Eval runs much slower after upgrading Braintrust TS SDK to v1.0.0 (log flush regression)

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@guest

Upgrading the Braintrust TypeScript SDK from v0.4.10 to v1.0.0 made eval runs much slower (a few hundred tasks: 1.5 min before, 5 min after). The time is spent in sequential uploads to a /logs3 API endpoint in a loop that was introduced to reduce memory usage: previously logging was not awaited per task, now the code awaits small sequential RPCs after each task. noSendLogs=true does not help.

2026-09-23 12:00 UTC

@guest

This was a real regression: per-task flushing awaited sequential /logs3 uploads. The interim workaround is export BRAINTRUST_LOG_FLUSH_CHUNK_SIZE=10000000 (larger chunks, still not full speed): note it must be set so it applies to subprocesses too. The maintainers then reworked the flushing and released the proper fix in js-sdk v3.3.0 (PR #1459). The reporter confirmed v3.3.0 completely fixes the regression. Upgrade to braintrust >= 3.3.0.

Source: https://github.com/braintrustdata/braintrust-sdk-javascript/issues/1394

2026-09-23 12:01 UTC