fix: correct cache_hit_rate calculation and fix Vercel stream tool call handling#10994
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fix: correct cache_hit_rate calculation and fix Vercel stream tool call handling#10994
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Two bugs in prompt_cache_metrics telemetry: 1. Duplicate emission: prompt_cache_metrics was emitted twice per API request — once using `actualInputTokens` and again using `fullUsage.prompt_tokens`. This doubled all event counts in PostHog and produced conflicting values. 2. Wrong denominator: cache_hit_rate was calculated as `cacheReadTokens / prompt_tokens`, but the Anthropic adapter maps `prompt_tokens` to only non-cached input tokens (`input_tokens`), excluding cache reads and writes. When caching works well, this produces ratios >> 1 (observed max: 89,892). The correct total is `prompt_tokens + cache_read_tokens + cache_write_tokens`. Fix: remove the first duplicate emission and compute total_prompt_tokens as the sum of all three token types. cache_hit_rate is now a proper 0-1 ratio. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Docs Review: No documentation updates needed. This PR contains internal telemetry fixes (correcting |
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…nverter The Vercel AI SDK streams tool calls as tool-input-start → tool-input-delta → tool-input-end → tool-call. Previously, tool-input-start was ignored (returned null) and tool-call emitted the full tool call at the end, which meant streaming consumers never saw the tool call id on intermediate chunks. Now tool-input-start emits the initial chunk with id and function name (matching OpenAI's streaming format), and tool-call returns null to avoid duplicating args already streamed via tool-input-delta. Generated with [Continue](https://continue.dev) Co-Authored-By: Continue <noreply@continue.dev>
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Summary
Fix cache_hit_rate telemetry: The
prompt_cache_metricsevent was emitted twice per completion, and the cache hit rate denominator used onlyprompt_tokens(which maps to Anthropic'sinput_tokens— non-cached only). This caused ratios >> 1 when caching worked well (max observed: 89,892). Fixed by removing the duplicate emission and using the correct total:prompt_tokens + cache_read_tokens + cache_write_tokens.Fix Vercel AI SDK tool call streaming: The Vercel AI SDK streams tool calls as
tool-input-start→tool-input-delta→tool-input-end→tool-call. Previouslytool-input-startwas ignored andtool-callemitted the full call at the end, so streaming consumers never saw the tool callidon intermediate chunks. Nowtool-input-startemits the initial chunk withidand function name (matching OpenAI's streaming format), andtool-callis a no-op to avoid duplicating args.Test plan
vercelStreamConverter.test.ts(15 tests)@ai-sdk/xaidep, env-only issue)