TokenMix Research Lab · 2026-04-10
GPT-5.4 Codex is OpenAI's dedicated coding model line, designed specifically for code generation, review, and agentic software engineering tasks. The lineup consists of two models: GPT Codex (the full-power version at
| Spec | GPT Codex | GPT Codex Mini |
|---|---|---|
| Base Model | GPT-5.4 (code-optimized) | GPT-5.4 Mini (code-optimized) |
| Input Price/M | .75 | $0.15 (special) / $0.40 (standard) |
| Output Price/M | 4.00 | $0.60 (special) / .60 (standard) |
| Cached Input/M | $0.44 | $0.04 (special) / $0.10 (standard) |
| Context Window | 1M tokens | 128K tokens |
| Max Output | 32K tokens | 16K tokens |
| SWE-bench Verified | ~80% | ~68% |
| HumanEval | ~95% | ~89% |
| Agentic Coding | Yes (Codex CLI) | Yes (Codex CLI) |
| Tool Use | Full function calling | Full function calling |
| Computer Use | Native | Native |
GPT-5.4 Codex is not just GPT-5.4 with a different name. It is a code-specialized variant that OpenAI has fine-tuned and optimized specifically for software engineering tasks. The key differences from base GPT-5.4:
Code-specific fine-tuning. Trained with emphasis on code generation, code review, debugging, refactoring, and test writing. Produces more structured, production-ready code compared to base GPT-5.4.
Agentic coding integration. Designed to work with OpenAI's Codex CLI, which provides a command-line coding agent similar to Claude Code. The model understands file system operations, test execution, git workflows, and multi-file editing patterns.
Optimized pricing. GPT Codex at .75/ 4 is 30% cheaper on input than base GPT-5.4 ($2.50/ 5). Codex Mini with special pricing ($0.15/$0.60) is 62% cheaper on input than standard GPT-5.4 Mini.
Code-aware context handling. The model's context management is optimized for code — it handles file references, import chains, and cross-file dependencies more effectively than the general-purpose model.
The Codex lineup directly targets Anthropic's Claude Code and the growing market for AI-powered software engineering tools. It represents OpenAI's answer to the question: can a dedicated coding model beat general-purpose models on code tasks?
GPT Codex is the flagship coding model. It takes GPT-5.4's full reasoning capabilities and adds code-specific optimizations.
GPT Codex scores approximately 80% on SWE-bench Verified, matching base GPT-5.4. On HumanEval (code generation benchmark), it reaches approximately 95%, slightly above base GPT-5.4's estimated 93%. The improvement is more noticeable on practical coding tasks: multi-file refactoring, test generation, and bug fixing show 10-15% better completion rates compared to base GPT-5.4 in TokenMix.ai internal testing.
The Codex CLI is OpenAI's equivalent of Claude Code. It provides:
The CLI uses GPT Codex as its default model, with automatic prompt engineering for agentic coding workflows. The user experience is similar to Claude Code: describe what you want, and the agent reads the relevant code, makes changes, runs tests, and iterates until the task is complete.
What it does well:
Trade-offs:
Best for: Teams invested in the OpenAI ecosystem who want the best coding model available from OpenAI. Complex software engineering tasks requiring deep reasoning and large codebase understanding.
Codex Mini is the cost-optimized coding model, based on GPT-5.4 Mini with code-specific fine-tuning. It offers two pricing tiers — standard and special — making it one of the most flexible options for coding workloads.
| Tier | Input/M | Output/M | Cached Input/M | When Available |
|---|---|---|---|---|
| Standard | $0.40 | .60 | $0.10 | Always |
| Special | $0.15 | $0.60 | $0.04 | During off-peak or batch |
The special pricing tier is available for batch API requests and during off-peak hours. At $0.15/$0.60, Codex Mini becomes one of the cheapest proprietary coding models available — only 2x the cost of DeepSeek V4 while maintaining stronger instruction following and more consistent output quality.
Codex Mini scores approximately 68% on SWE-bench Verified and 89% on HumanEval. This places it firmly in the "good enough for most tasks" category. It handles:
Where it falls short compared to full Codex: complex architectural reasoning, large-scale refactoring, and tasks requiring deep understanding of unfamiliar codebases.
