The new guidance on home offices is in the Commentary, not in the treaties. Spain's treaties were signed between the 1960s and today. Whether a 2025 text can explain a 1990 treaty is a serious question, and for taxpayers it cuts both ways.
The OECD Model is a template. Countries negotiate their bilateral treaties from it, and the Commentary records how the member countries understand each provision. It is not a treaty and it is not legislation. Its authority comes from the fact that the negotiators had it in front of them and that tax administrations of both treaty partners subscribe to it.
Article 5(1), the definition of a fixed place of business, was not changed in 2025. Only the explanation was. That is the source of the difficulty: the words of the treaties are the same as before, and what has changed is the agreed reading.
Country positions
The OECD's own position, stated in the introduction to the Model, is that later changes to the Commentary should be taken into account when interpreting treaties concluded before them, in so far as they reflect a consensus on the proper interpretation of existing provisions, and not where they follow a change in the wording of the Article. This is known as the ambulatory or dynamic approach.
Courts have not always agreed. The Spanish Supreme Court, in a judgment of 3 March 2020, declined to interpret a treaty in the light of Commentary adopted after it, stressing that the Commentaries are not a source of law and that a treaty cannot be altered in substance by a later text to which the other State did not consent through the treaty process. It has returned to the point since. The Spanish tax authorities, for their part, cite the current Commentary routinely.
The practical position is therefore that the 2025 paragraphs are a powerful argument in Spain, but not a guarantee, and their weight will depend on whether they are seen as clarifying what "place of business" always meant or as adding something new.
On the home office, the 2025 text mostly narrows the circumstances in which a permanent establishment arises, compared with a broad reading of the 2017 language about places "at the disposal" of the enterprise. A company defending itself can argue two things at once: that the 2025 paragraphs clarify the existing concept and should be followed; and that, even on the older reading, the Spanish administration had itself concluded in published rulings that the home of an employee who chose to work from Spain was not at the employer's disposal.
The reverse case is rarer but exists. Where the 2025 text points to a permanent establishment, as in the time-zone example, a taxpayer facing an assessment for earlier years may argue that this is a new idea that cannot be read back into an older treaty.
A treaty is bilateral, and the position of the other country counts. Several countries recorded observations or positions on the new paragraphs. For a company resident in one of them with staff in Spain, or the other way round, the two administrations may not read the treaty in the same way, and the result of a disagreement is a mutual agreement procedure, not a quick answer.
It also matters what the treaty says. Some of Spain's older treaties follow earlier versions of the Model, and a few depart from it in the permanent establishment article. And where there is no treaty at all, Spanish domestic law applies, with its own definition of a permanent establishment, which is not interpreted by the Commentary in the same way.
The substance of the tests is in the main guide. General background on treaties is on our page about double tax treaties.
Source: OECD (2026), Model Tax Convention on Income and on Capital 2025 (Full Version), Commentary on Article 5, paragraphs 44.1 to 44.21, added on 18 November 2025. The Commentary is described here in our own words; the paragraph numbers are given so that it can be checked against the original.
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