[herin049]

Description

Brings W3CBaggagePropagator in line with the W3C Baggage spec.

Also fixes #5811 and #5566
Closes #5814 #5791

• Multiple headers: all baggage headers are combined and the limits apply to all of them together.
• Percent encoding: values use quote/unquote instead of quote_plus/unquote_plus, so + is no longer
  turned into a space.
• Encoded whitespace: decoded values are no longer stripped, so %20 at either end is kept.
• Properties: ; properties are validated but no longer stored as part of the value. Before, they were
  re-sent as encoded value data.
• Keys: keys are treated as tokens. They are not percent-encoded or decoded and invalid keys are skipped
  on inject.
• Size limits: a header over 8192 bytes no longer drops all baggage. Whole entries are dropped until it fits.
• Performance: the [ \t]*,[ \t]* split regex took quadratic time on long whitespace runs. It is replaced
  with str.split(","), which also fixes parse_env_headers. Key and value validation now uses character sets
  instead of regexes.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• I am a human and not a bot
• I have run tox -e precommit
• I have run tox -e typecheck
• I have run the relevant tests and linting tox environments
• This requires the following PR in contrib:

[opentelemetry-pr-dashboard]

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Waiting on maintainers · refreshed 2026-10-27 00:36 UTC

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[Copilot]

🟡 Changes recommended

Oversized incoming headers allocate every split member before limits take effect, causing a verified memory-amplification regression.

1 open issue

• Avoid allocating all header members before enforcing the member limit · New

What changed in this PR

Updates the API’s W3C baggage propagation to address multiple-header handling (#5811) and percent encoding (#5566), alongside validation and size-limit changes.

Changes:

• Processes all baggage headers with shared limits and retains entries that fit.
• Preserves literal + and encoded whitespace, validates token keys, and separates properties from values.
• Replaces delimiter regex splitting and expands regression coverage.

File	Description
opentelemetry-api/​tests/​util/​test_re.py	Tests whitespace and empty header members.
opentelemetry-api/​tests/​propagators/​test_w3cbaggagepropagator.py	Covers revised extraction, injection, encoding, and limits.
opentelemetry-api/​tests/​baggage/​test_baggage.py	Tests character-set validation and property syntax.
opentelemetry-api/​src/​opentelemetry/​util/​re.py	Replaces regex-based environment-header splitting.
opentelemetry-api/​src/​opentelemetry/​baggage/​propagation/​__init__.py	Updates multi-header parsing, encoding, and key handling.
opentelemetry-api/​src/​opentelemetry/​baggage/​__init__.py	Uses character sets for baggage validation.
.changelog/​5823.fixed	Records the baggage compliance fixes.

_{Review effort: Balanced}