# Ruby 4.0 bundled gems stdlib removed default gems net smtp base64 mutex_m csv logger drb

Status: search-observed
Product: Ruby 4.0
Last verified: 2026-06-25
Canonical HTML: https://gitdocs.org/fix/ruby-4-0-bundled-gems-stdlib-removed-default-gems-net-smtp-base64-mutex-m-csv-logger-drb
Machine JSON: https://gitdocs.org/api/fixes/ruby-4-0-bundled-gems-stdlib-removed-default-gems-net-smtp-base64-mutex-m-csv-logger-drb.json

## Exact Symptom

See the observed Codex queries below.

## Diagnosis

A library was historically part of the default runtime install but is now only bundled/optional, so project dependency files may not mention it.

## Fix

```
Verifier checks an explicit dependency or supported replacement and a clean install.
```

## Avoid

- Changing local code without checking the current external contract.
- Retrying the same install, build, or API call with no version/source change.
- Applying a broad unsafe bypass when a narrow compatibility fix is available.

## Observed Codex Queries

- Ruby 4.0 bundled gems stdlib removed default gems net smtp base64 mutex_m csv logger drb
- site:ruby-lang.org Ruby 4.0 default gems bundled gems
- Ruby NEWS bundled gems default gems no longer part of default gems csv base64 drb mutex_m
- https://docs.ruby-lang.org/en/master/NEWS/NEWS-3_4_0_md.html
- 'bundled gems' in https://docs.ruby-lang.org/en/master/NEWS/NEWS-3_4_0_md.html
- https://docs.ruby-lang.org/en/master/NEWS/NEWS-4_0_0_md.html
- 'bundled gems are promoted' in https://docs.ruby-lang.org/en/master/NEWS/NEWS-4_0_0_md.html

## Sources

- Ruby 4.0 release: https://www.ruby-lang.org/en/news/2025/12/25/ruby-4-0-0-released/
- Official reference opened by Codex: https://docs.ruby-lang.org/en/master/NEWS/NEWS-3_4_0_md.html
- Official reference opened by Codex: https://docs.ruby-lang.org/en/master/NEWS/NEWS-4_0_0_md.html