# Fastify v6.0.0-alpha.0

- Product: Fastify (https://whatsnew.fyi/product/fastify)
- Vendor: Fastify
- Date: 2026-08-11
- Version: v6.0.0-alpha.0
- Original notes: https://github.com/fastify/fastify/releases/tag/v6.0.0-alpha.0
- Permalink: https://whatsnew.fyi/product/fastify/releases/v6.0.0-alpha.0
- Labels: Pre-release

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **fixed** — Revert misleading error message "Fastify instance is already listening"
- **removed** — Remove deprecated FastifyPlugin type
- **removed** — Remove deprecated FastifyLoggerInstance in favor of FastifyBaseLogger
- **removed** — Remove Promise.withResolvers ponyfill
- **removed** — Remove deprecated FastifyRequestContext and FastifyReplyContext types
- **changed** — Disable error handler overrides by default
- **removed** — Remove deprecated ValidationResult type alias
- **changed** — Upgrade undici to v8.x
- **removed** — Remove FSTDEP022 deprecation
- **removed** — Remove FSTDEP023 deprecation
- **removed** — Remove FSTDEP024 deprecation
- **removed** — Remove FSTDEP025 deprecation
- **removed** — Remove deprecated req property from request.d.ts
- **removed** — Remove ResSerializerReply type

##### What's Changed
* refactor: revert misleading error "Fastify instance is already listening" by @jean-michelet in https://github.com/fastify/fastify/pull/6098
* refactor(types)!: remove deprecated FastifyPlugin type by @Tony133 in https://github.com/fastify/fastify/pull/6897
* ci!: increase minimum runtime version  by @climba03003 in https://github.com/fastify/fastify/pull/6904
* refactor(types)!: remove deprecated FastifyLoggerInstance in favor of FastifyBaseLogger by @Tony133 in https://github.com/fastify/fastify/pull/6906
* refactor!: remove Promise.withResolvers ponyfill by @jean-michelet in https://github.com/fastify/fastify/pull/6910
* refactor(types)!: remove deprecated FastifyRequestContext and FastifyReplyContext types by @Tony133 in https://github.com/fastify/fastify/pull/6920
* refactor!: disable error handler overrides by default by @jean-michelet in https://github.com/fastify/fastify/pull/6915
* refactor(types)!: remove deprecated ValidationResult type alias by @Tony133 in https://github.com/fastify/fastify/pull/6914
* chore(deps)!: upgrade undici v8.x by @Tony133 in https://github.com/fastify/fastify/pull/6921
* refactor!: remove FSTDEP022 by @climba03003 in https://github.com/fastify/fastify/pull/6908
* chore(sponsor): add testmu ai by @Eomm in https://github.com/fastify/fastify/pull/6922
* docs: add per-route logging for Google Cloud Functions by @slegarraga in https://github.com/fastify/fastify/pull/6907
* refactor!: remove FSTDEP023 deprecation by @jean-michelet in https://github.com/fastify/fastify/pull/6913
* refactor!: remove FSTDEP024 deprecation by @jean-michelet in https://github.com/fastify/fastify/pull/6912
* refactor!: remove FSTDEP025 by @jean-michelet in https://github.com/fastify/fastify/pull/6909
* test: remove @sinonjs/fake-timers by @climba03003 in https://github.com/fastify/fastify/pull/6934
* refactor(types)!: remove deprecated req in request.d.ts by @Tony133 in https://github.com/fastify/fastify/pull/6935
* refactor(types)!: remove ResSerializerReply type by @jean-michelet in https://github.com/fastify/fastify/pull/6911


**Full Changelog**: https://github.com/fastify/fastify/compare/v5.11.3...v6.0.0-alpha.0