The rumors were true. And then the logs leaked.
Yesterday, February 3, 2026, the AI community spotted a ghost in the machine: claude-sonnet-5-20260203.
Found in Google Vertex AI's backend configuration logs, this string confirms that Anthropic's next-generation workhorse model, codenamed "Fennec", is not just in training—it's deployed.
Here is everything we know about the model that is about to redefine the "Price-Performance" ratio for developers.
The Leak: What Does 20260203 Mean?
The leaked ID follows Anthropic's strict versioning convention:
- Family:
claude-sonnet(The balanced "Workhorse" tier). - Generation:
5(A full generation leap over 3.5/4.5). - Date:
20260203(February 3rd, 2026).
Crucially, dates in API IDs usually represent a "snapshot" aimed for stability. The fact that this snapshot exists on a major cloud provider (Vertex AI) suggests a public release is imminent—likely within days.
The Specs: Why "Fennec" is a Beast
If the leaked benchmarks are to be believed, Sonnet 5 isn't just an "update." It's a paradigm shift.
1. The New Coding King (SWE-bench 82.1%)
For the past year, we've been impressed by scores in the 60s and 70s. Sonnet 5 reportedly shatters the ceiling with a SWE-bench Verified score of 82.1%.
This score puts it squarely in "Autonomous Engineer" territory. It doesn't just write snippets; it solves complex repository-level issues with a success rate that rivals human interns.
2. Aggressive Pricing ($3 / 1M Tokens)
This is the killer feature.
- Opus 4.5: ~$15 / 1M input tokens.
- Sonnet 5: $3 / 1M input tokens.
You are getting performance better than the previous flagship (Opus) for 20% of the price. This aggressive pricing strategy seems targeted directly at destroying the competition in the "Agentic AI" market, where agents need to read millions of tokens of context to do their job.
3. Built for Agents
"Fennec" (the Earless Fox) is known for its hearing. Similarly, Sonnet 5 is rumored to have vastly improved Listening (Context) capabilities. It is designed to be the engine for long-running autonomous agents (like Moltbot / OpenClawd)).
- Self-Correction: High tolerance for multi-step reasoning errors.
- Tool Use: Specifically optimized for calling external APIs without hallucinating parameters.
What This Means for Developers
1. Opus 4.5 is Obsolete (mostly) Unless you need the absolute maximum creative writing nuance of Opus, Sonnet 5 is now the default choice for logic, coding, and data extraction.
2. The Age of "Local" Agents With pricing this low, running a personal agent that reads your entire email inbox every morning is no longer a luxury—it's a commodity.
3. Wisdom Gate Support
We are already prepping our gateways. The moment claude-sonnet-5-20260203 goes live on the Anthropic/Vertex API, it will be available on Wisdom Gate.
Get Ready for Fennec. Ensure your credit balance is topped up and your agents are configured. Check Wisdom Gate Models