Grok 4.3 is the better raw-cost choice for output-heavy reasoning agents, while Gemini 3.5 Flash is the stronger default for multimodal, coding, and Google-grounded workflows. Both support 1M-token context windows, but their economics differ sharply: Grok 4.3 is officially priced at $1.25/M input and $2.50/M output, while Gemini 3.5 Flash is $1.50/M input and $9.00/M output. Through CometAPI, both are available at about 20% below official pricing.

In the fast-evolving AI landscape of mid-2026, Grok 4.3 (xAI) and Gemini 3.5 Flash (Google DeepMind) represent two powerful approaches: Grok emphasizes speed, agentic efficiency, and aggressive pricing, while Gemini 3.5 Flash delivers near-frontier intelligence with strong multimodal and coding capabilities at Flash-tier speeds.

Whether you're building autonomous agents, scaling RAG pipelines, or optimizing coding workflows, this guide provides data-backed insights to help you choose — and save money via CometAPI.

Grok 4.3, released by xAI around April 30, 2026, is a flagship reasoning model designed for agentic workflows, instruction-following, high factual accuracy, and complex multi-step tasks. For developers, Grok 4.3 is especially attractive when the workload is text-heavy and output-heavy: research synthesis, multi-step planning, knowledge work, document Q&A, support automation, and agents that may need many repair loops. Kilo Code’s coding benchmark page lists Grok 4.3 with a 42.2 AA Coding Index, 47.3% on SciCode, 37.9% on TerminalBench Hard, 64.3% on long-context reasoning, and 81.3% on IFBench instruction following.

Key Features:

• Context Window: 1 million tokens (with no strict output limit in many setups), ideal for long-document analysis, deep research, and persistent agent memory.
• Reasoning: Configurable effort levels (none/low/medium/high; default low) for balancing speed and depth.
• Multimodal: Text and image inputs; strong tool calling, structured outputs, and native support for agentic environments (code execution, web/X search, files).
• Strengths: Excels in agentic tasks (e.g., high Elo on GDPval-AA benchmarks), low hallucination rates in some evaluations, and real-world reliability for instruction following (e.g., ~81% IFBench, strong τ²-Bench).
• API Pricing (xAI): $1.25 / $2.50 per 1M input/output tokens. Prompt caching and optimizations available.

Grok 4.3 builds on prior versions with improved architecture, better agentic performance, and competitive intelligence scores (e.g., ~38-53 on Artificial Analysis Intelligence Index depending on configuration).

Gemini 3.5 Flash is Google’s newest Flash-tier model built for high-speed, agentic, multimodal, and coding workflows. Gemini 3.5 Flash is generally available, stable, and ready for scaled production use, with sustained frontier performance in coding, agentic execution, and long-horizon tasks. It supports a 1M-token input context window, up to 65K output tokens, thinking levels, and the same broad Gemini 3 family tool set, except Computer Use is not currently supported.

Key Features:

• Context Window: 1 million tokens input, up to ~65K output tokens.
• Multimodal: Strong native support for text, images, audio, video—giving it an edge in multimedia workflows.
• Reasoning & Tools: Built-in thinking modes, native tool use, function calling, and excellent performance on coding/agent benchmarks.
• Strengths: Leads or competes on intelligence vs. speed Pareto frontier, strong multimodal (e.g., high MMMU-Pro), reduced hallucinations, and fast execution for production agents.
• API Pricing (Google): Approximately $1.50 / $9.00 per 1M input/output tokens (varies by provider/endpoint; caching discounts available).

Gemini 3.5 Flash often punches above its "Flash" tier, rivaling larger models on many metrics while maintaining low latency.