Comparison ruleKeep the model/provider explicit. A model-quality difference is not evidence about the harness.

Start with the product you are shipping.

DeepSeek Harness

Compose and ship the runtime graph: providers, Agent Loop, tools, policy, Sessions, and interfaces.

Claude Code

Give Claude a governed coding workspace and extend it with CLAUDE.md, Skills, MCP, hooks, agents, and plugins.

Codex

Use a repository-aware coding agent across local and hosted workflows with AGENTS.md, Skills, MCP, plugins, sandboxing, and approvals.

Hybrid

Use a coding agent to build DSH extensions, or expose shared services through MCP.

Do not translate names literally.

Session / threadstate contract

Carry a reviewed summary and artifacts, not a copied transcript.

Plugin / Skill / MCPextension contract

Rebuild discovery, activation, policy, and removal for the target.

Sandbox / permissioneffect contract

Test filesystem, network, process, escalation, and admin policy separately.

No universal winner.

Choose Claude Code or Codex when the coding-agent product is the desired boundary. Evaluate DeepSeek Harness when your deliverable is the inspectable, replaceable control plane itself.

Run one controlled evaluation.

same repository snapshot
 same bounded task
 explicit model/provider
 recorded tools and policy
 restart and recovery test

Compare completion evidence, effect containment, durable state, extension lifecycle, latency, provider cost, and operator time. Feature-name parity is not an acceptance test.

Primary evidence.

Keep the complete decision matrix.

The canonical guide includes seven product dimensions, migration traps, a practical selection test, ten evaluation gates, and official sources for all three products.

Read the complete comparison