Claude Sonnet 5 Just Leaked. Anthropic Might Drop It During the Super Bowl.

Developers found 'claude-sonnet-5@20260203' in Google Vertex AI logs. Codenamed 'Fennec,' early tests show it matches Opus performance at half the price.

The Discovery

Early Tuesday morning, a developer running routine API diagnostics noticed something unusual in their Google Vertex AI logs: a model endpoint they hadn't seen before.

``` claude-sonnet-5@20260203 ```

Within hours, the discovery spread through developer communities on X and Discord. By noon Eastern, the evidence was mounting.

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What We Know

The Model Identifier

FieldValue Model nameclaude-sonnet-5 Version date20260203 (February 3, 2026) Internal codename'Fennec' (per Anthropic employee Slack leak) First sightingGoogle Vertex AI StatusNot publicly accessible

Early Benchmark Leaks

Anonymous sources claiming access to internal benchmarks shared these numbers:

BenchmarkSonnet 5Opus 4.5Sonnet 4.5 MMLU89.2%90.1%85.8% HumanEval93.1%94.1%88.4% MATH82.4%83.2%74.6% GPQA68.9%70.2%61.3% Key insight: Sonnet 5 appears to match or exceed Opus 4.5 on coding benchmarks while trailing slightly on pure knowledge tasks.

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The Super Bowl Theory

Why This Weekend?

Multiple factors point to a Super Bowl Sunday announcement:

1. Maximum visibility — 115 million+ viewers, the largest single-day audience in American media 2. Competitive timing — OpenAI has been quiet; Anthropic could dominate the news cycle 3. Historical pattern — Anthropic has launched major products during unexpected moments 4. Employee chatter — Slack messages suggest 'something big' is coming

The Precedent

Apple's famous 1984 Super Bowl ad launched the Macintosh. Google has run Super Bowl ads for AI products. An Anthropic announcement during the game would be unprecedented but effective.

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What This Means for Pricing

Current Claude Pricing

ModelInput (per 1M tokens)Output (per 1M tokens) Opus 4.5$15.00$75.00 Sonnet 4.5$3.00$15.00 Haiku 4.5$0.25$1.25

Expected Sonnet 5 Pricing

If Sonnet 5 matches Opus performance at Sonnet pricing, the value proposition is dramatic:

- 5x cheaper input than Opus - 5x cheaper output than Opus - Near-identical performance on key benchmarks

This would effectively make Opus 4.5 the 'premium' option for edge cases, with Sonnet 5 becoming the default for most applications.

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Developer Implications

If You're Building on Claude

Prepare now: 1. Abstract your model selection logic 2. Build A/B testing infrastructure 3. Define your evaluation criteria 4. Set up cost monitoring On release: 1. Test on your specific use case immediately 2. Compare output quality, not just benchmarks 3. Measure latency and throughput 4. Calculate actual cost savings

Migration Considerations

```python

Good: Model selection abstracted

model = get_model_for_task(task_type) response = client.messages.create(model=model, ...)

Bad: Hardcoded model

response = client.messages.create(model='claude-opus-4-5-20251101', ...) ```

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The Competitive Landscape

How This Affects the Market

ProviderCurrent BestAfter Sonnet 5 AnthropicOpus 4.5 ($15/75)Sonnet 5 (~$3/15) at Opus level OpenAIGPT-5 TurboPrice pressure likely GoogleGemini 2 UltraMay accelerate Gemini 3 MetaLlama 4Open source alternative

The Price War Continues

Sonnet 5 at rumored pricing would be: - 5x cheaper than GPT-5 Turbo at comparable quality - 50x cheaper than Opus for equivalent performance - The most cost-effective frontier model ever released

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Skeptic's Corner

Reasons for Caution

1. Vertex logs can be misleading — Model names appear before launch during testing 2. Benchmark leaks are unverified — Anonymous sources may be wrong 3. Super Bowl timing is speculation — Anthropic has denied nothing because they've said nothing 4. 'Fennec' codename is unconfirmed — Could be misinformation

What We Don't Know

- Actual pricing - Context window size - Vision/multimodal capabilities - Availability timeline - Whether it exists at all

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Timeline

DateEvent Feb 3, 2026Model version date (20260203) Feb 4, 2026First public sighting in Vertex logs Feb 8, 2026Today — speculation peaks Feb 9, 2026Super Bowl Sunday — potential launch? Feb 10, 2026If no launch, expectations deflate

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What to Watch

Signals of Imminent Launch

- Anthropic social media activity - Claude.ai interface changes - API documentation updates - Employee social media silence (often precedes announcements) - Press embargo lifts

Where to Get Official News

1. anthropic.com/news 2. @AnthropicAI on X 3. Claude API changelog 4. Anthropic Discord

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The Bottom Line

Whether Sonnet 5 drops during the Super Bowl or not, the model is clearly coming. The Vertex AI sighting, combined with Anthropic's release cadence, suggests weeks rather than months.

If the leaked benchmarks are accurate, this could be the most significant AI release of 2026: Opus-level performance at a fraction of the cost.

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