DeepSeek Harness vs Claude Code vs Codex: Open-Source Agent Frameworks Compared

DeepSeek Harness passed 170,000 GitHub stars within 11 days of release. Claude Code took more than a year to reach 140,000. Codex took 15 months to reach 103,000. The star count alone does not make a tool better. It does tell you where developer attention is moving.

This comparison covers three coding agent frameworks: DeepSeek Harness (dsh), Claude Code, and OpenAI Codex. We compare architecture, benchmarks, pricing, and extension models as of August 24, 2026.

Sources: DeepSeek Harness repo, OpenAI Codex stats, Claude Code pricing, DeepSeek API pricing, DeepSeek Claude Code integration, Codex custom providers

What Is an Agent Harness?

An agent harness is the layer between a language model and the real world. It gives the model file access, shell commands, tool calls, session logs, and approval rules. Without a harness, a model can only answer text. With a harness, it can edit code, run tests, and finish tasks.

Claude Code and Codex package this layer as commercial products. DeepSeek Harness makes the entire layer open source and replaceable. That difference shapes everything else in this comparison.

Quick Verdict

DeepSeek Harness: Everything Is a Plugin

DeepSeek published dsh on August 13, 2026 under the MIT license. The repo shows 170.8k stars, 18.4k forks, and 12,940 commits as of this writing. It is written in TypeScript and built on Cordis, a plugin kernel described in the paper A Programming Paradigm for Spatiotemporal Composability.

The core idea is simple: every capability is a plugin. Models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and the web UI are all swappable from configuration. There is no privileged core to patch.

Three concepts carry most of the design:

Profiles and bundles. A running instance is a plugin tree built at boot. The shipped profiles are web and headless. Each profile stacks bundles, and any config row can be replaced with a patch file. Teams override behavior without forking the code.

The session log. The append-only event log is the single source of truth for what the model sees. The documentation calls this invariant "model-visible means logged". Forking, resuming, and telemetry all come from this stream.

Capability seams. A seam is a swappable capability with three roles: service definition, provider, and consumer. Pointing the filesystem and subprocess providers at a remote sandbox moves Bash, PTY, and LSP tools with them.

The model adapter is just another plugin. You can run dsh against DeepSeek, Anthropic, OpenAI, or any OpenAI-compatible endpoint, including local models via Ollama. Claude Code and Codex are optimized for their vendors' models.

Claude Code: The Mature Commercial Agent

Claude Code is Anthropic's terminal-native coding agent. It reached roughly 140k GitHub stars by July 2026 and 20.2 million VS Code extension installs. It runs in your shell, reads your codebase, and handles git workflows in plain English.

Its extension system covers skills, hooks, MCP servers, and plugins. Anthropic is building a platform, not a chat wrapper. A change on June 15, 2026 split programmatic usage into a separate credit pool. Pro plans get a $20 monthly credit for the Agent SDK, claude -p, and GitHub Actions.

Claude Code is proprietary. The default setup works only with Anthropic models and an Anthropic account. You can point it at DeepSeek through the Anthropic-compatible API. DeepSeek documents this setup for Claude Code with environment variables. Local models are not supported.

OpenAI Codex: The Cloud-Connected Agent

Codex CLI launched in April 2025 under Apache 2.0 and was rewritten in Rust in June 2025. It reached 103,504 stars and over 5 million weekly users by July 2026. npm downloads hit 46.9 million over the last 30 days.

Codex spans more than the terminal: CLI, IDE extensions for VS Code and Cursor, a desktop app, a cloud agent at chatgpt.com/codex, and iOS. Cloud integrations include automatic code review and Slack.

The CLI is open source. The cloud agents and desktop app sit behind ChatGPT subscriptions, and billing moved to token-based credits on April 2, 2026. Codex also supports custom model providers through config.toml, so you can point it at DeepSeek or other OpenAI-compatible endpoints.

Architecture Comparison

Sources: VentureBeat launch analysis via flowtivity, gradually.ai Codex stats

Benchmarks: What the Numbers Really Measure

Benchmark results are the hardest part of this comparison to read. Each vendor reports its own numbers with its own methodology.

Two caveats matter.

DeepSeek's numbers are self-reported. The company tested V4-Pro-0813 inside its own Harness in minimal mode. Some headline results measure the model inside DeepSeek's execution environment, not the model alone. The same table shows Fable 5 ahead of DeepSeek on Toolathlon-Verified (77.9) and DSBench-FullStack (77.2).

