In plain English
FAR 52.227-4, Patent Indemnity-Construction Contracts, is a contract clause prescribed at FAR 27.201-2(d)(1), most recently dated Dec 2007. 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 27.201-2(d)(1), insert the following clause:
Prescribing reference: FAR 27.201-2(d)(1).
The official text, verbatim
As prescribed in 27.201-2(d)(1), insert the following clause:
Patent Indemnity-Construction Contracts (Dec 2007)
Except as otherwise provided, the Contractor shall indemnify the Government and its officers, agents, and employees against liability, including costs and expenses, for infringement of any United States patent (except a patent issued upon an application that is now or may hereafter be withheld from issue pursuant to a Secrecy Order under ( 35 U.S.C. 181) arising out of performing this contract or out of the use or disposal by or for the account of the Government of supplies furnished or work performed under this contract.
(End of clause)
Alternate I (Dec 2007). As prescribed in 27.201-2 (d)(2), designate the first paragraph of the basic clause as paragraph (a) and add the following paragraph (b) to the basic clause:
(b) This patent indemnification shall not apply to the following items: __________________________________________________ [Contracting Officer list the items to be excluded.]