Claude Opus 4.6 vs GPT-5.3 Codex: Complete Comparison

Release Context

Claude Opus 4.6 and GPT-5.3-Codex launched one day apart in February 2026 — Anthropic on February 4 and OpenAI on February 5. Both represent flagship coding-focused upgrades to their respective model families, making this the closest head-to-head release window in AI model history.

For detailed coverage of each model individually, see our Claude Opus 4.6 guide and GPT-5.3 Codex guide.

Head-to-Head Benchmarks

The pattern is clear: Claude Opus 4.6 leads on reasoning-heavy benchmarks (GPQA Diamond, MMLU Pro, TAU-bench), while GPT-5.3-Codex dominates terminal and computer-use workloads (Terminal-Bench, OSWorld). For how the previous generation compared, see our Claude 4.5 vs GPT-5.2 vs Gemini 3 comparison.

Coding & Agentic Capabilities

Both models target the same goal — autonomous software engineering — but take different architectural approaches. Here is how their coding capabilities compare across key dimensions.

In practice, Claude's strength lies in thoughtful, quality-focused code generation with visible reasoning, while GPT-5.3 excels when speed and throughput matter for large-scale agentic work. For broader patterns on multi-model agentic workflows, see our AI agent orchestration guide.

Beyond Coding: Reasoning & Multimodal

Coding ability is only part of the picture. Both models serve as general-purpose reasoning engines, and their non-coding capabilities influence how useful they are across a full engineering workflow.

Both models support vision capabilities for image and document analysis. Claude tends to produce more structured, detailed document summaries, while GPT-5.3 adds native desktop automation through OSWorld capabilities. For a broader landscape of AI coding tools beyond these two models, see our AI coding tools comparison.

Pricing & Availability

Claude's transparent per-token pricing makes cost modeling straightforward. OpenAI's Codex is available through subscription tiers today, with API token pricing expected in the coming weeks. For the GPT model lineage leading to this release, see our GPT-5.2 Codex model guide.

Safety & Security Approaches

Both companies have invested heavily in safety for these releases, but with distinctly different philosophies and frameworks.

Anthropic emphasizes behavioral alignment through constitutional constraints, while OpenAI focuses on structured deployment gates and ecosystem-level defenses. Both approaches represent the most comprehensive safety stacks either company has shipped to date. For the broader GPT-5 family context, see our OpenAI GPT-5 complete guide.

Which Model Should You Choose?

Implementation Recommendations

If your team decides to use both models, a routing configuration with fallback logic keeps things reliable. Here is a minimal pattern for task-based model routing.

// config/model-routing.ts
const MODEL_CONFIG = {
  reasoning: {
    model: "claude-opus-4-6",
    fallback: "gpt-5.3-codex",
    use: "GPQA-heavy analysis, long-context docs",
  },
  coding: {
    model: "gpt-5.3-codex",
    fallback: "claude-opus-4-6",
    use: "Agentic loops, terminal tasks, refactors",
  },
  maxRetries: 3,
  timeoutMs: 120_000,
};

Migration guidance

• From Claude Opus 4.5: Remove any response prefilling code (now disabled in 4.6), migrate extended thinking calls to adaptive thinking budget levels, and test compaction API for long-running sessions.
• From GPT-5.2-Codex: Keep 5.2 as failover while API access rolls out for 5.3. Pre-wire config toggles and observability dashboards. Run parallel evals on your real repositories.
• Multi-model setup: Use environment variables or feature flags for model routing. Track accepted patches, reruns, and reviewer edits per model to measure actual engineering throughput.

Frequently Asked Questions