What it does well:
Trade-offs:
Best for: High-volume coding tasks where cost efficiency matters. Autocomplete, test generation, documentation writing, simple bug fixes, and code formatting. Teams that use Codex Mini for routine tasks and escalate to full Codex for complex ones.
| Model | Input/M | Output/M | Cached/M | Target Use |
|---|---|---|---|---|
| GPT Codex | .75 | 4.00 | $0.44 | Complex coding |
| GPT-5.4 (base) | $2.50 | 5.00 | $0.63 | General + coding |
| Claude Opus 4 | 5.00 | $75.00 | $3.75 | Premium coding |
| Claude Sonnet 4.6 | $3.00 | 5.00 | $0.75 | Balanced coding |
| Codex Mini (standard) | $0.40 | .60 | $0.10 | Routine coding |
| Codex Mini (special) | $0.15 | $0.60 | $0.04 | Budget coding |
| DeepSeek V4 | $0.30 | $0.50 | $0.07 | Cheapest frontier |
Key pricing insights:
GPT Codex is 30% cheaper than base GPT-5.4 on input, 7% cheaper on output. If you are already using GPT-5.4 for coding, switching to Codex saves money with equal or better coding performance.
Codex Mini special pricing is competitive with DeepSeek V4. At $0.15/$0.60 vs. $0.30/$0.50, Codex Mini is cheaper on input but more expensive on output. For input-heavy workloads (code review, analysis), Codex Mini special can be cheaper than DeepSeek V4.
Claude Opus 4 is 8.5x more expensive than GPT Codex on input. The quality premium for Claude's coding capabilities comes at a steep price.
Codex models support prompt caching with aggressive discounts:
| Model | Standard Input | Cached Input | Savings |
|---|---|---|---|
| GPT Codex | .75/M | $0.44/M | 75% |
| Codex Mini (standard) | $0.40/M | $0.10/M | 75% |
| Codex Mini (special) | $0.15/M | $0.04/M | 73% |
For coding agents that send the same codebase context repeatedly, caching reduces input costs by 75%. A coding agent processing a 100K-token codebase context across 50 requests saves $8.75 in input costs on GPT Codex alone ( .75 vs. $0.44 per million tokens, applied to 5M cached tokens).
| Benchmark | GPT Codex | Codex Mini | Claude Opus 4 | Claude Sonnet 4.6 | DeepSeek V4 |
|---|---|---|---|---|---|
| SWE-bench Verified | ~80% | ~68% | ~75% | ~73% | ~81% |
| HumanEval | ~95% | ~89% | ~93% | ~92% | ~90% |
| MBPP | ~91% | ~84% | ~89% | ~88% | ~87% |
| CodeContests | ~42% | ~28% | ~38% | ~35% | ~40% |
| Aider Polyglot | ~78% | ~62% | ~82% | ~75% | ~73% |
GPT Codex matches DeepSeek V4 on SWE-bench (80% vs. 81%), within margin of error. For automated issue resolution, both are top-tier.
HumanEval advantage. GPT Codex's 95% on HumanEval is the highest in this comparison, suggesting it excels at self-contained code generation tasks.
Aider Polyglot gap. Claude Opus 4 leads on Aider's multi-language coding benchmark (82% vs. 78% for Codex), indicating better performance in interactive coding sessions across languages.
Codex Mini holds up. At 68% SWE-bench and 89% HumanEval, Codex Mini handles most routine coding tasks. The 12-point SWE-bench gap with full Codex only matters for complex, multi-file autonomous tasks.
This is the central comparison. Both are agentic coding tools backed by frontier models.
Claude Code uses Claude Opus 4 (default for complex tasks) and Claude Sonnet 4.6 (for faster operations). The Codex CLI uses GPT Codex.
On raw benchmarks, GPT Codex edges out Claude on SWE-bench (80% vs 75% for Opus) and HumanEval (95% vs 93%). Claude Opus 4 leads on Aider Polyglot (82% vs 78%), suggesting better performance in interactive, multi-language coding sessions.
