As a UK citizen, what if I obtain residency this year (2020) but my spouse arrives in 2021 or later?

Article 10 of the Withdrawal Agreement (WA), and Title III 'seems' to say that spouses would possess the same rights as their partners. The host state needs to facilitate the entry of the spouse, (so residence is fine) subject to conditions. Post-Transition unregistered partners will be subject to national legislation, and more stringent terms, which suggests that spouses/registered partners would NOT find it so stringent. Article 10 "Personal Scope" of the WA seems to support that as does TITLE III "Coordination of Social Security Provisions".

You can read the WA legal text here:

https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:12019W/TXT(02)&from=ES

And on the Withdrawal of the UK from the EU see here:
https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:12019W/TXT(02)&from=ES&fbclid=IwAR0246ynVQTfOPfPKr8QsvHkE2EDkHu0bi2AUKo4PKddPIgnal1fmjdCIbs

The WA protects our rights under existing FoM law, that same law says that our 3rd country spouses have the same rights and protections as us e.g. they have the right to reside with us now and are not currently subject to Spain's 3rd country immigration requisites, they all just go through a different registration system currently in order to obtain the EU family member Residencia card. So as the spouse's rights are protected should the 3rd country spouse be moving after end of transition.

Legal advice received is as follows: “See Part 2, Article 10 (ii) of the Withdrawal Agreement. You need to cross reference with the EU Directive 2004/38/EC. Article 2 point 2 of this defines family members which includes a) Spouse b)Those in a contracted registered partnership . An example of the latter would be a ‘pareja de hecho’ or a civil registered couple so spouses and registered partners are fine as far as Residencia is concerned. That still doesn't stop Spanish funcionarios applying what financial criteria they like but it should not be 3rd country amounts."

Further clarification from the lawyer is that non-registered partners are treated under national legislation. Apparently there are certainly going to be more stringent rules for the regional police and it will not be legitimate for them to ignore Spain’s national laws regarding both spouses and parejas de hecho situations.

So. It appears that all spouses can qualify for residency at a later date if their other half arrives before 2020 or during 2020 and already has residency. It does not seem to be the case that the later arriving spouse (in 2021 or later) would have to meet the much higher annual income requirements that are currently set for nationals of third countries. In short the answer is No! The Withdrawal Agreement should protect spouses arriving later so a wife or husband will be able to join their partner later on the same financial terms as the first of them.

Chris