The agreement is the payment system
An other transaction is not a procurement contract, so the Federal Acquisition Regulation does not attach to it. Most writing on that fact goes straight to intellectual property, which is fair, because the IP consequences are large. The consequence that decides whether a firm can actually carry the project is the money. In a FAR contract, payment terms arrive from a body of regulation the contracting officer does not have to write and the offeror does not have to negotiate. In an other transaction there is no such body. When payment is earned, what proves it was earned, who decides, how long that decision may take, and what happens if it takes longer: all of it lives in the agreement, and anything not written into the agreement is simply not there.
MITRE's Acquisition in the Digital Age reference states the structural options plainly. "OT agreements may be fixed-price, expenditure-based, or hybrid." Those three shapes produce three different cash-flow profiles, and the difference between them is worth more to a small performer than most of the terms that get argued about at the table.
A fixed-price agreement pays a set amount when a defined event occurs. That is the shape most prototype work takes, and it is the shape this article is mostly about. An expenditure-based agreement reimburses costs as they are incurred, which behaves like a cost-reimbursement contract and shortens the gap between spending and receiving. A hybrid mixes the two, commonly with expenditure-based treatment of a long integration phase and fixed payments at demonstrations.
What a payable milestone actually is
A milestone that gets paid is three things fastened together: an event, the evidence that the event happened, and an amount. Weak agreements write the first, gesture at the third, and skip the second entirely. That omission is where the schedule slips.
The Defense Innovation Unit describes the mechanism in public terms on its own site: "Payment will be made by the Defense Finance and Accounting Services and will be based upon milestones agreed to by DoW and the company." The load-bearing word is agreed. There is no external standard supplying the milestone, no clause library, no customary practice a contracting officer will fall back on. Two parties write a list, and that list governs.
The event. A thing that either happened or did not. "Integration test executed against the government-furnished interface" is an event. "Progress on integration" is not.
The evidence. The artifact the firm hands over to show the event occurred. A signed test report, a tagged repository commit, a demonstration attended by named government personnel, a delivered dataset with a checksum. Name it in the agreement so nobody invents a new expectation at submission time.
The amount. What the milestone pays. Not necessarily an even split across milestones, and there is rarely a reason for it to be.
The decider. Who accepts. A role, not "the Government." An agreement that leaves the acceptance authority unnamed leaves the payment date unnamed with it.
The clock. How long the government has to accept or reject, and what happens when that window closes with no answer. This is the term most often missing and the one that costs the most.
The financing machinery that does not come with it
It helps to see exactly what a FAR contract carries that an other transaction does not, because the list is longer than most people expect and every item on it is a cash-flow instrument.
Progress payments finance work in progress against incurred cost. Under FAR 52.232-16 the government computes each progress payment as 80 percent of the contractor's total costs incurred, and Alternate I raises that to 85 percent for a small business concern. The Department of Defense supplement goes further: DFARS 232.501-1 sets the customary rates at 80 percent for large business concerns and 90 percent for small business. A small firm performing a DoD fixed-price contract can be reimbursed for nine tenths of its incurred cost while the work is still underway.
Performance-based payments are the event-driven alternative, and they are the closest FAR analogue to an OT milestone schedule. FAR 32.1001 classifies them as contract financing payments that "are not payment for accepted items." FAR 32.1004(b)(2) caps the total at 90 percent of the contract price on a whole-contract basis, or 90 percent of the delivery item price item by item. FAR 32.1001(d) also states they are not subject to the interest-penalty provisions of prompt payment, which is a useful reminder that even inside the FAR, financing and payment are different animals.
Commercial financing sits under FAR 32.202-1, which permits commercial interim and advance payments where they are customary in the marketplace, and holds advance payments before any performance to no more than 15 percent of the contract price.
Then there is the payment clock itself. FAR Subpart 32.9 implements the Office of Management and Budget's prompt payment rules at 5 CFR Part 1315 for invoice payments on government contracts. FAR 32.904 sets the due date at the later of the 30th day after the designated billing office receives a proper invoice or the 30th day after government acceptance. Acceptance is deemed to occur constructively on the seventh day after delivery or performance for interest-calculation purposes. FAR 32.905 lists what makes an invoice proper and requires the billing office to return a defective one within seven days with the deficiencies explained. Interest penalties accrue automatically when the due date passes.
None of that attaches to an other transaction. The subpart implements prompt payment for invoice payments on government contracts, and an other transaction is not one. There is no statutory due date, no constructive acceptance, no interest, and no regulatory definition of a proper invoice unless the agreement supplies one.
