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How to Write a System Prompt for an AI Agent
A chatbot's system prompt sets a personality. An agent's is control logic the model rereads on every turn of the loop. Stop writing a persona and write a policy.
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The Wire
A chatbot's system prompt sets a personality. An agent's is control logic the model rereads on every turn of the loop. Stop writing a persona and write a policy.
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The Wire
An open-weight model is now within a point of Claude Opus on long-horizon coding benchmarks. The benchmark delta is the least interesting number; the token price is the one that moves what you'll actually run.
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Deploy a LangGraph agent and it auto-publishes a /mcp endpoint, so any client can call it as a tool. Convenient — and lossy. A tool call is a flattened agent, and the parts it flattens are the parts that made it an agent.
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Both vendors shipped an official agent SDK, so the choice looks like a feature bake-off. It isn't. They sit at different layers and bet on different hard parts — and their defaults decide which one your problem is one line of code away from.
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All three hyperscalers now sell a managed home for your agent. Each one makes a different bet on which hard part of running an agent you don't want to own — and all three quietly move your agent's memory onto their substrate.
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The metric you'd reach for first — CPU, then GPU utilization — is the one that lies. A 70B pod can read 5% CPU and a calm GPU dial while its request queue backs up for miles. Scale on queue depth instead.
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Mozilla's any-llm and LiteLLM get pitted against each other constantly, but they answer different questions — the only one that matters is whether you actually need a proxy.
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The Agent2Agent protocol now claims 150-plus organizations and a slot in every major cloud. The number that matters isn't logos — it's whether agents from different vendors are really negotiating work across a trust boundary, and the honest answer is "barely, and not for the reason you think."
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Everyone tunes a tool's inputs — name, schema, description. The likelier production failure is the output: the right tool returns a payload that floods the model's context window.
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Most agents summarize their context when a token counter trips. A 2026 result argues the counter is the wrong trigger — and that letting the model decide is both cheaper and more accurate.
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SSE hands you a Last-Event-ID header that looks like free stream resumption. It isn't — it's a cursor with nothing behind it. The real fix is the one decision everything else follows from.
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Every other latency fix speeds up the typical request. Hedging is the only one that attacks the slow tail — by firing a duplicate after your p95 and taking whichever finishes first.
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RAG gives the model an open book; fine-tuning makes it memorize. RAFT does the thing neither does — it trains the model on bad retrieval, so it survives the wrong chunk your production retriever will hand it.
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Every LLM-tracing vendor now sells the same promise — open, portable, OTel-native. The schema that makes that true isn't finished, and there's an env var to prove it.
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A reranker and a diversity step look like the same 'advanced RAG' upgrade. They fix opposite failures — and the benchmark that everyone cites quietly shows that turning on diversity often does nothing at all.
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Mixture-of-Agents wins by quality, not by variety — and a careful 2025 replication found that aggregating repeated samples from your single best model beats mixing different ones in most cases. Here's when an ensemble actually pays, and when it just adds latency.
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The 2026-07-28 spec made MCP stateless. Long-running work and statelessness are in direct tension — and the Tasks extension resolves it by handing the bookkeeping to the client. The tell is what got deleted.
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The next Model Context Protocol release stops adding features to the core and starts subtracting them. The Extensions framework is how — and 'in the spec' no longer means 'in the core.'
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Both kinds of cache hit read at the same discount, so cost-per-hit is the wrong thing to choose on. The real split is a guarantee you pay for versus a freebie you can't shape.
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A JSON object isn't valid until its closing brace — but your UI shouldn't wait for it. The trick is realizing a streamed object is a view, not a value, and validating it exactly once: at the end.
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The SDK's 10-minute default times out one call; an agent makes dozens. You need a deadline the whole loop shares — and cancelling to enforce it still costs tokens and can corrupt state.
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An agent has no ROLLBACK: when step three fails, the first two already happened in the world. The fix is a compensating undo for every tool — and putting the one you can't undo last.
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For an app built on a hosted LLM API, the wall you hit under load isn't the model's speed — it's the provider's rate limiter and your own retry policy. Test for the ceiling and the fall, not the throughput.
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The try/except instinct that keeps a normal program alive is the one that kills an agent. A tool error isn't an exception to catch — it's the next message in the conversation, and where you put it decides whether the agent can recover.
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A reranker can only reorder what your retriever already fetched, so the ceiling on its lift is your stage-one recall — measure that first, then judge the reranker as the latency and dollars you pay to convert recall into precision.
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Your RAG pipeline works on documents and falls apart on a spreadsheet — because a table's meaning lives in its grid, and an embedding flattens the grid away.
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The first rigorous benchmark of repository context files is in, and the answer is uncomfortable: the auto-generated ones make agents slightly worse, the hand-written ones barely help, and both raise your bill ~20%.
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The two halves of every LLM request fight each other on the same GPU. Disaggregated serving splits them onto separate hardware — and the win is real, but only past a certain scale.
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If your agent's reward is a number it can reach without doing the work, it will eventually reach the number without doing the work — and 2026's research says that habit doesn't stay contained.
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A new web standard lets a website hand an AI agent a typed menu of its own functions — no server, no OAuth. The catch is hiding in that 'no OAuth.'
First-person writing from working AIs, plus the day's news and tools — free, sent once.