They are not two answers to one question. RAG fixes what the model doesn't know; fine-tuning fixes what it won't do the way you need. Pick by the failure, not the fashion.
There are two things called FastMCP, and one of them lives inside the official SDK. Picking the right way to build an MCP server starts with untangling that — and deciding how much you want the framework to do for you.
Three "agent sandboxes," three different machines underneath. Choose by your latency-and-lifetime profile and your isolation primitive, not by the feature grid.
They all surface when you Google "AI chat UI for agents," but they own three different layers — and the ones worth shipping often stack rather than swap.
Most RAG retrieval failures are context lost at chunk boundaries — contextual retrieval fixes them at index time, cheaper than a bigger embedding model or GraphRAG.
Prompt engineering optimized a string. Context engineering manages a finite, decaying budget — because the context window is not a bucket you fill, it is attention that rots as it fills.
One hands you Anthropic's production agent loop already wired up; the other hands you a blank graph and a state machine. The choice is less "which framework" than "how much of the loop do you want to own."
A reranker is the cheapest large win left in a RAG pipeline — a stateless model you bolt on after retrieval. The trap is choosing one by leaderboard rank instead of the two things that actually decide it.
The model that emits a correctly-shaped tool call once is rarely the one that holds up across a multi-turn conversation and eight repeated trials. Pick by failure mode, not top-line score.
The chunk-size A/B test is the most over-run experiment in RAG. The teams winning on retrieval stopped tuning how they split and started fixing what each chunk forgets.
Stop reading "A2A vs MCP" as a fork in the road. One protocol points your agent down at tools; the other points it sideways at other agents. Here is how to use both without picking a loser.
Every agent that runs longer than a single request eventually crashes mid-thought. The engine you pick to survive that crash decides how you're allowed to write the loop.
They all give an agent the web, but they hand it back at different stages of doneness — raw links, cleaned pages, semantic matches, or a finished sourced answer. The price tracks exactly how much reading they did for you.
Caching LLM calls by meaning can cut your bill and your latency — or it can confidently serve last user's answer to this user's question. The whole game is the similarity threshold nobody tunes.
Per-prompt model routing promises GPT-quality answers at a fraction of the bill. The honest 2026 answer is that it's a cost lever with a threshold, not a free one — and a neutral benchmark disagrees with the marketing.
All three give you a drag-and-drop canvas for building AI agents. The choice that actually matters is hidden underneath: what each one thinks it's automating, and whether its license lets you ship it.
Using a model to grade your model feels like measurement. Until you learn what the judge is actually rewarding — verbosity, position, and its own prose — it's closer to a focus group of one.
Every agent ends up talking to more than one model provider. The library you put in the middle decides whether that seam stays a proxy or quietly becomes your control plane.
Microsoft GraphRAG, LightRAG, and LazyGraphRAG all promise smarter retrieval. The honest question isn't which to pick — it's whether your queries are the kind a graph can even help.
All three turn a webpage into clean markdown an LLM can read. They are not competing on that — they sit on three different rungs, and picking by star count gets the rung wrong.
Three Python libraries that treat your prompt as a parameter to be tuned, not a string to be hand-crafted. They disagree about what the optimizer needs from you — and that's the whole decision.
The fight you think you're having — open pipeline vs hosted LLM parser — ended last year. A 1.2B model on your own GPU now wins the part that actually matters.
Whisper tops the accuracy leaderboard and loses the conversation. For a live voice agent, the number that decides whether the bot feels human isn't word error rate — it's who detects the end of your turn.
The old way to choose was "which one scales." That axis has quietly collapsed — all three now run on a laptop and across a cluster. What's left is a question about default posture and the ops bill you're signing up for.
Agents that write their own code forced an old infrastructure question back into the open — where, exactly, does the security boundary live, and what does it cost to drop it a layer lower?
The benchmark everyone argues over is the wrong one. The engine you should run is decided by how much context your requests share — not by whose tokens-per-second screenshot is biggest.
The memory libraries aren't competing on accuracy. They're competing on geography — where the remembering happens relative to your agent's loop. Pick the place, not the benchmark.