Cache (Simple & Semantic)

Semantic caching requires a vector database.

Cache LLM responses to serve requests up to 20x faster and cheaper.

Mode	How it Works	Best For	Supported Routes
Simple	Exact match on input	Repeated identical prompts	All models including image generation
Semantic	Matches semantically similar requests	Denoising variations in phrasing	`/chat/completions`, `/completions`

Enable Cache

Add cache to your config object:

{ "cache": { "mode": "simple" } }

{ "cache": { "mode": "semantic" } }

{ "cache": { "mode": "semantic", "max_age": 60 } }

Caching won’t work if x-portkey-debug: "false" header is included.

Simple Cache

Returns the cached response when the exact same request is sent again. Hit when all of these match a cached entry:

Full request body (messages or prompt, model, temperature, max_tokens, and every other parameter)
x-portkey-metadata (if used)
x-portkey-cache-namespace (if used)
The entry is still within max_age

Miss when:

The request is sent for the first time
Any field in the body changes—even one character in the prompt or a different parameter
The cached entry has expired
x-portkey-cache-force-refresh: true is set on the request

Semantic Cache

Matches requests with similar meaning using cosine similarity, not just identical text. Learn more →

Semantic cache is a superset of simple cache. The Prisma AIRS AI Gateway checks for an exact match first and only runs semantic search on a miss.

Semantic cache works with requests under 8,191 tokens and ≤4 messages.

Hit when all of these are true (after a simple-cache miss):

User text has similar meaning to a cached request — cosine similarity above the threshold (default 0.95)
model, temperature, max_tokens, and any other body parameter match exactly
x-portkey-metadata matches exactly (if used)
The system prompt is ignored — changing it does not affect cache hits
At least one user message must be present

Example — same model, different wording → semantic hit:

// First request (cached)
{
  "model": "gpt-4o",
  "messages": [{ "role": "user", "content": "Who is the US president?" }]
}

// Second request — SEMANTIC HIT
{
  "model": "gpt-4o",
  "messages": [{ "role": "user", "content": "Tell me who is the president of the US." }]
}

Set up semantic caching (self-hosted)

To enable semantic caching on a self-hosted AI Gateway, configure the embedding provider and a vector database.

Configure the embedding provider

Set the following environment variables in your gateway environment for generating vector embeddings:

SEMANTIC_CACHE_EMBEDDING_PROVIDER=openai   # supported: openai, azure-openai, google, vertex-ai
SEMANTIC_CACHE_EMBEDDINGS_URL=https://api.openai.com/v1/embeddings
SEMANTIC_CACHE_EMBEDDING_MODEL=text-embedding-3-small
SEMANTIC_CACHE_EMBEDDING_API_KEY=<openai-api-key>
SEMANTIC_CACHE_SIMILARITY_THRESHOLD=0.95
SEMANTIC_CACHE_EMBEDDING_DIMENSIONS=1536

SEMANTIC_CACHE_EMBEDDING_PROVIDER accepts openai, azure-openai, google (Gemini embeddings), or vertex-ai (Vertex AI embeddings). Set SEMANTIC_CACHE_EMBEDDINGS_URL, SEMANTIC_CACHE_EMBEDDING_MODEL, and SEMANTIC_CACHE_EMBEDDING_DIMENSIONS to match the chosen provider’s embedding model.For Azure OpenAI, set the variables as follows:

SEMANTIC_CACHE_EMBEDDING_PROVIDER=azure-openai
SEMANTIC_CACHE_EMBEDDINGS_URL=https://YOUR-RESOURCE-NAME.openai.azure.com/openai/v1/embeddings
SEMANTIC_CACHE_EMBEDDING_MODEL=text-embedding-3-small
SEMANTIC_CACHE_EMBEDDING_API_KEY=<azure-openai-api-key>
SEMANTIC_CACHE_SIMILARITY_THRESHOLD=0.95
SEMANTIC_CACHE_EMBEDDING_DIMENSIONS=1536

SEMANTIC_CACHE_EMBEDDING_MODEL must match your Azure deployment name. SEMANTIC_CACHE_EMBEDDING_API_KEY must be a plain Azure OpenAI API key; Managed Identity / Entra ID token auth is not supported for this call.

