Prompt Caching

Prompt caching

Prompt caching means the model provider can reuse unchanged prompt prefixes (usually system/developer instructions and other stable context) across turns instead of re-processing them every time. The first matching request writes cache tokens (cacheWrite), and later matching requests can read them back (cacheRead).

Why this matters: lower token cost, faster responses, and more predictable performance for long-running sessions. Without caching, repeated prompts pay the full prompt cost on every turn even when most input did not change.

This page covers all cache-related knobs that affect prompt reuse and token cost.

For Anthropic pricing details, see: https://docs.anthropic.com/docs/build-with-claude/prompt-caching

Primary knobs

`cacheRetention` (global default, model, and per-agent)

Set cache retention as a global default for all models:

agents:
  defaults:
    params:
      cacheRetention: "long" # none | short | long

Override per-model:

agents:
  defaults:
    models:
      "anthropic/claude-opus-4-6":
        params:
          cacheRetention: "short" # none | short | long

Per-agent override:

agents:
  list:
    - id: "alerts"
      params:
        cacheRetention: "none"

Config merge order:

agents.defaults.params (global default — applies to all models)
agents.defaults.models["provider/model"].params (per-model override)
agents.list[].params (matching agent id; overrides by key)

Legacy `cacheControlTtl`

Legacy values are still accepted and mapped:

5m -> short
1h -> long

Prefer cacheRetention for new config.

`contextPruning.mode: "cache-ttl"`

Prunes old tool-result context after cache TTL windows so post-idle requests do not re-cache oversized history.

agents:
  defaults:
    contextPruning:
      mode: "cache-ttl"
      ttl: "1h"

See Session Pruning for full behavior.

Heartbeat keep-warm

Heartbeat can keep cache windows warm and reduce repeated cache writes after idle gaps.

agents:
  defaults:
    heartbeat:
      every: "55m"

Per-agent heartbeat is supported at agents.list[].heartbeat.

Provider behavior

Anthropic (direct API)

cacheRetention is supported.
With Anthropic API-key auth profiles, OpenClaw seeds cacheRetention: "short" for Anthropic model refs when unset.

Amazon Bedrock

Anthropic Claude model refs (amazon-bedrock/*anthropic.claude*) support explicit cacheRetention pass-through.
Non-Anthropic Bedrock models are forced to cacheRetention: "none" at runtime.

OpenRouter Anthropic models

For openrouter/anthropic/* model refs, OpenClaw injects Anthropic cache_control on system/developer prompt blocks to improve prompt-cache reuse.

Other providers

If the provider does not support this cache mode, cacheRetention has no effect.

Tuning patterns

Mixed traffic (recommended default)

Keep a long-lived baseline on your main agent, disable caching on bursty notifier agents:

agents:
  defaults:
    model:
      primary: "anthropic/claude-opus-4-6"
    models:
      "anthropic/claude-opus-4-6":
        params:
          cacheRetention: "long"
  list:
    - id: "research"
      default: true
      heartbeat:
        every: "55m"
    - id: "alerts"
      params:
        cacheRetention: "none"

Cost-first baseline

Set baseline cacheRetention: "short".
Enable contextPruning.mode: "cache-ttl".
Keep heartbeat below your TTL only for agents that benefit from warm caches.

Cache diagnostics

OpenClaw exposes dedicated cache-trace diagnostics for embedded agent runs.

`diagnostics.cacheTrace` config

diagnostics:
  cacheTrace:
    enabled: true
    filePath: "~/.openclaw/logs/cache-trace.jsonl" # optional
    includeMessages: false # default true
    includePrompt: false # default true
    includeSystem: false # default true

Defaults:

filePath: $OPENCLAW_STATE_DIR/logs/cache-trace.jsonl
includeMessages: true
includePrompt: true
includeSystem: true

Env toggles (one-off debugging)

OPENCLAW_CACHE_TRACE=1 enables cache tracing.
OPENCLAW_CACHE_TRACE_FILE=/path/to/cache-trace.jsonl overrides output path.
OPENCLAW_CACHE_TRACE_MESSAGES=0|1 toggles full message payload capture.
OPENCLAW_CACHE_TRACE_PROMPT=0|1 toggles prompt text capture.
OPENCLAW_CACHE_TRACE_SYSTEM=0|1 toggles system prompt capture.

What to inspect

Cache trace events are JSONL and include staged snapshots like session:loaded, prompt:before, stream:context, and session:after.
Per-turn cache token impact is visible in normal usage surfaces via cacheRead and cacheWrite (for example /usage full and session usage summaries).

Quick troubleshooting

High cacheWrite on most turns: check for volatile system-prompt inputs and verify model/provider supports your cache settings.
No effect from cacheRetention: confirm model key matches agents.defaults.models["provider/model"].
Bedrock Nova/Mistral requests with cache settings: expected runtime force to none.

Related docs: