Claude Opus 4.8 vs GPT-5.3-Codex
Claude Opus 4.8 and GPT-5.3-Codex are the direct 2026 API-model choice for agentic software engineering. Opus is the stronger high-autonomy pick: it leads on SWE-bench Pro, SWE-bench Verified, OSWorld computer use, provider breadth, and 1M-token context. GPT-5.3-Codex is the lower-cost OpenAI-native option, with a narrow Terminal-Bench 2.0 edge and first-class fit for teams already standardized on Codex CLI and OpenAI API workflows.
Pick Claude Opus 4.8 for autonomous repo work, complex multi-file engineering, computer-use agents, and long-context sessions: it leads GPT-5.3-Codex by 12.4 points on SWE-bench Pro and 18.7 points on OSWorld, with 1M context versus 400K. Pick GPT-5.3-Codex for cost-sensitive coding pipelines, OpenAI-native Codex workflows, and terminal automation where its $1.75/M input price and 77.3% Terminal-Bench 2.0 score matter more than the harder agent benchmarks.
Decision scorecard
Local evidence first| Signal | Claude Opus 4.8 | GPT-5.3-Codex |
|---|---|---|
| Product type | Standalone API model | Coding-specialized model |
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | custom coding agents, code generation, and tool loops |
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 1m | 400k |
| Cheapest output | $25/1M tokens | $14/1M tokens |
| Provider routes | 6 tracked | 3 tracked |
| Shared benchmarks | SWE-bench Verified leader | 2 shared |
Decision tradeoffs
- Claude Opus 4.8 holds a shared-benchmark lead on SWE-bench Verified, ahead by 3.6 points.
- Claude Opus 4.8 has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Claude Opus 4.8 has broader tracked provider coverage for fallback and route flexibility.
- Claude Opus 4.8 uniquely exposes Multimodal and Parallel agents in local model data.
- Local decision data tags Claude Opus 4.8 for Coding, RAG, and Agents.
- GPT-5.3-Codex has the lower cheapest tracked output price at $14/1M tokens.
- Local decision data tags GPT-5.3-Codex for Coding, RAG, and Agents.
Monthly cost at traffic
Estimate token spend from the cheapest tracked input and output route or tier on this page.
Claude Opus 4.8
$10,250
Cheapest tracked route/tier: Anthropic
GPT-5.3-Codex
$4,900
Cheapest tracked route/tier: OpenRouter
Estimated monthly gap: $5,350. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
- GPT-5.3-Codex is $11/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Multimodal and Parallel agents before moving production traffic.
- Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
- Claude Opus 4.8 is $11/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Claude Opus 4.8 adds Multimodal and Parallel agents in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-05-28 | 2026-02-05 |
| Context window | 1m | 400k |
| Parameters | — | — |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Weights | Not released | Not released |
| Code | Not released | Unknown |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | 2026-01 | 2025-08 |
Pricing and availability
| Pricing attribute | Claude Opus 4.8 | GPT-5.3-Codex |
|---|---|---|
| Input price | $5/1M tokens | $1.75/1M tokens |
| Output price | $25/1M tokens | $14/1M tokens |
| Providers |
Capabilities
| Capability | Claude Opus 4.8 | GPT-5.3-Codex |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | No |
| Reasoning | Yes | Yes |
| JSON / Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | Yes |
| IDE integration | No | No |
| Computer use | Yes | Yes |
| Parallel agents | Yes | No |
Benchmarks
| Benchmark | Claude Opus 4.8 | GPT-5.3-Codex |
|---|---|---|
| SWE-bench Verified | 88.6 | 85.0 |
| SWE-bench Pro | 69.2 | 56.8 |
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Last reviewed: 2026-07-26. Data sourced from public model cards and provider documentation.