In plain English
FAR 52.237-9, Waiver of Limitation on Severance Payments to Foreign Nationals, is a contract clause prescribed at FAR 37.113-2(b), most recently dated Dec 2022. The complete official text is reproduced below, verbatim, from GSA's published FAR source files.
Its text contains no sentence requiring insertion into subcontracts; see the flowdown section below for what that does and does not mean.
Does it flow down to subcontracts?
No flowdown mandate found in the clause text
We scanned the full clause text and found no sentence directing the contractor to insert this clause into subcontracts. That is a statement about the text, not legal advice: a prime contractor may still flow terms down contractually, an agency supplement (DFARS, VAAR, …) may add requirements, and clauses listed below (if any) may order this clause into subcontracts from the outside.
Where it's prescribed
As prescribed in 37.113-2(b), use the following clause:
Prescribing reference: FAR 37.113-2(b).
The official text, verbatim
As prescribed in 37.113-2(b), use the following clause:
Waiver of Limitation on Severance Payments to Foreign Nationals (Dec 2022)
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(a) Pursuant to 10 U.S.C. 3744(b) or 41 U.S.C. 4304(b)(1), as applicable, the cost allowability limitations in FAR 31.205-6(g)(6) are waived.
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(b) This clause may be incorporated into subcontracts issued under this contract, if approved by the Contracting Officer.
(End of clause)