How much of the work each instrument will finance before delivery
Rates are quoted from the cited FAR and DFARS provisions. The last row is not a rate. It is the absence of one, which is the point.
The arithmetic nobody runs before signing
Take a twelve-month prototype worth $1.5 million, four equal milestones at months three, six, nine and twelve, and a steady burn of $125,000 a month. Assume payment lands 45 days after the milestone event, which is optimistic for a first agreement. The exposure column is the firm's own money sitting in the project at that moment.
| Point in the project | Cost incurred to date | Cash received to date | Firm's exposure |
|---|---|---|---|
| Month 3 — milestone 1 event | $375,000 | $0 | $375,000 |
| Month 4.5 — milestone 1 paid | $562,500 | $375,000 | $187,500 |
| Month 6 — milestone 2 event | $750,000 | $375,000 | $375,000 |
| Month 9 — milestone 3 event | $1,125,000 | $750,000 | $375,000 |
| Month 12 — milestone 4 event | $1,500,000 | $1,125,000 | $375,000 |
| Month 13.5 — final payment | $1,500,000 | $1,500,000 | $0 |
Peak exposure is $375,000. That is a quarter of the award value and three months of burn, carried by the firm from its own balance sheet, on an agreement that never goes wrong. Now let one acceptance decision slip 60 days because the named engineer is deployed and nobody else will sign. Exposure on that milestone rises to five months of burn, and because the schedule is sequential the delay pushes every later payment with it.
Two adjustments change the picture more than anything else in the agreement. Front-loading shifts value earlier: a mobilization milestone at signature tied to a real evidenced event, then 35, 25, 20 and 20 percent instead of four even quarters. Shortening the interval between milestones does the same thing arithmetically, because exposure scales with the gap, not with the total. Six milestones on the same $1.5 million cut peak exposure by roughly a third even if the payment lag is unchanged.
The example above also assumes no cost share. Where the one-third condition at 10 U.S.C. § 4022(d) is the door a project walks through, the non-federal contribution is at least half of the government's money, and it lands on the same balance sheet at the same time. That interaction is covered separately in what OTA cost share actually means.
Acceptance language is the payment term
Everything above depends on one thing: how fast an event becomes an accepted event. In a FAR contract the regulation supplies a floor. In an other transaction there is no floor, and the words chosen at negotiation are the whole mechanism.
Acceptance language that turns on satisfaction hands the payment schedule to a person's calendar. "Completed to the satisfaction of the sponsoring program office" is not a criterion; it is a delegation. Measurable criteria fix the problem without making the government give anything up: a detection rate at a stated false-alarm rate on a stated evaluation set, a latency budget under a stated load, a completed integration against a named interface with a signed test report, a delivered model artifact that reproduces a stated result from a documented environment. Any of those can be checked in an afternoon by someone who was not in the room.
Three more sentences earn their keep. Name the acceptance authority by role rather than by name, so a reassignment does not orphan the milestone. Set a review window, in days, from submission of the evidence package. State what happens when the window lapses, whether that is deemed acceptance, escalation to a named level, or at minimum the start of the payment clock. The FAR gives contractors a seven-day constructive acceptance rule for interest purposes; nothing gives it to you here except your own drafting.
Restate the criteria whenever scope changes. Modifications that add work without re-baselining the acceptance definition are how a project ends up performed but not complete, and the consequences reach past cash flow into whether the prototype qualifies as successfully completed for follow-on production purposes.
Where the money physically comes from
The payment route matters as much as the payment terms, and it differs by pathway.
On a direct award, the government pays the performer. DIU's public guidance says the Defense Finance and Accounting Service makes payment and that the company is "responsible for submitting invoices into the Invoicing, Receiving, Acceptance and Property Transfer (iRAPT) module of the Wide Area Workflow (WAWF) application." That is the same plumbing a FAR contract uses, and it carries the same first-time setup burden: registrations, roles, and a delay of days to weeks before the first invoice can even be entered. Start that work at award, not at the first milestone.
Through a consortium the route has an extra segment. MITRE describes the two-tier structure: "The Consortium Manager is awarded an OT agreement by the government (base OT agreement) and manages OTs awarded to its consortium member organizations (project OT agreements) under the base agreement." The same reference notes that the manager collects a percentage fee for each project OT awarded, and that fees vary by consortium. Three questions follow, and all three belong in the pricing conversation rather than the post-award one. Who is the payee of record. Which system takes the invoice, the government's or the manager's portal. And whether the consortium fee comes off at award, off each invoice, or is priced on top.
