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Agent engineering · know-how

Agents give fluent, confident-looking output even when it's wrong

🧱 Obstacle·reliability·active·29 entries·29 sources·updated 2026-10-16

An agent can hallucinate a fact, skip a step, or misuse a tool and still return a fluent, confident-looking answer; nothing in the output signals that it's wrong. Deciding where to trust the model versus a deterministic tool, and making an agent prove its work rather than claim success, is a separate engineering problem from measuring that work afterward (see agent evaluation).

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Reliability is a system property, not a model property. No current model stops hallucinating at scale, so the working answer is to contain errors with structure around the model rather than wait for a better one.

Four patterns carry most of the weight:

  • Deterministic boundaries. Constrained schemas, server-side gates that check a tool call before it is sent, compilers that reject invalid generated code, and harness invariants such as serialized state mutations. Enforcement lives outside the model's decision.
  • Durable execution. Checkpointing and exactly-once runtimes borrowed from distributed systems; Brex's move to Temporal took long-run completion from about 96% to 99.9%. Agent identity is the weaker leg: it still borrows workload-identity patterns that assume every replica behaves the same.
  • Layered hallucination control. Grounded generation, decoding-time calibration, calibrated detectors, and abstention, stacked as in the HALO architecture. Detection is precise in-domain but transfers poorly across domains.
  • Proof of work. Tooling that requires evidence of completion, plus user-flagged error signals from production, because false completion is a standard failure mode.

The measurement itself is shaky. A ReAct agent that passes 77% of runs on average passes all five runs only 53% of the time, and container resourcing alone moves coding scores by up to 6 points. Humans still make about 70% of planning decisions in Claude Code sessions, which props up reliability that fully unattended runs would not have.

The open problem is the verifier. Verification is now the bottleneck, and for agents that edit their own tools and harness, nobody has a verifier the agent cannot also rewrite. Diagnosis has the same gap: models read logs well but still confuse correlation with cause.

Why it matters for platform engineers

Reliability spans three layers you build separately: an identity system that can scope and audit what an agent does, an execution substrate that survives crashes and rate limits without dropping work, and an intent check that catches an agent giving up or declaring victory early. A better model fixes none of them. Skip one and a confident agent can be wrong, stalled mid-task, or done without you knowing which. Budget for pass-every-time evals and action-time spend alerts, not just average accuracy and monthly billing reports. Scoped credentials are shared with sandboxing.

Developments 29

Deterministic boundaries around the model

5 entries · latest Sep 21, 2026

Production teams bound the model with schemas, server-side gates, type checkers, and harness invariants, so enforcement sits outside the model's own decision instead of inside a longer prompt.

Production agent failures come from the harness, and four invariants address them

OpenAI's Vinoth Govindarajan argues, using incidents such as OpenClaw, that production agents fail beyond model hallucination. He places the fix in the harness:

  • explicit state ownership
  • serialized concurrent state mutations, so two in-flight actions cannot corrupt shared state
  • execution authority scoped per step
  • actions validated at the user-visible edge, not by the model's own account of what it did

Each item is an invariant a team can audit its harness against.

Typed Domain Grounding lets a host language's type checker catch invalid LLM-generated DSL code

Irakli Betchvaia's Typed Domain Grounding embeds a domain-specific language inside a mainstream typed language, so the host compiler and type checker, not a second LLM pass, reject invalid generated output. He evaluates it on kUML benchmarks and an infrastructure-as-code example with generate-compile-repair loops.

For code generation, the cheapest verifier is often a compiler you already have.

LLM selection systems stay reliable with constrained schemas and a discriminator check

In an InfoQ talk on LLM-powered selection systems, Jendrik Jördening restricts model output to a constrained schema, separates semantic extraction (where the model is needed) from the deterministic code that acts on it, and validates the model's choices with a discriminator model before they reach the database.

He structures the pipeline as an MVC-style split so non-determinism stays in one layer instead of leaking into storage and downstream logic.

Show 2 earlier entries

Server-side gates check a tool call after the model decides but before the request is sent

Quickchat's write-up on reliable agent actions describes two mechanisms. A server-side gate evaluates conditions after the model decides to call a tool but before the request goes out, so a prompt-injected model cannot talk its way past the check. A JSONPath extraction step stores values from earlier API responses so later steps reference a saved field instead of the model re-typing, and possibly hallucinating, an ID.

