Bernstein vs PythonRuntime: quick decision guide

Install both

pipx install bernstein

Feature matrix

Adapter source: src/bernstein/adapters/python_runtime.py

Verifiable facts

The brief for this surface requires at least three facts that a reader can verify against a primary source. The list below is built from the bernstein adapter source and, when available, the upstream project's own pages.

1. Bernstein ships a PythonRuntime adapter at src/bernstein/adapters/python_runtime.py that wraps the upstream CLI as one of 42 routable agents. [source: bernstein adapter source, as of 2026-08-10]
2. Bernstein is an open-source Multi-agent orchestrator licensed Apache-2.0, with a deterministic Python scheduler that routes work across CLI agents in parallel git worktrees. [source: bernstein repo, as of 2026-08-10]
3. Bernstein records lineage and a replay journal on every run; with the audit log enabled it also writes an HMAC-SHA256 chained record under .sdd/ that lets a reviewer replay every routing and quality-gate decision. [source: bernstein repo, as of 2026-08-10]

Where PythonRuntime fits in Bernstein

Bernstein registers PythonRuntime under the slug "python-runtime" and the registry name "python_runtime". The adapter source lives at src/bernstein/adapters/python_runtime.py in the bernstein repo and was last touched at build time 2026-08-10. The PythonRuntime adapter file is 223 lines and 8,507 bytes long, fingerprinted cd386203637df55c (first 16 hex chars of SHA-256). No upstream GitHub repository is recorded in the bernstein adapter for PythonRuntime; refer to the upstream vendor's documentation when auditing. The bernstein adapter file for PythonRuntime does not yet carry a "Last verified against upstream" line; this means the adapter still tracks an unpinned upstream binary. Bernstein routes tasks to PythonRuntime when its pass rate on similar work clears the configured threshold, otherwise the deterministic Python scheduler picks a different adapter from the 40+ adapter catalog.

Adapter source excerpt

The module docstring of the PythonRuntime adapter, as it stands in the bernstein repo. Punctuation is normalised for the web; the wording is the author's. Length: 1156 characters.

Generic Python-invoked agent-runtime adapter (#2959). Drives a Python-invoked agent runtime in a subprocess-isolated worker running :mod:`bernstein.adapters.python_runtime_runner`. The runtime is named by the caller (``runtime_module`` + ``runtime_entrypoint``); the runner imports it, calls the entrypoint inside the task workdir, and writes one JSON object per line describing the run's boundary (start, result, error) to stdout, which the worker captures into the session log. Configuration arrives through the per-spawn ``mcp_config`` mapping, mirroring :mod:`bernstein.adapters.openai_agents`: ``runtime_module`` Required. Import path of the module exposing the runtime entrypoint. ``runtime_entrypoint`` Optional. Attribute name of the callable to invoke; defaults to ``chat``. There is no permission surface between Bernstein and the runtime - the runner imports and calls it directly - which is what the declared ``DangerousModeStrategy.ALWAYS_ON`` means for this adapter: selecting it authorises unattended execution of the configured module. Nothing about the declaration makes the runtime safe; it records that no approval prompt exists to skip.

Adapter telemetry

When to pick which

FAQ