Quantizing Embeddings: int8, Binary, and Matryoshka

Why Quantize

A 1024-dim float32 embedding is 4 KB. Ten million of them is 40 GB. Quantization reduces this dramatically with modest recall impact:

• int8 quantization: 4x smaller (~1 KB per vector)
• Binary quantization: 32x smaller (~128 bytes per vector)
• Matryoshka: configurable, often 2-4x smaller

For large corpora, quantization is the difference between fitting in RAM and not.

The Three Approaches

flowchart TB
    Quant[Quantization] --> Q1[int8: scale to 8 bits per dim]
    Quant --> Q2[Binary: 1 bit per dim]
    Quant --> Q3[Matryoshka: truncate to fewer dims]

int8 Quantization

Each float32 dimension is mapped to an int8. A scale factor and zero point are stored per vector or per group.

• Recall impact: typically 1-3 percent drop
• Storage: 4x smaller
• Compute: SIMD-friendly; often faster

The 2026 default for cost-conscious deployments.

Binary Quantization

Each dimension reduced to 1 bit (sign of the value). Distance computed via Hamming distance.

• Recall impact: can be substantial (5-15 percent)
• Storage: 32x smaller
• Compute: very fast (XOR popcount)
• Re-rank: typically rerank top candidates with full-precision

Binary works best with rerank: candidate generation in binary; final scoring in full precision.

Matryoshka Embeddings

The embedding model is trained so that truncating to fewer dimensions still produces useful vectors. Truncate to 256 or 512 dims for storage savings; rehydrate to full dims for accurate scoring.

• Recall impact: small if the model is Matryoshka-trained
• Storage: configurable
• Best with models that explicitly support it: OpenAI text-embedding-3, Cohere embed-v4

Decision Matrix

flowchart TD
    Q1{Storage critical?} -->|Yes, extreme| Bin[Binary]
    Q1 -->|Yes, modest| int8[int8]
    Q1 -->|No| Q2{Model supports Matryoshka?}
    Q2 -->|Yes| Mat[Matryoshka truncation]
    Q2 -->|No| Full[Keep full precision]

For most cost-sensitive deployments in 2026, int8 is the sweet spot: substantial savings, small recall impact.

Combining Approaches

You can combine:

• Matryoshka truncation to 512 dims, then int8 quantization → 8x storage saved
• Binary for top-K candidate generation, full precision for top-N rerank → 30x candidate-stage savings, full quality at top

These compositions are how 2026 production systems hit 1B+ vector scale on reasonable hardware.

What Quantization Does Not Help

• Very small corpora — savings are dollars, not real
• Latency-bound, RAM-constrained workloads where recall is paramount
• Recall-critical use cases that cannot tolerate even 1 percent drop

Implementation in 2026

• pgvector: native int8 support added in recent versions
• Qdrant: int8 + binary + Matryoshka support
• Milvus: native quantization support
• Pinecone: int8 / binary modes available
• FAISS: extensive quantization options (PQ, OPQ, etc.)

For most cloud vector DBs, quantization is a configuration toggle, not custom code.

Recall vs Storage Curve

Empirical 2026 numbers (varies by domain):

Setting	Storage	Recall@10 vs full
float32	1x	100%
int8	0.25x	98-99%
Matryoshka 512	0.5x	99%
Matryoshka 256	0.25x	96-98%
Binary	0.03x	85-92%
Binary + rerank	0.03x	96-98%

The "binary + rerank" combination is especially compelling.

Common Gotchas

• Mixing quantized and unquantized vectors in the same query — distances are not comparable
• Re-quantizing on small data — quantization is fitted on the data; small samples produce poor mappings
• Forgetting to renormalize after quantization where it matters
• Comparing quantized vectors with different schemes

Sources

• "Matryoshka Representation Learning" — https://arxiv.org/abs/2205.13147
• Cohere embed quantization — https://docs.cohere.com
• pgvector quantization — https://github.com/pgvector/pgvector
• Qdrant quantization documentation — https://qdrant.tech/documentation
• "Binary embeddings" research — https://arxiv.org

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