本文主要讨论关于中美 Tax Treaty 20(c) 中提到的中国赴美留学生每年 5000 美元的工资免税额能否用于 OPT 转 H-1B 的第一年，也就是前九个月是 F-1 ，后三个月是 H-1B 的情况。目前有争议的是如果报税人全年都用 resident alien 报税还能不能享受 tax treaty. 根据我的理解，resident alien 依然可以报 tax treaty。
免责申明：我只是为了自己报税专门抱佛脚查阅了文档。我没有任何法律基础，英语也不太好，可能有所疏漏。以下分享我得出结论的依据，请自行判断，也欢迎指正！
请注意一般情况下 OPT 转 H-1B 第一年是不可以用 resident alien 报全年的税的，以下是一些我知道的例外：F-1 签证在美五年以上；在第一年年底前结婚并且在第二年申请延迟报税；配偶是 resident alien 并且选择夫妻联合报税。具体原因和如何使用这些例外本文不做展开，可以参考这篇文章。
Tax Treaty 怎么说
https://www.irs.gov/pub/irs-trty/china.pdf
A student, business apprentice or trainee who is, or was immediately before visiting a Contracting State, a resident of the other Contracting State and who is present in the first- mentioned Contracting State solely for the purpose of his education, training or obtaining special technical experience shall be exempt from tax in that Contracting State with respect to:
(a) payments received from abroad for the purpose of his maintenance, education, study, research or training;
(b) grants or awards from a government, scientific, educational or other tax-exempt organization;
and
(c) income from personal services performed in that Contracting State in an amount not in excess of 5,000 United States dollars or its equivalent in Chinese yuan for any taxable year.The benefits provided under this Article shall extend only for such period of time as is reasonably necessary to complete the education or training.
以上为中美 Tax Treaty Article 20.
这里的 Contracting State 指的是中国，the other Contracting State 为美国。
第一段提到了两个条件：一个是来美国是为了读书以及相关工作 (education, training or obtaining special technical experience) ，F-1 OPT 的身份无疑是符合的。还有就是刚进入美国前或现在依然是中国居民。这里并没有提到不能是美国居民。
接下来是哪些收入可以免税。(a) 来自国外的生活费；(b) 政科教机构给的经费，应该是指奖学金；(c) 在美工作获得的前 $5000 收入。
最后一段提到了时效，这项福利直到完成学业或相关工作前都可以享受。原文只提到了 reasonably necessary to complete the education or training. 我把这句话解读为持续到 OPT 结束。也就是说，受益人只能减免前九个月的收入。
Notwithstanding any provision of the Agreement, the United States may tax its citizens. Except as provided in paragraph 2 of Article 8, paragraph 2 of Article 17, and Articles 18, 19, 20, 22, 23, 24 and 26 of this Agreement, the United States may tax its residents (as determined under Article 4).
以上为中美 Tax Treaty Protocol 1 Paragraph 2.
这段提到，除了 Article 20 等，美国依然可以向美国居民收税。换句话说 resident alien，甚至可能连 permanent resident 都可以享受 Article 20。当然前提是要满足 Article 20 的条件。
IRS 怎么说
Generally, you must be a nonresident alien student, apprentice, or trainee in order to claim a tax treaty exemption for remittances from abroad (including scholarship and fellowship grants) for study and maintenance in the United States. However, if you entered the United States as a nonresident alien, but you are now a resident alien for U.S. tax purposes, the treaty exemption will continue to apply if the tax treaty has an exception to the treaty’s saving clause.
一般来说只有 nonresident alien 可以享受 tax treaty. （这句话在 IRS 的各个页面出现，可能是误会的原因之一。）但是如果学生在美国从 nonresident alien 变成 resident alien，会根据具体的 treaty 决定是否依然可以享受免税福利。
中国的条款已在上文提到。IRS 也在这段话下面把中美条款作为例子特别说明。
Article 20 of the U.S.-China income tax treaty allows an exemption from tax for scholarship income received by a Chinese student temporarily present in the United States. Under the Internal Revenue Code, a student may become a resident alien for tax purposes if his or her stay in the United States exceeds 5 calendar years. However, the treaty allows the provisions of Article 20 to continue to apply even after the Chinese student becomes a resident alien of the United States.
尽管 IRS 只提到了生活费和奖学金，没有提到学生工资，但我认为既然 Article 20 中把三项收入平行地提出，那么学生工资应该是同理的。
非官方的容易看懂的文章
https://global.utexas.edu/isss/advising-services/taxes/tax-treaties
If within the time limit, the student may claim tax treaty even if s(he) qualifies as “resident” for tax purposes but not applicable for permanent resident or immigrant status. Students from PR China however, may claim the treaty as long as they are primarily enrolled to be a student, even if they become US permanent residents or have immigrant status.
UT Austin 非常友好地为国际学生提供了报税指南，其中明确提到了中国学生不论是成为了 resident alien 还是 permanent resident 都可以继续用 treaty.
（与本文无关）这篇文章还让我了解到了挺多有意思的条款。比如有些国家的学生不需要在美国待五年就可以选择以 resident alien 身份报税。还有很多国家会在自己的 tax treaty 里设置年限，很多都会规定只有前五年的学生工资可以减税，这也正好防止小留学生们纠结自己五年以后变成 resident alien 了还能不能用 tax treaty。（都给你们规定好了，不让用！）
容易引起误会的文章
Generally, neither you nor your spouse can claim tax treaty benefits as a resident of a foreign country for a tax year for which the choice is in effect. However, the exception to the saving clause of a tax treaty might allow a tax treaty benefit on certain specified income.
https://www.irs.gov/individuals/international-taxpayers/nonresident-alien-spouse
再分享一个当时差点让我断章取义不敢报 treaty 的文章。如果 resident alien 选择让自己的 nonresident alien 配偶也按照 resident alien 进行夫妻联合报税，一般来说双方都将无法享受其他国家的 tax treaty. 但是！但是又出现了！各个 treaty 会有自己的例外。
前文提到了中美 treaty 的 Article 20 就是个例外。