OpenBench

A benchmark for comparing coding-agent harnesses — the CLI tools that wrap a model in a run loop, tool set, and permission policy (codex, pi, opencode, cursor, devin, and open-model claude). The question it answers is: given the same underlying model and task, how much does the harness around it matter?

New here? WRITEUP.md tells the story arc; RESULTS.md has the milestone analyses; SETUP.md is the practical runbook for a first local cell, Docker, imported tasks, and open-model keys. Evaluating harnesses on a private codebase? Start with docs/private-evals.md (obench init, author a task from a small code slice, validate polarity, run, report — transcripts stay local). To run OpenBench tasks on Harbor cloud sandboxes, see docs/harbor-export.md (obench export harbor). To pull Harbor-format tasks into OpenBench, see docs/harbor-import.md (obench import harbor).

Live results: https://minghinmatthewlam.github.io/openbench/

What this measures

Each harness runs headlessly against a set of self-contained coding tasks. A task is graded by a checker script (exit 0 = solved, optional SCORE: for partial credit), never by the harness's own claim of success. Current tiers:

• Core synthetic tasks (tasks/). Small-to-medium tasks built in this repo, including partial-credit harder tasks such as make-ci-green, add-feature, and misleading-error.
• Exercism imported tier (tasks-imported/exercism/). MIT-licensed problem- specification tasks with per-task provenance.
• Terminal-Bench imported frontier tier (tasks-imported/terminal-bench/). Five Apache-2.0 Terminal-Bench tasks adapted for OpenBench's Docker lane and scored separately from the core tier.

Two result framings are used:

• Track A — same model, harness varies. Every compatible harness is pinned to the same canonical model, gpt-5.5-medium, so differences come from the harness (scaffolding, tools, prompting, permissions), not the model.
• Open-model panels. Open models (glm-5.2, deepseek-v4-flash, kimi-k2.7-code, glm-4.7-flash) run through adapters that can reach the providers. pi, opencode, and claude call providers directly; codex uses the local Responses↔Chat bridge in bench/openmodel_bridge.sh.

Honest caveats: devin is flaky in the latest published analysis and is excluded from M4.5 rankings; cursor/devin have closed model menus for open models; claude is open-model-only here so a run cannot accidentally bill an Anthropic subscription.

Headline findings so far

• Correctness saturates for frontier harnesses on repo-authored tasks. M3 and M4.5 both hit the ceiling: clean frontier harnesses solved every core task, so correctness does not support a leaderboard on those tiers.
• Efficiency separates even when correctness does not. Wall-clock spread is up to ~4× and token tax up to ~8× on the early matrices; pi is repeatedly the fastest/leanest harness in the measured panels.
• Open models are surprisingly close. In M4, three of four open models reached the GPT-5.5-medium frontier baseline on the same hard tasks; the 72-run open- model matrix cost about $1.02 in first-party API spend.
• Terminal-Bench is the new frontier tier. The current local TB frontier run covers 45 cells (3 harnesses × 5 TB tasks × 3 trials) and lands at 12/15 per harness (mean score 0.80), finally below the synthetic-task ceiling. The raw TB run log currently lives under local-only results/ and should be promoted to a committed dataset before citing it externally.

Hardware and accounts

No GPU is required. Core and Exercism tasks run on a normal laptop; Terminal-Bench cells can take minutes and should use Docker isolation. Real harness runs require that harness's CLI and auth. Frontier Track A uses subscription/OAuth logins; open-model panels use first-party provider API keys kept outside the repo. See SETUP.md for install/auth caveats and one-cell commands.

Reproduce a cheap open-model panel (~$1)

The committed M4 open-model matrix — two harnesses (pi, opencode) × four open models × three harder tasks × three trials — reproduces for about $1 of API credit. The dataset is in data/m4-2026-07-03/.

Create ~/.openbench/keys.env (or export the same names) with names only in the repo docs; values stay local:

ZAI_API_KEY=
DEEPSEEK_API_KEY=
MOONSHOT_API_KEY=

Preflight (no token spend):

obench doctor --harness pi,opencode --model glm-4.7-flash

Run the resumable matrix:

for m in glm-4.7-flash glm-5.2 deepseek-v4-flash kimi-k2.7-code; do
  obench run --harness pi,opencode \
    --task make-ci-green,add-feature,misleading-error \
    --model "$m" --trials 3
done

Report:

obench report --efficiency --results-path results/results.jsonl

For a single first run, Docker, imported tasks, claude, or codex open-model runs through the bridge, use SETUP.md.

