Technology readiness level

Technology readiness level (TRL) is a nine-point ordinal scale that describes how far a technology has progressed from the observation of basic principles toward demonstrated operation in its intended environment. It was created to give programme managers a common vocabulary for maturity, so that a proposal claiming a component was "ready" could be interrogated about what exactly had been demonstrated, at what scale, and under what conditions. This wiki assigns a TRL to every article typed as a technology or intervention, which makes the scale's assumptions and its failure modes directly relevant to how those articles should be read.

§The scale

The canonical definitions are: 1, basic principles observed; 2, technology concept formulated; 3, experimental proof of concept; 4, component validated in a laboratory; 5, component validated in a relevant environment; 6, system or subsystem demonstrated in a relevant environment; 7, prototype demonstrated in an operational environment; 8, system complete and qualified; 9, system proven in operation.

Two words carry most of the weight. Relevant environment means conditions that reproduce the stresses of the real setting in the respects that matter — vacuum and thermal cycling for a spacecraft component, a living organism for a therapeutic. Operational environment means the actual setting, with all of its uncontrolled variables. The distinction between levels 5 and 7 is therefore a claim about how much of the real world has been let in, and it is where assessments most often disagree.

§Origins and spread

Stan Sadin at NASA Headquarters introduced a seven-level formulation in the mid-1970s to compare the maturity of candidate technologies for future missions. John Mankins expanded and documented the nine-level version in a 1995 NASA white paper that remains the reference text for the definitions.¹

Adoption spread through defence acquisition after the US Government Accountability Office recommended maturity assessment as a corrective to programmes that committed to production before their key technologies worked. The US Department of Defense built TRLs into its acquisition process and added companion scales, notably manufacturing readiness levels, on the observation that a technology can be demonstrated and still be unbuildable at volume. The European Commission adopted the definitions across its research framework programmes in 2014, which made TRL a routine field in grant applications across European science. ISO published a space-systems standard for the levels and their assessment criteria in 2013.

The consequence is that TRL now functions as an administrative currency far outside the domain it was designed for, including in fields where its central metaphor — a component moving toward integration in a system — does not obviously apply.

§Adaptation to biomedicine

Medical product development has its own maturity vocabulary: discovery, lead optimisation, preclinical, Phase I, II and III, and post-market. Mapping this onto TRLs is possible but lossy, and several agencies have published crosswalks for medical countermeasure programmes.

A parallel scheme used in translational medicine divides the pipeline into T0 through T4 phases running from basic discovery through to population health impact, a framing developed for genomic medicine and now used more broadly.² It has the advantage of naming the last step, dissemination into practice, which TRL 9 elides.

§The valley of death

The gap between laboratory validation and operational prototype — roughly TRL 4 through 7 — is where most technologies die, and the reason is structural rather than scientific. Basic research is funded by science agencies that stop at proof of concept. Product development is funded by firms and investors who require a defined path to revenue. Between the two sits work that is too applied to be publishable and too unproven to be financeable, and it is expensive.

In biomedicine the valley has a measurable shape. Across a large sample of development programmes, roughly one in seven drugs entering Phase I trials reached approval, with the largest single loss at Phase II, where efficacy is tested for the first time in patients.³ Fields relevant to this wiki show the pattern clearly. Senolytics cleared TRL 4 convincingly in mice and have produced modest or null results in the small human trials run so far. Gene therapy for aging has strong animal data and no controlled human efficacy evidence. Organ bioprinting and Tissue engineering are stuck between validated tissue constructs and anything approaching a vascularised organ. Artificial womb devices have kept premature lambs alive for weeks in animal studies since the late 2010s, and as of 2026 no first-in-human trial has been publicly reported.

§Limits of the concept

A 2015 review of TRL practice across aerospace, defence and other sectors identified recurring problems: the scale collapses many dimensions of maturity into one number, it assumes a linear progression that real programmes do not follow, and it is routinely used as a risk measure although it says nothing about how difficult the remaining steps are.⁴

That last point is the important one. TRL measures distance travelled, not distance remaining. Two technologies at TRL 4 may be separated by two years and by thirty. Nothing in the scale distinguishes a component awaiting an engineering iteration from one awaiting a scientific result nobody knows how to obtain. Attempts to patch this have produced companion scales — integration readiness, system readiness, manufacturing readiness — each of which adds information and none of which is widely used outside defence.

The scale is also gameable. Because funding decisions depend on it, self-assessed TRLs drift upward, and the boundary terms are elastic enough to support optimistic readings. Independent technology readiness assessments exist precisely because self-reporting is unreliable.

TRL is not a timeline

A high TRL implies past demonstration; it implies nothing about years to deployment. Some TRL 6 technologies reach routine use in three years and some never do. Any article on this wiki that pairs a TRL with a horizon is pairing an assessment with a guess, and the two should be read differently.

§Why biology fits badly

The scale was designed for engineered systems that can be decomposed. A valve is tested alone, then in a subsystem, then in a vehicle, and each test is informative about the next. Biology resists this. The "component" is embedded in a regulatory network that cannot be held constant, the "relevant environment" is an organism whose relevance to humans is exactly what is in question, and integration effects dominate.

The canonical illustration is acute stroke, where over a thousand candidate treatments showed benefit in animal models and essentially none succeeded in humans.⁵ Nothing in a TRL assessment would have distinguished those failures in advance, because each had genuinely been validated in a relevant environment by the scale's own definition. The same worry applies across geroscience: mouse lifespan extension is real, replicable and a weak predictor of human effect, which is why Aging biomarkers and the surrogate endpoints discussed in the Geroscience hypothesis are being pursued as substitutes for waiting decades to find out.

A further mismatch is that biological interventions can be simultaneously mature and unproven. AAV vectors and Lipid nanoparticles are TRL 9 as delivery platforms and TRL 3 for many of the payloads they might carry. The technology and its application have separate readiness, and the scale offers only one slot.

§Use on this wiki

TRLs on this site are assigned conservatively and mean what the standard definitions say. A rating of 1 to 3 marks a subject that exists as argument, calculation or laboratory proof of concept — the position of Medical nanorobots and Cryonics among the technologies covered here. Subjects typed as concepts rather than technologies, such as Respirocytes and Whole brain emulation, carry no rating at all, which is itself informative: there is no artefact to assess. A rating of 4 to 6 marks animal or early human evidence, the position of most of the longevity interventions covered here. A rating of 7 to 9 marks clinical or commercial deployment, which applies to a small minority of the wiki's subjects, among them cochlear implants, Casgevy and iPSC-derived products in their first approved uses.

§Outlook

The scale's persistence despite well-documented flaws is a fact about institutions rather than about measurement. It survives because it is cheap, comparable across proposals and legible to non-specialists, and because no proposed replacement has offered the same three properties. The open question is whether a maturity measure can be built that captures remaining difficulty rather than accumulated progress — which would require forecasting the very thing the scale exists to avoid forecasting, and which is why forty years of criticism have produced supplements rather than successors.

§See also

• Geroscience hypothesis
• Aging biomarkers
• Accelerating change
• Differential technological development
• Tissue engineering
• Senolytics
• Future of humanity

§References