Claude Code's score comes from a third-party scan. The 78.9 figure for Opus 4.8 on Terminal-Bench 2.1 comes from morphllm's 2026 CLI comparison, not from Anthropic. Anthropic does not publish a Terminal-Bench score for Claude Code.

Treat all four rows as directional, not as a race result.

Pricing: Free Software, Paid Models

DeepSeek Harness is free. The MIT license permits commercial use, modification, and redistribution. You pay only for model API usage. Because the model adapter is a plugin, you can point it at Ollama and pay nothing beyond your own hardware.

Claude Code starts at $20 per month for Pro. Max plans cost $100 or $200 per month. Team Premium is $100 per seat with a 5-seat minimum. Pay-per-token API billing is also available. The June 15, 2026 programmatic credit change means heavy SDK use draws from a separate pool.

Codex starts at $20 per month through ChatGPT Plus. Billing is token-based since April 2, 2026. The cloud agent and desktop app require a paid plan.

DeepSeek API Pricing Changed on August 16, 2026

DeepSeek replaced flat API pricing with peak and off-peak rates on August 16, 2026. Peak windows are 01:00-04:00 UTC and 06:00-10:00 UTC, Monday through Friday.

V4-Pro output at peak is $3.96 per million tokens, up from $0.87 flat. That is a 355 percent increase. Off-peak rates are half of peak, and cache hits cost a fraction of cache-miss input.

The pricing shift does not change the tool comparison. dsh software stays free. It changes the operating cost of running DeepSeek models inside any agent. Early testers report a 99 percent cache hit rate inside dsh, which cuts effective input costs dramatically on repeated tasks.

Source: DeepSeek API pricing, techtimes pricing report

Extension Model: The Real Difference

All three tools support plugins. The difference is scope.

Claude Code extends through skills, hooks, MCP servers, and plugins. The core product is fixed; you add around it.

Codex extends through skills, MCP, and custom agents. The core is fixed; you add around it.

DeepSeek Harness replaces the core itself. The agent loop, the model adapter, the session log, the sandbox, and the UI are all plugins. Remove one, and the system returns to the exact state it had before that plugin loaded. The Cordis paper proves this property, called compositional recovery. It validates the design on Koishi, a chatbot framework with 4,000 plugins running in production for four years.

For most developers, Claude Code's fixed core is a feature, not a limitation. It works well without configuration. dsh's replaceable core matters most to agent builders. It also matters to teams that swap models frequently, and to anyone who audits every token that reaches a model.

When Each Tool Makes Sense

Choose DeepSeek Harness when:

• You build agents or agent infrastructure, not just use them
• You want to swap models as prices shift
• You need to inspect and audit the full runtime
• You want local models with no vendor lock-in
• You accept developer-preview instability

Choose Claude Code when:

• You want the most mature coding agent today
• You work in VS Code, JetBrains, or the terminal
• You value the highest user satisfaction ratings
• You prefer a product over a framework
• You accept Claude as the default model (DeepSeek works through env config)

Choose Codex when:

• You live inside the OpenAI ecosystem
• You need cloud agents and automatic code review
• You want the strongest current Terminal-Bench score
• You accept OpenAI as the default model (DeepSeek works through config.toml)

How to Start with DeepSeek Harness

Install Node.js, then run one command:

npx @deepseek-ai/dsh web

The command starts a web UI at http://127.0.0.1:3080. Open Settings, then Models, and paste a DeepSeek API key. Pick a workspace, then start a session.

The download is heavy. The first npx pull takes several minutes on a fast connection. Expect a full application, not a lightweight script.

A headless profile ships for one-shot runs, and a Python SDK covers programmatic use. Community guides describe working Ollama and OpenRouter setups in under ten minutes.

Bottom Line

DeepSeek Harness is the most architecturally ambitious of the three. It is also the youngest, labeled a developer preview with breaking changes ahead. The repo warns in capitals: "THERE WILL BE COMPATIBILITY-BREAKING CHANGES."

Claude Code remains the safest default for everyday coding. Codex is the strongest choice inside the OpenAI world. dsh is the one to evaluate now if you build agents or want control over every layer.

The pattern dsh legitimizes, a fully composable agent runtime with auditable session logs and swappable everything, is the direction serious agent teams are moving. It is now available to anyone for free.