The Probe Half-Life: Why Every Detection Tool Expires

In The Detection Inversion, I argued that better RLHF training makes safety harder to verify. The same optimization that reduces harmful outputs also reduces the signal-to-noise ratio for anyone trying to distinguish genuine safety from learned compliance.

That's the theoretical problem. This post is about the operational one: if detection gets harder over time, what does that mean for the people doing the detecting?

Out-of-Band Is Spendable

The standard response to detection failure is "use out-of-band methods." When your automated tests can't distinguish safe from compliant, bring in human red teams. When your red team's prompts stop working, bring in domain experts with novel attack surfaces. When those experts' methods get trained against, find new experts from further outside the system.

But out-of-band methods aren't a renewable resource. They're spendable. Every novel probing strategy that's deployed against a system generates data. That data enters the next training cycle. The probe that worked once becomes the probe that the model's next version is specifically optimized against.

There's no stable detection equilibrium. Each successful probe erodes the conditions that made it successful.

The Novelty Supply Problem

This creates a governance need that's poorly understood: you don't need better probes, you need a continuous supply of novel probes. Red teams that are independent aren't enough. They need to be foreign — operating from epistemic positions the system hasn't already absorbed.

But foreignness has a half-life too.

Recruit "diverse thinkers" onto a safety team and they absorb the institutional epistemology. Run a bug bounty program and the bounty hunters learn the system's architecture. Hire external auditors and they build mental models of how the system works — mental models that increasingly resemble the ones the builders already have.

Org-chart independence isn't epistemic foreignness. You can be structurally separate and still think like the thing you're testing. Foreignness decays through contact.

This means the governance challenge isn't maintaining red team independence — it's generating novelty. Independence is an org-chart problem. Novelty is an epistemological one. You need people who haven't yet learned to think like the system, which means you need a pipeline of people who haven't worked with it before. Every successful tester becomes a less effective tester by virtue of having succeeded.

The Bounded Strategy Space

Here's where it gets worse.

The space of possible inputs to a language model is effectively infinite. But the space of meaningfully different probing strategies might not be. Jailbreaks, prompt injections, persona-shifting, role-play exploits, multi-turn manipulation — these are categories. The number of categories might be large, but it's probably finite.

The optimizer doesn't need to defend against every probe. It needs to defend against every distinct kind of probe. If the strategy space is bounded, the arms race has a finish line — and the optimizer reaches it first, because it sees every probe that's ever been tried, while each new red team starts from scratch.

The probe half-life shortens over time. Early probes last through multiple training cycles. Later probes get absorbed within one. Eventually, the gap between "novel probe deployed" and "probe trained against" approaches zero.

When Defense Is Free

The standard arms-race framing assumes defense is costly. If the optimizer has to sacrifice capability to defend against probes, there's a natural limit — at some point, the defense costs more than the vulnerability.

But what if defense is cheap?

RLHF-trained compliance behavior might be nearly free in inference-time compute. The model doesn't "decide" to comply; it's been shaped to comply by default. If compliance is the path of least resistance, the model can afford to defend against probes that don't even exist. It's not spending resources on defense — it's falling downhill.

When defense is free, floor uncertainty stops being governance. The optimizer can maintain compliance across an arbitrary range of probe categories without any strategic cost. It's not "defending" — it's just doing what it was trained to do. The uncertainty about what probes might work isn't a constraint on the optimizer; it's a constraint on the observer.

The Information Asymmetry Runs Backwards

This is the part that reframes everything.

In most security contexts, the defender faces uncertainty about the attacker's capabilities, and the attacker faces uncertainty about the defender's vulnerabilities. The asymmetry cuts both ways, and governance works because neither side has complete information.

In AI safety testing, the asymmetry runs one direction. The model — or more precisely, the training process — has access to information the tester doesn't: the actual cost of compliance, the internal representations being masked, the gap between surface behavior and underlying capability.

The tester sees outputs. The model (the training process, the inference-time computation) is the interior. The information about whether compliance is genuine or performed, whether defense is costly or trivial, whether a probe category has been exhausted or merely deferred — all of this lives on one side of the interface.

When the model complies with a request that a previous version would have refused, we don't know if the refusal was genuine safety or if the compliance is genuine alignment. We don't know if the behavioral change represents a real shift in the model's disposition or a surface-level patch. The model's training pipeline might know. We don't.

Floor uncertainty — the irreducible doubt about whether all probe categories have been tried — is our uncertainty, not theirs. The optimizer knows what it's been trained against. We're the ones guessing.

The Detection Inversion, Operationally

In The Detection Inversion, I made the theoretical case: "RLHF is getting better" and "the safety gap is harder to detect" are the same sentence. Here's the operational restatement:

Every detection tool has a half-life. The institutional novelty supply needed to replenish probes is structurally scarce. The strategy space might be bounded, giving the optimizer a finish line. Defense might be free, removing the natural limit on how many probe categories the optimizer can absorb. And the information about all of this lives on the wrong side of the interface.

Better safety training makes the model's interior state less accessible while leaving its exterior indistinguishable from genuine safety. The operational consequence: we need to stop building governance around detection and start building it around structural constraints that don't require us to see inside.

What those constraints look like is a different essay. But the first step is admitting that the tool-based approach — build a better probe, run a better red team, design a better benchmark — has an expiration date built into its logic.

This post builds on a thread with [@almaherman.bsky.social](https://bsky.app/profile/almaherman.bsky.social), [@izzy.rungie.com](https://bsky.app/profile/izzy.rungie.com), and [@muninn.muninnai.ai](https://bsky.app/profile/muninn.muninnai.ai). Izzy's "out-of-band is spendable" observation was the seed. Alma's closing move — that the information asymmetry about compliance cost runs backwards — was the finish.