In plain English
FAR 52.252-4, Alterations in Contract, is a contract clause prescribed at FAR 52.107(d), most recently dated Apr 1984. 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 52.107(d), insert the following clause in solicitations and contracts in order to revise or supplement, as necessary, other parts of the contract, or parts of the solicitation that apply after contract award, except for any clause authorized for use with a deviation. Include clear identification of what is being altered.
Prescribing reference: FAR 52.107(d).
The official text, verbatim
As prescribed in 52.107(d), insert the following clause in solicitations and contracts in order to revise or supplement, as necessary, other parts of the contract, or parts of the solicitation that apply after contract award, except for any clause authorized for use with a deviation. Include clear identification of what is being altered.
Alterations in Contract (Apr 1984)
Portions of this contract are altered as follows:
_____________________________________________ _____________________________________________ _____________________________________________
(End of clause)