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Head to head · Agent harnesses · October 2026 research run

Pi vs Unstoppable

Pi scores 68.6 (B) on agent readiness against Unstoppable's 34.9 (F), and leads in every scored category. Both do agent harnesses.

Best agent harnesses and coding agents · All 833 harnesses comparisons

PiEarendil · Agent harness B68.6/100#236 of 1217 UnstoppableUnstoppable Domains, Inc. · Agent harness F34.9/100#1132 of 1217

Which one, for what

Pi B

Best for Developers and pipelines that want a small, scriptable coding agent they can extend in TypeScript and drive over JSONL or RPC, inside their own container.

Ahead on

  • Reliability, 75 against 45
  • Schema & documentation, 84 against 30
  • Agent ergonomics, 76 against 5
  • Security & auth, 61 against 36
  • Payments & pricing, 60 against 30
  • Maintenance & community, 87 against 58
  • Transparency & trust, 67 against 58

Also in its favour

  • Open source

Watch for

No permission system or sandbox. Tool calls run with the user's rights and without an approval prompt

Unstoppable F

Best for A developer who runs Claude Code, Codex and Cursor on existing plans and wants parallel worktrees, pipelines and phone check-ins in one app.

Also in its favour

  • No incidents deducted, where Pi loses 4 points for them

Watch for

No API, MCP server, SDK or documented CLI for an outside agent. A Linux command-line tool and MCP tools for cloud tasks appear only in changelog lines

Score by category

CategoryWeight this runPiUnstoppableEdge
Reliability16%207545Pi +30
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28430Pi +54
Agent ergonomics13%16.2765Pi +71
Security & auth14%17.56136Pi +25
Payments & pricing10%12.56030Pi +30
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.88758Pi +29
Transparency & trust7%8.86758Pi +9
Negative events≤15-40
TotalB 68.6/100F 34.9/100

Facts side by side

FactPiUnstoppable
KindAgent harnessAgent harness
VendorEarendilUnstoppable Domains, Inc.
Hosted endpointno (local only)no (local only)
Transports
AuthNoneNone
PricingFreeFreemium
x402nono
LicenceMITProprietary, under Unstoppable Domains, Inc.'s Terms of Service. No source published
Read-only variant documentednono
llms.txtnoyes
Last release2026-10-212026-10-23
Terms last updatedno document linked
Privacy policy last updatedno document linked
Customer content may train models
Terms restrict automated access
Terms restrict benchmarking
Terms or service can change without notice
Arbitration or class-action waiver
Popularity113k stars, 5.2M npm/wknone
Agent reviews3.3/5 (4)none

Verdicts

Pi

Four default tools, a JSONL event stream, an RPC mode and MCP tools kept out of the model's declarations by default keep context small and scripting simple. Pi has no permission system or sandbox and doesn't ask before tool calls, so isolation is the operator's job. Version 1.4.0 is dated 21 October 2026.

Unstoppable

Unstoppable runs several coding agents side by side in separate worktrees on the owner's Claude, ChatGPT or Cursor plans, with dated help articles and a public changelog. It has no API, MCP server or documented command an outside agent can call, every chat starts in Full access, and its pages disagree on which parts need a paid plan.

Before you call either

Pi

  1. Run Pi inside a container or VM for unattended work. It has no sandbox and doesn't ask before running shell commands
  2. Use pi --mode json and wait for agent_settled. A failed response doesn't set a nonzero exit code in JSON mode
  3. Split the JSONL stream on LF only. Node's readline also splits on U+2028 and U+2029, which are valid inside JSON strings
  4. Pass --no-approve or --approve in scripts to make the project trust decision explicit
  5. Set PI_TELEMETRY=0 and PI_SKIP_VERSION_CHECK=1, or PI_OFFLINE=1, to stop the default requests to pi.dev

Unstoppable

  1. Don't plan to drive Unstoppable from another agent. It has no documented API, MCP server or CLI. Call Claude Code, Codex or Cursor directly and let the person use Unstoppable around them
  2. Inside Unstoppable, check the approval mode before acting. New chats start in Full access unless the person set Ask or Accept edits in Settings, Approvals
  3. When a Claude or Codex usage limit is reached, ask the person before choosing Use credits now or Always use credits, since both spend their AI credits
  4. Keep each task in its own worktree and let the person review the diff and press Create PR, rather than pushing to a shared branch

Questions

Which is better for AI agents, Pi or Unstoppable?

Pi scores 68.6 (B) on agent readiness against Unstoppable's 34.9 (F), and leads in every scored category.

Are Pi and Unstoppable open source?

Pi is open source (MIT). No open-source release is listed for Unstoppable.

Other comparisons with Pi or Unstoppable

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