THE SHORT ANSWER
An RFI is commonly used to learn about the market; an RFP asks for proposals under stated instructions and evaluation factors. A prime contractor has the direct contract with the government. A subcontractor performs work for a prime rather than directly for the agency.
RFI and RFP serve different moments
A request for information (RFI) helps an agency understand possible solutions, capabilities, or market conditions. Under FAR Part 15, an RFI response is not an offer the government can accept to form a binding contract. A request for proposals (RFP) is a solicitation that tells offerors what to submit and how the agency will evaluate responses. The specific document controls; acronyms are shortcuts, not substitutes for reading it.
A firm may benefit from responding to an RFI because it can explain what is feasible. That should be treated as market engagement, not a booked sales opportunity or an implied endorsement.
Prime and subcontractor describe responsibility
The Small Business Administration explains that a prime works directly with the government and is responsible for contract performance, including managing its subcontractors. A subcontractor works for the prime. The commercial relationship, reporting path, and obligations differ.
Subcontracting can be a way to contribute specialized engineering without taking on every responsibility of a prime contract. The actual subcontract and prime contract terms determine the work and constraints.
What to ask before responding
Is this market research, a live solicitation, or a subcontracting opportunity? Who will buy and accept the work? What evidence of capability is requested? What data, security, accessibility, staffing, and delivery obligations would apply? Those questions prevent a technology team from treating a procurement document like an ordinary sales lead.
Illustrative example: an agency posts an RFI on AI-assisted document review. A technology firm could describe a feasible architecture and questions the agency should resolve. If a later RFP is issued, a proposal would need to follow its specific instructions; participation in the RFI alone would not create an award.
Original sources
The process explanations above are educational summaries. The linked primary sources govern their own terms and can change; check them for current requirements.