Claude Sonnet 4.5 vs GPT-5.3-Codex
Claude Sonnet 4.5 (2025) and GPT-5.3-Codex (2026) are agentic coding models from Anthropic and OpenAI. Claude Sonnet 4.5 ships a 200K-token context window, while GPT-5.3-Codex ships a 400K-token context window. On pricing, GPT-5.3-Codex costs $1.75/1M input tokens versus $3/1M for the alternative. This comparison covers specs, pricing, capabilities, benchmarks, provider availability, and production fit. It focuses on practical selection signals rather than broad model-family marketing.
GPT-5.3-Codex is ~71% cheaper at $1.75/1M; pay for Claude Sonnet 4.5 only for vision-heavy evaluation.
Decision scorecard
Local evidence first| Signal | Claude Sonnet 4.5 | GPT-5.3-Codex |
|---|---|---|
| Decision fit | RAG, Agents, and Long context | Coding, RAG, and Agents |
| Context window | 200K | 400K |
| Cheapest output | $15/1M tokens | $14/1M tokens |
| Provider routes | 7 tracked | 2 tracked |
| Shared benchmarks | 0 rows | 0 rows |
Decision tradeoffs
- Claude Sonnet 4.5 has broader tracked provider coverage for fallback and procurement flexibility.
- Claude Sonnet 4.5 uniquely exposes Multimodal in local model data.
- Local decision data tags Claude Sonnet 4.5 for RAG, Agents, and Long context.
- GPT-5.3-Codex has the larger context window for long prompts, retrieval packs, or transcript analysis.
- GPT-5.3-Codex has the lower cheapest tracked output price at $14/1M tokens.
- GPT-5.3-Codex uniquely exposes Code execution in local model data.
- 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 prices on this page.
Claude Sonnet 4.5
$6,150
Cheapest tracked route: Microsoft Foundry
GPT-5.3-Codex
$4,900
Cheapest tracked route: OpenRouter
Estimated monthly gap: $1,250. Batch, cache, and negotiated pricing are excluded from this local estimate.
Switch friction
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- GPT-5.3-Codex is $1/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Check replacement coverage for Multimodal before moving production traffic.
- GPT-5.3-Codex adds Code execution in local capability data.
- Provider overlap exists on OpenRouter; start route-level A/B tests there.
- Claude Sonnet 4.5 is $1/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Code execution before moving production traffic.
- Claude Sonnet 4.5 adds Multimodal in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2025-09-29 | 2026-02-05 |
| Context window | 200K | 400K |
| Parameters | — | — |
| Architecture | decoder only | decoder only |
| License | Proprietary | Proprietary |
| Knowledge cutoff | 2025-12 | 2025-08 |
Pricing and availability
| Pricing attribute | Claude Sonnet 4.5 | GPT-5.3-Codex |
|---|---|---|
| Input price | $3/1M tokens | $1.75/1M tokens |
| Output price | $15/1M tokens | $14/1M tokens |
| Providers |
Capabilities
| Capability | Claude Sonnet 4.5 | GPT-5.3-Codex |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | No |
| Reasoning | Yes | Yes |
| Function calling | Yes | Yes |
| Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | No | Yes |
Benchmarks
No shared benchmark rows are currently sourced for this pair.
Deep dive
The capability footprint differs most on multimodal input: Claude Sonnet 4.5 and code execution: GPT-5.3-Codex. Both models share vision, reasoning mode, function calling, and tool use, so the practical split is not just feature count. Use those differences to decide whether the page is about raw model quality, agentic coding support, multimodal ingestion, or predictable structured API behavior.
For cost, Claude Sonnet 4.5 lists $3/1M input and $15/1M output tokens, while GPT-5.3-Codex lists $1.75/1M input and $14/1M output tokens on the cheapest tracked provider. A 70/30 input-output blend puts GPT-5.3-Codex lower by about $1.17 per million blended tokens. Availability is 7 providers versus 2, so concentration risk also matters.
Choose Claude Sonnet 4.5 when vision-heavy evaluation and broader provider choice are central to the workload. Choose GPT-5.3-Codex when coding workflow support, larger context windows, and lower input-token cost are more important. For production, rerun your own prompts through the exact provider, region, and tool stack you plan to ship. This keeps the decision grounded in measurable tradeoffs instead of brand-level assumptions. It also helps separate model capability from provider packaging, which can change cost and latency.
FAQ
Which has a larger context window, Claude Sonnet 4.5 or GPT-5.3-Codex?
GPT-5.3-Codex supports 400K tokens, while Claude Sonnet 4.5 supports 200K tokens. That gap matters most for long documents, large codebases, retrieval-heavy agents, and conversations where earlier context must remain visible.
Which is cheaper, Claude Sonnet 4.5 or GPT-5.3-Codex?
GPT-5.3-Codex is cheaper on tracked token pricing. Claude Sonnet 4.5 costs $3/1M input and $15/1M output tokens. GPT-5.3-Codex costs $1.75/1M input and $14/1M output tokens. Provider discounts or batch pricing can still change the final bill.
Is Claude Sonnet 4.5 or GPT-5.3-Codex open source?
Claude Sonnet 4.5 is listed under Proprietary. GPT-5.3-Codex is listed under Proprietary. License labels affect whether you can self-host, redistribute weights, or rely only on hosted APIs, so confirm the upstream license before deployment.
Which is better for vision, Claude Sonnet 4.5 or GPT-5.3-Codex?
Both Claude Sonnet 4.5 and GPT-5.3-Codex expose vision. The better choice depends on benchmark fit, context budget, pricing, and whether your provider route exposes the same capability surface. Use this as a quick comparison signal, then confirm the provider-specific limits before committing to production.
Which is better for multimodal input, Claude Sonnet 4.5 or GPT-5.3-Codex?
Claude Sonnet 4.5 has the clearer documented multimodal input signal in this comparison. If multimodal input is mission-critical, validate it against the provider endpoint because model-level support and API-level exposure can differ.
Where can I run Claude Sonnet 4.5 and GPT-5.3-Codex?
Claude Sonnet 4.5 is available on Microsoft Foundry, Anthropic, Snowflake Cortex, GCP Vertex AI, and AWS Bedrock. GPT-5.3-Codex is available on OpenRouter and OpenAI API. Provider coverage can affect latency, region availability, compliance posture, and fallback options.
Continue comparing
Last reviewed: 2026-05-19. Data sourced from public model cards and provider documentation.