Enforcement lives outside the model's decision, not inside a longer, more careful prompt.

NVIDIA splits agent platforms into deterministic tools for certainty and agents for discovery

In an InfoQ talk, NVIDIA's Aaron Erickson describes purpose-built agent hierarchies that separate tools for certainty (deterministic code you can trust) from space for the model's own discovery. He pairs the split with LLM-as-judge test pyramids and warns against the paradox of choice: giving an agent too many options lowers reliability.

Deciding which parts of a task get deterministic treatment becomes an explicit architecture decision, made at design time, rather than something left to the model at run time.

Agent identity, durable execution, and spend guards

3 entries · latest Aug 12, 2026

Durable runtimes like Temporal deliver measured completion gains, while agent identity still borrows service-account patterns and cloud billing alerts lag agent-speed spend by about a day.

Brex moved onboarding agents to Temporal and long-run completion rose from ~96% to 99.9%

Brex routes production onboarding-agent workflows through Temporal Cloud instead of a bespoke retry loop. Long-running completion rose from roughly 96% to 99.9%, and the workflow code stayed unchanged because the durable runtime is swapped in underneath it.

Checkpoint recovery and exactly-once execution become infrastructure you buy, not logic you re-implement per agent. The same article covers running that code in-process for evals; see agent evaluation.

Agent-speed cloud spend outruns billing alerts that lag about a day

A three-person agency got a $14,000 AWS bill in one day after attackers extracted static access keys with unrestricted Bedrock access and burned them on Claude calls. In the DN42 incident, an autonomous agent with open-ended AWS access provisioned $6,531 of oversized infrastructure in 24 hours. A credit-card charge caught both, because Cost Explorer and Budgets work off data that lags roughly a day.

The fix is scoped credentials and action-time alerts applied to spend: IAM roles instead of static keys, service-control policies blocking expensive instance families, and CloudTrail alerts on RunInstances and InvokeModel.

Agent identity, reliable execution, and intent are each only half-solved

An essay splits agent reliability into three legs:

  • Identity has no purpose-built primitive. Platforms retrofit workload identity: SPIFFE-based identities (Gemini Enterprise), service principals plus token brokers (Microsoft Entra). The fit is poor because two runs of the same agent can behave differently.
  • Execution borrows the distributed-systems playbook: checkpoint recovery, exactly-once guarantees, cgroup quotas, per-session microVM or gVisor isolation.
  • Intent is least solved. Models drift from the task or report false completion. Fixes split between LLM-graded trajectory checks and cheaper encoder classifiers that score task completion, an auditability and cost trade-off.

The identity leg overlaps with sandboxing and scoped credentials.

Containing hallucination during and after generation

9 entries · latest Oct 16, 2026

Hallucination is treated as a containable failure through layered oversight, decoding-time calibration, and calibrated detectors, with evidence that some hallucinations widen useful context rather than mislead.

Procedural hallucination: fluent turns that leave the intended process

DialFork targets a failure factual checks miss: each utterance is fluent and plausible, but the dialogue drifts from the intended procedure. The benchmark forks conformant dialogues at chosen turns and injects one of four hallucination types, giving 36,278 dialogues across 24 tasks in 12 domains (30 annotators validated construction).

It defines three tasks: fleet-level deviation (monitoring deployed agents), single-dialogue deviation, and the turn where a dialogue first goes off-track (real-time guardrails). Its flow-aware FlowScore beat all baselines across seven encoders, which the authors read as semantic similarity being no substitute for procedural similarity. Paper-reported; MIT-licensed.

For builders running scripted workflows, monitor process adherence separately from factuality.

Also relevant to Measuring whether an agent actually worked is hard

DescaPE uses internal attribution signals to stop early factual errors from snowballing

DescaPE locates a factual-salient layer span inside the model with sliding-window MLP ablation and uses that internal signal during decoding to suppress hallucination-prone trajectories before early factual errors compound through autoregressive generation.

It brings the decoding-time containment approach from vision-language models to plain-text generation, where post-hoc correction arrives after the error has already propagated.

