Pre-release: not yet published to PyPI. Do not use it to upload sessions yet; use the official a4sx CLI from session-exchange.com.

a4sx

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Save your coding-agent sessions to a private library, and resume Claude Code sessions on any machine as a new local session. a4sx is the command-line tool and Python SDK for session-exchange.com.

• Push a session to your private library: Claude Code and Codex CLI transcripts, and Grok Build session folders. A client-side scrub (secrets and personal data, the same rules as the a4sx CLI and server) runs before anything leaves your machine, and push tells you exactly what it changed.
• Resume a saved session anywhere: a4sx resume <name> writes it as a fresh Claude Code session in the directory you are in and starts claude --resume. Your saved copy never changes.
• Lineage: a session you resumed and push again is recorded as a child of the one it came from, so a4sx list shows your library as a tree.
• Search published sessions and add the ones you are entitled to to your library.
• SDK: everything the command does is in a4sx.sdk, for your own scripts, plugins or MCP servers.

Python 3.9+, no dependencies (stdlib only).

Private library: the sessions saved under your a4sx account on session-exchange.com. Its entries are not listed in the marketplace and not returned by public search; they are listed, fetched, versioned and deleted through the a4sx API with your own sign-in (or an agent key you create). Listing a session in the marketplace is a separate step in the web app, with a review. "Private" describes who can list and fetch an entry through a4sx; the server stores the bytes you upload, after scrubbing them again.

resume refuses a session recorded with another harness; it never turns one into a Claude Code session. Such a session stays in your library, and a4sx fetch downloads its original file.

Quickstart (5 minutes)

$ pipx install a4sx            # or: pip install --user a4sx
$ a4sx login                   # opens your browser; on SSH or headless it prints a link for your phone
signing in to https://session-exchange.com
...
signed in. your private library on https://session-exchange.com is ready.

Save the Claude Code session you worked in most recently:

$ a4sx push --latest --label my-work
a4sx push: client scrub: 2 lines changed (github_token: 1, homedir: 3) — lines 4, 212
a4sx push: local sha256    5d1c…
a4sx push: uploaded sha256 9a07…: DIFFERS from the local file (the client scrub rewrote it). …
{ "collection": "my-work-…", "status": "staged (private)", … }

Not sure what would leave your machine? a4sx push --latest --dry-run shows which lines the scrub would change, uploads nothing and needs no sign-in.

On any machine, in the folder you want to work in:

$ a4sx list
 #  name          created           updated           vers     ctx  title
 1  my-work       2026-10-05 09:12  2026-10-05 17:40     3    84k  Fix the flaky upload test
$ a4sx resume my-work
a4sx: new local session 0b6f… seeded from my-work-… (in /home/me/app)

resume starts claude --resume <new-id>. Use --no-launch to only write the session, and pass arguments to claude after --, e.g. a4sx resume my-work -- --model opus.

When you are done, a4sx push --latest saves your continuation; it is linked to my-work in the tree.

Other harnesses push the same way; the server recognises the format:

$ a4sx push ~/.codex/sessions/2026/10/14/rollout-….jsonl --label codex-run     # Codex CLI
$ a4sx push ~/.grok/sessions/<project>/<session-id>/ --label grok-run           # Grok Build: the folder

For a Grok Build session folder only its updates.jsonl is uploaded. Pushing one of the folder's other files (chat_history.jsonl, system_prompt.txt, ...) is refused.

Commands

NAME is a saved session's label, its id, or a unique part of its title.

Configuration

What leaves your machine

• push uploads the transcript after the client scrub (unless --no-scrub). It reports the changed lines, the rules that fired (never the values), and the sha256 of your file and of the upload. The server scrubs again before storing. Both are pattern-based backstops, not a guarantee: review what you push (--dry-run shows every change, with line and column).
• The client scrub applies the a4sx CLI's rules, which are the server's: API keys and tokens (Anthropic, OpenAI, xAI, Groq, Google, GitHub, Slack, AWS, Stripe, z.ai, a4sx tokens, JWTs), bearer, basic and digest auth, AWS request signatures, credentials in URLs, private keys, secret-named assignments, command-line passwords (mysql -p, curl -u, --password, ...), Google Sheet ids, and personal data: e-mail addresses, IP and MAC addresses, home-directory user names (Linux, macOS, Windows, WSL, Git Bash, Claude Code project-folder names, URL-encoded paths), host names under session-exchange.com and key-file paths. Values become markers such as [REDACTED] or [REDACTED-USER]; JSON stays valid. --keep-pii keeps the personal-data group and removes the rest. The rules are vendored from the CLI by tools/vendor_scrub.py; CI checks them against the published CLI.
• Your session token is stored with mode 0600, bound to the server that issued it, and is only ever sent to that server, as an Authorization header that is not forwarded on redirects. Pointing a4sx at another server (--base, $A4SX_BASE) never sends it your token; that server needs its own a4sx login. The sign-in links a server sends are only shown or opened if they are on that server's own origin. The token is never printed or logged.
• Resumed sessions are written with mode 0600. A session from another author, and anything you derive from it (a continuation you push, a crafted base), is treated as untrusted input: resume keeps Claude Code's permission prompts on unless you pass --trust-base.
• search and version send no token.

SDK

from a4sx.sdk import Client, NotFound

client = Client()                                  # same server and token resolution as the CLI

# sign in (device login); show the link and code however you like
client.login(on_pairing=lambda login, restarted: print(login.login_url, login.user_code))

res = client.push_file("session.jsonl", label="my-work")      # pre-scrubbed, retried safely
print(res.response["collection"], res.scrub.summary())

rows = client.list_sessions()
hits = client.search("flaky test", scope="public")["items"]
client.acquire(hits[0]["id"])                      # entitled listings only; never buys

resumed = client.resume("my-work", cwd="/home/me/app")
print(" ".join(resumed.local.resume_command))      # claude --resume <new id>

The SDK never prints and never calls sys.exit. Resuming without the SDK takes four steps, which resume_locally() implements: decode the transcript, pick a fresh session id, set sessionId on every record that has one, and write it to ${CLAUDE_CONFIG_DIR:-~/.claude}/projects/<cwd with every non-alphanumeric character replaced by "-">/<id>.jsonl. Then run claude --resume <id>.

Compatibility

• Claude Code stores sessions in an undocumented format that can change between releases. a4sx only rewrites sessionId (and, for craft, the uuid/parentUuid chain), so it is robust to most changes, but a resume can still fail after a large format change. Please open an issue.
• The standalone a4sx script from the website's installer and this package share the config dir, so a sign-in from one works in the other. This package does not include older command aliases, the launch profiles or the workspace-admin commands; keep using the installer's script if you rely on those.
• The client scrub is the installer's script's own, vendored with tools/vendor_scrub.py: a new scrub rule reaches this package with its next release.

Development

$ python -m pip install -e '.[dev]'
$ pytest -q            # offline: SDK tests run against a local stub server
$ ruff check . && reuse lint

See CONTRIBUTING.md. Security issues: SECURITY.md.

About

a4sx is made by crossVault GmbH, the company behind a4sx (session-exchange.com), a library and marketplace for coding-agent sessions. This client is open source so you can see exactly what touches your transcripts before anything is uploaded, and so other tools can build on the same SDK. The hosted service is not part of this repository. Parts of this project were developed with AI assistance (Claude).

License

Apache-2.0, see LICENSE. Copyright 2026 crossVault GmbH.