devenv 2.1: Nix with zsh, fish, and nushell via libghostty

May 7, 2026

devenv 2.0 gave you hot reload, the status line, and instant cache hits, but devenv shell always dropped you into bash, and you still needed direnv for activation on cd.

devenv 2.1 closes both gaps and adds structured handles for coding agents.

Every shell, first class

Native zsh, fish, and nushell

Shell reloading in zsh

devenv 2.1 adds native support for zsh, fish, and nushell (devenv#2718) with rcfile generation, environment diff tracking, reload hooks, and prompt integration implemented per shell rather than shimmed through bash. The shell is picked from $SHELL, or set explicitly:

$ devenv shell
$ SHELL=/bin/zsh devenv shell

Closes devenv#36 (open since November 2022), devenv#2487, and devenv#2592.

libghostty under the hood

The virtual terminal emulator was replaced with libghostty, the terminal engine from Ghostty, giving devenv a single VT parser that handles every shell the same way.

Building libghostty reliably on Nix took upstream patches in libghostty-rs#27, ghostty#12364, and ghostty#12548. Thanks to the Ghostty maintainers for landing them.

Auto reload

2.0 required Ctrl+Alt+R to apply environment changes after a rebuild, and that keybind clashed with reverse search on macOS. 2.1 re evaluates in the background on file changes and applies the new environment at the next prompt (devenv#2595).

Auto activation without direnv

devenv hook replaces direnv for cd based activation. Add one line to your shell config:

eval "$(devenv hook bash)"

eval "$(devenv hook zsh)"

devenv hook fish | source

devenv hook nu | save --force ~/.cache/devenv/hook.nu
source ~/.cache/devenv/hook.nu

Activation happens on cd into a trusted directory and reverses on the way out. No .envrc, no external dependencies. Trust is managed with devenv allow and devenv revoke.

For coding agents

In 2.0, an agent that wanted to restart your API after a config change had to kill the whole devenv session or scrape the TUI through ANSI codes. 2.1 replaces that with structured handles.

Process management from the command line

New subcommands act on a running devenv up (devenv#2621):

$ devenv processes list
$ devenv processes status
$ devenv processes logs api
$ devenv processes restart api
$ devenv processes stop worker
$ devenv processes start worker

These work with the native process manager and are also exposed as MCP tools.

Quiet mode by default

devenv detects agents via CLAUDECODE, OPENCODE_CLIENT, and AI_AGENT and switches to quiet mode automatically, suppressing TUI progress output that would waste tokens (devenv#2723). Override with --verbose or --tui.

OpenTelemetry trace export

devenv 2.1 exports OTLP traces (devenv#2415). Every Nix evaluation, derivation build, task run, and managed process becomes a span with attributes like devenv.activity.kind, devenv.derivation_path, devenv.url, and devenv.outcome.

Enable it through the new unified --trace-to flag:

$ devenv --trace-to otlp-grpc shell
$ devenv --trace-to otlp-http-protobuf:http://localhost:4318 shell

Three OTLP formats are supported: otlp-grpc (built in), otlp-http-protobuf, and otlp-http-json (opt in via cargo features). Endpoints can be set on the flag or via the standard OTEL_EXPORTER_OTLP_* variables.

Trace context propagates across process boundaries: spawned tasks, shell commands, and processes inherit TRACEPARENT and TRACESTATE, so instrumented children show up on the same trace as the parent devenv up run.

--trace-to replaces --trace-output and --trace-format with a single [format:]destination syntax, and accepts multiple destinations:

$ devenv --trace-to pretty:stderr --trace-to otlp-grpc shell
$ DEVENV_TRACE_TO=json:file:/tmp/trace.json,otlp-grpc devenv shell

Tasks and processes

devenv tasks run defaults to before mode, so dependencies run too (devenv#2551); --mode single restores the old behavior. The same --mode flag now also controls which processes devenv up starts (devenv#2721).

Tasks can print messages on shell entry by writing to $DEVENV_TASK_OUTPUT_FILE (devenv#2500).

And more

Nix 2.34. Multithreaded tarball unpacking, evaluator performance improvements, and REPL enhancements.

require_version in devenv.yaml. Enforce a minimum devenv CLI version for your project. Set require_version: true to match the modules version, or use a constraint string like ">=2.1" (devenv#2391).

ROCm support. New nixpkgs.rocmSupport option for enabling ROCm in nixpkgs configuration.

Full stack traces on error. show-trace is now always enabled, so evaluation errors include the full stack trace instead of a truncated message suggesting a nonexistent --show-trace flag (devenv#2725).

Ctrl+X to stop processes. Stop individual processes from the TUI while keeping them visible and restartable.

Ctrl+H to hide stopped processes. Toggle hiding stopped processes in the TUI to focus on what’s still running. Failed processes stay visible, and the process count shows how many are hidden (devenv#2692).

Port allocation fixes. Port values (config.processes.<name>.ports.<port>.value) now resolve correctly in devenv shell and devenv tasks run, matching the ports allocated by devenv up (devenv#2710). Ports bound to 0.0.0.0 or [::] are now detected, preventing multiple devenv instances from allocating the same port (devenv#2567). Strict port restarts no longer fail with “port already in use” during kernel socket teardown (devenv#2647).

Dozens of other bug fixes. File watcher deduplication, import precedence, eval cache consistency, process lifecycle fixes, and terminal compatibility improvements. See the full changelog for details.

Breaking changes

devenv tasks run now runs dependencies by default (before mode instead of single). Use --mode single for the old behavior.

Final words

Open an issue or join the Discord with feedback.

Domen