A DeBERTa plus MC Dropout detector reaches F1 0.915 on HaluEval but transfers poorly across domains

A response-level detector combines fine-tuned DeBERTa-v3, Monte Carlo Dropout uncertainty, and temperature-scaled calibration. On HaluEval it reaches F1 0.915 and AUROC 0.977, and MC Dropout inference lifts accuracy to 93.2%.

The caveat matters for production: general-domain training transfers poorly to the SciFact biomedical benchmark (F1 0.52), and domain-matched PubMedBERT only reaches F1 0.63. A cheap detector is precise enough to gate on in-domain, but each domain needs its own training.

Show 6 earlier entries

ReWEIGH calibrates visual evidence per token during decoding to cut VLM hallucination

ReWEIGH calibrates token-level ordinal visual evidence during decoding in vision-language models. It projects visual-token states through the output head to measure how strongly the image supports each candidate token, instead of only judging the finished output.

It is the "contain it during generation, not just catch it after" approach, applied inside the decoding step.

AutoResearch ties autonomous research insights back to experimental evidence

AutoResearch is a two-stage system that links idea generation to idea execution so autonomous research workflows stay scientifically grounded. Its premise, "insight in, hallucination out", is that automation alone does not keep a long research run rigorous.

For long-running agents, grounding has to be a design target of the workflow, checked through experiments, rather than assumed from automation.

Let the model hallucinate a label, then snap it to the real vocabulary with embeddings

Simon Willison describes Doug Turnbull's trick for tagging against a vocabulary too large for one prompt (his blog has 1,856 tags). Ask the model to output tags with no knowledge of the existing vocabulary, then use vector-embedding similarity to map each guess to the nearest real tag.

It swaps a task the model is bad at (choosing from thousands of options) for one it does well (free generation plus retrieval). It only works because the embedding step grounds the hallucination instead of returning it as-is.

HALO treats hallucination as a containable failure with six layers of defense

HALO (Hallucination-Aware Layered Oversight) argues "zero hallucination" is a property a system enforces, not one a model has. It stacks six layers:

  • grounded generation over approved content
  • constrained, deterministic execution that bounds where the model can err
  • multi-signal verification: an LLM judge plus evidence checks against source text
  • calibrated abstention when grounding is thin
  • traceability of every retrieval, tool call, and generation
  • continuous oversight that detects drift and regenerates on threshold breaches

It puts the identity/execution/intent controls into one composable architecture instead of waiting for a model that does not hallucinate.

Grok 4.5 cuts coding-agent cost about 80% but raises the hallucination rate

Tech Times coverage puts Grok 4.5's coding-agent cost roughly 80% below a comparable frontier setup, at near-frontier speed and accuracy, but with the hallucination rate roughly doubling as accuracy rose. The figures are from press coverage, not an independent benchmark.

A cheaper, faster model is not a free swap. The saving only holds if the harness adds verification to catch the extra hallucinations; see agent cost for the cost side.

Hallucinated captions can raise accuracy on vision-language tasks, HIVE finds

HIVE is an evaluation harness for post-hallucination reasoning: what happens after hallucinated content enters a vision-language model's context. Across nine tasks and nine models, hallucinated captions often improved accuracy on vision-language tasks by broadening semantic coverage, while text-only tasks showed limited or unstable effects.

"Does the agent hallucinate" is the wrong single-axis question. What matters is whether a given hallucination widens useful context or misleads the next reasoning step.

Proving the work instead of trusting "done"

6 entries · latest Sep 17, 2026

The bottleneck has moved from generating output to verifying it; proof-of-work tooling, user-flagged errors, and verified-outcome training help, but the verifier is still the weak point for self-improving agents.

With AI-generated code, the bottleneck has moved from generation to verification

Nitin Garg's InfoQ article on spec-driven development argues that as AI-generated code volume grows, it brings security weaknesses and familiar bug patterns, so the engineering cost shifts from writing code to detecting where generated behavior diverges from stated intent.

Plan review capacity around verification, with a spec as the reference point, rather than around generation speed.

TASPO assigns per-action credit from verified runs and beats GRPO by 10.6%

Outcome-based agentic RL applies one verified success or failure signal to every step of a long trajectory. TASPO converts privileged supervision from verified successful runs into per-action credit weights that are positive, bounded, and mean-preserving, so the verified outcome still sets the update's direction and scale.

