pi-sub-anthropic

A pi extension that registers a second Anthropic provider, pi-sub-anthropic, which authenticates with a Claude Pro/Max subscription instead of API credits. Ported from omp v17.4.2.

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⚠️ Warning — read this first

This project is not official. It is not affiliated with, endorsed by, or supported by either Anthropic or the pi project. Nobody upstream has reviewed, blessed, or agreed to maintain it.

Using it may get your Anthropic account restricted or banned. To make a subscription credential work outside Claude Code, this extension reproduces Claude Code's wire fingerprint byte-for-byte: its user-agent, beta headers, system-block layout, token clamp, tool naming, and a billing attestation hash. That is, by construction, presenting a third-party client as a first-party one.

Understand what that means before you install:

• It may violate Anthropic's Terms of Service / Usage Policies. Read them and decide for yourself. This project takes no position and offers no defence.
• Detection is trivial for Anthropic and entirely within their control. They can identify, rate-limit, suspend, or terminate accounts at any time, without notice, and this extension can do nothing about it.
• The account at risk is your Claude subscription account — the same one you use in Claude.ai and Claude Code. There is no sandbox and no way to limit the blast radius.
• The fingerprint is pinned and does not self-update. If Anthropic changes anything server-side, requests start failing — possibly conspicuously.
• No warranty, no support, no liability. You run this entirely at your own risk. If you are not prepared to lose the account, use an API key instead (PI_SUB_ANTHROPIC_API_KEY) or pi's built-in anthropic provider.

If any of that is unacceptable to you, stop here.

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Install

Needs Node >= 22.6, pi >= 0.83.0, and a Claude Pro or Max subscription for the OAuth path. pi loads the extension with the Node that runs pi — not necessarily the node first on your PATH — and that interpreter must be >= 22.6 or type stripping fails at load.

pi install npm:pi-sub-anthropic          # tracks latest
pi install npm:pi-sub-anthropic@0.1.4    # pinned; pinned specs are skipped by pi update

Published from CI with npm provenance, so the tarball is attestably built from this repository. Straight from git works too, if you would rather track the default branch:

pi install git:github.com/spksoft/pi-sub-anthropic

Or by hand, adding the absolute path to a local copy in ~/.pi/agent/settings.json:

{
  "extensions": ["/absolute/path/to/pi-sub-anthropic"]
}

No runtime npm dependencies and no build step: the Messages API is spoken directly over fetch, from TypeScript sources pi type-strips at load.

Working on the code instead? See CONTRIBUTING.md.

Use

/login pi-sub-anthropic                 # OAuth against your Claude subscription
/model pi-sub-anthropic/claude-opus-5

Non-interactively:

pi --provider pi-sub-anthropic --model claude-opus-5

To make it the default, in ~/.pi/agent/settings.json:

{
  "defaultProvider": "pi-sub-anthropic",
  "defaultModel": "claude-opus-5"
}

Nine models are registered, mirroring pi's own Anthropic catalog: Opus 5 / 4.8 / 4.7 / 4.6 / 4.5, Sonnet 5 / 4.6 / 4.5, Haiku 4.5.

Two credentials, two behaviours

	/login pi-sub-anthropic (OAuth)	PI_SUB_ANTHROPIC_API_KEY
Credential	sk-ant-oat… subscription token	sk-ant-api… key
Billed to	your Claude Pro/Max plan quota	per-token API credits
Auth header	Authorization: Bearer …	X-Api-Key
Identity sent	full Claude Code fingerprint	plain API request
max_tokens	clamped to 64k	full model ceiling
Tool names	prefixed _	unchanged
System prompt	relocated to a user turn	left in system

Both paths work; they differ in what pays for the tokens. Why the OAuth column looks like that is documented in docs/internals.md.

Environment variables

var	effect
PI_SUB_ANTHROPIC_API_KEY	use an API key instead of OAuth (billed as API credits)
PI_SUB_ANTHROPIC_DEBUG=1	print resolved URL / headers / max_tokens to stderr (auth redacted)
PI_SUB_ANTHROPIC_EXTRA_BETAS	comma-separated extra anthropic-beta values
PI_SUB_ANTHROPIC_DUMP_BODY	path to write the outgoing request body to

Troubleshooting

Is it installed? pi --list-models pi-sub-anthropic lists 9 models, and a real round-trip is pi -p --provider pi-sub-anthropic --model claude-sonnet-5 "hi".

pi auth check --provider pi-sub-anthropic says provider_not_found. Expected, and not a fault: those subcommands resolve providers without loading extensions. Look for a pi-sub-anthropic key in ~/.pi/agent/auth.json instead.

A 1M-context model 429s with "Usage credits are required for long context requests". Subscription credentials carry no long-context credit, so 1M betas are never advertised on OAuth. Natively-1M models such as claude-sonnet-5 still serve their full window; use an API key if you need a beta-gated 1M model.

Requests started failing after working before. The fingerprint is pinned and does not self-update. Check PI_SUB_ANTHROPIC_DEBUG=1 output, then the upstream constants.

Rate limits. Plan limits are Anthropic's, not this extension's. Hitting your Pro/Max ceiling throttles exactly as it would in Claude Code.

Uninstall

pi remove npm:pi-sub-anthropic                        # or the git:/path source you installed

Or delete the extensions[] line. Nothing else in pi is touched; the stored credential lives under its own id in ~/.pi/agent/auth.json.

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More

How it works, and what was measured	docs/internals.md
Development, tests, releases	CONTRIBUTING.md
Package on npm	https://www.npmjs.com/package/pi-sub-anthropic
Listing in the pi gallery	https://pi.dev/packages/pi-sub-anthropic

Attribution and license

The Anthropic provider logic here — the OAuth flow, wire fingerprint, beta profile, token clamp, tool naming, billing header and cch attestation — is derived from omp (@oh-my-pi/pi-coding-agent / @oh-my-pi/pi-ai), pinned to v17.4.2. Credit for the behaviour this extension reproduces belongs upstream; this repository contributes a Node-compatible translation, tests and documentation — not the discovery.

omp is MIT licensed:

Copyright (c) 2025      Mario Zechner
Copyright (c) 2025-2026 Can Bölük
Copyright (c) 2026      Stencil Labs, Inc.

This port is MIT licensed too — see LICENSE, which carries both omp's notice above and the port's own copyright line.

omp (upstream source of the logic)	https://github.com/can1357/oh-my-pi
pi (the host agent)	https://github.com/badlogic/pi-mono
Anthropic Messages API	https://docs.anthropic.com/en/api/messages
Anthropic Usage Policy	https://www.anthropic.com/legal/aup
Anthropic Consumer Terms	https://www.anthropic.com/legal/consumer-terms

Not an official Anthropic or pi project. Use at your own risk.