签证延期是否要填写 Affidavit of Support I-134？

「Affidavit of Support」即「经济担保」，B1/B2 签证延期通常不需要提交。

根据 USCIS 的说明，Affidavit of Support 通常是用于移民申请：

An affidavit of support is a document an individual signs to accept financial responsibility for another person, usually a relative, who is coming to the United States to live permanently. The person who signs the affidavit of support becomes the sponsor of the relative (or other individual) coming to live in the United States. The sponsor is usually the petitioner of an immigrant petition for a family member.

USCIS 有两个表格都叫「Affidavit of Support」：

I-864：这是给移民签证用的（详情见填写指示），不适用于B1/B2签证延期。
I-134：这是个令很多人困惑的表格，用于需要经济担保的非移民签证，最常见的情况是美国公民的未婚夫（妻）或配偶，他们可以申请 K-1/K-3 非移民签证、并且同时有在美国永久定居团聚的意愿（dual intent）。若申请人没有足够的经济条件，可能会占用美国福利、成为美国政府和人民的负担，则该美国公民需要提供经济担保。

B1/B2 签证及延期通常无需填写 I-134。Maryland 律师事务所 Murthy Law Firm 写了一篇文章，「Form I-134 Affidavit of Support for B-1/B-2 Visitor Visas」，表示：

The reality is that, ordinarily, one cannot actually be sponsored for a standard B-1/B-2 visa; but, it is possible for a person in the U.S. to provide financial sponsorship through the submission of a signed affidavit of support, using form I-134. For many applicants, however, submitting this form could actually do more harm than good.」以及：「Avoid Submission of Form I-134 unless Specifically Requested.

我为岳父母申请延期的时候，他们没有提供任何经济证明（因为他们的材料都在中国），我在申请信中明确表示会负担他们的开销（参见这里），并且附上了我的 Bank Statements，没有填写 I-134，结果顺利批准。B1/B2 签证延期的教程参见这里。