Subjectively, Claude Code produces more readable, better-documented code. GPT Codex generates more efficient, performance-oriented code. The difference is stylistic and depends on team preferences.
| Scenario | Claude Code (Opus 4) | Codex CLI (GPT Codex) | Codex CLI (Codex Mini) |
|---|---|---|---|
| Simple task (10K in, 2K out) | $0.300 | $0.046 | $0.005 (special) |
| Complex task (100K in, 10K out) | $2.250 | $0.315 | $0.021 (special) |
| Full-day coding (1M in, 200K out) | $30.000 | $4.550 | $0.270 (special) |
GPT Codex is 6.5x cheaper than Claude Opus 4 for coding tasks. Codex Mini at special pricing is 60-110x cheaper. This is the defining cost difference.
| Feature | Claude Code | Codex CLI |
|---|---|---|
| CLI tool maturity | Mature, widely adopted | Newer, growing |
| IDE integration | VS Code extension | VS Code extension |
| Git integration | Built-in | Built-in |
| Test execution | Built-in | Built-in |
| Computer use | Beta | Native |
| Multi-model routing | No (Anthropic only) | No (OpenAI only) |
| Community size | Large | Growing |
Verdict: Claude Code has a more mature ecosystem and arguably better code quality. Codex CLI is dramatically cheaper and has stronger computer use capabilities. For budget-conscious teams, the cost difference is decisive. For teams where code quality and developer experience are paramount, Claude Code justifies its premium.
DeepSeek V4 is the elephant in the room for coding model comparisons. It matches or beats GPT Codex on SWE-bench (81% vs 80%) at a fraction of the cost.
| Dimension | GPT Codex | DeepSeek V4 |
|---|---|---|
| SWE-bench Verified | ~80% | ~81% |
| HumanEval | ~95% | ~90% |
| Code quality (subjective) | High | Good |
| Instruction following | Excellent | Good |
| Error recovery | Excellent | Fair |
| Consistency | High | Moderate |
| Scenario | GPT Codex | DeepSeek V4 | Codex Premium |
|---|---|---|---|
| 1M input + 200K output | $4.55 | $0.40 | 11.4x |
| 100K coding tasks/month | $45,500 | $4,000 | 11.4x |
GPT Codex costs 11.4x more than DeepSeek V4 for the same token volume. The question is whether the 5-point HumanEval advantage, better error recovery, and higher consistency justify this premium.
TokenMix.ai enables teams to use both models through a single API: DeepSeek V4 for volume tasks and GPT Codex for quality-critical tasks. This hybrid approach typically costs 40-60% less than using GPT Codex exclusively while maintaining quality where it matters.
| Feature | GPT Codex | Codex Mini | Claude Opus 4 | Claude Sonnet 4.6 | DeepSeek V4 |
|---|---|---|---|---|---|
| Input/M | .75 | $0.15-$0.40 | 5.00 | $3.00 | $0.30 |
| Output/M | 4.00 | $0.60- .60 | $75.00 | 5.00 | $0.50 |
| Context Window | 1M | 128K | 200K | 200K | 1M |
| SWE-bench | ~80% | ~68% | ~75% | ~73% | ~81% |
| HumanEval | ~95% | ~89% | ~93% | ~92% | ~90% |
| Agentic CLI | Codex CLI | Codex CLI | Claude Code | Claude Code | Third-party |
| Computer Use | Native | Native | Beta | Beta | No |
| API Uptime | ~99.5% | ~99.5% | ~99.3% | ~99.3% | ~97-98% |
| Best For | Full-stack coding | Routine coding | Premium coding | Balanced coding | Budget coding |
| Model | Monthly Cost |
|---|---|
| GPT Codex | $23 |
| Codex Mini (special) | .35 |
| Claude Code (Opus 4) | 50 |
| DeepSeek V4 | $2 |
| Model | Monthly Cost |
|---|---|
| GPT Codex | $228 |
| Codex Mini (special) | 4 |
| Claude Code (Opus 4) | ,500 |
| DeepSeek V4 | $20 |
| Model | Monthly Cost |
|---|---|
| GPT Codex | $910 |
| Codex Mini (special) | $54 |
| Claude Code (Opus 4) | $6,000 |
| DeepSeek V4 | $80 |
| Your Situation | Best Choice | Why |
|---|---|---|
