How to Install Fugu on Windows: WSL or Native Setup

Sakana’s one-line Fugu installer officially supports Ubuntu and macOS — on Windows, the official documentation points you to manual setup. In practice, Windows users have two good paths: run the official installer inside WSL and get the full managed experience for Sakana Fugu, or wire the coding agents up natively with a few configuration steps. This guide covers both, plus the pitfalls specific to Windows. Official facts verified against Sakana’s repository and get-started page on August 19, 2026; the WSL walkthrough and PowerShell translations are our own guidance, clearly marked.

Why the one-liner doesn’t run on Windows

The installer is a bash script: it clones a repo to ~/.fugu, writes POSIX-style config paths, installs launchers into ~/.local/bin, and manages file permissions the Unix way. None of that maps cleanly onto native Windows, and Sakana doesn’t pretend it does — the README says plainly that the one-line install supports Ubuntu and macOS, and that on Windows you should set things up by hand.

That leaves a fork in the road. If you’re comfortable with WSL (Windows Subsystem for Linux), you get everything the Linux experience offers — the launcher, version pinning, backups, update checks. If you want to stay native, the manual configuration is entirely doable because it’s just files and environment variables.

Path A: WSL — the full experience (our recommendation)

This walkthrough is ours, not Sakana’s — but it simply runs the official installer inside the environment it supports: Ubuntu.

1. Install WSL with Ubuntu. In an administrator PowerShell: wsl --install (installs WSL2 with Ubuntu by default on current Windows versions), then reboot if prompted and create your Linux user.
2. Inside the Ubuntu shell, install the coding agent you plan to use (Codex and/or Claude Code, per their own docs), so the Fugu installer has something to configure.
3. Run the official one-liner exactly as on Linux: curl -fsSL https://sakana.ai/fugu/install | bash — pick Codex, Claude Code, or both, and paste your fish_ API key when prompted.
4. Launch with codex-fugu or claude-fugu from the Ubuntu shell. Your Windows files are reachable under /mnt/c/..., and for best performance keep active projects inside the Linux filesystem.

A detail we enjoyed finding: Fugu’s model catalog ships safety instructions telling its agents to be careful with commands like wsl --shutdown that would kill their own environment — Sakana clearly expects Fugu to be driven from WSL. If a session ever ends abruptly after such a command, just reopen Ubuntu and relaunch.

Path B: native Windows, manually

Claude Code, natively

The Claude Code integration needs no installer at all — it’s environment variables. Sakana documents them for a POSIX shell; the PowerShell translation (ours) is mechanical:

$env:ANTHROPIC_BASE_URL = "https://api.sakana.ai"
$env:ANTHROPIC_AUTH_TOKEN = "fish_..."                  # your Sakana key
$env:ANTHROPIC_DEFAULT_OPUS_MODEL = "fugu-ultra[1m]"
$env:ANTHROPIC_DEFAULT_SONNET_MODEL = "fugu[1m]"
$env:ANTHROPIC_DEFAULT_HAIKU_MODEL = "fugu[1m]"
$env:ANTHROPIC_DEFAULT_FABLE_MODEL = "fugu-cyber[1m]"   # optional (access-gated)
$env:CLAUDE_CODE_SUBAGENT_MODEL = "fugu[1m]"
claude

Two rules carry over from the official docs: it must be ANTHROPIC_AUTH_TOKEN (a bearer token), not ANTHROPIC_API_KEY, and the variables last only for the current shell session. To persist them across sessions, set them as user environment variables (System Properties → Environment Variables, or [Environment]::SetEnvironmentVariable(..., "User")) — remembering that a plain claude will then always talk to Fugu until you remove them, which is exactly the always-on behavior the Linux launcher avoids.

Codex, natively

Codex’s manual setup is three files, exactly as in the Codex guide, with Windows paths: the model catalog to %USERPROFILE%.codexfugu.json, the profile to %USERPROFILE%.codexfugu.config.toml (point model_catalog_json at the catalog’s full path), and the [model_providers.sakana] block into %USERPROFILE%.codexconfig.toml. Copy the file contents verbatim from Sakana’s get-started page — they’re the same bytes on every platform. Then:

$env:SAKANA_API_KEY = "fish_..."
codex -p fugu

What you give up natively is everything the launcher does: no pinned-version management (Sakana verifies its configs against Codex 0.147.0 as of August 19, 2026 — matching it manually is wise), no automatic config updates, no managed backups. Check Sakana’s repo occasionally for catalog updates — new Fugu models arrive as fugu.json changes.

Windows-specific pitfalls

Pitfall	What to do
Running the one-liner in PowerShell or cmd	It’s a bash script — it won’t run natively. Use WSL (Path A) or go manual (Path B).
ANTHROPIC_API_KEY instead of ANTHROPIC_AUTH_TOKEN	The most common auth failure on any platform. Fugu needs the bearer-token variable.
Env vars vanish in new terminals	$env: assignments are session-only. Persist them as user environment variables — knowing that makes Fugu the permanent default.
Editing TOML/JSON with an editor that changes encoding	Save config files as plain UTF-8. If Codex misbehaves after an edit, validate with codex doctor.
Mixing WSL and native setups	WSL’s ~/.codex and Windows’ %USERPROFILE%.codex are different directories with separate configs and keys. Pick one home per agent and stick to it.
Slow agent performance on /mnt/c projects in WSL	Keep working repos in the Linux filesystem (e.g. ~/projects) for dramatically better file I/O.

Which path should you take?

If you’ll use Fugu daily, WSL is worth the one-time setup: you inherit the launcher’s update checks, the version pinning, and the backup system, and you’re running the exact configuration Sakana tests. Go native if WSL isn’t an option in your environment, or if you only need the Claude Code path — which is genuinely just seven variables. Either way, the models, the API, and the billing are identical; only the plumbing differs.

Related: the Claude Code guide, the Codex guide, and install troubleshooting when something misbehaves. Not sure Fugu is worth the setup? Try it first in the browser playground — no install at all.