WEEK OF DEC 13 – 19, 2025

Open weights hit 309B and frontier Flash went to $0.50/M — while the agent stack shipped three CVEs

In a single week, two open-weight families landed within a few points of closed frontier models on coding benchmarks, Google pushed frontier intelligence into the default search path, and Anthropic's own reference MCP server disclosed a prompt-injection chain to remote code execution.

The week of December 15 was decided by three numbers: 309, 15, and $0.50. Xiaomi shipped a 309-billion-parameter open-weight model that activates 15 billion per token, and Google's new default model in the Gemini app and AI Mode in Search costs $0.50 per million input tokens. NVIDIA, meanwhile, put its hybrid Mamba-Transformer Nemotron 3 Nano on Hugging Face with weights, data and recipes.

The same seven days produced the clearest example yet of agent infrastructure as attack surface. Three CVEs in Anthropic's official Git MCP server — the reference implementation developers are expected to copy — chain with a second MCP server to reach code execution through nothing more than a poisoned README. All three were patched in December, months after disclosure.

And OpenAI shipped a coding agent that set state of the art on terminal benchmarks, then published the detail that a security researcher using its previous coding model had found three previously unknown React vulnerabilities. Frontier capability and frontier capability-as-weapon arrived in the same blog post.

THU · Dec 18, 2025agentic codinglong horizoncompactionsecurityopenai

OpenAI ships GPT-5.2-Codex with native compaction — and says a coding agent found the React bugs

OpenAI released GPT-5.2-Codex on December 18 as a GPT-5.2 variant tuned for agentic coding in Codex, adding native context compaction for long-horizon work, stronger large-refactor and migration performance, improved tool calling and vision, and better behavior in native Windows environments. OpenAI says it reaches state of the art on SWE-Bench Pro and Terminal-Bench 2.0, and that it is the strongest cybersecurity model it has shipped while still falling short of High cyber capability under its Preparedness Framework. It rolled out the same day across Codex surfaces to paid ChatGPT users, with API access described as coming in the following weeks and an invite-only trusted-access pilot for vetted defensive security professionals.

The post also disclosed provenance for three React vulnerabilities published on December 11: a principal security engineer at Privy, using GPT-5.1-Codex-Max with Codex CLI, was working to reproduce the React2Shell RCE disclosed on December 3 when the model surfaced unexpected behavior, and a week of guided fuzzing under expert direction led to three previously unknown flaws that were responsibly disclosed and patched.

WHY IT MATTERS

Native compaction is the operationally meaningful line item: long agent sessions previously died on context limits mid-refactor, and a model that summarizes its own history changes how you size sessions, checkpoints and retries in your harness. The React disclosure is the second half of the argument — the same class of tool accelerates both finding and exploiting vulnerabilities, so if you automate patch discovery you should expect your dependency tree to be scanned by agent-driven attackers at the same rate. Note the access constraint: API availability is deferred and cyber-capable access is gated behind a vetting pilot, which is a procurement variable if you build security tooling.

WED · Dec 17, 2025securitymcpagent harnessprompt injection

Three CVEs in Anthropic's reference Git MCP server chain to remote code execution

Three advisories for mcp-server-git — Anthropic's official Git Model Context Protocol server — published on December 17 describe a path-validation bypass when the repository flag is set (CVE-2025-68145), an unrestricted git_init tool that would create a repository in any writable directory (CVE-2025-68143), and argument injection in git_diff and git_checkout that let an attacker overwrite arbitrary files with an empty diff (CVE-2025-68144). The fixes shipped in versions 2025.9.25 and 2025.12.18, and the git_init tool was deleted outright.

The chain matters more than the individual scores: agentic-security firm Cyata, which reported to Anthropic in June, demonstrated that git_init plus a Filesystem MCP server lets an attacker write a malicious .git/config with a clean filter and a .gitattributes file, so a later git_add call executes an attacker shell script. The entry point is indirect prompt injection — a README, a poisoned issue description, or a web page the assistant reads — and no user error is required. Cyata said it saw no indication of exploitation in the wild.

Three CVEs in Anthropic's reference Git MCP server chain to remote code execution
github.githubassets.com

WHY IT MATTERS

This is the canonical Git MCP server, the one teams copy when they wire their own — and it broke under composition, not under isolated misuse. Your threat model cannot be per-server: you need the effective, chained permissions of the whole agent (filesystem plus git plus shell) enumerated, and tool sets that can write .git/config or .gitattributes should be treated as code execution primitives. If you run mcp-server-git anywhere, pin to 2025.12.18 or later, and drop the Git and Filesystem servers from the same agent session unless the workflow genuinely requires both.

