What was going on
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.
What fixed it
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.