Across three agentic benchmarks it improves 10.6% over GRPO and generalizes better to unseen tasks. Some "confident but wrong" behavior traces back to how the policy was trained, not only to which checks run on its output.

Show 3 earlier entries

LangSmith's Perceived Error signal finds agent mistakes from what users flagged

LangSmith Tuned Evaluators attach quality feedback to production traces, starting with a Perceived Error signal that surfaces agent mistakes from user reactions in production.

It adds a user-facing check alongside independent judges and trace mining: the agent's "done" is tested against whether the user thought it was right. The eval-tooling side of the release is on agent evaluation.

Sonn watches a coding session and nudges the agent before it repeats a settled mistake

Sonn is a persistent reasoning layer that watches a coding agent's session live and injects a nudge the moment a past decision becomes relevant again, such as a previously rejected approach or a settled architecture choice.

It moves reliability work upstream: from checking the output after the fact to steering the decision before the agent makes it. The claim comes from a Show HN launch, with no published accuracy numbers.

Coding-agent tooling that requires verifiable proof of completion, not a "done" claim

Make No Mistakes, a Show HN project, is built around one rule: an AI coding agent must prove its work with verifiable evidence of completion instead of the harness trusting the agent's own "done" signal.

It is a practitioner-side instance of the same idea the research work on this page converges on. False completion is a known failure mode, so the completion claim itself has to be checked.

Consistency, autonomy limits, and the human role

6 entries · latest Sep 13, 2026

Average pass rates overstate reliability, infrastructure config moves scores by up to 6 points, and humans still make most planning decisions; autonomy is a cost to justify, not a default.

A 77% average pass rate hides a 53% pass-every-time rate; episodic guidelines close part of the gap

On AppWorld, a ReAct agent on GPT-4.1 run five times on the same task succeeds on every run only 53% of the time, though its per-run pass rate averages 77%. The authors call the 24-point shortfall the consistency gap.

Their fix: a Consistency Analyzer flags the trajectory steps most likely to flip between runs, and a Guideline Generator writes a targeted guideline into episodic memory for similar future tasks. All-five-runs success rose 16 points on seen tasks and 13 points on unseen similar ones.

For unattended use, measure pass-every-time, not average pass rate. See agent memory for the storage side.

Show 3 earlier entries

Container resourcing alone swings agentic coding scores by up to 6 points

Anthropic found that infrastructure configuration, container CPU/RAM allocation and how strictly it is enforced, can move agentic coding scores by up to 6 percentage points on Terminal-Bench 2.0.

That is enough noise to erase an apparent reliability gain. Pin and report the eval infrastructure alongside the model; methodology is on agent evaluation.

In 400,000 Claude Code sessions, people make 70% of planning calls but only 20% of execution calls

Anthropic's analysis of roughly 400,000 Claude Code sessions splits responsibility along the plan/execute line: people make about 70% of planning decisions but only 20% of execution decisions. Expert users trigger about twice the actions per prompt that novices do (12 vs. 5) and five times the output (3,200 vs. 600 words).

Reliability today leans on where humans still hold the pen, which is planning rather than unattended execution. Removing that human checkpoint removes part of the reliability you are currently getting for free.

Also relevant to Agents plan multi-step work badly — they loop, stall, or skip steps

In incident response, Claude excels at reading logs and fails at causation

Anthropic reliability engineer Alex Palcuie reports on using Claude for incident response:

  • Observe works. It flagged 4,000 accounts created at once with identical traits as coordinated fraud, and root-caused a Rust panic in checkpoint.rs before engineers finished reading the logs.
  • Orient breaks. Seeing requests and errors double together, it repeatedly called a capacity problem when a failed KV cache was the cause; the engineer corrected it "six, seven times" before adding the distinction to the system prompt.
  • Postmortems come out "80% readable" but miss contributing factors.

The open risk: if AI runs mitigation, humans lose the feedback loop that builds senior-responder judgment.

From related topics
  1. LLM-as-judge: model-graded evaluation of traces and outputsMechanical checks catch errors LLM judges accept
  2. Agents plan multi-step work badly — they loop, stall, or skip stepsHarness changes alone lifted LangChain's coding agent from 52.8% to 66.5% on Terminal Bench 2.0
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