| OpenAI ecosystem, want best coding | GPT Codex | Top HumanEval, 30% cheaper than GPT-5.4 |
| High-volume routine coding | Codex Mini (special) | $0.15/$0.60 is near-cheapest |
| Maximum code quality, cost no issue | Claude Opus 4 | Best subjective code quality |
| Cheapest frontier-quality coding | DeepSeek V4 | 81% SWE-bench at $0.30/$0.50 |
| Balanced quality and cost | GPT Codex or Claude Sonnet 4.6 | Mid-range pricing, strong performance |
| CI/CD automation at scale | Codex Mini | Low cost, adequate quality for automated tasks |
| Startup with tight budget | DeepSeek V4 + Codex Mini hybrid | Route by task complexity |
GPT-5.4 Codex is OpenAI's strongest play in the coding model market. GPT Codex delivers top-tier performance at 30% less than base GPT-5.4, and Codex Mini's special pricing makes it one of the cheapest proprietary coding options available.
The competitive landscape is clear: Claude Code (via Opus 4) produces the best code quality but at the highest price. DeepSeek V4 matches Codex on SWE-bench at 1/6th the cost. Codex Mini at special pricing offers the sweet spot — proprietary model quality at near-open-source pricing.
For most teams, the optimal strategy is a multi-model approach: Codex Mini for routine tasks, GPT Codex for complex tasks, and DeepSeek V4 as a cost-efficient fallback. TokenMix.ai enables this routing through a single API integration with automatic model selection based on task complexity and budget constraints.
GPT Codex is a code-specialized variant of GPT-5.4 that OpenAI has optimized for software engineering tasks. It is 30% cheaper on input ( .75 vs $2.50 per million tokens), shows 10-15% better performance on practical coding tasks, and integrates with OpenAI's Codex CLI for agentic coding workflows. It shares the same 1M context window and general architecture.
GPT Codex costs .75/M input and 4.00/M output tokens. Codex Mini has two tiers: standard ($0.40/ .60) and special ($0.15/$0.60). Cached input tokens are discounted 75%. A solo developer using approximately 5M tokens per month pays roughly $23 for GPT Codex or .35 for Codex Mini at special pricing.
GPT Codex scores higher on HumanEval (95% vs 93%) and SWE-bench (80% vs 75%). Claude Code (via Opus 4) scores higher on Aider Polyglot (82% vs 78%) and subjectively produces more readable, better-documented code. GPT Codex is 6.5x cheaper. Choose Codex for cost efficiency and OpenAI ecosystem; choose Claude for code quality and mature agentic tooling.
Codex Mini special pricing ($0.15/$0.60 per million tokens) is available for batch API requests and during off-peak hours. It is 62% cheaper than standard Codex Mini pricing and competitive with DeepSeek V4. Availability depends on server capacity, but TokenMix.ai tracking shows special pricing is available 60-80% of the time.
GPT Codex via the Codex CLI is designed for different use cases than Copilot. Copilot excels at inline code completion within an IDE. Codex CLI excels at agentic multi-file tasks (refactoring, test writing, bug fixing) from the command line. Many developers use both: Copilot for real-time suggestions and Codex for larger tasks. They are complementary, not substitutes.
DeepSeek V4 scores 1 point higher on SWE-bench (81% vs 80%) and costs 5.8x less ($0.30/$0.50 vs .75/ 4). GPT Codex scores 5 points higher on HumanEval (95% vs 90%) and offers better instruction following, error recovery, and output consistency. Choose DeepSeek V4 for budget-sensitive batch coding. Choose GPT Codex for interactive, quality-critical coding work.
Author: TokenMix Research Lab | Last Updated: April 2026 | Data Source: OpenAI, Anthropic, DeepSeek, TokenMix.ai