How Do I Combine Claude Opus and Codex in My Development Workflow?

Mar 19, 2026

Purpose

I kept hearing developers talk about using multiple AI models together, but I didn’t understand how. Wasn’t one good model enough? After trying both Claude Opus and Codex separately, I realized they solve different problems. The question wasn’t “which one?”—it was “how do I use both?”

This post shows the workflow I developed: Opus for thinking, Codex for executing.

The Problem

Using a single AI model for everything creates friction:

┌─────────────────────────────────────────────────────────────┐
│                   USING ONLY ONE MODEL                       │
├─────────────────────────────────────────────────────────────┤
│                                                             │
│   With Opus Only:                                           │
│   ├── Great at planning, but implementation wanders        │
│   ├── Suggests alternatives when I need decisions           │
│   └── Too creative for precise execution                    │
│                                                             │
│   With Codex Only:                                          │
│   ├── Fast implementation, but misses context              │
│   ├── Follows instructions but lacks vision                 │
│   └── Doesn't help with "what should I build?"              │
│                                                             │
└─────────────────────────────────────────────────────────────┘

Neither tool optimizes for both strategic thinking and detailed implementation simultaneously. I needed a way to use each for its strengths.

The Solution: Think-Then-Execute

My workflow now follows this pattern:

Opus → Think through the problem, define spec/structure
  ↓
Codex → Execute the well-defined tasks
  ↓
Opus → Review and refine

Phase 1: Strategic Planning (Claude Opus)

I start with Opus for:

Problem analysis and decomposition
Architecture design and decisions
Specification writing
Task breakdowns

What this looks like in practice:

Project: User Authentication System

Architecture Decision:
├── JWT tokens for stateless auth
├── Refresh token rotation
├── Bcrypt for password hashing
└── Rate limiting for login attempts

Task Breakdown:
1. Create user model with validation
2. Implement password hashing utility
3. Build JWT generation service
4. Create login endpoint
5. Add refresh token logic
6. Implement logout functionality

Opus helps me think through edge cases, consider alternatives, and create a solid plan before writing code.

Phase 2: Implementation (Codex)

Each task from Opus gets passed to Codex with full context:

Task: Create a User model

Prompt to Codex:
"Create a User model with email validation, password field,
and timestamps. Use TypeScript with proper typing.
Include input validation for email format and password strength."

Codex output: Clean, precise code that follows the spec.

Codex shines at this step. It takes well-defined tasks and executes them without unnecessary interpretation or alternatives.

Phase 3: Quality Assurance (Both)

After implementation, I use both for review:

Review Type	Model	Purpose
Architecture review	Opus	Does this fit the bigger picture?
Code review	Codex	Are there bugs or edge cases?
Security review	Both	Different models catch different issues
Documentation	Codex	Generate from the implemented code

Advanced Technique: Model Roleplay

For complex decisions, I use both models in conversation:

Round 1: Opus Proposes
─────────────────────
"I recommend GraphQL because:
 - Flexible querying
 - Single endpoint
 - Strong typing
 However, consider complexity for simple use cases..."

Round 2: Codex Implementation Feedback
─────────────────────────────────────
"Implementing GraphQL here requires:
 - Apollo Server setup (~2 days)
 - Schema definitions for 15 entities
 - 40+ resolver files
 Alternative: REST would be faster to implement
 and easier for team onboarding..."

Round 3: Opus Final Decision
───────────────────────────
"Based on implementation feedback, use REST for MVP:
 - Faster time to market
 - Team already familiar
 - Can migrate later if needed
 Here's the revised API structure..."

This technique improves decisions. When I tell models their output goes to another model for review, they sharpen their reasoning.

Todo-Driven Development

One pattern that works well: I ask Codex to create a todo.md from Opus’s specifications.

## Authentication Implementation

- [x] Design user schema (Opus completed)
- [ ] Create user model file
  - [ ] Define SQLAlchemy model
  - [ ] Add email validation
  - [ ] Add password hashing hook
- [ ] Implement password utilities
  - [ ] Create utils/password.py
  - [ ] Add bcrypt hashing
- [ ] Build login endpoint
  - [ ] POST /auth/login route
  - [ ] Request validation
- [ ] Add OAuth2 support
  - [ ] Google OAuth flow
  - [ ] GitHub OAuth flow

Codex then executes each task while I track progress. This combines Opus’s planning with Codex’s execution.

Common Mistakes

Mistake 1: Using Codex for architecture Codex generates code fast, but misses long-term implications. Always start with Opus for architectural thinking.

Mistake 2: Skipping specifications Direct code generation without specs leads to inconsistent results. Create detailed specs with Opus first.

Mistake 3: One-pass workflow One-and-done generation misses quality improvements. Implement review cycles between models.

Mistake 4: Not documenting handoffs When switching models, document context. Without it, the handoff loses information.

Why This Works

┌─────────────────────────────────────────────────────────────┐
│                                                             │
│   Claude Opus Strengths:          Codex Strengths:          │
│   ────────────────────           ──────────────────         │
│   Deep reasoning                 Fast code generation       │
│   Context understanding          Execution accuracy         │
│   Architectural thinking         Technical implementation   │
│   Exploring alternatives         Following instructions     │
│                                                             │
│   ───────────────────────────────────────────────────────   │
│                                                             │
│   Opus: "What should we build and why?"                     │
│   Codex: "How do we build exactly that?"                     │
│                                                             │
└─────────────────────────────────────────────────────────────┘

The benefits I’ve seen:

Faster development through parallel processing
Higher quality from structured specifications
Less rework from better upfront planning
More maintainable code from thoughtful architecture

Summary

In this post, I showed how to combine Claude Opus and Codex in a development workflow. The key point is: use Opus for thinking (planning, architecture, specs) and Codex for executing (implementation, precise code).

Start with a 15-minute Opus planning session before writing any code. Create specifications, break down tasks, then pass each task to Codex with full context. Review the output with both models to catch different types of issues.

This multi-model approach produces better-architected, more maintainable code than using either model alone.

Final Words + More Resources

My intention with this article was to help others share my knowledge and experience. If you want to contact me, you can contact by email: Email me

Here are also the most important links from this article along with some further resources that will help you in this scope:

👨‍💻 Reddit Discussion: Codex vs Opus Workflow

Oh, and if you found these resources useful, don’t forget to support me by starring the repo on GitHub!