[pcbeingused333]

💡 Motivation and Context

In the Claude Agent SDK integration, _GenerationTracker takes the input and cache token counts from message_start and, from message_delta, only output_tokens. A message_delta usage is cumulative: with server tools (web search, web fetch, code execution) its input and cache counts grow past the message_start values, and it also carries server_tool_use.web_search_requests. Streamed generations therefore under-reported $ai_input_tokens and the cache counts, and $ai_web_search_count was never set (the Anthropic wrapper in this repo sets all of them since #1074).

The tracker now keeps the larger of the message_start and message_delta values for the input, cache read and cache creation counts (a field the delta omits keeps its message_start value), and sets $ai_web_search_count from server_tool_use.web_search_requests when it is positive.

💚 How did you test it?

• test_message_delta_usage_is_cumulative_with_server_tools runs a stream whose message_start has 120 input tokens and whose message_delta has 5120 input, 300 output, 64 cache read, 32 cache creation and 2 web searches, and checks the captured $ai_generation properties. It fails on main (input 120, no cache or web search properties) and passes with the change.
• test_message_delta_without_input_counts_keeps_message_start checks that a delta with only output_tokens leaves the message_start counts and does not add a web search count; it passes before and after.
• posthog/test/ai/claude_agent_sdk: 44 passed.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed. (n/a)
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran sampo add to generate a changeset file (added .sampo/changesets/claude-agent-sdk-message-delta-usage.md in the same format)

🤖 Agent context

Autonomy: Fully autonomous

• The bug was found and the fix, tests and description were written by Claude Code; the diff and the explanation were reviewed before submitting.

[marandaneto]

The code looks good; no qualifying findings. Verdict: correct.