Claude Sonnet 4.6 vs GPT-5.5 Instant
Claude Sonnet 4.6 (2026) and GPT-5.5 Instant (2026) are frontier reasoning models from Anthropic and OpenAI. Claude Sonnet 4.6 ships a 1m-token context window, while GPT-5.5 Instant ships a 400k-token context window. On MMMU Pro, GPT-5.5 Instant leads by 0.4 pts. On pricing, Claude Sonnet 4.6 costs $3/1M input tokens versus $5/1M for the alternative. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.
Claude Sonnet 4.6 is ~67% cheaper at $3/1M; pay for GPT-5.5 Instant only for coding workflow support.
Decision scorecard
Local evidence first| Signal | Claude Sonnet 4.6 | GPT-5.5 Instant |
|---|---|---|
| Best for | reasoning-heavy apps, multimodal apps, and tool-calling agents | multimodal apps and tool-calling agents |
| Decision fit | Coding, RAG, and Agents | Coding, RAG, and Agents |
| Context window | 1m | 400k |
| Cheapest output | $15/1M tokens | $30/1M tokens |
| Provider routes | 6 tracked | 1 tracked |
| Shared benchmarks | 1 shared | MMMU Pro leader |
Decision tradeoffs
- Claude Sonnet 4.6 has the larger context window for long prompts, retrieval packs, or transcript analysis.
- Claude Sonnet 4.6 has the lower cheapest tracked output price at $15/1M tokens.
- Claude Sonnet 4.6 has broader tracked provider coverage for fallback and route flexibility.
- Claude Sonnet 4.6 uniquely exposes Reasoning, Computer use, and Parallel agents in local model data.
- Local decision data tags Claude Sonnet 4.6 for Coding, RAG, and Agents.
- GPT-5.5 Instant holds a shared-benchmark lead on MMMU Pro, ahead by 0.4 points.
- Local decision data tags GPT-5.5 Instant 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 Sonnet 4.6
$6,150
Cheapest tracked route/tier: OpenRouter
GPT-5.5 Instant
$11,500
Cheapest tracked route/tier: OpenAI API
Estimated monthly gap: $5,350. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.
Switch friction
- No overlapping tracked provider route is sourced for Claude Sonnet 4.6 and GPT-5.5 Instant; plan for SDK, billing, or endpoint changes.
- GPT-5.5 Instant is $15/1M tokens higher on cheapest tracked output pricing, so quality gains need to justify the spend.
- Check replacement coverage for Reasoning, Computer use, and Parallel agents before moving production traffic.
- No overlapping tracked provider route is sourced for GPT-5.5 Instant and Claude Sonnet 4.6; plan for SDK, billing, or endpoint changes.
- Claude Sonnet 4.6 is $15/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
- Claude Sonnet 4.6 adds Reasoning, Computer use, and Parallel agents in local capability data.
Specs
| Specification | ||
|---|---|---|
| Released | 2026-02-17 | 2026-05-05 |
| Context window | 1m | 400k |
| Parameters | — | — |
| Architecture | Decoder Only | Decoder Only |
| License | Proprietary | Proprietary |
| Openness | Proprietary | Proprietary |
| Weights | Not released | Not released |
| Code | Unknown | Unknown |
| Commercial use | Commercial use: conditional | Commercial use: conditional |
| Knowledge cutoff | 2025-08 | 2025-08 |
Pricing and availability
| Pricing attribute | Claude Sonnet 4.6 | GPT-5.5 Instant |
|---|---|---|
| Input price | $3/1M tokens | $5/1M tokens |
| Output price | $15/1M tokens | $30/1M tokens |
| Providers |
Capabilities
| Capability | Claude Sonnet 4.6 | GPT-5.5 Instant |
|---|---|---|
| Vision | Yes | Yes |
| Multimodal | Yes | Yes |
| Reasoning | Yes | No |
| JSON / Tool use | Yes | Yes |
| Structured outputs | Yes | Yes |
| Code execution | Yes | Yes |
| IDE integration | No | No |
| Computer use | Yes | No |
| Parallel agents | Yes | No |
Benchmarks
| Benchmark | Claude Sonnet 4.6 | GPT-5.5 Instant |
|---|---|---|
| MMMU Pro | 75.6 | 76.0 |
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Last reviewed: 2026-07-26. Data sourced from public model cards and provider documentation.