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Experimental backlog

Overview

This page lists experimental feature flags that do not yet have dedicated wiki leaves in this domain. Each entry is a one-line purpose and a pointer to the upstream manual—not a deep dive.

For how flags move from experimental to stable, use Tracking Stabilization as the lifecycle hub. For enabling flags and the full Nix 2.34 inventory, see Feature flags overview. Flags already covered here have sibling leaf pages linked from those two pages.

Version stamp (Phase 5.1 re-check, 2026-07-31): backlog checked against the Nix stable manual for 2.34.x (experimental features → /manual/nix/2.34/…; manual title 2.34.9; local nix (Nix) 2.34.8). Flag names and descriptions change between releases—re-check that page and release notes when upgrading.

Details

Maintenance cadence. After each Nix stable release (and when NixOS pins a new nix version—see Release cadence):

  1. Diff the manual flag list against this backlog, Feature flags overview, and sibling leaves.
  2. Move flags off this page when a dedicated leaf is written; add new manual-only flags here; drop rows when a flag is stabilized or removed (release notes).
  3. Do not invent stabilization dates—follow release notes and per-flag tracking issues linked from the manual.

Flags with wiki leaves (not backlog). Use these for behavior and enablement instead of this page:

Flag Wiki leaf
auto-allocate-uids auto-allocate-uids
ca-derivations ca-derivations
cgroups cgroups
dynamic-derivations dynamic-derivations
fetch-tree fetch-tree-and-git
flakes flakes
git-hashing fetch-tree-and-git
impure-derivations impure-derivations
nix-command nix-command
pipe-operators pipe-operators-and-lang
recursive-nix recursive-nix
verified-fetches fetch-tree-and-git

Backlog (Nix 2.34.x stable manual — 9 of 21 flags). No dedicated leaf yet—see the manual section for each flag and its GitHub tracking link:

Flag One-line purpose
blake3-hashes Enables support for BLAKE3 hashes.
configurable-impure-env Allows the impure-env nix.conf setting.
daemon-trust-override Lets nix-daemon force trust or distrust of clients (testing and nix-daemon --stdio experiments).
external-builders Enables support for external builders / sandbox providers.
fetch-closure Enables the fetchClosure built-in in the Nix language.
local-overlay-store Allows use of the local overlay store.
mounted-ssh-store Allows use of the mounted SSH store.
parse-toml-timestamps Allows parsing of timestamps in builtins.fromTOML.
read-only-local-store Allows the read-only parameter in local store URIs.

Authoritative descriptions and stabilization tracking: Nix manual — Experimental features (one section per flag above).

Examples

See which experimental features are effective on this machine (requires nix-command):

nix config show experimental-features

Example output (Nix 2.34.x; yours will differ):

fetch-tree flakes nix-command

Confirm the full upstream list for your Nix version—the manual is the source of truth, not this wiki table:

nix --version
# Open: https://nix.dev/manual/nix/stable/development/experimental-features.html

After upgrading, skim release notes for flags added, changed, stabilized, or removed before assuming a backlog entry still applies.

References

See also