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

Background

Sentry’s Transaction Sampling feature was introduced in SDK version 6.0.0. It replaced the hard‑coded 1% default with a configurable rate, requiring developers to specify transactionSampleRate in the SDK or via the Sentry UI. Legacy SDKs (pre‑6.0.0) retain the 1% default if the new key is absent.

Constraints

• New projects must explicitly set transactionSampleRate or rely on the current default of 0.1% (1 in 1000).
• Upgrading existing projects that still use tracesSampleRate can unintentionally shift the effective rate if the SDK interprets the new key with higher priority.
• All supported languages are compatible, but older language SDKs lacking the new key will fall back to 1%.

Unresolved Decision

The documentation states that the default for new projects should be 0.1%, but also notes that this may change pending community feedback. It is unclear whether the 1% legacy default should be preserved, replaced, or made optional.

Specific Questions

1. What should the definitive default sampling rate be for new projects moving forward?
2. How will a shift from 0.1% to 1% (or vice versa) impact data volume and performance for projects that have not yet migrated?
3. Is there a recommended migration path that ensures consistent sampling behavior when transitioning from tracesSampleRate to transactionSampleRate across all supported SDKs?