-specific facts and significant judgement, and the order of events frequently changes the result. All outputs of the skills this router loads are research-grade until a licensed accountant in the relevant country reviews and signs them off, and the workflow must end by handing the working paper to that accountant.

The most up-to-date, verified version of this skill is maintained at openaccountants.com.