Layout

tasks/                 core benchmark tasks (see "Task format")
tasks-imported/        separately scored Exercism and Terminal-Bench tiers
obench/                installable package (CLI: obench)
obench/run.py          the runner (one row per task x harness x trial)
obench/report.py       aggregates results into a table with Wilson CIs
obench/adapters/*.py   one adapter per harness (+ built-in "null" control)
obench/ADAPTER_SPEC.md the adapter contract
obench/openmodel_bridge.sh  foreground Codex Responses↔Chat bridge for open models
obench/scrub.py        PII scrubber for transcripts (local-only; see below)
obench/entry.py        in-container entrypoint for --exec docker
obench/docker_exec.py  container-per-cell execution backend
obench/docker/         isolation image for --exec docker
bench/*.py             thin deprecation shims → obench
validate_tasks.py      forwarding shim → obench validate
results/results.jsonl  append-only local results log (gitignored)
transcripts/           per-cell agent transcripts (gitignored, local-only)

Install

The framework installs as obench (the PyPI name openbench is taken):

# from this checkout
pip install -e .

# or, without cloning first
pip install "git+https://github.com/minghinmatthewlam/openbench.git"

# future: pip install obench

Then use the umbrella CLI: obench init, obench run, obench report, obench doctor, obench validate, obench gate, obench compare, obench publish, obench verify, obench export, obench import. Legacy python3 bench/run.py (and friends) still forward with a deprecation note.

Quickstart

Everything in the core harness runner is Python 3 standard library only — no third-party Python dependencies. Real harnesses, Docker, and the Codex open-model bridge have external CLI/tool requirements; see SETUP.md.

1. Validate the tasks. Confirms each checker fails on the untouched workspace and passes on the golden solution (see "Task format"). This covers both tasks/ and imported tiers under tasks-imported/:

obench validate
# legacy: python3 validate_tasks.py

2. Preflight.

obench doctor
# legacy: python3 bench/doctor.py

For each harness it checks — spending no tokens — that the CLI is installed, its auth/login or required key name is present, and the canonical model pin resolves to the harness's own model string. A failing preflight exits nonzero.

3. Run. Pick harnesses and tasks. Start with the zero-cost null control to confirm the plumbing, then add real harnesses:

# negative control — does nothing, so every task should fail (no tokens used)
obench run --harness null --task fix-failing-test,build-a-cli,make-it-run
# legacy: python3 bench/run.py --harness null --task ...

# a real harness, 3 trials per task
obench run --harness codex --task fix-failing-test,build-a-cli,make-it-run --trials 3

Multiple harnesses/tasks are comma-separated. The run loop is resumable: a cell whose run_id already appears in results/results.jsonl is skipped, so you can stop and re-run freely. Use --force to re-run existing cells. Full options: obench run --help.

4. Report.

obench report
# legacy: python3 bench/report.py

Example output (from the null control on two tasks):

harness  fix-failing-test  make-it-run  overall   wilson95        mean_s  tokens
-------  ----------------  -----------  --------  --------------  ------  ------
null     0/1               0/1          0/2 (0%)  [0.000, 0.658]  0.00    -

Task format

A core task is a directory under tasks/<name>/; an imported task is addressed as tasks-imported/<collection>/<name>/ and run with --tasks-dir tasks-imported:

instruction.md      what the harness is told (reads as a normal engineering request)
workspace/          starting files; copied fresh into a temp dir for every run
                    OR workspace.toml — git-ref materialization (see below)
checker.sh          grades the result; exit 0 = solved
solution/           golden files, used ONLY by validate_tasks.py (never shown to the harness)
checker_data/       optional: inputs/expected outputs the checker owns (kept out of workspace/)

Contract the runner honors for every cell:

• The starting workspace is materialized into a disposable temp dir; the harness edits that copy. The source under tasks/ is never modified.
  • Snapshot mode: workspace/ is copytree'd.
  • Git mode: workspace.toml exports a git ref via git archive (optional subdir / setup script). See docs/private-evals.md. Provide exactly one of workspace/ or workspace.toml.
• checker.sh runs with cwd = the temp workspace copy and the environment variable TASK_DIR set to the absolute task directory. Checkers reference their own data via $TASK_DIR/checker_data/... rather than a relative path, so they work regardless of cwd.
• Instructions never mention the checker, the solution, or that this is a benchmark.

