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Token Usage Attributes

Understanding the GenAI token usage attributes in OpenClaw observability.

Token Attributes Overview

Attribute Description Cost Impact
gen_ai.usage.input_tokens Tokens in the prompt sent to the model Standard input rate
gen_ai.usage.output_tokens Tokens in the model's response Higher rate (typically 3-5x input)
gen_ai.usage.cache_read_tokens Tokens read from prompt cache 90% cheaper than input
gen_ai.usage.cache_write_tokens Tokens written to prompt cache 25% more expensive than input
gen_ai.usage.total_tokens Sum of all token types —

How Tokens Are Calculated

Input Tokens

What counts: Everything you send to the model: - System prompt (AGENTS.md, SOUL.md, TOOLS.md, etc.) - Conversation history (all previous messages) - Current user message - Tool definitions and descriptions - Any injected context

Example breakdown: 

System prompt:     ~8,000 tokens (workspace files + tool list)
History:           ~5,000 tokens (previous messages)
Current message:      ~50 tokens (user's question)
─────────────────────────────────
Total input:      ~13,050 tokens

Output Tokens

What counts: Everything the model generates: - The assistant's response text - Tool calls (function names + arguments) - Thinking/reasoning (if using extended thinking)

Note: Output tokens are typically 3-5x more expensive than input tokens.

Cache Read Tokens

What it is: Anthropic's prompt caching feature. When you send the same prefix (system prompt + early conversation), Claude can reuse a cached version instead of reprocessing it.

When it happens: - Same system prompt across requests - Stable conversation history prefix - Request made within cache TTL (typically 5 minutes)

Cost benefit: Cache reads cost ~90% less than regular input tokens.

Your example: 918,174 cache read tokens means the model reused ~918K tokens from cache instead of reprocessing them. This saved significant cost!

Cache Write Tokens

What it is: When new content is added to the cache for future requests.

When it happens: - First request with a new system prompt - Conversation grows beyond previously cached content - Cache TTL expired and content needs re-caching

Cost impact: Cache writes cost ~25% more than regular input tokens, but enable cheaper cache reads on subsequent requests.

Your example: 62,437 cache write tokens means new content was cached for future use.

Real-World Example

Your span shows: 

cache_read:   918,174 tokens  (reused from cache — very cheap!)
cache_write:   62,437 tokens  (newly cached — slight premium)
input:            156 tokens  (new content not in cache)
output:        17,831 tokens  (model's response)
─────────────────────────────────
total:        998,598 tokens

What this means:

  1. Large context reuse — 918K tokens were already cached (system prompt + conversation history). You paid ~10% of normal input cost for these.

  2. Incremental caching — 62K new tokens were added to cache. Slightly more expensive now, but future requests can read them cheaply.

  3. Minimal new input — Only 156 tokens were truly "new" input (probably just the latest message).

  4. Reasonable output — 17,831 tokens is a substantial response (maybe code generation or detailed explanation).

Cost Calculation

Current Anthropic API Pricing (2026)

Model Input Output Cache Read Cache Write
Opus 4.5 $5/MTok $25/MTok $0.50/MTok $6.25/MTok
Sonnet 4.5 $3/MTok $15/MTok $0.30/MTok $3.75/MTok
Haiku 4.5 $1/MTok $5/MTok $0.10/MTok $1.25/MTok

(MTok = Million Tokens)

Example Cost Breakdown (Opus 4.5)

Token Type Count Rate (per 1M) Cost
Cache read 918,174 $0.50 $0.46
Cache write 62,437 $6.25 $0.39
Input 156 $5.00 $0.001
Output 17,831 $25.00 $0.45
Total ~$1.30

Without caching, the same request would cost: - All input at standard rate: (918,174 + 62,437 + 156) × $5/1M = $4.90 - Output: $0.45 - Total without cache: $5.35

Savings from caching: ~76%

Important: Subscriptions vs API

Claude Subscription API (OpenClaw uses this)
Free: $0 Pay per token
Pro: $20/month No monthly fee
Max: $100-200/month Billed to API account

Your Claude Pro/Max subscription does NOT cover OpenClaw usage! OpenClaw uses the API, which is billed separately.

Why Total Doesn't Equal Sum

You might notice: 

cache_read + cache_write + input + output = 998,598

The total_tokens is the sum of all types. Some backends may calculate it differently or include additional overhead tokens.

Optimizing Token Usage

Reduce Input Tokens

  1. Trim workspace files — Keep AGENTS.md, SOUL.md concise
  2. Use /compact — Summarize long conversations
  3. Prune tool list — Disable unused tools/skills

Maximize Cache Hits

  1. Stable system prompts — Don't change workspace files frequently
  2. Consistent conversation prefix — Same session = better caching
  3. Heartbeat within TTL — Keep cache warm with periodic requests

Control Output

  1. Be specific — Vague prompts generate verbose responses
  2. Request concise answers — "Brief answer:" prefix helps
  3. Use appropriate models — Smaller models for simple tasks

Monitoring Token Usage

Key Metrics to Watch

# Total token cost over time
sum(rate(openclaw_tokens_total[5m])) by (model)

# Cache hit ratio
sum(openclaw_tokens{type="cache_read"}) / 
sum(openclaw_tokens{type=~"cache_read|input"})

# Output to input ratio (efficiency)
sum(openclaw_tokens{type="output"}) /
sum(openclaw_tokens{type="input"})

Alerting Thresholds

Consider alerts for: - Single request > 100K output tokens - Cache hit ratio < 50% - Hourly cost > $X threshold

See Also