Claude Sonnet 5 'Fennec' Leaked: Anthropic's Next-Gen AI Model Launching Tomorrow

BREAKING: A major leak from Google's Vertex AI platform has revealed what appears to be Anthropic's next flagship AI model - Claude Sonnet 5, codenamed "Fennec" - set to launch on February 6, 2026.

The Leak: What We Know

Between February 1-2, multiple developers independently discovered identical model identifiers in Vertex AI logs: claude-sonnet-5@20260203. The internal codename "Fennec" - a desert fox known for its distinctively large ears - appears to be a playful reference to the model's most impressive feature.

The timing couldn't be more significant. With Claude Code already hitting $1 billion ARR in just six months, Anthropic is doubling down on what's working: AI that can actually code.

Record-Breaking Specifications

SWE-Bench Dominance: 82.1%

The most stunning revelation is Fennec's performance on SWE-Bench, the gold standard benchmark for evaluating AI coding capabilities. At 82.1%, this would represent a significant leap over current models and firmly establish Anthropic's lead in agentic coding.

For context, SWE-Bench tests models on real software engineering tasks - fixing actual bugs, implementing features, and navigating complex codebases. An 82.1% score means Fennec can solve the vast majority of real-world programming challenges.

1 Million Token Context Window

The "Fennec" codename makes sense now: big ears for listening to massive amounts of context.

A 1 million token context window means developers can feed entire codebases into a single conversation. No more chunking, no more losing context, no more explaining the same architecture repeatedly. This is transformative for enterprise development.

What 1M tokens can hold:

Complete monorepos with hundreds of files
Full documentation sets
Entire test suites alongside source code
Historical commit context

Aggressive Pricing: Half of Opus 4.5

Perhaps the most disruptive aspect is the pricing:

Model	Input (per 1M tokens)	Output (per 1M tokens)
Claude Sonnet 5 "Fennec"	$3	$15
Claude Opus 4.5	$6	$30

This positions Fennec as the optimal choice for agentic workflows where high token throughput is essential but cost still matters.

Built for Agentic Workflows

Sources indicate Fennec was specifically optimized for multi-agent architectures:

One agent writes APIs while another generates tests
A manager agent oversees and coordinates
Parallel execution with shared context

This matches the industry shift toward "agentic AI" - autonomous systems that can break down complex tasks and collaborate to solve them.

Running on Google TPUs

The Vertex AI logs confirm Fennec runs on Google's Tensor Processing Units, explaining the competitive pricing. Google's infrastructure investment is paying dividends for Anthropic's scaling strategy.

What This Means for Developers

Immediate Implications

Cost reduction: Teams running Opus 4.5 for coding tasks can potentially halve their AI compute costs
Larger projects: The 1M context window enables working with enterprise-scale codebases in single sessions
Better reliability: The 82.1% SWE-Bench score suggests fewer hallucinations and more accurate code generation

The Agentic Future

Fennec appears designed for a world where:

AI agents collaborate on complex projects
Human developers orchestrate rather than implement
Code review becomes AI-assisted validation
Entire feature development cycles are automated

Industry Response

The leak has sent ripples through the AI industry:

OpenAI is reportedly scrambling with GPT-5 development timelines
Google may accelerate Gemini 2.5 Pro release plans
Enterprise customers are already inquiring about migration paths

Verification Status

Multiple independent sources have confirmed seeing identical Vertex AI logs, lending significant credibility to the leak. The consistent model identifier (claude-sonnet-5@20260203) and matching specifications across reports suggest this is legitimate.

What Happens Tomorrow?

If the February 6 launch date holds, we can expect:

Official announcement from Anthropic
API access rollout (likely phased)
Updated Claude Code integration
Detailed technical documentation

The Bigger Picture

This leak represents more than just a new model announcement. It's a signal that:

Anthropic is winning the agentic AI race - Their focus on code-first capabilities is paying off
Context windows are the new battleground - 1M tokens sets a new standard
Pricing pressure is increasing - Competition benefits developers
The future is multi-agent - Single-model paradigms are becoming obsolete

Stay tuned for official confirmation. We'll update this article as more information becomes available.

Note: This article is based on leaked information that has not been officially confirmed by Anthropic. Specifications and launch dates may change.