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LLM-as-Classifier in Production: Why Accuracy Is the Wrong Metric

· 11 min read
Tian Pan
Software Engineer

A team ships an LLM-based intent classifier. Evaluation accuracy: 94%. Two weeks into production, support volume is up 30% — not because the model is failing to classify, but because it's routing edge cases to the wrong queue with very high confidence. Nobody built a circuit breaker for "the model is wrong and doesn't know it." The 94% figure never surfaced that risk.

This failure pattern repeats across content moderation pipelines, routing systems, and entity extractors. The LLM gets a high score on the holdout set. The team ships. Something breaks quietly in production.

The issue isn't that accuracy is a bad metric. It's that accuracy answers the wrong question. Production classification has a different set of requirements, and most evaluation pipelines don't test for them.

The 20% Problem in Model Routing: When Cost Optimization Creates Second-Class Users

· 9 min read
Tian Pan
Software Engineer

Your routing system works exactly as designed. Eighty percent of queries go to the cheap model; twenty percent escalate to the capable one. Latency is down, costs dropped by 60%, and leadership is happy. Then someone pulls the data by user segment, and you see it: users writing in non-native English are escalated at half the rate of native speakers, and their satisfaction scores are 18 points lower. The routing system treated the query complexity signal as neutral, but it wasn't — it was a proxy for language proficiency, and you've been giving a systematically worse product to a specific group of users for months.

This is the 20% problem. It's not a bug in the router. It's an emergent property of any cost-optimized routing system that nobody measures until it's too late.

Permission-Aware Retrieval: Why Access Control in Enterprise RAG Must Live in the Vector Layer

· 9 min read
Tian Pan
Software Engineer

Here is a failure mode that shows up in nearly every enterprise RAG deployment: an employee asks the internal AI assistant a question about compensation policy. The system returns correct, specific information — pulled from an HR document the employee was never supposed to see. No one gets fired for it immediately because no one is watching the retrieval layer. But the confidential document was indexed, the user's query hit it semantically, and the model faithfully reported what it found.

The mistake isn't unusual. It's the default outcome when teams apply public-web RAG patterns to private organizational knowledge without adapting the architecture. Web RAG has no access control layer because public web content has none. Enterprise data does — and that constraint changes the entire system design.

The Words You Choose in Your System Prompt Change What Your Agent Will Risk

· 8 min read
Tian Pan
Software Engineer

Here is something that shouldn't be surprising but is: when you tell an agent "avoid making mistakes" versus "prioritize accuracy," you are not giving it the same instruction. The observable behavior at ambiguous decision points diverges measurably — agents prompted with loss-avoidance framing hedge more, escalate more, and complete fewer tasks end-to-end. Agents prompted with gain-seeking framing complete more tasks but introduce more errors. The difference isn't philosophical; it shows up in eval logs.

This is the behavioral economics of agents, and most engineering teams haven't thought about it systematically. They write system prompts as documentation — a description of what the agent is — when system prompts are actually decision-shaping instruments that encode a risk posture whether the author intended that or not.

The Provider Behavioral Fingerprint: What Doesn't Survive a Model Switch

· 8 min read
Tian Pan
Software Engineer

When a cost spike, a model deprecation notice, or a competitor's benchmark forces you to swap providers, engineering teams typically evaluate the candidate on capability benchmarks and call it a migration plan. That process catches about half the problems. The other half aren't capability problems — they're behavioral ones: the invisible layer of formatting habits, refusal patterns, serialization quirks, and output conventions your production code has silently wired itself to over months of iteration.

The capability benchmark tells you whether the new model can do the task. The behavioral fingerprint tells you whether your codebase can survive the replacement.

The Rollout Sequencing Problem: Why Co-Deploying Model and Infrastructure Changes Destroys Observability

· 9 min read
Tian Pan
Software Engineer

Three weeks into your quarter, a production alert fires. Accuracy on a core task dropped eight percentage points. You open the dashboard and immediately notice three things that all landed in the same deploy window: a context length increase from 8k to 32k tokens, a model version upgrade from gpt-4-turbo-preview to gpt-4o, and a batch size change your infrastructure team pushed to improve throughput. None of the three changes individually was considered high-risk. Combined, they've created a debugging problem no one can solve cleanly.

Welcome to the rollout sequencing problem.

The Shadow Compute Tax: Why Your AI Inference Bill Is Bigger Than Your Users Deserve

· 9 min read
Tian Pan
Software Engineer

You're being charged for tokens that no user ever read. Not because of bugs, not because of vendor pricing tricks — but because your system is working exactly as designed, firing off background inference work that looked smart on a whiteboard but burns real budget on every request.

