Generations

Generations are an event that capture an LLM request. The generations tab lists them along with the properties autocaptured by PostHog like the person, model, total cost, token usage, and more.

When you expand a generation, it includes the properties, metadata, a conversation history, the role (system, user, assistant), input content, and output content.

Event properties

A generation is a single call to an LLM.

Event Name: $ai_generation

Property	Description
`$ai_trace_id`	The trace ID (a UUID to group AI events) like `conversation_id` Must contain only letters, numbers, and special characters: `-`, `_`, `~`, `.`, `@`, `(`, `)`, `!`, `'`, `:`, `\|`
`$ai_model`	The model used Example: `gpt-3.5-turbo`
`$ai_provider`	The LLM provider Example: `openai`, `anthropic`, `gemini`
`$ai_input`	List of messages sent to the LLM Example: `[{"role": "user", "content": [{"type": "text", "text": "What's in this image?"}, {"type": "image", "image": "https://example.com/image.jpg"}, {"type": "function", "function": {"name": "get_weather", "arguments": {"location": "San Francisco"}}}]}]`
`$ai_input_tokens`	The number of tokens in the input (often found in response.usage)
`$ai_output_choices`	List of response choices from the LLM Example: `[{"role": "assistant", "content": [{"type": "text", "text": "I can see a hedgehog in the image."}, {"type": "function", "function": {"name": "get_weather", "arguments": {"location": "San Francisco"}}}]}]`
`$ai_output_tokens`	The number of tokens in the output (often found in response.usage)
`$ai_latency`	Optional The latency of the LLM call in seconds
`$ai_http_status`	Optional The HTTP status code of the response
`$ai_base_url`	Optional The base URL of the LLM provider Example: `https://api.openai.com/v1`
`$ai_request_url`	Optional The full URL of the request made to the LLM API Example: `https://api.openai.com/v1/chat/completions`
`$ai_is_error`	Optional Boolean to indicate if the request was an error
`$ai_error`	Optional The error message or object
Cost Properties	Optional - If not provided, costs will be calculated automatically from token counts
`$ai_input_cost_usd`	Optional The cost in USD of the input tokens
`$ai_output_cost_usd`	Optional The cost in USD of the output tokens
`$ai_total_cost_usd`	Optional The total cost in USD (input + output)
Cache Properties
`$ai_cache_read_input_tokens`	Optional Number of tokens read from cache
`$ai_cache_creation_input_tokens`	Optional Number of tokens written to cache (Anthropic-specific)
Model Parameters
`$ai_temperature`	Optional Temperature parameter used in the LLM request
`$ai_stream`	Optional Whether the response was streamed
`$ai_max_tokens`	Optional Maximum tokens setting for the LLM response
`$ai_tools`	Optional Tools/functions available to the LLM Example: `[{"type": "function", "function": {"name": "get_weather", "parameters": {...}}}]`
Span/Trace Properties
`$ai_span_id`	Optional Unique identifier for this generation
`$ai_span_name`	Optional Name given to this generation Example: `summarize_text`
`$ai_parent_id`	Optional Parent span ID for tree view grouping

Example

Terminal

curl -X POST "https://us.i.posthog.com/i/v0/e/" \
     -H "Content-Type: application/json" \
     -d '{
         "api_key": "<ph_project_api_key>",
         "event": "$ai_generation",
         "properties": {
             "distinct_id": "user_123",
             "$ai_trace_id": "d9222e05-8708-41b8-98ea-d4a21849e761",
             "$ai_model": "gpt-4o",
             "$ai_provider": "openai",
             "$ai_input": [{"role": "user", "content": [{"type": "text", "text": "Analyze this data and suggest improvements"}]}],
             "$ai_input_tokens": 150,
             "$ai_output_choices": [{"role": "assistant", "content": [{"type": "text", "text": "Based on the data, here are my suggestions..."}]}],
             "$ai_output_tokens": 280,
             "$ai_latency": 2.45,
             "$ai_http_status": 200,
             "$ai_base_url": "https://api.openai.com/v1",
             "$ai_request_url": "https://api.openai.com/v1/chat/completions",
             "$ai_is_error": false,
             "$ai_temperature": 0.7,
             "$ai_stream": false,
             "$ai_max_tokens": 500,
             "$ai_tools": [{"type": "function", "function": {"name": "analyze_data", "description": "Analyzes data and provides insights", "parameters": {"type": "object", "properties": {"data_type": {"type": "string"}}}}}],
             "$ai_cache_read_input_tokens": 50,
             "$ai_span_name": "data_analysis_chat"
         },
         "timestamp": "2025-01-30T12:00:00Z"
     }'

Event properties

Example

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