WED · Dec 17, 2025frontier modelspricinggooglerouting

Gemini 3 Flash becomes Google's default everywhere at $0.50/M input tokens

Google released Gemini 3 Flash on December 17 and immediately made it the default model in the Gemini app and in AI Mode in Search, replacing Gemini 2.5 Flash. Pricing is $0.50 per million input tokens and $3.00 per million output tokens, with a 1M-token context window and configurable thinking levels. Google reports 78% on SWE-bench Verified for agentic coding — claiming it edges out Gemini 3 Pro — plus 90.4% on GPQA Diamond and 68.7% on SimpleQA Verified, against 28.1% for the 2.5 Flash it replaces.

The distribution is the story: the model is not just an API endpoint but the default reasoning tier behind consumer search and the Gemini app, and it reaches developers through the Gemini API, AI Studio, Vertex AI, Gemini CLI, Android Studio and Antigravity simultaneously. Google says JetBrains, Figma, Cursor, Harvey and Latitude are already building on it.

Gemini 3 Flash becomes Google's default everywhere at $0.50/M input tokens
storage.googleapis.com

WHY IT MATTERS

A Flash-tier model that matches the previous Pro tier and sits behind the default search surface sets the price ceiling for reasoning in high-volume workflows: extraction, classification, video and document analysis, and evaluation harnesses that would have been unaffordable a month earlier. Architect for routing rather than a single model — send cheap high-frequency calls to Flash and reserve Pro for hard reasoning, since the capability gap between tiers is now narrower than the price gap. Flash-tier latency also changes what you can put in the interactive path.

TUE · Dec 16, 2025open weightscodingmoelong context

Xiaomi open-sources MiMo-V2-Flash: 309B total, 15B active, 256K context

Xiaomi's LLM-Core team released MiMo-V2-Flash on December 16 with full weights on GitHub and Hugging Face, plus a base model, a technical report and separately open-sourced three-layer Multi-Token Prediction weights. The architecture is a 309B-parameter MoE that activates 15B per token, interleaving sliding-window attention with global attention in a 5:1 ratio at a 128-token window, which the team says cuts KV-cache storage by nearly 6x while a learnable attention-sink bias preserves long-context quality. It was pre-trained on 27 trillion tokens and supports a 256K-token context.

On Xiaomi's own evaluations the post-trained model scores 73.4% on SWE-bench Verified and 71.7% on SWE-bench Multilingual, edging Kimi K2 Thinking at 71.3% and DeepSeek V3.2 Thinking at 73.1% at a fraction of their total parameters — DeepSeek V3.2 carries 671B total and Kimi K2 over 1T. Those are vendor-run tables, not independent testing, and none of the numbers were reproduced by a third party in the week of release.

WHY IT MATTERS

A 15B-active model with 256K context is the first serious candidate for self-hosting a coding agent rather than renting one: you can run it behind vLLM or SGLang, fine-tune it on private repositories, and avoid sending source code to a third-party API entirely. It also resets your make-versus-buy maths — if open weights reach within about four points of Claude Sonnet 4.5 on SWE-bench Verified for the cost of GPUs you already own, the license terms, not the benchmark gap, become the deciding factor. Check the terms before shipping: the release materials do not carry an OSI license label on the model card.

MON · Dec 15, 2025open weightsnvidiamoelong contextself-hosting

NVIDIA ships Nemotron 3 Nano: 30B params, 3B active, 1M context, weights and data included

NVIDIA announced the Nemotron 3 family on December 15 and made only the smallest member available: Nano is a 30-billion-parameter mixture-of-experts model that activates 3.2 billion parameters per forward pass, built on a hybrid Mamba-2 and transformer architecture with grouped-query attention. It supports context lengths up to 1 million tokens, and NVIDIA claims up to 4x higher token throughput than Nemotron 2 Nano with reasoning-token generation cut by up to 60%.

The release is unusually open for a vendor model: checkpoints in FP8, BF16 and base BF16, the pre-training and post-training datasets, the training recipes, and NVIDIA's NeMo Gym, NeMo RL and NeMo Evaluator tooling, all under the NVIDIA Nemotron Open Model License. Super, at roughly 100B total and 10B active, and Ultra are announced but not yet shipped, so the firm is staging the family the way it stages GPUs.

WHY IT MATTERS

A 30B model that fires 3B parameters and holds 1M tokens changes the economics of local and self-hosted inference: you can serve agent loops with long tool-output histories on a single node instead of paying per-token to a frontier API. Because the data, recipes and RL environments ship too, you can post-train on your own codebase rather than prompt around someone else's alignment. If you build multi-agent orchestration, the throughput-per-dollar number — not the benchmark score — is the one to read.