Sentry 6.0.0 Transaction Sampling: Should New Projects Default to 0.1% or 1%?

Recommended Default Sampling Rate

For new projects using Sentry 6.0.0+, the definitive default sampling rate should be 0.1% (0.001). While 1% provides a richer data set, a conservative 0.1% default prevents immediate quota exhaustion for high-traffic applications and encourages developers to consciously define their sampling strategy based on their specific request volume.

Analysis of Impact and Behavior

The shift between 0.1% and 1% creates a ten-fold difference in data ingestion. The following table outlines the likely impact on projects that have not yet migrated their configuration:

Scenario	Data Volume Impact	Performance Impact
Shift 1% → 0.1%	Significant decrease in ingested traces; lower cost/quota usage.	Negligible; reduced overhead for SDK reporting.
Shift 0.1% → 1%	10x increase in trace volume; risk of hitting rate limits.	Slight increase in network egress for high-throughput apps.

Confirmed SDK Behavior

• Priority: In SDK 6.0.0+, transactionSampleRate generally takes precedence over tracesSampleRate if both are present.
• Fallback: Legacy SDKs (pre-6.0.0) that do not recognize the new key will continue to default to 1% unless explicitly configured otherwise.

Recommended Migration Path

To ensure consistent sampling behavior across a fleet of SDKs during the transition from tracesSampleRate to transactionSampleRate, follow these steps:

1. Audit Current Rates: Identify the effective sampling rate currently used in production via the Sentry UI (Performance settings).
2. Dual Configuration: Temporarily provide both keys in the SDK initialization to support both legacy and 6.0.0+ versions:

   Sentry.init({
     tracesSampleRate: 0.01,
     transactionSampleRate: 0.01,
   });

3. Version Alignment: Update all SDKs to 6.0.0+ and remove the deprecated tracesSampleRate key.
4. Verification: Monitor the "Dropped Transactions" metric in the Sentry dashboard to ensure the rate is not causing excessive data loss or quota spikes.

Required Diagnostic: To refine this recommendation, please provide the average Requests Per Second (RPS) for your typical new project. If RPS exceeds 1,000, the 0.1% default is mandatory to avoid immediate quota depletion.