LLM Reference

Claude Sonnet 4.5 vs o3

Claude Sonnet 4.5 (2025) and o3 (2025) are frontier-tier reasoning models from Anthropic and OpenAI. Claude Sonnet 4.5 ships a 200k-token context window, while o3 ships a 200k-token context window. On SWE-bench Verified, Claude Sonnet 4.5 leads by 5.5 pts. This comparison covers specs, pricing, API access, capabilities, benchmarks, input and output token costs, and production fit for coding and agent workloads.

Claude Sonnet 4.5 is safer overall; choose o3 when coding workflow support matters.

Decision scorecard

Local evidence first
SignalClaude Sonnet 4.5o3
Best forreasoning-heavy apps, multimodal apps, and tool-calling agentsreasoning-heavy apps, multimodal apps, and tool-calling agents
Decision fitCoding, RAG, and AgentsCoding, RAG, and Agents
Context window200k200k
Cheapest output$15/1M tokens$8/1M tokens
Provider routes8 tracked3 tracked
Shared benchmarksSWE-bench Verified leader4 shared

Decision tradeoffs

Choose Claude Sonnet 4.5 when...
  • Claude Sonnet 4.5 holds a shared-benchmark lead on SWE-bench Verified, ahead by 5.5 points.
  • Claude Sonnet 4.5 has broader tracked provider coverage for fallback and route flexibility.
  • Local decision data tags Claude Sonnet 4.5 for Coding, RAG, and Agents.
Choose o3 when...
  • o3 holds a shared-benchmark lead on Google-Proof Q&A, ahead by 4.3 points.
  • o3 has the lower cheapest tracked output price at $8/1M tokens.
  • o3 uniquely exposes Code execution in local model data.
  • Local decision data tags o3 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.

Lower estimate o3

Claude Sonnet 4.5

$6,150

Cheapest tracked route/tier: Microsoft Foundry

o3

$3,600

Cheapest tracked route/tier: OpenAI API

Estimated monthly gap: $2,550. Batch, cache, alternate speed tiers, and negotiated pricing are excluded from this local estimate.

Switch friction

Claude Sonnet 4.5 -> o3
  • Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
  • o3 is $7/1M tokens lower on cheapest tracked output pricing before cache, batch, or negotiated discounts.
  • o3 adds Code execution in local capability data.
o3 -> Claude Sonnet 4.5
  • Provider overlap exists on OpenRouter and Vercel AI Gateway; start route-level A/B tests there.
  • Claude Sonnet 4.5 is $7/1M 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.

Specs

Specification
Released2025-09-292025-04-16
Context window200k200k
Parameters——
ArchitectureDecoder OnlyDecoder Only
LicenseProprietaryProprietary
OpennessProprietaryProprietary
WeightsNot releasedNot released
CodeUnknownUnknown
Commercial useCommercial use: conditionalCommercial use: conditional
Knowledge cutoff2025-122024-06

Pricing and availability

Pricing attributeClaude Sonnet 4.5o3
Input price
0-200,001t
$3/1M tokens
200,001t+
$6/1M tokens
$2/1M tokens
Output price
0-200,001t
$15/1M tokens
200,001t+
$22.50/1M tokens
$8/1M tokens
Providers
Microsoft FoundryAnthropicSnowflake CortexGCP Vertex AIAWS BedrockReplicate API
OpenAI APIOpenRouterVercel AI Gateway

Capabilities

CapabilityClaude Sonnet 4.5o3
VisionYesYes
MultimodalYesYes
ReasoningYesYes
JSON / Tool useYesYes
Structured outputsYesYes
Code executionNoYes
IDE integrationNoNo
Computer useNoNo
Parallel agentsNoNo

Benchmarks

BenchmarkClaude Sonnet 4.5o3
SWE-bench Verified77.271.7
Google-Proof Q&A83.487.7
Massive Multi-discipline Multimodal Understanding77.882.9
MMMU Pro68.976.4

Continue comparing

Model pages
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Last reviewed: 2026-07-26. Data sourced from public model cards and provider documentation.