Capability · Comparison
Claude 3.5 Sonnet vs GPT-4o
Claude 3.5 Sonnet and GPT-4o were the flagship mid-tier models of 2024. They still run in many production stacks. Claude 3.5 Sonnet was the first model to make coding agents feel genuinely reliable; GPT-4o pioneered real-time voice. For new work in 2026 both are superseded — but the comparison still explains a lot of how modern stacks look.
Side-by-side
| Criterion | Claude 3.5 Sonnet | GPT-4o |
|---|---|---|
| Context window | 200,000 tokens | 128,000 tokens |
| Coding (SWE-bench Verified) | ~49% (landmark 2024 score) | ~33% |
| MMLU | ~88% | ~88% |
| Multimodal | Text, vision | Text, vision, audio |
| Real-time voice | No | Yes — Realtime API |
| Tool-call reliability | Very strong | Strong |
| Pricing ($/M input) Historical rates. | $3 | $2.50 |
| Pricing ($/M output) | $15 | $10 |
| Status in 2026 | Legacy — replaced by Sonnet 4.5/4.6 | Legacy — replaced by GPT-5 mini |
Verdict
This was the defining 2024 matchup. Claude 3.5 Sonnet is the model that made coding agents possible and the foundation of every modern dev-tools IDE plugin. GPT-4o is the model that proved real-time voice could feel magical. Both have since been replaced by stronger successors; the comparison remains useful as a snapshot of the era that shaped today's stacks.
When to choose each
Choose Claude 3.5 Sonnet if…
- You have a legacy 3.5 Sonnet deployment that works and is pinned.
- You need a reproducible baseline for research or regression testing.
- You're on a legacy Bedrock contract.
- You need long context (200k) without upgrading yet.
Choose GPT-4o if…
- You have legacy voice infrastructure built on GPT-4o Realtime.
- Your stack is pinned to GPT-4o for reproducibility.
- You're on Azure OpenAI's legacy tier.
- You explicitly need unified audio in/out that GPT-4o pioneered.
Frequently asked questions
Should I still be using Claude 3.5 Sonnet in 2026?
Only for pinned deployments. Sonnet 4.6 is meaningfully better on every axis and costs roughly the same.
What replaced GPT-4o?
GPT-5 mini for cost-sensitive text+vision, GPT-5 for quality-critical multimodal. The Realtime API has migrated to newer models natively.
Why does this comparison still matter?
Because a huge fraction of production AI stacks still run one or both of these models. Understanding where they came from is useful when planning migrations.
Sources
- Anthropic — Claude 3.5 Sonnet — accessed 2026-04-20
- OpenAI — GPT-4o — accessed 2026-04-20