Markdown-KV format achieves 60.7% LLM comprehension accuracy vs 44.3% for CSV — a 16-point gap from format alone. But retrieval and comprehension have different optimal formats: metadata prepend + row-wise key-value is the current best combination for table RAG.
Models don't understand text — they only understand numbers. Embeddings map each token to a vector of several hundred dimensions, where semantically similar words end up close together in vector space. This is the shared foundation behind search, RAG, and classification.
You don't need to become a researcher to understand AI models systematically. This series starts from what you can see (tokens, context windows) and works up to self-hosting open-source models — 18 articles covering everything you need to choose models, read benchmarks, and estimate costs.
Anthropic Contextual Retrieval uses an LLM to prefix each chunk with 50-100 tokens, cutting failure rate from 5.7% to 1.9% with rerank at ~$1.02/1M tokens; Late Chunking encodes the full 32K-window document first then mean-pools by chunk boundaries for zero extra LLM cost — the trade-off is window, latency, and update shape.
Cohere is the only family that ships generation, retrieval, reranking, and multilingual as distinct products. Command A runs 256K context on two GPUs at 111B, Embed v4 does mixed image-text retrieval, Rerank v4 handles 32K semi-structured data, and Aya covers 101 languages — a four-piece stack built for RAG. This post breaks down each pillar's positioning, licensing, and selection guide.
In 2026, AI models span seven major categories and more than 20 subcategories. This introduction to the AI Model Families series maps use cases to models and models to families, with current rankings and selection advice for each use case.
Chroma manages embeddings, documents, and metadata through collections; it embeds into Python locally, uses HNSW on a single node, and separates compute from storage with object storage, SSD caches, and SPANN in distributed deployments.
pgvector is a PostgreSQL extension, not a standalone vector database. It adds exact and approximate vector search to the same data model, transactions, and operations stack, while leaving index tuning and horizontal scaling as PostgreSQL concerns.
The Workers AI catalog currently holds 84 models. For general chat pick glm-4.7-flash ($0.06 / $0.40 per M, 131K context), for vision pick gemma-4-26b-a4b-it ($0.10 / $0.30, 256K), for cheap high-volume steps pick granite-4.0-h-micro ($0.017 / $0.112), and for embeddings pick qwen3-embedding-0.6b or bge-m3 (both $0.012 per M). This post is updated on a schedule.
CS230's second lecture derives embeddings through three case studies: day/night classification teaches you to use humans as a proxy for choosing resolution, trigger-word detection teaches you to manufacture a million training examples in three hours, and face verification walks you through designing your first loss function. The final step — from supervised triplets to self-supervised pairs — is why modern models can consume billions of unlabeled images.
Standard RAG gives a wrong answer when it retrieves the wrong chunk, and nothing in the system will notice. Agentic RAG adds a self-check, at the cost of the evaluator paradox: the ceiling on self-correction is whatever the evaluating LLM can judge about relevance.
Cosine similarity and relevance systematically diverge across an entire class of scenarios: negation (most IR models score at or below random on NevIR), exact identifiers, numeric thresholds, and logical combinations (SoTA models achieve recall@100 < 20 on LIMIT) -- some of these hit the theoretical ceiling of the single-vector paradigm, and switching to a larger model will not help. Recommended remedy order: hybrid BM25 -> reranker (Anthropic measured -67%) -> upstream metadata routing -> domain fine-tuning / multi-vector.
Traditional Chinese RAG retrieval failures are a three-layer stack: embedding granularity defects (BGE/GTE from 0.1B to 7B all mis-rank on simple queries like 'fried chicken'), Simplified Chinese / English corpus dominance causing local vocabulary drift ('premium', 'exclusion clause' alignment is unreliable), and MTEB Chinese benchmarks being Simplified Chinese making model selection signals misleading. The fix is architectural: OpenCC normalization -> hybrid + jieba segmentation -> reranker -> local fine-tuning last -- and the prerequisite for all of it is building a Traditional Chinese eval set first.
A six-layer deterministic pipeline that handles everything from URL ingestion to vector embedding automatically, filtering out garbage before it enters your RAG system through an eight-dimension scoring system.
2026 Q1 saw a full-blown open-source model explosion: on the LLM front, GLM-5, Kimi K2.5, and Qwen3.5 caught up with closed-source models; Embedding and Reranker are dominated by Qwen3 and BGE; speech has Voxtral TTS and Whisper V3; image has FLUX.2; and video has Wan 2.2 rivaling Sora. This is the complete navigation map.
Query: 'I just sent Beauty in the Mirror 5.11b — recommend routes of similar difficulty.' The results came back full of routes with similar-sounding names, not similar grades. Root cause: dense embeddings compress multiple attributes into a single vector, and the rarity of the route name drowns out the grade signal. The fix: three layers of defense — metadata pre-filtering, query rewriting, and score fusion.
RAG has evolved far beyond simple 'search + generate' into a technology ecosystem spanning ten generations — and since 2025 into an Agentic/Reasoning era. This article is a systematic navigation guide: from Naive RAG to Multi-Agent/LongRAG across ten generations, the post-ten Agentic Era (Search-R1/RL search, MCP, GraphRAG 3.x, vision-native retrieval), retrieval strategies, chunking, embedding, reranking, evaluation frameworks, observability, and cost optimization. Each topic has a dedicated deep-dive article.
Your choice of embedding model directly determines RAG search quality. BGE-M3's multilingual training, 1024-dimensional vectors, and matching Reranker make it a practical pick for Traditional Chinese RAG.
When you split a document into chunks, each chunk loses its place in the original document. Contextual Retrieval solves the isolated-chunk problem by generating a per-chunk context from the whole document and prepending it at index time.
Vector search handles semantics; BM25 handles keywords. Combining them with RRF is what lets you handle both fuzzy queries and exact terms at the same time.
Have an LLM generate an 'ideal answer' first, then embed that hypothetical document for search — it outperforms searching with the raw query.
A dynamically composable RAG pipeline built on Cloudflare Workers AI (gemma-3-12b-it + bge-m3): 14 base steps + 6 LangGraph-specific nodes, with three strategy graphs (Baseline / Agentic / Plan-Execute) selected at runtime.