Claude Opus 4.6 vs GPT-5.3 Codex for Coding
A data-backed comparison of the two best AI coding models in Feb 2026. Benchmarks, pricing, and when to use each one.
Two models sit at the top of the AI coding stack right now: Claude Opus 4.6 and GPT-5.3 Codex. Both launched in February 2026. Both score above 95% on HumanEval. Both cost real money.
They're built for different jobs. Codex is a code generation machine with the largest output window in the business. Opus 4.6 is an agentic coding tool that plans, uses tools, and executes multi-step workflows. Picking the wrong one wastes either money or capability.
The Numbers
| Claude Opus 4.6 | GPT-5.3 Codex | |
|---|---|---|
| Input price | $5/1M tokens | $2/1M tokens |
| Output price | $25/1M tokens | $16/1M tokens |
| Context window | 200K (1M in beta) | 200K |
| Max output | 32K tokens | 65K tokens |
| HumanEval | 95.0% | 96.5% |
| MMLU-Pro | 89.5 | 90.0 |
| GPQA | 75.5 | 78.0 |
Source: EveryRank model data, cross-referenced with Anthropic and OpenAI pricing pages.
GPT-5.3 Codex wins on every measurable dimension except one: tool use. More on that below.
Where Codex Pulls Ahead
GPT-5.3 Codex has the highest HumanEval score of any model we track at 96.5%. That 1.5-point gap over Opus 4.6 is small on paper, but it translates to fewer syntax errors and edge-case failures in generated code. OpenAI built this model specifically for code, and it shows.
The 65K output window is what really separates them. If you're generating entire files, large refactors, or migration scripts, Codex can produce roughly twice as much code in a single response as Opus 4.6's 32K limit. For batch code generation workflows, that cuts your API calls in half.
Pricing seals the deal for pure generation tasks. At $2/$16 vs $5/$25, Codex is 2.5x cheaper on input and 36% cheaper on output. If you're running a pipeline that feeds large codebases in and gets code out, the cost difference adds up fast.
API access for GPT-5.3 Codex is still rolling out. If you need it today, GPT-5.2 Codex at $1.75/$14 is available now with 95.5% HumanEval.
Where Opus 4.6 Wins
Benchmarks tell you how well a model generates code in isolation. They don't tell you how well it works inside your development environment. And that's where Opus 4.6 pulls away.
Claude Opus 4.6 is the best model for agentic coding. It can use tools, run commands, read file trees, execute tests, and iterate on errors without you hand-holding each step. If you're using Claude Code, Cursor, or any IDE that gives the model tool access, Opus 4.6 will outperform Codex because it actually knows how to use those tools.
HumanEval measures writing a function from a docstring. That's a solved problem at 95%+. The hard part of AI-assisted coding in 2026 is everything around the code: understanding a project's structure, finding the right files to edit, running the test suite, fixing failures, and committing clean changes. Opus 4.6 handles the full loop. Codex generates the code and expects you to handle the rest.
Anthropic also offers a 1M context beta for Tier 4 users. For teams working on large monorepos, that means feeding an entire project into context instead of carefully selecting which files to include. Long-context pricing jumps to $10/$37.50 above 200K tokens, so it's not cheap, but for large-codebase refactoring it saves the engineering time you'd spend on context management.
Pricing Breakdown for Real Workloads
Abstract per-token pricing is hard to reason about. Here's what a typical coding session costs in dollars.
A mid-complexity coding task (reading ~50K tokens of context, generating ~5K tokens of output):
- Opus 4.6: $0.25 input + $0.125 output = $0.375 per task
- Codex: $0.10 input + $0.08 output = $0.18 per task
Over 100 tasks in a day, that's $37.50 vs $18. Over a month of weekday usage, roughly $750 vs $360. For a team of 5 developers, $3,750/month vs $1,800/month.
That gap is real. But it assumes both models need the same number of iterations to finish a task. In practice, Opus 4.6's tool use means it often resolves something in one shot that would take Codex 2-3 manual rounds. If an engineer's time costs $80/hour and each extra round takes 5 minutes, those saved iterations close the price gap quickly.
o3: The Budget Alternative
If your coding budget is tight, neither of these flagships is the right answer.
OpenAI's o3 at $0.40/$1.60 scores 94.5% on HumanEval. That's within 2 points of Opus 4.6 and 2 points of Codex, at a fraction of the price. It also has a 200K context window and 100K max output.
o3 is a reasoning model, so it's slower. It thinks through problems step-by-step, which eats into throughput. But for coding tasks where correctness matters more than speed, paying $0.028 per task instead of $0.18 or $0.375 is a 6-13x cost reduction for at most 2 percentage points on HumanEval.
| Model | Input | Output | HumanEval | Cost per task* |
|---|---|---|---|---|
| o3 | $0.40 | $1.60 | 94.5% | $0.028 |
| GPT-5.3 Codex | $2.00 | $16.00 | 96.5% | $0.18 |
| Claude Opus 4.6 | $5.00 | $25.00 | 95.0% | $0.375 |
*50K input tokens, 5K output tokens
Claude Sonnet 4.6 at $3/$15 and 94.0% HumanEval is another option worth considering. You get most of Opus's agentic capabilities at 40% lower cost, with the trade-off being slightly weaker performance on the hardest tasks.
So Which One Should You Actually Use?
Use GPT-5.3 Codex for bulk code generation. Migrations, boilerplate, scaffolding, any task where you need the model to produce a lot of code and you'll validate it yourself. The 65K output window and $2/$16 pricing make it the best pure code generator available.
Use Claude Opus 4.6 for IDE-integrated coding. If your workflow involves reading files, editing code, running tests, and iterating on failures, Opus's tool-use capabilities save more time than the benchmark gap costs. Especially in Claude Code, Cursor, or Windsurf where the model has full filesystem and terminal access.
Use o3 if budget matters and you can tolerate slower responses. 94.5% HumanEval at $0.40/$1.60 is the best value-for-quality ratio in AI coding right now.
The Bottom Line
GPT-5.3 Codex is the better code generator. Claude Opus 4.6 is the better coding partner.
If you think of AI as a function that turns prompts into code, Codex wins on price and raw output quality. If you think of AI as a junior developer that can work through your codebase, run your tests, and ship working changes, Opus 4.6 is ahead.
For most developers working inside an IDE in 2026, the agentic capabilities matter more than a 1.5% HumanEval gap. Opus 4.6 is my pick for daily coding work. For code generation pipelines or maximum output length, Codex. And for anyone watching their spend, o3 at $0.40/$1.60 is doing 94.5% HumanEval work for pennies.
Compare all three side-by-side on EveryRank.