HTTP Headers are not sent by default, unless `sendDefaultPii` is enabled.

[0xbbadbeef]

SDK

JavaScript SDK

Description

Sentry version:

    "@sentry/browser": "10.51.0",
    "@sentry/nextjs": "10.51.0",

The docs mention here that

By default, the Sentry SDK sends HTTP response or request headers.

However, this is not true or needs clarifying since at least the NextJS SDK requires the SentryConfig to have sendDefaultPii to be true.

Response headers;
sendDefaultPii disabled;

sendDefaultPii enabled;

Request headers do seem to send headers but with some entries omitted, though this isn't mentioned on the docs.

Suggested Solution

Depending what the expected behavior is here;

• If we do not expect to send headers by default, the docs should be updated here to mention that sendDefaultPii should be enabled for response headers and most request headers.
• If we do expect to send headers by default, there may be a bug in the Sentry JavaScript SDK.

Also, it would be useful to understand what exactly is and isn't included behind the sendDefaultPii field to make a decision if we should enable this or not. Perhaps also linking to the data-collected page from the interface/config API here.

[linear-code]

DOCS-2644