Configure the vector database

Set the following environment variables in your gateway environment to connect to your vector store (Milvus or Pinecone):

VECTOR_STORE=milvus # supported values: milvus, pinecone
VECTOR_STORE_ADDRESS=<your-vector-store-address>
VECTOR_STORE_COLLECTION_NAME=<your-collection-name>
VECTOR_STORE_API_KEY=<your-vector-db-api-key>

MilvusCreate a collection whose name matches SEMANTIC_CACHE_EMBEDDING_MODEL (for example, text-embedding-3-small when using that model). The collection must define these fields:

Field	Type
`id`	`Varchar`
`values`	`FloatVector` with dimension 1536 (must match `SEMANTIC_CACHE_EMBEDDING_DIMENSIONS`)
`metadata`	`JSON`

If you change the embedding model or dimension, update the collection schema and SEMANTIC_CACHE_EMBEDDING_DIMENSIONS so the vector field size stays aligned.Pinecone

VECTOR_STORE_COLLECTION_NAME — Omit this; it is not used for Pinecone.
VECTOR_STORE_ADDRESS — Set to your Pinecone index name (not a generic host string).
SEMANTIC_CACHE_EMBEDDING_DIMENSIONS — Must match the dimension configured on the index (same as your embedding vectors).
In the Pinecone console, create or use an index with cosine as the similarity metric so it matches the AI Gateway’s semantic cache behavior.

Enable semantic caching per request

Set the cache mode to semantic in your config object for each LLM request:

{ "cache": { "mode": "semantic" } }

Limitations: - Embedding generation supports OpenAI, Azure OpenAI, Google (Gemini), and Vertex AI embedding providers. - The LLM model used for generating responses must be OpenAI-compatible. - Each request must include at least one user message along with system messages. Requests with only system messages are dropped.

Cache TTL

Set expiration with max_age (in seconds):

{ "cache": { "mode": "semantic", "max_age": 60 } }

Setting	Value
Minimum	60 seconds
Maximum	90 days (7,776,000 seconds)
Default	7 days (604,800 seconds)

Organisation-Level TTL

Admins can set default TTL for all workspaces to align with data retention policies:

Go to Admin Settings → Organisation Properties → Cache Settings
Enter default TTL (seconds)
Save

Precedence:

No max_age in request → org default used
Request max_age > org default → org default wins
Request max_age < org default → request value honored

Max org-level TTL: 25,923,000 seconds.

Force Refresh

Fetch a fresh response even when a cached response exists. This is set per-request (not in Config):

curl https://aigw.portkey.ai/v1/chat/completions \
  -H "Authorization: Bearer $PORTKEY_API_KEY" \
  -H "x-portkey-config: pc-cache-xxx" \
  -H "x-portkey-cache-force-refresh: true" \
  -d '{"model": "@openai-prod/gpt-4o", "messages": [{"role": "user","content": "Hello!"}]}'

Requires cache config to be passed - For semantic hits, refreshes ALL matching entries

Cache Namespace

By default, the AI Gateway partitions cache by all request headers. Use a custom namespace to partition only by your custom string—useful for per-user caching or optimizing hit ratio:

curl https://aigw.portkey.ai/v1/chat/completions \
  -H "Authorization: Bearer $PORTKEY_API_KEY" \
  -H "x-portkey-config: pc-cache-xxx" \
  -H "x-portkey-cache-namespace: user-123" \
  -d '{"model": "@openai-prod/gpt-4o", "messages": [{"role": "user","content": "Hello!"}]}'

Cache with Configs

Set cache at top-level or per-target:

{
  "cache": { "mode": "semantic", "max_age": 60 },
  "strategy": { "mode": "fallback" },
  "targets": [
    { "override_params": { "model": "@openai-prod/gpt-4o" } },
    {
      "override_params": {
        "model": "@anthropic-prod/claude-3-5-sonnet-20241022"
      }
    }
  ]
}

{
  "strategy": { "mode": "fallback" },
  "targets": [
    {
      "override_params": { "model": "@openai-prod/gpt-4o" },
      "cache": { "mode": "simple", "max_age": 200 }
    },
    {
      "override_params": {
        "model": "@anthropic-prod/claude-3-5-sonnet-20241022"
      },
      "cache": { "mode": "semantic", "max_age": 100 }
    }
  ]
}

Target-level cache takes precedence over top-level.

Targets with override_params need that exact param combination cached before hits occur.

Analytics & Logs

Analytics → Cache tab shows:

Cache hit rate
Latency savings
Cost savings

Logs → Status column shows: Cache Hit, Cache Semantic Hit, Cache Miss, Cache Refreshed, or Cache Disabled. Learn more →

Introduction

Product

Cache (Simple & Semantic)

Enable Cache

Simple Cache

Semantic Cache

Set up semantic caching (self-hosted)

Cache TTL

Organisation-Level TTL

Force Refresh

Cache Namespace

Cache with Configs

Analytics & Logs

​Enable Cache

​Simple Cache

​Semantic Cache

​Set up semantic caching (self-hosted)

​Cache TTL

​Organisation-Level TTL

​Force Refresh

​Cache Namespace

​Cache with Configs

​Analytics & Logs

Enable Cache

Simple Cache

Semantic Cache

Set up semantic caching (self-hosted)

Cache TTL

Organisation-Level TTL

Force Refresh

Cache Namespace

Cache with Configs

Analytics & Logs