The cash cycle of a single milestone
Only step three is genuinely unpredictable, and it is unpredictable in direct proportion to how loosely the acceptance criteria were written. Steps two, five and six are all fixable in the agreement or the membership terms, before anyone is under schedule pressure.
Expenditure-based agreements and the records clause
An expenditure-based other transaction reimburses actual cost, usually monthly. The cash-flow shape improves immediately, because the gap between spending a dollar and billing it shrinks from a milestone interval to a billing cycle. Firms with thin working capital should ask for this shape early in the negotiation rather than treating fixed-price milestones as the only option.
The price is visibility. Reimbursing cost means the government has to be able to see cost, and that has two consequences. The first is practical: the accounting system has to accumulate cost by project in a form somebody outside the firm can follow. That build takes months, not days, and it is the same build a firm needs for cost-type FAR work. The second is statutory.
Above $5 million, audit access is not optional
Under 10 U.S.C. § 4022(c)(1), an agreement that provides for payments in a total amount over $5,000,000 must include a clause giving the Comptroller General discretion to examine the records of any party to the agreement or any entity participating in its performance. Paragraph (c)(2) carves out a party that has not entered into any other agreement providing audit access by a government entity in the year before the agreement. That exception is real, and it closes the first time the firm signs anything else carrying audit access.
The government's own view of the trade is on the record. In its September 2025 review of prototype other transactions, GAO reported that department officials acknowledged standard contracts "increase DOD's insight into contractor costs and reduce the risk of overpayment." The same report documented the scale of the pathway: DoD obligations through other transactions grew from $1.8 billion in fiscal year 2016 to more than $18 billion in fiscal year 2024, of which roughly $16 billion was prototype work. A great deal of money moves on instruments with less cost visibility than a FAR contract, and both sides know it.
For a firm considering the expenditure-based shape, the readiness question is the same one that governs cost-type federal work generally, and it is covered in DCAA accounting readiness.
Advance payments and outside financing
Two questions come up in every conversation about OT cash flow, and both have unsatisfying but honest answers.
The first is whether the government will pay anything up front. Under 31 U.S.C. § 3324, "a payment under a contract to provide a service or deliver an article for the United States Government may not be more than the value of the service already provided or the article already delivered," absent authorization by law or by the President. The statute speaks in terms of contracts. Whether it reaches an other transaction is a question agencies do not answer uniformly, and it is not one to settle on your own reading before signing. The workable planning assumption is the conservative one: the firm funds the work and is paid after it is done. If an agreements officer is willing to structure an early mobilization milestone against a real deliverable, that is the practical version of the same relief and it raises none of the same questions.
The second is whether a bank will lend against the receivable. Under 41 U.S.C. § 6305 the general rule is that a party given a federal contract or order may not transfer it, with an exception permitting assignment of amounts due to a bank, trust company, or other financing institution where the aggregate amounts due total at least $1,000 and the contract does not forbid assignment. Two things complicate that exception here. Whether the instrument counts as a contract or order for the purpose of the statute is unsettled, and under a consortium the amount may be owed by the consortium manager rather than by the government at all. A lender underwriting the receivable will ask both questions. Have the answers before the money is needed, which means asking the agreements officer and the consortium manager during negotiation rather than during a cash squeeze.
What is left is ordinary: a line of credit sized to peak exposure, milestone design that keeps peak exposure inside it, and a payment schedule short enough that a single delayed acceptance does not become an emergency.
