After six months of using GPT-5.6 as my primary coding model, I switched to Claude Opus 5 for two weeks. Not because GPT was bad, but because Opus 5 launched at $5/$25 and I wanted to see if the hype was justified.
Here is what actually changed, with no marketing spin.
My workflow
I work on a TypeScript monorepo (180K lines, 12 packages). My daily tasks include:
- Code review and refactoring
- Bug fixes and debugging
- Feature development
- Writing tests
- Documentation
I use Claude Code as my primary coding agent. Before the switch, I was using GPT-5.6 Sol through OpenRouter.
What got better
1. Complex refactoring
Opus 5 handles multi-file refactoring significantly better than GPT-5.6 Sol. When I asked both models to refactor a database access layer across 8 files, Opus 5 made consistent changes across all files in one pass. GPT-5.6 required 3 iterations to catch edge cases.
2. Code review quality
Opus 5’s code reviews are more thorough. It catches subtle issues like race conditions, memory leaks, and security vulnerabilities that GPT-5.6 often misses. The 5-level effort control means I can dial up reasoning for security-critical code.
3. Long-context understanding
With 1M context and 128K max output, Opus 5 handles large codebases better. I can paste an entire module (50K+ tokens) and get accurate analysis. GPT-5.6 Sol’s 128K context is smaller, and the output limit sometimes truncates responses.
4. Instruction following
Opus 5 follows complex, multi-step instructions more reliably. When I write detailed specs for a feature, Opus 5 implements them as written. GPT-5.6 sometimes interprets instructions creatively, which is frustrating when you need exact behavior.
What got worse
1. Speed
Opus 5 at ~80 tok/s is noticeably slower than GPT-5.6 Sol at ~150 tok/s. For interactive coding sessions, the slower speed adds up. Simple questions that take 2 seconds with Sol take 4-5 seconds with Opus 5.
2. Cost
At $5/$25, Opus 5 is actually slightly cheaper on output than Sol at $5/$30. But I use fast mode at $10/$50 for time-sensitive tasks, which pushes my effective spend above Sol’s standard pricing. If you stick to Opus 5’s standard tier, it is competitive with or cheaper than Sol. If you lean on fast mode often, budget for a higher bill.
3. Creative writing
For creative writing tasks (marketing copy, blog post drafts), GPT-5.6 produces more engaging, varied output. Opus 5 is more precise and structured, which is better for technical writing but worse for creative work.
4. Availability
During peak hours, Opus 5 sometimes hits rate limits or returns slower responses. GPT-5.6 Sol has better availability in my experience.
What stayed the same
1. Simple coding tasks
For straightforward tasks (add a button, fix a typo, write a simple function), both models perform identically. The difference only shows up in complex, multi-step work.
2. Test generation
Both models generate good unit tests. Opus 5 catches slightly more edge cases, but the difference is marginal for most test suites.
3. Documentation
Both models write clear, accurate documentation. No meaningful difference.
4. Onboarding to my codebase
Both models needed the same amount of context to work effectively: a project README, a summary of the folder structure, and a couple of example files showing our conventions. Neither model figured out our internal naming conventions without being told explicitly. This surprised me a little, I expected Opus 5’s reasoning to infer more from context alone, but in practice both models need the same upfront investment.
5. Handling ambiguous requests
When I gave both models a deliberately vague ticket (“the search feature feels slow, look into it”), neither jumped straight to a fix. Both asked clarifying questions about which search, what “slow” means in this context, and whether I wanted a diagnosis or a fix. That was reassuring. Neither model guessed wildly at an ambiguous request.
Team rollout considerations
Switching one developer’s workflow is easy. Rolling this out to a team is a different decision. A few things I would flag before recommending a full switch:
- Cost predictability. Opus 5’s per-task cost varies more than Sol’s, since complex tasks trigger more reasoning tokens. Budget for variance, not just an average.
- Consistency across the team. If half your team uses Opus 5 and half uses Sol, code review conventions may drift slightly, since the models have different “voices” in generated comments and commit messages.
- Onboarding cost. Expect a short adjustment period. Developers used to GPT-5.6’s more flexible interpretation of instructions need to write slightly more explicit prompts to get the most out of Opus 5’s literal instruction-following.
The cost breakdown
Over two weeks of daily use:
| Metric | GPT-5.6 Sol | Claude Opus 5 |
|---|---|---|
| Daily spend | $8-12 | $10-15 |
| Tasks completed | ~50/day | ~45/day |
| Cost per task | $0.18 avg | $0.28 avg |
| Rework rate | 12% | 8% |
Opus 5 costs more per task but has a lower rework rate. The total cost difference is about 30% more for Opus 5.
My take
For complex, multi-step coding work, Opus 5 is worth the switch. The better instruction following, long-context understanding, and code review quality justify the higher cost and slower speed.
For simple, high-volume coding tasks, GPT-5.6 Sol is better. The faster speed and lower cost matter when you are doing 50+ tasks per day.
My current setup: Opus 5 for complex work (20% of tasks), GPT-5.6 Luna at $0.20/$1.20 for simple work (80% of tasks). This hybrid approach gives me the best of both worlds.
If you are on a budget, start with Luna and Sonnet 5. Only switch to Opus 5 when you need the extra reasoning capability.
FAQ
Should I switch from GPT to Claude?
It depends on your work. For complex coding, yes. For simple tasks, no. For most developers, a hybrid approach (Luna for simple, Opus 5 for complex) is optimal.
Is Claude Opus 5 better than GPT-5.6 Sol?
For reasoning and instruction following, yes. For speed and availability, no. For cost, they are similar. The best choice depends on your specific workflow.
What about Claude Sonnet 5?
Sonnet 5 at $2/$10 is the best value for most tasks. It is faster than Opus 5 (180 vs 80 tok/s) and cheaper. Use Sonnet 5 as your default and escalate to Opus 5 only when needed.
Can I use both models?
Yes. Most developers use multiple models for different tasks. Use Luna for bulk work, Sonnet 5 for quality, and Opus 5 for complex problems. Model routing saves money and improves results.
What is the biggest difference?
Instruction following. Opus 5 does what you ask, exactly as you ask it. GPT-5.6 sometimes interprets instructions creatively. For precise, multi-step tasks, Opus 5’s reliability matters.
Related: Claude Opus 5 Complete Guide | GPT-5.6 Sol, Terra, Luna Complete Guide | Claude Opus 5 vs GPT-5.6 Sol | How to Use Claude Code | GPT-5.6 Luna Price Drop