Partial credit (the SCORE: contract)

A checker exit code is binary, but a checker MAY also emit a SCORE: line to grade partial progress. The rules the runner applies:

• A checker may print SCORE: <float 0.0–1.0> to stdout. The last parseable such line wins; a malformed value is ignored (as if that line were absent), and values are clamped to [0.0, 1.0].
• Exit 0 is always a full pass — success = true and score is coerced to 1.0 regardless of any SCORE: line.
• Nonzero exit — success = false, and score is the checker's SCORE: value if present, else 0.0. This is how a task awards partial credit.
• A checker timeout records score = 0.0.

SCORE: is optional and backward compatible: a checker that never prints one behaves exactly as before (pass → 1.0, fail → 0.0).

Validation discipline

validate_tasks.py enforces that each checker is correctly polarized:

1. Run the checker against a freshly materialized workspace → it must fail (otherwise the task is scored solved before the agent does anything).
2. Run it against that workspace with solution/ overlaid → it must pass (otherwise a correct answer would be rejected).

This catches the two ways a checker can silently lie about difficulty, and is why expected outputs for data-driven tasks are generated from the golden solution rather than written by hand. Current validated tiers are 8 core tasks, 11 Exercism imports, and 5 Terminal-Bench imports; each tier is reported and scored separately.

Adapters

Each harness is a module obench/adapters/<name>.py exposing NAME, a MODELS map, and run(instruction, workdir, model, timeout_s) -> dict. The adapter maps the canonical model name to the harness's own flags, runs the CLI headlessly with cwd = workdir, enforces the timeout via subprocess (no timeout command — macOS has none), and returns completed / error / tokens / turns / cmd. completed means the CLI exited cleanly; it is not task success — the checker decides that. Full contract: docs/adapter-contract.md. Adapters may optionally export DOCTOR = {"cli", "auth"} so obench doctor picks them up without editing the doctor allowlist; third-party CLIs use --candidate manifests instead (see docs/byo-harnesses.md).

Auth is handled inside each adapter, read-only — the user's real config files are never modified:

Harness	Frontier gpt-5.5-medium	Open models	Auth handling
codex	gpt-5.5, model_reasoning_effort=medium	Via foreground bench/openmodel_bridge.sh	Uses existing codex login for frontier; bridge/vendor keys for open models.
pi	gpt-5.5, --thinking medium	Direct vendor endpoints	Isolated HOME (temp dir) with only .pi/agent/auth.json copied in, plus --no-extensions, so personal extensions never load.
opencode	openai/gpt-5.5, --variant medium	Direct vendor endpoints	Strips OPENAI_API_KEY from frontier child env to force subscription OAuth; open models use provider keys.
cursor	gpt-5.5-medium (effort baked into name)	Not supported (closed menu)	Uses the existing cursor-agent login as-is.
devin	gpt-5.5 / configured pin (see caveats)	Not supported (closed menu)	Uses the existing devin login; latest data is flaky and excluded where noted.
claude	Not supported by design	Direct Anthropic-compatible vendor endpoints	Open-model-only adapter; isolated config and vendor keys, never Anthropic subscription/OAuth.

The built-in null adapter does nothing and reports completed=True. Because it never edits the workspace, every task's checker fails — it is the benchmark's negative control, and uses no tokens.

Results

Findings from the milestone runs are in RESULTS.md, with committed datasets under data/. Local scratch runs stay under gitignored results/ unless intentionally promoted to data/.

bench/run.py appends one JSON object per line to results/results.jsonl. The fields:

Field	Meaning
run_id	harness:task:model:trialN — the resumable identity of the cell
ts_iso	local timestamp when the cell ran
harness	adapter name (or null)
model	canonical model name (default gpt-5.5-medium)
task	task directory name
trial	1-based trial index
success	the graded result — checker_exit == 0
completed	harness CLI exited cleanly (self-reported; not success)
error	timeout / crash / adapter exception, else null
wall_time_s	adapter wall-clock seconds
tokens	fresh tokens reported by the harness (uncached input + output), else null
turns	turns reported by the harness, else null
cmd	the command line executed (for auditability)
checker_exit	checker's integer exit code, or "timeout"
exec_mode	local or docker (what actually ran, after any fallback)
score	graded score in [0.0, 1.0] (see the SCORE: contract); 1.0/0.0 for a plain pass/fail
harness_version	version string from the adapter's optional version(), "builtin" for null, else null
timeout_s	per-cell adapter timeout cap used for this row (default 2400)

Rows written before score, harness_version, or timeout_s existed simply omit them; the report derives a score from success (1.0/0.0) for those.

bench/report.py reads that log and prints one row per harness: per-task success (x/n), overall success with a Wilson 95% interval, mean score (averaged over all trials, the discriminating number for partial-credit tasks), mean wall-clock time, tokens-per-solve, and mean turns. --efficiency prints a per-harness efficiency summary; --results-path points it at an alternate log.