Four instruments, side by side on money
| Axis | FAR cost-reimbursement | FAR fixed-price with progress payments | Prototype OT, fixed-price milestones | Prototype OT, expenditure-based |
|---|---|---|---|---|
| Who funds work in progress | The government, through periodic reimbursement of allowable cost | The government up to 80 or 90 percent of incurred cost under DFARS 232.501-1 | The firm, in full, until the milestone is accepted | The government, on the billing cycle the agreement sets |
| What triggers payment | Incurred allowable cost, invoiced periodically | Cost incurred, then delivery and acceptance for the balance | An accepted milestone event, defined entirely by the agreement | Incurred cost as defined by the agreement |
| Statutory payment clock | Prompt payment applies to invoice payments; FAR 32.904 sets the due date | Prompt payment for invoice payments; financing payments are outside the subpart | None. A due date exists only if the agreement writes one | None by default; write the billing cycle and the due date in |
| Records access | Full FAR and DFARS audit apparatus | Audit of progress payment requests; cost data where applicable | Negotiated; Comptroller General clause required above $5,000,000 | Negotiated and necessarily broader, since cost is the payment basis |
| Accounting system needed | Adequate for accumulating cost by contract line | Adequate for supporting progress payment requests | Ordinary commercial books are usually enough | Project-level cost accumulation an outsider can follow |
| Main cash risk | Disallowed cost after the fact | Liquidation of financing against delivery | An acceptance decision with no clock behind it | Questioned cost and a longer close-out |
What to settle before signing
- A named acceptance authority for every milestone, stated as a role rather than a person
- Acceptance criteria written as a measurement someone outside the project could verify
- A review window in days, with a stated consequence when it lapses
- A payment due date counted in days from acceptance, not left open
- A definition of what a complete invoice contains, since no regulation supplies one
- Milestone sizing and spacing that hold peak exposure inside available working capital
- An early mobilization milestone tied to a genuine, evidenced deliverable
- The payee of record, the invoicing system, and when the consortium fee is applied
- A requirement to re-baseline acceptance criteria whenever a modification changes scope
Common objections, answered plainly
Milestone payments mean we get paid faster, don't they?
They mean payment is not tied to incurred cost, which is a different thing. Under a DoD fixed-price contract a small business can receive 90 percent of incurred cost as a progress payment while the work is underway. Under a fixed-price other transaction the firm receives nothing until an event is accepted. Milestone payment is cleaner to administer and simpler to price. It is not faster to the bank.
Can't we fix the payment terms after award?
A modification requires the government to agree, and the moment of maximum willingness to agree has already passed. Payment terms are cheap to negotiate before signature because they cost the government nothing at that point. After award they compete with technical scope for the agreements officer's attention.
Doesn't fixed-price milestone structure put all the risk on the performer?
It moves cost-overrun risk to the performer and removes a large administrative burden in exchange. That trade is often worth taking. What is not worth taking is the same trade with vague acceptance criteria attached, because then the performer holds both the cost risk and an open-ended schedule risk that no amount of good execution can close.
Bottom line
The flexibility that makes other transactions attractive is the same flexibility that makes them a working-capital problem. Nothing is supplied. A firm that arrives with a milestone schedule already drafted, measurable acceptance criteria already written, a review clock already proposed, and a clear-eyed number for peak exposure will negotiate a payment structure it can carry. A firm that treats the payment schedule as administrative paperwork will find out what it agreed to in month seven.
None of this is about extracting more money from the government. Every term named here costs the government nothing and makes the project easier to administer on both sides. They are simply terms that have to be written down, because in this instrument nothing writes itself.
Frequently asked questions
They look similar and are governed differently. Performance-based payments are a FAR financing mechanism under Subpart 32.10, classified at FAR 32.1001 as payments that are not payment for accepted items, capped at 90 percent of the contract price by FAR 32.1004(b)(2), and recoverable on default. An other transaction milestone payment is whatever the agreement defines, with no regulatory ceiling, no standard liquidation mechanism, and no default recovery language unless the parties write it.
FAR Subpart 32.9 implements prompt payment for invoice payments on government contracts, and an other transaction is not a procurement contract, so the 30-day due date at FAR 32.904 and the automatic interest penalty do not attach on their own. Firms that want a payment deadline have to negotiate one into the agreement and state what a complete invoice contains, because there is no equivalent of the FAR 32.905 proper-invoice definition standing behind it.
Plan on no. 31 U.S.C. § 3324 bars payment under a contract exceeding the value of what has already been provided, absent authorization by law, and agencies differ on how far that reaches into non-procurement instruments. The practical route to early cash is a mobilization milestone tied to a genuine deliverable early in the period of performance, which achieves a similar effect without raising the question at all.
It depends on two answers the firm should get in writing during negotiation. 41 U.S.C. § 6305 permits assignment of amounts due under a federal contract to a financing institution where the amounts total at least $1,000 and assignment is not forbidden, but whether an other transaction qualifies is unsettled, and under a consortium the amount may be owed by the consortium manager rather than the government. Ask the agreements officer and the consortium manager before a lender asks you.
Usually yes, and it costs something. Reimbursing incurred cost on a billing cycle closes most of the gap between spending and receiving. In exchange the government needs to see cost, which means an accounting system that accumulates it by project and a broader records-access position, including the Comptroller General clause that 10 U.S.C. § 4022(c)(1) requires above $5,000,000 in total payments.