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Head to head · Agent harnesses · October 2026 research run

Devin vs Unstoppable

Devin scores 55.7 (C) on agent readiness against Unstoppable's 34.9 (F), and leads in 5 of 7 scored categories. Unstoppable leads on reliability and payments & pricing. Both do agent harnesses.

Best agent harnesses and coding agents · All 833 harnesses comparisons

DevinCognition AI, Inc. · Agent harness C55.7/100#757 of 1217 UnstoppableUnstoppable Domains, Inc. · Agent harness F34.9/100#1132 of 1217

Which one, for what

Devin C

Best for A team that wants to hand whole tasks to a cloud agent and collect pull requests, driven from a pipeline or another agent.

Ahead on

  • Schema & documentation, 80 against 30
  • Agent ergonomics, 62 against 5
  • Security & auth, 72 against 36
  • Maintenance & community, 63 against 58
  • Transparency & trust, 69 against 58

Also in its favour

  • A hosted endpoint, with nothing to install

Watch for

www.devinstatus.com lists three critical incidents (22 July, 13 August, 24 September 2026) and six major ones on the cloud agent or web app since 10 July 2026

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.

Ahead on

  • Reliability, 45 against 30
  • Payments & pricing, 30 against 20

Also in its favour

  • No key needed to call it
  • Free to start without a card

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 runDevinUnstoppableEdge
Reliability16%203045Unstoppable +15
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28030Devin +50
Agent ergonomics13%16.2625Devin +57
Security & auth14%17.57236Devin +36
Payments & pricing10%12.52030Unstoppable +10
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.86358Devin +5
Transparency & trust7%8.86958Devin +11
Negative events≤1500
TotalC 55.7/100F 34.9/100

Facts side by side

FactDevinUnstoppable
KindAgent harnessAgent harness
VendorCognition AI, Inc.Unstoppable Domains, Inc.
Hosted endpointhttps://mcp.devin.ai/mcpno (local only)
TransportsHTTP
AuthAPI keyNone
PricingFreemiumFreemium
x402nono
LicenceProprietary service under Cognition's Platform Terms of ServiceProprietary, under Unstoppable Domains, Inc.'s Terms of Service. No source published
Tools exposed13none
Read-only variant documentedyesno
llms.txtyesyes
Last release2026-10-072026-10-23
Terms last updated2026-06-30
Privacy policy last updated2026-03-09
Customer content may train modelsyes, with an opt-out
Terms restrict automated accessnot found in the text
Terms restrict benchmarkingyes
Terms or service can change without noticenot found in the text
Arbitration or class-action waiveryes

Verdicts

Devin

The v3 API is well specified, with a public OpenAPI 3.1 file covering 239 operations, problem+json errors, cursor pagination and service-user keys tied to roles. The status page records three critical and several major incidents on the cloud agent between 22 July and 24 September 2026, and no rate limit figures or retry guidance were found in the reviewed documentation.

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

Devin

  1. Use a cog_ service-user key with the Member role. Legacy apk_ keys fail against v3 and the MCP server with 401 or 403
  2. Set max_acu_limit on every session you create. Usage is metered by the work done and has no published unit rate
  3. Session creation is not idempotent in v3. After a timeout, list sessions by tag before creating again
  4. Enterprise keys and personal access tokens must send X-Org-Id to the MCP server. Organisation-scoped keys resolve it automatically
  5. Create scheduled work as an automation. POST to the schedules endpoint returns 403 for migrated organisations since 24 September 2026

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, Devin or Unstoppable?

Devin scores 55.7 (C) on agent readiness against Unstoppable's 34.9 (F), and leads in 5 of 7 scored categories. Unstoppable leads on reliability and payments & pricing.

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