feat(ai): add $ai_tokens_source property to detect token value overrides#3147
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andrewm4894 merged 1 commit intomainfrom Feb 25, 2026
Merged
feat(ai): add $ai_tokens_source property to detect token value overrides#3147andrewm4894 merged 1 commit intomainfrom
andrewm4894 merged 1 commit intomainfrom
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Adds "sdk" or "passthrough" to $ai_generation events to flag when token properties are externally overridden via posthogProperties. Mirrors the same change in posthog-python (PostHog/posthog-python#444).
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| $ai_trace_id: traceId, | ||
| $ai_base_url: baseURL, | ||
| ...params.posthogProperties, | ||
| $ai_tokens_source: getTokensSource(params.posthogProperties), |
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This sets $ai_tokens_source only inside sendEventToPosthog, but $ai_generation events emitted by the LangChain callback handler still bypass this helper and call client.capture directly (packages/ai/src/langchain/callbacks.ts, around the $ai_generation capture block), so those events will never include the new property. Any analysis that segments by $ai_tokens_source will therefore silently drop/misclassify LangChain traffic, which undermines the new override-detection signal.
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Size Change: +5.44 kB (+0.09%) Total Size: 6.17 MB
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carlos-marchal-ph
approved these changes
Feb 25, 2026
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Summary
$ai_tokens_sourceproperty ("sdk"or"passthrough") to all$ai_generationevents in@posthog/ai$ai_input_tokens,$ai_output_tokens,$ai_total_tokens, etc.) viaposthogProperties, the property is set to"passthrough"-- otherwise"sdk"Test plan
getTokensSourcehelper (10 parameterized cases covering undefined, empty, unrelated, and each token key)"sdk"value