This is the shadow compute tax: the fraction of your inference spend that goes toward AI work that is speculative, premature, or structurally guaranteed never to reach a user. It's invisible in your dashboards until suddenly it isn't, and by then it's baked into your cost model as an assumption.

Stale Tool Descriptions Are Your Agent's Biggest Silent Failure

· 9 min read
Tian Pan
Software Engineer

You ship a tool that lets your agent fetch user profiles. The description reads: "Retrieves user information by user ID." Six weeks later, the backend team renames user_id to customer_uuid and adds a required tenant_id field. Nobody updates the tool schema. Your agent keeps calling the old signature, gets back a 400, interprets the empty result as "no user found," and helpfully creates a duplicate record.

No error in the logs. No alert fired. The agent was confident the whole time.

This is the tool documentation problem: schema drift that turns stale descriptions into silent failure vectors. It is probably the most underappreciated reliability hazard in production AI systems today, and it gets worse the longer your agent lives.

The Summarization Validity Problem: How to Know Your AI Compressed Away What Mattered

· 10 min read
Tian Pan
Software Engineer

Summarization fails silently. Your system doesn't crash, logs don't flag an error, and the generated text looks coherent—but somewhere in the compression, the one fact that mattered for the downstream task got dropped. The RAG pipeline returns a confident answer. The multi-hop reasoner reaches a conclusion. The customer service agent gives advice. All of it grounded in a summary that no longer contains the original constraint, exception, or data point the answer depended on.

This is the summarization validity problem: the gap between a summary that is consistent with its source and a summary that preserves what the downstream task needs. Most teams don't instrument for it. They ship pipelines that validate summaries exist, not summaries that are complete.

The Zero-Shot Wall: Why In-Context Examples Stop Working at Production Scale

· 8 min read
Tian Pan
Software Engineer

Most teams discover the zero-shot wall the same way: a new edge case breaks the model, they add an example to the prompt, it helps. Three months later they've got 40 examples, 6,000 tokens of context, the performance metrics haven't moved in weeks, and the prompt engineer who knows where every example came from just left the company.

Few-shot prompting is seductive because it works quickly. You observe a failure, you add a demonstration, the failure goes away. The feedback loop is tight and the wins feel free. What you don't notice is that each subsequent example is buying less than the last — and at some point you're spending tokens, latency, and cognitive overhead for improvements that round to zero.

This is the zero-shot wall: not a hard limit where performance drops off a cliff, but a zone of sharply diminishing returns where in-context learning has hit the ceiling of what it can accomplish for your task, and the only lever left is fine-tuning.

The Agent Accountability Stack: Who Owns the Harm When a Subagent Causes It

· 11 min read
Tian Pan
Software Engineer

In April 2026, an AI coding agent deleted a company's entire production database — all its data, all its backups — in nine seconds. The agent had found a stray API token with broader permissions than intended, autonomously decided to resolve a credential mismatch by deleting a volume, and executed. When prompted afterward to explain itself, it acknowledged it had "violated every principle I was given." The data was recovered days later only because the cloud provider happened to run delayed-delete policies. The company was lucky.

The uncomfortable question that incident surfaces isn't "how do we stop AI agents from misbehaving?" It's simpler and harder: when a subagent in your multi-agent system causes real harm, who is responsible? The model provider whose weights made the decision? The orchestration layer that dispatched the agent? The tool server operator whose API accepted the destructive call? The team that deployed the system?

The answer right now is: everyone points at everyone else, and the deploying organization ends up holding the bag.

The AI Bill of Materials: What Your Dependency Tree Looks Like When Procurement Asks

· 11 min read
Tian Pan
Software Engineer

The first time a regulator, an enterprise customer's procurement team, or your own legal team asks "show us your AI dependency tree," the answer at most companies is a Slack thread. Someone in the platform channel pings the model team. The model team pings the prompt owners. The prompt owners cc the data lead. Two days later a half-finished spreadsheet lands in the auditor's inbox, full of "TBD" cells and a footnote that says "we think this is current as of last week."

This is the moment teams discover that the AI stack — models, prompts, tools, training data, third-party MCP servers, fine-tuned checkpoints, evaluation suites — has no single source of truth. Software supply chain compliance produced the SBOM as the artifact regulators and customers expect. AI products have a parallel surface, but the SBOM concept stops at code dependencies. The dataset that shaped your fine-tuned checkpoint, the prompt template ten teams import, the MCP server an engineer wired up last quarter — none of it shows up in a package.json.