Tokens-per-solve is basis-aware: it uses self-reported tokens when present, otherwise the counting-proxy fresh total (tokens_proxy_input_uncached + tokens_proxy_output) when token_basis_proxy is proxy_measured. Cache-read is not mixed into that number. Proxy-derived figures are marked *; mixed-basis tables print a warning. HTML publish/report cards use the same rule and badge arms as unmetered / self-reported / proxy-measured.

Transcripts are LOCAL-ONLY

Alongside each results row, the runner writes that cell's full agent transcript to transcripts/<results-file-stem>/<run_id>.txt (a transcripts/ sibling of the results log; override with --transcripts-dir). These are the raw, unscrubbed harness output and can contain your absolute home paths, username, hostname, email, or secrets the agent echoed (API keys, tokens).

Hard rule: transcripts are never published as-is. transcripts/ is gitignored. obench publish builds a shareable comparison bundle (HTML card + filtered results + provenance) and refuses to include transcripts; see docs/publish.md. Before sharing any transcript you must do a manual review pass:

python3 -m obench.scrub transcripts/ --check          # REPORT potential PII (exit 1 if any)
python3 -m obench.scrub transcripts/ --out scrubbed/   # write scrubbed copies (originals untouched)
python3 -m obench.scrub scrubbed/ --check             # confirm the copies are clean (idempotent)

scrub.py replaces emails, home paths, the local username, hostnames, and key/token-shaped strings with placeholders (<EMAIL>, <HOME>, <USER>, <HOST>, <REDACTED_KEY>, …). It never modifies originals and over-redacts on purpose — a false positive is cheap, a leaked secret is not. --check is a report only; read it with your own eyes before trusting the scrubbed output.

Reading the Wilson interval

Every success rate here is estimated from a handful of trials, so the point estimate (say "2/3 = 67%") is noisy. The Wilson 95% confidence interval is the range of true success rates consistent with what was observed — we are about 95% confident the harness's real success rate lies inside it. Two things to keep in mind: with few trials the interval is wide (3 trials can easily span most of 0–100%), so overlapping intervals mean the harnesses are not distinguishable yet; and the interval shrinks as trials grow. Wilson (rather than the textbook p ± z·√(p(1−p)/n)) is used because it stays inside [0, 1] and behaves sensibly at 0/n and n/n, which the naive formula does not.

Methodology & limitations

• Same-model pinning (Track A). All harnesses target gpt-5.5-medium so the harness is the variable — with the devin exception noted above.
• Fresh workspace per run. Every cell gets an untouched copy of the task workspace; runs cannot contaminate each other or the source tree.
• Checker is the sole judge. Success is checker.sh exit 0, never the harness's self-report. validate_tasks.py guarantees each checker actually discriminates a solved workspace from an unsolved one.
• Negative control. The null adapter should score 0% everywhere; a nonzero null success would indicate a broken (too-lenient) checker.
• Isolation modes. --exec local (default) runs on the host; --exec docker runs each cell in a fresh disposable container built from obench/docker/ (docker build -t openbench-harness:latest obench/docker). The same adapter module runs unchanged in both modes — the container only adds isolation, with auth bind-mounted read-only at runtime (never baked into the image). Docker is fail-closed by default; pass --docker-fallback to opt into whole-run local homogenization when the daemon/image is unavailable (mixed lanes still abort).
• Docker image is partial. codex, pi, and open-model claude are installed and version-checked in the default image; opencode, cursor, and devin are behind --build-arg INSTALL_UNVERIFIED=true and their Linux installs are not yet confirmed. For those harnesses, use --exec local for now.
• Sample size. These are small tasks in small numbers; the current results are a plumbing/shakedown sample, not a verdict. Read the Wilson intervals, not the point estimates, and treat cross-harness gaps as real only when the intervals separate.

License

OpenBench is available under the MIT License. See LICENSE.